Caliper brake for mountain bicycles having wide tires

• US 4,765,443 A
• Filed: 03/31/1987
• Issued: 08/23/1988
• Est. Priority Date: 06/03/1985
• Status: Expired due to Fees

• Current Assignee: Riverwood Natural Resoureces Corporation
• Original Assignee: Charles B. Cunningham
• Inventors: Cunningham, Charles B.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): OBERLEY, ALVIN E
• Application Number:
  US07/032,956
• Time in Patent Office: 511 Days
• Field of Search: 188/24.11, 188/24.12, 188/24.13, 188/24.14, 188/24.15, 188/24.16, 188/24.18, 188/24.19, 188/24.21, 188/24.22
• US Class Current: 188/24.21
• CPC Class Codes: B62L 1/16 the axes being located intermediate the ends of the levers
• CPC Class Codes: B62L 3/00 Brake-actuating mechanisms for back-pedalling brakes B62L5/00; Arrangements thereof

Abstract

A caliper brake for wide-tire mountain bicycles. Each caliper arm is pivotally mounted to a stationary pivot post of the bicycle frame via a cylindrical bushing to which the arm is press fitted. A return spring is retained around the pivot post in a normally stationary portion enabling purposeful adjustment. A brake shoe holder is mounted on one end of the caliper arm, and a roller-mounting post is secured to the other end. A cam roller is mounted rotatably on the roller mounting post by a low-friction bearing and has a circumferential groove engaging a cammed edge of a cam plate, to which a brake-actuating cable is secured. The brake shoe holder is preferably asymmetrical and is mounted for adjustment lengthwise of the caliper arm and for rotation around it and is also made adjustable as to the spacing from the caliper arm and as to the rotational position around an axis perpendicular to that arm.

Claims

1. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rim and a tire wide relative to the rim, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, one on each of the opposite sides of the tire and rim,

a caliper arm for each said pivot post having an intermediate pivot portion rotatably mounted on said pivot post, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

a polygonal keyed retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times while said retention means is fully tight, and at all times enabling relative rotary movement of said spring relatively to said pivot post,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachement end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable.

2. The brake of claim 1 wherein

each said return spring is a spring with its active part, the part which flexes during its use cycle, being substantially linear and straight when in its relaxed state and an outboard end engaging and pushing on said roller-mounting post with a strong spring force increasing at a high rate due to the linear structure and tending to urge that roller mounting post toward the one on the other caliper arm, and

said retention means comprises

a polygonal keyed member to which said spring is secured, and frictional means for holding said keyed member stationary relative to said pivot post, while enabling purposeful rotation thereof by a standard wrench, for adjusting the spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post.

3. The brake of claim 2 wherein

said polygonal keyed member is a flat plate having, brazed thereto, a split sleeve, and

said linear wire spring extends into said split sleeve and is held rigidly, though removably, therein.

4. The brake of claim 2 wherein said polygonal keyed member is a hexagonal headed nut with a passage therethrough into which an end of said linear wire spring extends, said spring having an arcuate portion leading to said spring end.

5. The brake of claim 1 wherein said brake shoe holder comprises

support means,

shoe retaining means,

attachment means for securing said support means to said shoe-retaining means for adjustment of the spacing of the shoe in said shoe retaining means from said support means and for rotation relative to each other, to rotate the position of the shoe relative to said support means,

positioning means for securing said support means to said caliper arm for adjustment lengthwise of the support means on said caliper arm and for adjustment rotationally of the support means relative to the lengthwise centerline of said caliper arm, and

clamping means for releasably clamping said support means rigidly to said caliper arm when adjustment has been made,

whereby the position of the shoe relative to said caliper arm can be adjusted lengthwise and rotationally by the movement of said support means relative to said caliper arm and the spacing of the shoe relative to said support means and the rotational portion of said shoe relative to said support means can also be separately adjusted,

said shoe retaining means being asymmetrically secured to said support means, in a way such that the shoe retaining means extends to one side of the support means and away from the portion of said frame supporting said post and on the forward side of said frame portion relative to the direction of travel of said bicycle, so that the rim moves toward the shoe after passing said frame portion and so that upon release of said cam from said rollers said shoes can be forced apart from each other by said return springs for removal of the wide tire without interference from said shoe retaining means and said frame.

6. The brake of claim 1 wherein said shoe-holder is asymmetrically secured to said caliper arm, so that the shoe therein extends to one side of said caliper arm and away from said frame on the other side, of said portion supporting said post in the direction toward which said wheel and rim are moving, where it is so spaced that it does not engage said frame when said cam rollers are released from said cam and said caliper arms are moved apart from each other by said return springs.

7. The brake of claim 1 wherein each said caliper arm has a plurality of roller-mounting post-receiving openings at its said cam-facing end, any one of which may be chosen for use.

8. The brake of claim 1 wherein said cam plate edges are shaped to provide

a pair of depressions at the end of said cam plate nearer said cable, in which said rollers normally rest when the brake is not engaged and which act upon release of said brake to accelerate retraction of said shoes from said rim,

a brake actuation ramp for non-linear accelerating engagement of the brake, providing means causing the brake caliper arms to move quickly from said depressions so that said shoes move up to said rim, and, when said shoe is in contact with said rim, to move more slowly but with greater mechanical advantage as the shoe is clamped more tightly on said rim and causing said brake calipers to act oppositely therefrom when said brake is released, and

a safety stop at the end of said cam plate further from said cable to prevent accidental disengagement of the rollers and edges at the extremity of the brake stroke.

9. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rim and a tire wide relative to the rim, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, each said pivot post being brazed to said frame to secure complete rigidity therewith and one on each of the oppostie sides of the tire and rim,

a cylindrical bushing rotatably mounted on each said pivot post,

a caliper arm having an intermediate pivot portion separate from but snugly affixed to each said bushing to enable adjustment of the position of the arm on said bushing relative to the axis of said bushing, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity, each said caliper arm being press-fitted to its said bushing, to enable said adjustment relative to the axis of said bushing at a time of alignment while otherwise said bushing is firmly retained in relation to said caliper arm and enabling low-friction rotation of said bushing with said caliper arm relative to said pivot post,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and at all times enabling relative rotary movement of said bushing relative to said spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable, said bushing being longer than said caliper arm is thick so that the axial adjustment of said caliper arm relative to said bushing at the time of press fitting can provide proper alignment of said cable and cam plate with the groove of said cam roller.

10. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rim and a tire wide relative to the rim, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, one on each of the opposite sides of the tire and rim,

a cylindrical bushing rotatably mounted on each said pivot post,

a caliper arm having an intermediate pivot portion separate from but snugly affixed to each said bushing to enable adjustment of the position of the arm on said bushing relative to the axis of said bushing, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times,

each said return spring having an extended portion with an outboard end engaging and pushing on said roller-mounting post and tending to urge that roller mounting post toward the one on the other caliper arm,

said retention means comprising

a keyed member to which said spring is secured, and frictional means for holding said keyed member stationary relative to said pivot post, while enabling purposeful rotation thereof for adjusting the spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable,

said pivot post providing two spaced-apart abutments,

said bushing being mounted between them and shorter than the distance between them,

said retention means urging said polygonal keyed member against one of said abutments, so that there is clearance between said keyed member and said bushing, enabling adjustment of spring tension without moving said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable.

11. The brake of claim 10 in which

said post has a stop near said frame comprising one said abutment and an outer end providing the other abutment and is provided with an interiorly threaded portion extending in from said outer end,

said retention means comprising a machine screw threaded into said interiorly threaded portion and having a head and a washer urged by said head to engage said polygonal keyed member and force it against said outer end.

12. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rim and a wide tire, including in combination

a pair of stationary pivot posts rigidly secured directly to said frame, one on each of the opposite sides of the tire and rim, each said pivot post being a twice-stepped member, the steps providing two spaced-apart abutments, one an inner abutment near said frame, the other an outer abutment with a reduced-diameter exteriorly threaded portion extending therebeyond,

a cylindrical bushing rotatably mounted on each said pivot post, said bushing being mounted between said abutments and shorter than the distance between them,

a caliper arm having an intermediate pivot portion separate from but snugly affixed to each said bushing to enable adjustment of the position of the arm on said bushing, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and at all times enabling relative rotary movement of said bushing relative to said spring,

said retention means comprising a polygonal keyed member to which said spring is secured and frictional means for holding said keyed member stationary relative to said pivot post, while enabling purposeful rotation thereof by a standard key-engaging tool for adjusting the spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post, said retention means comprising a nut threaded onto said threaded portion and a washer urged by said nut to force said polygonal keyed member against said outer abutment, said retention means urging said polygonal keyed member against one of said abutments, so that there is clearance between said keyed member and said bushing, enabling adjustment of spring tension without moving said caliper arm,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm, each said return spring being a linear spring with an outboard end engaging said roller-mounting post and tending to urge that roller mounting post toward the one on the other caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable.

13. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rin and a wide tire, including in combination

a pair of stationary pivot posts rigidly secured directly to said frame, one on each of the opposite sides of the tire and rim,

a cylindrical bushing rotatably mounted on each said pivot post,

a caliper arm having an intermediate pivot portion affixed to each said bushing, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and at all times enabling relative rotary movement of said bushing relative to said spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said brake shoe holder comprising

support means,

shoe retaining means,

attachment means for securing said support means to said shoe-retaining means for adjustment of them lengthwise relative to each other and for rotation relative to each other,

positioning means for securing said support means to said caliper arm for adjustment lengthwise of the support means on said caliper arm and for adjustment rotationally of the support means relative to the lengthwise centerline of said caliper arm, and

clamping means for releasably clamping said support means rigidly to said caliper arm when adjustment has been made,

said caliper arm including a cylindrical stem,

said positioning means comprises a clamp member with an end portion having a threaded opening therethrough and a pair of looped arms extending out from the upper end of the end portion and, via an arcuate, generally semicircular opposite-end portion, back to the said end portion, a clamp block having an end wall facing the end portion of the clamp member, an arcuate portion at the other end from said end wall, a through opening in between the end wall and the arcuate portion and perpendicular to the planes of said arms and in between them, and a slot extend into said through opening, and a said screw engaging said threaded opening and facing and engaging said end wall,

said support means including a cylindrical rod portion extending into and through said through opening,

whereby said support means, and therefore said shoe retaining means, is adjustable longitudinally and rotationally relative to said clamp block and said clamp block and clamp member combination is adjustable rotationally and longitudinally relative to said stem.

14. A caliper brake for wide-tire bicycles having a frame and wheels with a narrow rin and a tire wide relative to the rim, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, one on each of the opposite sides of the tire and rim,

a caliper arm for each said pivot post having an intermediate pivot portion rotatably mounted on said pivot post, said caliper arms each having fore and aft faces, one face being substantially flat and the other face tapered from a thick portion at and near said pivot portion to a thin portion at said cam-facing end, so that the two caliper arms can be exchanged and inverted to provide different operating conditions,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

retention means for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and at all times enabling relative rotary movement of said spring relative to said pivot post,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to said cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing enabling alignment of said caliper arm thereon with said cable.

15. A caliper brake for wide-tire mountain bicycles having a bifurcated frame and wide tires mounted on narrow rims, including in combination

a pair of stationary pivot posts rigidly and permanently secured to said frame, one on each of the opposite sides of the tire and tire rim, each said pivot post having an inner shoulder near said frame, an outer shoulder, and an outboard end,

a cylindrical bushing rotatably mounted on each said pivot post in between said shoulders and shorter than the distances between them,

a caliper arm thinner than the length of said bushing and having an intermediate pivot opening press-fitted to each said bushing, a shoe-attachment end, and a cam-facing end,

a spring support member around each said pivot post and abutting said outer shoulder and having a keyed polygonal head,

a linear wire return spring having one end secured to said spring support member and extending out toward said cam-facing end of said caliper arm,

clamping means for clamping said spring support member against said outer shoulder for clearance between it and said bushing sufficiently to retain the spring support member by friction in a stationary position relative to said post while enabling purposeful adjustment of that position without interfering with rotary movement of said bushing relative to said spring support member,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm and in engagement with the outboard end of said wire spring at a locus where it urges that roller-mounting post toward the one on the other caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a cam plate having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof,

whereby said return springs can be individually adjusted to vary the force urging the roller mounting posts toward each other and the shoe holders apart from each other by varying the rotational position of said spring support member relative to said pivot post, and

whereby the relative position of each bushing and its caliper arm, when press-fitted together, serves to align the cam roller grove, cam plate, and cable properly.

16. The brake of claim 15 wherein said cable is secured to said cam plate by a clamp plate having a cable-receiving groove on a face facing said cam plate and means for clamping said cam plate and said clamp plate together with said cable in between them in said groove.

17. The brake of claim 15 wherein

said caliper arm includes a cylindrical stem, and

said shoe holder includes

a ring around said stem for adjustment thereon lengthwise and rotationally,

clamping means for releasably clamping said ring rigidly to said caliper arm stem when adjustment has been made,

a shoe retainer for said shoe,

a threaded stud rigidly attached to said shoe retainer and threaded into said ring for adjustment lengthwise relative to said ring and also for adjustment of their relative rotational position, and

a lock nut for locking said threaded stud in position relative to said ring.

18. The brake of claim 17 wherein said brake is asymmetrically mounted so that it extends further on the side away from the frame than on the other side and is never in any plane extending perpendicularly through both parts of the frame that lie on opposite sides of said tire.

19. The brake of claim 17 wherein said caliper arms each have fore and aft faces, one being substantially flat and the other tapered from a thick portion at and near said pivot portion to a thin portion at said camfacing end, so that the two caliper arms can be exchanged and inverted to provide different operating conditions.

20. The brake of claim 17 wherein said cam plate edges are shaped to provide a pair of depressions in which said rollers normally rest when the brake is not engaged, a brake actuation ramp for non-linear accelerating engagement of the brake, and a safety stop to prevent accidental disengagement of the rollers and edges at the extremity of the brake stroke.

21. A caliper brake for wide-tire bicycles having a frame with two portions, one on each side of a wheel having a tire and a tire rim, including in combination

a pair of stationary pivot posts rigidly secured to said frame, one on each of the opposite sides of the tire and tire rim,

a caliper arm pivoted at an intermediate point to each said pivot post, said caliper arm having a shoe-attachment end with a cylindrical stem, and a cam-facing end, said caliper arms each having fore and aft faces, one being substantially flat and the other tapered from a thick portion at and near said pivot portion to a thin portion at said cam-facing end, so that the two caliper arms can be exchanged and inverted to provide different operating conditions,

return spring means at each said pivot post for urging said shoe attachment ends apart from each other, and

a brake shoe holder connected to said shoe-attachment end and holding a brake shoe,

said shoe holder being asymmetrically secured to said arm so that the shoe extends further on one side of said arm than on the other side, so that said shoe is spaced away from said post and on the side of said post toward which the wheel and rim rotate forwardly, thereby enabling quick release of the wheel.

22. A caliper brake for wide-tire bicycles having a frame, including in combination

a pair of stationary pivot posts rigidly secured to said frame, one on each of the opposite sides of the tire and tire rim,

a caliper arm pivoted at an intermediate point to each said pivot post, said caliper arm having a shoe-attachment end, and a cam-facing end, said caliper arms each having fore and aft faces, one being substantially flat and the other tapered from a thick portion at and near said pivot portion to a thin portion at said cam-facing end, so that the two caliper arms can be exchanged and inverted to provide different operating conditions,

return spring means for normally urging said cam facing ends toward each other and said shoe attachment ends away from each other,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm and in engagement with the outboard end of said wire spring,

low-friction bearing means mounted on said roller-mounting post,

a cam roller mounted rotatably on each said bearing means having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to increase the mechanical advantage thereof as the braking force of the bicycle rider increases, and

a brake-actuating cable secured to said cam plate along the central axis thereof.

23. A caliper brake for wide-tire bicycles having a frame, including in combination

a pair of stationary pivot posts rigidly secured to said frame, one on each of the opposite sides of the tire and tire rim,

a caliper arm pivoted at an intermediate point to each said pivot post, said caliper arm having a shoe-attachment end, and a cam-facing end,

return spring means for normally urging said cam facing ends toward each other and said shoe attachment ends away from each other,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm and in engagement with the outboard end of said wire spring,

a ballbearing sealed against the entry of mud and water, mounted on said roller-mounting post,

a cam roller mounted rotatably on each said sealed ball bearing having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to increase the mechanical advantage thereof as the braking force of the bicycle rider increases, and

a brake-actuating cable secured to said cam plate along the central axis thereof, whereby said sealed ball bearing is unaffected by said roller and said roller mounting post passing through mud or water and by the dried residue from mud and muddy water and wet-dry cycles,

said cam plate edges being shaped to provide

a pair of depressions at the end of said cam plate nearer said cable, in which said rollers normally rest when the brake is not engaged and which act upon the release of said brake to accelerate retraction of said shoe from said rim,

a brake actuation ramp for non-linear accelerating engagement of the brake, providing means causing the brake caliper arms to move quickly from said depressions so that said shoes move up to said rim, and, when said shoe is in contact with said rim, to move more slowly but with greater mechanical advantage as the shoe is clamped more tightly on said rim and causing said brake to act oppositely therefrom when said brake is released, and

a safety stop at the end of said cam plate further from said cable to prevent accidental disengagement of the rollers and edges at the extremity of the brake stroke.

24. A wide-tire mountain-type bicycle, including in combination:

a frame having a head tube, a down tube, a seat tube, a pair of seat stays, and a pair of chain stays having upper and lower surfaces, and also having a fork rotatably mounted in said head tube, said fork having a pair of blades with forward facing surfaces, and a handlebar on the upper end of said fork,

a front wheel and a rear wheel, each with a rim and a wide tire,

two pairs of stationary pivot posts rigidly, permanently, and immovably secured to said frame, one on each of the opposite sides of each tire and tire rim, one pair mounted to the forward-facing surfaces of said fork blades and one pair mounted on one said pair of stays, each said post having a pair of stops, one inboard near said blades or stays and one outboard from which projects a reduced-diameter threaded outboard end,

a cylindrical bushing rotatably mounted on each said post inboard of said threaded outboard end, between said shoulders and shorter than the distance between said shoulders,

a caliper arm thinner than said bushing is long, having an intermediate pivot opening press-fitted to and coaxial with each said bushing so that said arm and its said bushing can be adjusted axially relative to each other, a shoe-attachment end, and a cam-facing end,

each said caliper arm being press-fitted to its said bushing, to enable adjustment relative to the axis of said bushing at a time of alignment while otherwise said bushing is firmly retained in relation to said caliper arm and enabling low-friction rotation of said bushing with said caliper arm relative to said pivot post,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm,

polygonal keyed retention means mounted on said pivot post for frictonally retaining any desired position of said return spring to which it is set and for enabling purposeful resetting of said return spring, and at all times enabling relative rotary movement of said bushing relative to said return spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of each said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a pair of cam plates, one for each wheel, having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, said cammed edges causing substantial increases in mechanical advantage and braking force as said cam plate is moved to actuate the brake,

a brake-actuating cable secured to each said cam plate along the central axis thereof, and

a brake lever for each said brake mounted on the handlebar, one connected to each said cable at the end opposite from said cam plate,

whereby said return springs can be individually adjusted to govern the effect on their respective brake shoes by varying their rotational position relative to said pivot post and they also act on each other through said cam plate,

said bushing enabling alignment of said caliper arm thereon with said cable, said bushing being longer than said caliper arm is thick so that the axial adjustment of said caliper arm relative to said bushing at the time of press fitting can provide proper alignment of said cable and cam plate with the groove of said cam roller.

25. The wide-tire bicycle of claim 24 wherein

each said return spring is a spring with its active part, the part which flexes during its use cycle, substantially linear and straight when in its relaxed state, an outboard end engaging said roller-mounting post, tending to urge that roller mounting post toward the one on the other caliper arm, and

each said retention means comprises a polygonal keyed member to which said spring is secured and frictional means for holding said keyed member stationary relative to said pivot post with an especially strong spring force due to the linear structure, while enabling purposeful rotation thereof by a key-engaging tool for adjusting spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post.

26. The wide-tire bicycle of claim 24 wherein said shoe is asymmetrically secured to said arm, so that the shoe extends mostly on one side of the arm than on the other side and away from said frame on the side toward which its said wheel and rim move, said shoes and shoe-retainers being thereby spaced so that they can be spread apart without touching said frame in order to facilitate removal of the wheel with its narrow rim and wide tire.

27. A wide-tire mountain-type bicycle, including in combination:

a frame having a head tube, a down tube, a seat tube, a pair of seat stays, and a pair of chain stays having upper and lower surfaces, and also having a fork rotatably mounted in said head tube, said fork having a pair of blades with forward facing surfaces, and a handlebar on the upper end of said fork,

a front wheel and a rear wheel, each with a rim and a wide tire,

two pairs of stationary pivot posts rigidly, permanently, and immovably secured to said frame, one on each of the opposite sides of each tire and tire rim, one pair mounted to the forward-facing surfaces of said fork blades and one pair mounted on one said pair of stays, each said post having a pair of stops, one inboard near said blades or stays and one outboard from which projects a reduced-diameter threaded outboard end,

each said pivot post being brazed to said frame to secure complete rigidity therewith and each said caliper arm being press-fitted to its said bushing, said bushing being longer than said caliper arm is thick to enable position adjustment during press fitting that ensures proper alignment of said cable, cam plate, and the grove of said cam roller,

a cylindrical bushing rotatably mounted on each said post inboard of said threaded outboard end, between said shoulders and shorter than the distance between said shoulders,

a caliper arm thinner than said bushing is long, having an intermediate pivot opening press-fitted to and coaxial with each said bushing so that said arm and its said bushing can be adjusted axially relative to each other, a shoe-attachment end, and a cam-facing end,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm,

polygonal keyed retention means mounted on said pivot post for frictionally retaining any desired position of said return spring to which it is set and for enabling purposeful resetting of said return spring at any time by a polygonal wrench without disassembly or loosening and at all times enabling relative rotary movement of said bushing relative to said return spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of each said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a pair of cam plates, one for each wheel, having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, said cammed edges causing substantial increases in mechanical advantage and braking force as said cam plate is moved to actuate the brake,

a brake-actuating cable secured to each said cam plate along the central axis thereof, and

a brake lever for each said brake mounted on the handlebar, one connected to each said cable at the end opposite from said cam plate,

whereby said return springs can be individually adjusted to govern the effect of their respective brake shoes by varying their rotational position relative to said pivot post and they also act on each other through said cam plate.

28. A wide-tire mountain-type bicycle, including in combination:

a frame having a head tube, a down tube, a seat tube, a pair of seat stays, and a pair of chain stays having upper and lower sufaces, the brake for the rear wheel being mounted on the lower surface of and lying below said chain stays and also having a fork rotatably mounted in said head tube, said fork having a pair of blades with forwarding facing surfaces, and a handlebar on the upper end of said fork,

a front wheel and a rear wheel, each with a rim and a wide tire,

two pairs of stationary pivot posts rigidly, permanently, and immovably secured to said frame, one on each of the opposite sides of each tire and tire rim, one pair mounted to the forward-facing surfaces of said fork blades and one pair mounted on one said pair of stays, each said post having a pair of stops, one inboard near said blades or stays and one outboard from which projects a reduced-diameter threaded outboard end,

a cyclindrical bushing rotatably mounted on each said post inboard of said threaded outboard end, between said shoulders and shorter than the distance between said shoulders,

a caliper arm thinner than said bushing is long, having an intermediate pivot opening press-fitted to and coaxial with each said bushing so that said arm and its said bushing can be adjusted axially relative to each other, a shoe-attachment end, and a cam-facing end,

a separate return spring for each pivot post, each having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm,

polygonal keyed retention means mounted on said pivot post for frictionally retaining any desired position of said return spring to which it is set and for enabling purposeful resetting of said return spring at any time and at all times enabling relative rotary movement of said bushing relative to said return spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of each said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a pair of cam plates, one for each wheel, having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, said cammed edges causing substantial increases in mechanical advantage and braking force as said cam plate is moved to actuate the brake,

a brake-actuating cable secured to each said cam plate along the central axis thereof, and

a brake lever for each said brake mounted on the handlebar, one connected to each said cable at the end opposite from said cam plate,

whereby said return springs can be individually adjusted to govern the effect on their respective brake shoes by varying their rotational position relative to said pivot post and they also act on each other through said cam plate.

29. A wide-tire mountain-type bicycle, including in combination:

a frame having a head tube, a down tube, a seat tube, a pair of seat stays, and a pair of chain stays having upper and lower surfaces, and also having a fork rotatably mounted in said head tube, said fork having a pair of blades with forward facing surfaces, and a handlebar on the upper end of said fork,

a front wheel and a rear wheel, each with a rim and a wide tire,

two pairs of stationary pivot posts rigidly and permanently secured to said frame, one on each of the opposite sides of each tire and tire rim, one pair mounted to the forward-facing surfaces of said fork blades and one pair mounted on opposite said stays, each said post having a pair of stops, one inboard near said blades or stays and one outboard from which springs a reduced-diameter threaded outboard end,

a cyclindrical bushing rotatably mounted on each said post inboard of said threaded outboard end, between said shoulders and shorter than the distance between said shoulders,

a caliper arm thinner than said bushing is long, having an intermediate pivot opening press-fitted to each said bushing, a shoe-attachment end, and a cam-facing end,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm,

retention means mounted on said pivot post for frictionally retaining any desired position of said return spring to which it is set and for enabling purposeful resetting of said return spring at any time, and at all times enabling relative rotary movement of said bushing relative to said return spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of each said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a pair of cam plates, one for each wheel, having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, said cammed edges causing substantial increases in mechanical advantage and braking force as said cam plate is moved to actuate the brake,

a brake-actuating cable secured to each said cam plate along the central axis thereof, and

a brake lever for each said brake mounted on the handlebar, one connected to each said cable at the end opposite from said cam plate,

whereby said return springs can be individually adjusted to govern the effect on their respective brake shoes by varying their rotational position relative to said pivot post and they also act on each other through said cam plate,

said brake shoe holder comprising

support means,

shoe retaining means,

attachment means for securing said support means to said shoe-retaining means for adjustment of them lengthwise relative to each other and for rotation relative to each other,

positioning means for securing said support means to said caliper arm for adjustment lengthwise of the support means on said caliper arm and for adjustment rotationally of the support means relative to the lengthwise centerline of said caliper arm, and

clamping means for releasably clamping said support means rigidly to said caliper arm when adjustment has been made,

said caliper arm including a cylindrical stem,

said positioning means comprising a clamp member with an end portion having a threaded opening therethrough and a pair of looped arms extending out from the upper end of the end portion and, via an arcuate, generally semicircular opposite end portion, back to the said end portion, a clamp block having an end wall facing the end portion of the clamp member, an arcuate portion at the other end for said end wall, a through opening in between the end wall and the arcuate portion and perpendicular to the planes of said arms and in between them, and a slot extending into said through opening, and a said screw engaging said threaded opening and facing and engaging said end wall,

said support means including a cyclindrical rod portion extending into and through said through opening,

whereby said support means, and therefore said shoe retaining means, is adjustable longitudinally and rotationally relative to said clamp block and said clamp block and clamp member combination is adjustable rotationally and longitudinally relative to said stem.

30. The wide-tire bicycle of claim 29 wherein

said caliper arm includes a cylindrical stem,

said positioning means comprising a ring portion of said support means to which is attached said clamping means,

said support means including a socket rigidly attached to said ring and threaded to a stud extending from said shoe retaining means,

said attachment means including a lock nut for locking said threaded stud relative to said ring.

31. A wide-tire mountain-type bicycle, including in combination:

a frame having a head tube, a down tube, a seat tube, a pair of seat stays, and a pair of chain stays having upper and lower surfaces, and also having a fork rotatably mounted in said head tube, said fork having a pair of blades with forward facing surfaces, and a handlebar on the upper end of said fork,

a front wheel and a rear wheel, each with a rim and a wide tire,

two pairs of stationary pivot posts rigidly and permanently secured to said frame, one on each of the opposite sides of each tire and tire rim, one pair mounted to the forward-facing surfaces of said fork blades and one pair mounted on opposite sides of said stays, each said post having a pair of stops, one inboard near said blades or stays and one outboard from which springs a reduced-diameter threaded outboard end,

a cylindrical bushing rotatably mounted on each said post inboard of said threaded outboard end, between said shoulders and shorter than the distance between said shoulders,

a caliper arm thinner than said bushing is long, having an intermediate pivot opening press-fitted to each said bushing, a shoe-attachment end, and a cam-facing end,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm.

retention means mounted on said pivot post for frictionally retaining any desired position of said return spring to which it is set and for enabling purposeful resetting of said return spring at any time, and at all times enabling relative rotary movement of said bushing relative to said return spring,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of each said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post between said spring and said caliper arm, each said roller having a circumferential groove therein,

a pair of cam plates, one for each wheel, having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, said cammed edges causing substantial increases in mechanical advantage and braking force as said cam plate is moved to actuate the brake, said cam plate for the rear wheel brake having its cammed edges steeper than those of the cam plate for the front wheel brake, to impart stronger braking response for the rear wheel brake than for the front wheel brake

a brake-actuating cable secured to each said cam plate along the central axis thereof, and

a brake lever for each said brake mounted on the handlebar, one connected to each said cable at the end opposite from said cam plate,

whereby said return springs can be individually adjusted to govern the effect on their respective brake shoes by varying their rotational position relative to said pivot post and they also act on each other through said cam plate.

32. A retrofit kit for applying replacement brakes to a mountain-type wide-tire bicycle having a frame with a rear brake cable and a front brake cable, said kit comprising

four stationary pivot posts to be rigidly and immovably secured directly to said frame, one on each of the opposite sides of each tire and tire rim,

four caliper arms, each having an intermediate pivot portion for attachment to each said pivot post and each having a shoe-attachment end, and a cam-facing end,

four identical return springs each having one end that is to be adjustably secured relative to said pivot post and a second end for acting on said caliper arm,

polygonal keyed retention means for each said return spring for retaining said spring member in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times while said retention means is fully tight and also at all times enabling relative rotary movement of said spring relative to said pivot post,

four identical brake shoe holders, each with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

four identical roller-mounting posts, each secured to the cam-facing end of a said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein, and

two cam plates, each with means for securement along its central axis to one said brake cable, each having two opposite cammed edges in engagement with said grooves in two said rollers, said cammed edges causing a substantial increase in mechanical advantage the further the cam is moved during brake actuation.

33. The kit of claim 32 wherein

each said return spring is a spring with its active part, the part which flaxes during its use cycle being substantially linear and straight when in its relaxed state, an outboard end of said spring engaging said roller-mounting post, tending to urge that roller mounting post toward the one on the other caliper arm of a pair, and

said retention means comprises a polygonal keyed member to which said spring is secured and frictional means for holding said keyed member stationary relative to said pivot post with an especially strong spring force due to the linear structure, while enabling purposeful rotation thereof by a key-engaging tool for adjusting spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post.

34. A retrofit kit for applying replacement brakes to a mountain-type wide-tire bicycle having a frame with a rear brake cable and a front brake cable, said kit comprising

four stationary pivot posts to be rigidly secured directly to said frame, one on each of the opposite sides of each tire and tire rim,

four identical cylindrical bushings for rotatable mounting on each said pivot post,

four caliper arms, each having an intermediate pivot portion for affixation to each said bushing by press fitting and each having a shoe-attachment end, and a cam-facing end,

four identical return springs each having one end that is to be adjustably secured relative to said pivot post and a second end for acting on said caliper arm,

retention means for each said return spring for retaining said spring member in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and also at all times enabling relative rotary movement of said bushing relative to said spring,

four identical brake shoe holders, each with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

four identical roller-mounting posts, each secured to the cam-facing end of a said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein, and

two cam plates, each with means for securement along its central axis to one said brake cable, each having two opposite cammed edges in engagement with said grooves in two said rollers, said cammed edges causing a substantial increase in mechanical advantage the further the cam is moved during brake actuation, the two cam plates being different from each other, one, for use on a rear brake, having a steeper cammed edge than the other, for use on a front brake.

35. A retrofit kit for applying replacement brakes to a mountain-type wide-tire bicycle having a frame with a rear brake cable and a front brake cable, said kit comprising

four stationary pivot posts to be rigidly and immovably secured directly to said frame, one on each of the opposite sides of each tire and tire rim,

four caliper arms, each having an intermediate pivot portion for attachment to a said pivot post and each having a shoe-attachment end, and a cam-facing end,

said caliper arms each having fore and aft faces, one being substantially flat and the other tapered from a thick portion at and near said pivot portion to a thin portion at said cam-facing end, so that the two caliper arms can be exchanged and inverted to provide different operating conditions,

four identical return springs each having one end that is to be adjustably secured relative to said pivot post and a second end for acting on said caliper arm,

polygonal keyed retention means for each said return spring for retaining said spring member in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and also at all times enabling relative rotary movement of said spring relative to said pivot post

four identical brake shoe holders, each with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

four identical roller-mounting posts, each secured to the cam-facing end of a said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein, and

two cam plates, each with means for securement along its central axis to one said brake cable, each having two opposite cammed edges in engagement with said grooves in two said rollers, said cammed edges causing a substantial increase in mechanical advantage the further the cam is moved during brake actuation.

36. A retrofit kit for applying replacement brakes to a mountain-type wide-tire bicycle having a frame with a rear brake cable and a front brake cable, said kit comprising

four stationary pivot posts to be rigidly secured directly to said frame, one on each of the opposite sides of each tire and tire rim,

four identical cylindrical bushings for rotatable mounting on each said pivot post,

four caliper arms, each having an intermediate pivot portion for affixation to each said bushing by press fitting and each having a shoe-attachment end having a cylindrical stem, and a cam-facing end,

four identical return springs each having one end that is to be adjustably secured relative to said pivot post and a second end for acting on said caliper arm,

retention means for each said return spring for retaining said spring member in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times and also at all times enabling relative rotary movement of said bushing relative to said spring,

four identical brake shoe holders, each with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

four identical roller-mounting posts, each secured to the cam-facing end of said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

two cam plates, each with means for securement along its central axis to one said brake cable, each having two opposite cammed edges in engagement with said grooves in two said rollers, said cammed edges causing a substantial increase in mechanical advantage the further the cam is moved during brake actuation,

each said brake shoe holder comprising,

support means,

shoe retaining means,

attachment means for securing said support means to said shoe-retaining means for adjustment of them lengthwise relative to each other and for rotation relative to each other,

positioning means for securing said support means to said caliper arm for adjustment lengthwise of the support means on said caliper arm and for adjustment rotationally of the support means relative to the lengthwise centerline of said caliper arm, and

clamping means for releasably clamping said support means rigidly to said caliper arm when adjustment has been made,

said positioning means comprising a clamp member with an end portion having a threaded opening therethrough and a pair of looped arms extending out from the upper end of the end portion and, via an arcuate, generally semicircular opposite end portion, back to the said end portion, a clamp block having an end wall facing the end portion of the clamp member, an arcuate portion at the other end for said end wall, a through opening is between the end wall and the arcuate portion and perpendicular to the planes of said arms and in between them, and a slot extend into said through opening, and a said screw engaging said threaded opening and facing and engaging said end wall,

said support means including a cylindrical rod portion extending into and through said through opening,

whereby said support means, and therefore said shoe retaining means, is adjustable longitudinally and rotationally relative to said clamp block and said clamp block and clamp member combination is adjustable rotationally and longitudinally relative to said stem.

37. The kit of claim 36 wherein said shoe retaining means is asymmetrically secured to said support means, in a way such that the shoe retaining means extends further on the side of the support means distant from said frame than on the other side closer to said frame, so that upon release of said cam from said rollers said shoes can be spaced apart from each other without interference from said tire.

38. In a caliper brake for wide-tire bicycles having a frame and wheels with a narrow rim and a wide tire and having a pair of caliper arms pivoted at an intermediate pivot portion and having a shoe-attachment end on one extremity, and brake actuating means at its other extremity the combination therewith of:

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

said brake shoe holder comprising

support means,

shoe retaining means,

attachment means for securing said support means to said shoe-retaining means for adjustment of them lengthwise relative to each other and for rotation relative to each other,

positioning means for securing said support means to said caliper arm for adjustment lengthwise of the support means on said caliper arm and for adjustment rotationally of the support means relative to the lengthwise centerline of said caliper arm, and

clamping means for releasably clamping said support means rigidly to said caliper arm when adjustment has been made,

said caliper arm including a cylindrical stem,

said positioning means comprises a clamp member with an end portion having a threaded opening therethrough and a pair of looped arms extending out from the upper end of the end portion and, via an arcuate, generally semicircular opposite-end portion, back to the said end portion, a clamp block having an end wall facing the end portion of the clamp member, an arcuate portion at the other end from said end wall, a through opening in between the end wall and the arcuate portion and perpendicular to the planes of said arms and in between them, and a slot extend into said through opening, and a said screw engaging said threaded opening and facing and engaging said end wall,

said support means including a cylindrical rod portion extending into and through said through opening,

whereby said support means, and therefore said shoe retaining means, is adjustable longitudinally and rotationally relative to said clamp block and said clamp block and clamp member combination is adjustable rotationally and longitudinally relative to said stem.

39. A brake shoe holder to be mounted on a caliper arm including a cylindrical stem, including in combination:

positioning means comprising a clamp member with an end portion having a threaded opening therethrough and a pair of looped arms extending out from the upper end of the end portion and, via an arcuate, generally semicircular opposite end portion, back to the said end portion, a clamp block having an end wall facing the end portion of the clamp member, an arcuate portion at the other end of said end wall, a through opening in between the end wall and the arcuate portion and perpendicular to the planes of said arms and in between them, and a slot extend into said through opening, and a said screw engaging said threaded opening and facing and engaging said end wall,

support means including a cylindrical rod portion extending into and through said through opening,

whereby said support means, is adjustable longitudinally and rotationally relative to said clamp block and said clamp block and clamp member combination is adjustable rotationally and longitudinally relative to said stem.

40. A caliper brake for bicycles having a frame and wheels with a rim and a tire, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, one on each of the opposite sides of the tire and rim,

a caliper arm mounted on each said pivot post and having an intermediate pivot portion, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

a polygonal keyed member secured to said spring for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment of that position while said retention means is kept fully tightened, enabling purposeful relative rotary movement of said spring relative to said pivot post,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly.

41. The brake of claim 40 wherein

each said return spring is a spring with its active part, the part which flexes during its use cycle, being substantially linear and straight when in its relaxed state and an outboard end engaging and pushing on said roller-mounting post with an especially strong spring force, due to the linear structure, and tending to urge that roller mounting post toward the one on the other caliper arm, and

said retention means comprises

a polygonal keyed member to which said spring is secured, and frictional means for holding said keyed member stationary relative to said pivot post, while enabling purposeful rotation thereof by a standard wrench, for adjusting the spring tension on said roller-mounting post by adjusting the rotational position of said keyed member relative to said pivot post.

42. A caliper brake for bicycles having a frame and wheels with a rim and a tire, including in combination

a pair of stationary pivot posts rigidly, permanently, and immovably secured directly to said frame, one on each of the opposite sides of the tire and rim,

a cylindrical bushing for each said pivot post for relative rotation of said bushing about said pivot post,

a caliper arm having an intermediate pivot portion separate from but snugly affixed to each said bushing, a shoe-attachment end on one extremity, and a cam-facing end at its other extremity,

a return spring for each pivot post having one end adjustably secured relative to said pivot post and a second end acting on said caliper arm to exert a return force thereon,

a polygonal keyed member secured to said spring for frictionally retaining said spring in a stationary position relative to said pivot post while enabling purposeful adjustment and enabling purposeful relative rotary movement of said bushing relative to said spring by application of a simple wrench to said keyed member,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein,

a cam plate having two opposite cammed edges in engagement with said grooves in said rollers, said cammed edges being shaped to cause substantial increases in force the further said cam plate is moved during brake application relative to aid cam rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof for moving said cam plate relative to said cam rollers and thereby to spread said cam rollers apart and force said brake shoes inwardly,

said bushing being longer than said caliper arm is thick, so that adjustments along their relative axial positions can result in obtaining accurate alignment of said cable and said cam plate relative to the groove of said cam roller,

said caliper arm and bushing being held together by a press fit, for enabling said adjustments of their relative axial position at the time of initial installation with retention of said relative positions thereafter.

43. A caliper brake for wide-tire mountain bicycles having a bifurcated frame and wide tires mounted on narrow rims, including in combination

a pair of stationary pivot posts rigidly, immovably and permanently secured to said frame, one on each of the opposite sides of the tire and tire rim, each said pivot post having an inner shoulder near said frame and an outboard end,

a cylindrical bushing rotatably mounted on each said pivot post in between said shoulder and said outboard end and shorter than the distances between them,

a caliper arm thinner than the length of said bushing and having an intermediate pivot opening press-fitted to each said bushing, a shoe-attachment end, and a cam-facing end,

a spring support member around each said pivot post and abutting said post and having a keyed polygonal head,

a wire return spring having one end secured to said spring support member and exerting pressure on said caliper arm,

clamping means for clamping said spring support member against said outboard end for clearance between it and said bushing sufficiently to retain the spring support member by friction in a stationary position relative to said post while enabling purposeful adjustment of that position without interfering with rotary movement of said bushing relative to said spring support member,

a brake shoe holder with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

a roller-mounting post secured to the cam-facing end of each caliper arm,

a cam roller mounted rotatably on each said roller mounting post, each said roller having a circumferential groove therein,

a cam plate having two opposite cammed edges and mounted with the cammed edges in engagement with said grooves in said rollers, and

a brake-actuating cable secured to said cam plate along the central axis thereof,

whereby said return springs can be individually adjusted to vary the force urging the roller mounting posts toward each other and the shoe holders apart from each other by varying the rotational position of said spring support member relative to said pivot post.

44. A retrofit kit for applying a replacement brake to a mountain-type wide-tire bicycle having a frame with a rear brake cable and a front brake cable, said kit comprising

two stationary pivot posts to be rigidly and immovably secured directly to said frame, one on each of the opposite sides of one tire and tire rim,

two caliper arms, each having an intermediate pivot portion for support by each said pivot post and each having a shoe-attachment end, and a cam-facing end,

two identical return springs each having one end that is to be adjustably secured relative to said pivot post and a second end for acting on said caliper arm,

polygonal keyed retention means for each said return spring for retaining said spring member in a stationary position relative to said pivot post while enabling purposeful adjustment of that position at all times while said retention means is fully tight and also at all times enabling relative rotary movement of said spring relative to said pivot post,

two identical brake shoe holders, each with a brake shoe therein, mounted on the shoe-attachment end of said caliper arm,

two identical roller-mounting posts, each secured to the cam-facing end of a said caliper arm,

a cam roller mounted rotatably on each said roller mounting post and having a circumferential groove therein, and

a cam plate, each with means for securement along its central axis to one said brake cable, having two opposite cammed edges in engagement with said grooves in two said rollers, said cammed edges causing a substantial increase in mechanical advantage the further the cam is moved during brake actuation.