The Stoplight is the first of Paul Price's brake designs. Made in Chico, California.
Mechanical explanation of the Stoplight. The arms are machined from billet 6061-T6 aluminum alloy with a 3.5" length. The upper 70mm are based on a 12.5mm diameter cylinder bent outward at 25mm from the bottom of this section of the arm. The remaining 45mm have the front face milled away leaving it flat, and have three holes drilled through this upper section to reduce weight. The lower 25mm has an 11mm slot milled through it that is 1/4" (6.35mm) wide for the brake pad holder (eyebolt) to pass through and adjust up and down. At the bottom of the arm is a base, again machined from the same single piece of aluminum, that is 19mm (1/2") wide, 21.3mm hugh and 16.3mm deep. This base incorporates the pivot for the arm and supports the spring.
One of the problems Paul tried to address in his design is the imperfections in the outer surface of the mounting stud that the brake are pivot on. His way around this was to carefully machine then hone the interior of a brass bushing that machine pressed into a precisely drilled hole through the base. Paul then machines from stainless steel another bushing with a honed and polished outer wall. This steel piece fits over the frame or fork mounting stud and the brass sleeved pivot/arm slides down over the top. The bottom of the base has a 16mm hole in the bottom to recess the outer skirt of the steel bushing and the O-ring that surrounds it. This O-ring at the bottom of the base prevents dirt migration into the common bearing surface between the steel and brass pieces. The top of the brass bushing has a machined round depression around it for the O-ring used to seal the common bearing surface from the top. Paul believes that its likely to ride a season on the brake, disassemble it and find only clean grease between the surface with no dirt. The tolerances the parts are machined to, makes this possible. On the front face of the base is a hole for one end of the internal tension spring to fit into.
A square shaped machined aluminum piece fits over the other end of the spring and has a recessed hole to seat the brake arm mounting bolt. This aluminum piece has square sides spaced at 16mm and is the spring tension adjuster. Turning it one direction tightens the spring , the other loosens it. The mounting bolt, when tightened, holds the springs tension. The springs are colored Silver to indicate a left and Gold to indicate a right arm spring. Each of the included mounting bolts is made of stainless steel with 6mm x 1mm threads, a 5mm hex fitting, has a 20mm length and a 6 gram weight. There are five pieces used to hold and position the brake pad. Two are machined aluminum washers that have one concave face and one flat face. The larger diameter of the two at 19.07mm (3/4") in outer diameter is placed on the front of the arm. The smaller at a 16mm diameter goes to the back, a steel washer and stainless steel nut fit behind it with the pad holer passing through from the front. The pad holder is machined from stainless steel with the head in a barrel graduating barrel shape that hold the brake pad base washer in place even when there is no pad in place. The front face of the pad holder has a 5mm hex fitting for easy, quick final adjustments. The shank of the pad holder has 6mm x 1mm threads and is 22.5mm long. There are no known Titanium replacements for this original pad holder which weighs 9 grams.
The rear tightening can be replaced with a Ti version (our part # 06-91-010). The Stoplights straddle cable and cable carrier are made by Dia-Compe. The straddle cable is 300mm long with a barrel shaped lead anchor, and a second lead fitting for a finger grip to use in quick release opening of the brake. The anchor for the other end of the cable is a machined clamp. Turned down from 8mm hex shaped rod stock, the interior is bored and tapped with threads. A 2.4mm hole drilled through the side of the aluminum piece allows the cable to pass through. The cable is held in place when a bolt is screwed into the piece. Either of the cable anchors will fit into the top of either arm. The carrier is made of stamped aluminum plate. It has a keyed steel bolt with a hole through it. The brake inner wire passes through this hole and a steel nut tightens two washers clamping the wire to the carrier. The carrier with steel parts weighs 11 grams. End of mechanical.
The Stoplight doesn't come with brake pads, you will need to order them separately. The Stoplight has an extremely low profile, we found it to have a Bike-Pro brake profile measurement of 30mm. The Stoplight can be used as either a front or a rear brake. The brake weighs 121 grams. To this add 12.5 grams for the mounting bolts, and 11 grams for the cable carrier to bring the total to 144.5 grams. The Stoplight arms are available in 5 anodized colors, Blue, Black, Green, Lavender or Silver. You will need brake pads separately,
Color-B-BK-GN-L-S $ Price in Catalog
The Stoplight MC reduces some of the mechanical intricacy used and a bit of the mass of the base area.
Mechanical explanation of the Stoplight MC. The arm is again 70mm long above the base and is 12.6mm (1/2") in diameter. The upper arm doesn't have it's front milled flat, nor is there 3 holes drilled through it. The same milled slot for the pad holder occurs on the lower half of the arm. The base is roughly 16mm by 16mm by 16mm. This smaller size is achieved by the elimination of the brass sleeve and the cutting away of every extra bit of aluminum. The MC uses the same machined stainless steel bushing but it rotates inside of the honed and anodized aluminum base. An O-ring again shields the bottom of the stainless to aluminum contact, and there's also one at the top to prevent dirt and dust from contaminating the grease. The same springs are used with their ends fitting into the base at one end and into a machined square aluminum piece. This aluminum piece has square sides spaced at 16mm and is the spring tension adjuster. Turning it one direction tightens the spring , the other loosens it. The spring adjuster has a recessed hole in the top for the mounting bolt.
Once the spring is properly tensioned the mounting bolt holds the brake, and the spring tension. The same steel pad holder is used with two 19.04mm (3/4") diameter concave washers to make flat the roundness of the arm. Once again the a stainless steel flat washer and a 6mm by 1mm threaded nut with a 10mm outer hex are used to tighten the brake pad assembly. The Stoplight MC comes with a pair of 6mm by 1mm by 15.5mm length mounting bolt. Each of these bolts has a 5mm hex fitting and weighs 5.5 grams. Black Kool-Stop Eagle Claws come with the MC brake, but they have a steel instead of the standard aluminum mounting post making the pair of brake pads weigh 46.5 grams.
The same Dia-Compe straddle cable and a similar cable carrier used in the Stoplight are again provided. The steel acorn nut of the Stoplight has been changed to an aluminum version here with a 3 gram weight loss. The machined aluminum cable end clamp is again used here. The lead end of the cable fits into the top of the left arm, the end clamp fits into the right arm top. End of mechanical.
We found the Stoplight MC to have a Bike-Pro brake profile measurement of 30mm. The MC can be used as a front or a rear. The brake weighs 169 grams, (including 46.5 grams of brake pad). To this add 11 grams for the mounting bolts, and 8 grams for the cable carrier bringing it to total of 188 grams. The arms are available in 4 anodized colors Blue, Black, Lavender, or Silver
Color-B-BK-L-S $ Price in Catalog
This cantilever from Paul's is based on the IRD Widget. The pivot cam is the same design, while the brake arms are a longer version of the Stoplight MC. No cable hanger is used with this brake. The brake housing runs straight to the brake arm. The Crosstop comes with Kool Stop Eagle Claw 1's that weigh 46.5 grams. The brake without pads weighs 156.5 grams so the total weight is 203 grams. Paul's Crosstop comes in Blue, Black, Lavender or Silver.
Color-B-BK-L-S $ Price in Catalog