Actuation mechanisms Bicycle brake

1 actuation mechanisms

1.1 mechanical
1.2 hydraulic

1.2.1 hydraulic brake fluid


1.3 hybrid
1.4 brake levers

actuation mechanisms

the actuation mechanism part of brake system transmits force rider part of system actual braking. brake system actuation mechanisms either mechanical or hydraulic.

mechanical

the primary modern mechanical actuation mechanism uses brake levers coupled bowden cables move brake arms, forcing pads against braking surface. cable mechanisms less expensive, may require maintenance related exposed areas of cable. other mechanical actuation mechanisms exist: see coaster brakes back-pedal actuation mechanisms, , rod-actuated brakes mechanism incorporating metal rods. first spoon brakes actuated cable pulled twisting end of handlebar.

hydraulic

hydraulic brakes use brake levers push fluid through hose move pistons in caliper, forcing pads against braking surface. while hydraulic rim brakes exist, today hydraulic actuation mechanism identified disc brakes. 2 types of brake fluid used today: mineral oil , dot fluid. mineral oil inert, while dot corrosive frame paint has higher boiling point. using wrong fluid can cause seals swell or become corroded. hydraulic mechanism closed , therefore less have problems related contamination @ exposed areas. hydraulic brakes fail, failure tends complete. hydraulic systems require specialized equipment repair.

hydraulic brake fluid

hydraulic disc brakes make use of 2 common forms of fluid. automotive grade dot 4 or dot 5.1 hygroscopic , has boiling point of 230 °c, , mineral oil not hygroscopic , has varying boiling points depending on type. o-rings , seals inside brake designed work 1 or other fluid. using incorrect fluid type cause seals fail resulting in squishy feeling in lever, , caliper pistons unable retract, scraping disc common. brake fluid reservoir marked indicate type of brake fluid used.

hybrid

some older designs, amp , mountain cycles brakes, use cable lever caliper, use master cylinder integrated piston. santana tandem bicycles used cable lever master cylinder mounted near head tube, hydraulic line rear wheel caliper. such hybrid designs allow leverage of hydraulic system while allowing use of cable brake levers, may heavier , can suffer grit intrusion in standard cable.

an older sachs drum brake kit ( hydro pull ) allows rebuild regular sachs bicycle drum brake hydraulic lever , action. piston added outside drum instead of bowden clamp. solution seen on modified long john cargo bikes, allowing low friction lever pull front wheel brake action. after sachs ceased production of kit similar solution done welding on magura piston drum cylinder lever. welding necessary because magura action reverse of sachs kit.

brake levers

brake levers on drop handlebars of road bike integrated shifters

brake levers mounted on handlebars within easy reach of rider s hands. may distinct or integrated shifting mechanism. brake lever transmits force applied rider through either mechanical or hydraulic mechanism.

bicycles drop handlebars may have more 1 brake lever each brake facilitate braking multiple hand positions. levers allow rider work brakes tops of bars, introduced in 70s, called extension levers, safety levers or, reputation being unable actuate full range of travel of main brake lever, suicide levers. modern top-mounted brake levers, called interrupt brake levers, use entirely different method of actuation , considered safer.

the mechanical advantage of brake lever must matched brake connected in order rider have sufficient leverage , travel actuate brake. using mismatched brakes , levers result in mechanical advantage , hence not enough travel actuate brake (v-brakes conventional levers) or little mechanical advantage, requiring strong pull apply brakes hard (v-brake levers other types of brake).

mechanical (cable) brake levers come in 2 varieties based on length of brake cable pulled given amount of lever movement:

standard pull levers work brake designs, including caliper brakes, traditional cantilever brakes, , mechanically actuated disc brakes branded road .
long pull levers work direct-pull cantilever brakes, such shimano v-brakes , , mechanically actuated disc brakes branded mountain .

adapters available allow use of 1 type of lever otherwise incompatible type of rim brake. brake levers have adjustable leverage can made work either type of brake. others vary mechanical advantage lever moves move pad @ first, provide more leverage once contact brake surface. hydraulic brake levers move piston in fluid reservoir. mechanical advantage of lever depends on brake system design.