Innovative Energy Engineering



Brakes

A variety of brakes are used to decelerate. Older types, still used on children bikes, are coaster brakes that brake the rearwheel by pedaling backwards. Most modern adult bikes have a front and rear brake. Cable-actuated rim brakes used to be the most common type and are being replaced by hydraulic disc brakes.

Hydraulic disc brakes work better when conditions are wet or dirty or when wider tires are used. Disc brakes also don't wear out the rim. Even when the disc brake itself is heavier than a rim brake, it leaves the wheel designer more choice to use lighter rims. This reduces rotational mass. Another advantage of hydraulic is that less force is wasted by cable friction and cable stretch. Cables can also freeze and need replacement after years of use and possible corrosion. Cheap bicycles use cable-disc brakes which improve wet performance and tire clearance, but inherit the cable problems.

For normal riders front rotors should be 180mm and rear rotors should be 160mm. This provides a nice front-bias and provides sufficient brake power and heat dissipation. Only dedicated downhill bikes require 204 mm front (and possibly 180mm rear) rotors. Unfortunately many bikes are delivered with 160mm front rotors only. Cheap road bikes only have 140 mm rotors. This is concerning since road bikes can be very fast on descents. Kinetic energy increases with he square of the speed and the heat generated when braking from high speeds can damage the rotor metal. At minimum it can create temporary fading (loss of brake power due to heat). Not good when going downhill very fast. Sometimes you can see road bikes with dis-colored front rotors due to heat.

Two types of brake fluid are used: DOT fluid (like in cars) and mineral oil. DOT fluid attracts water (reduces boiling point) and needs to be replaced frequently. Mineral oil has a higher boiling point and does not attract water and requires much less frequent replacement. In my experience Shimano brakes are very easy to service, and the use of mineral oil makes that service less frequent. Shimano bleeding kits (to de-aerate or replace brake fluid) are also easy to use and inexpensive.

Rim Brakes

Typically it is difficult to upgrade a rim brake bike to disc brake. The frame and fork need to have the appropriate mounts and he hubs also need to be disc type. Because road bikes use brifters (combination of brake and shifter) an upgrade to cable or hydraulic disc brakes involves a shifter upgrade, which may require derailleur upgrade. Unless the bicycle is very valuable, it usually is better to buy a new bike with hydraulic disc brakes or keep the rim brakes. So, if you have rim brakes make sure they perform as well as they can. for this true the wheels as well as you can, set the brakes up as good as possible and use a high-friction brake pad like the Kool-Stop Salmon. This won't overcome the inherent disadvantages of rim brakes, but at least you have a chance at good braking performance.

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