I mostly ride touristic style, and its not uncommon descents of few hundred meters or even 1000 meters (vertically, usually average gradient is around 5-10%). What's the best technique to brake to avoid glazing of brakes?
I've heard following advices:
- pulse brake instead of constantly braking
- use alternately front and rear brake
- create as much of aerodynamic drag as you can to reduce the pressure on brakes
Apart from that, I have following theories:
- brake pads have some temperature above which they will start to glaze, so I should brake in such way, to avoid exceeding this temperature
- if I brake suddenly with great power, brake pads/disc rotors/rims will have to absorb a lot of energy which translates to heat, if I brake gently - less heat is generated
- if I brake with both brakes energy will be divided between two brakes so as heat (though not necessarily evenly - division depends on the force applied on brake levers)
- the greater the speed, the greater aero drag, so if I go faster, less energy (in total) will need to be absorbed by brakes
- the lower the speed, the longer the time that it takes to ride, so longer the time to dissipate the heat from brake system
So based on all above I have two strategies for braking:
- Brake as little as possible, but when needed (ex. before hairpin turn) brake shortly with great power and both brakes
- Brake constantly using both brakes and maintain low speed (below 20km/h?)
First strategy is trying to use as much aero drag as possible and then it will generate a lot of heat in brake system. Though during the brakes it will have time to cool down again. Second strategy maintains constant high temperature of brakes, but provided low travelling speed I assume that temperature will not exceed glazing temperature.
These strategies I discarded:
- Brake constantly and maintain low speed using alternating brakes. This means that although the brake that's not operating is chilling down the other gets full load and its temperature will be higher improving risk of exceeding glazing temperature.
I've already glazed a few disc rotors:
- In my commuting bike, I have one hill (700m long, 4% gradient), and I brake shortly but with great force
- In my trekking bike - downhill on straight asphalt, starting with gradient above 10% where I gained ~50km/h later I tried to not gain any more speed using alternating brakes technique
Also I have a feeling, that after glazing, when I experience lower braking strength, if I ride a few downhills when I'm more gentle towards this brake it regains its effectiveness. Is it possible?
Though it might be problem solvable using different means (reduce my weight, use larger rotors). I'm looking that would work best, even on non-disc-brake bikes.
To reduce number of variables, my final question is: Given:
The speed Vn - which is the speed the biker would get if he would not brake nor pedal at all, when areo drag is preventing him from gaining any more speed from gravitational force.
Desired speed the biker would like to go Vd = R * Vn
What are the optimum braking strategies that:
- Minimize time that it takes to ride 10km of such slope
- Prevent brakes glazing
Depending on the R. If R >= 1 then the strategy is just not to brake at all, that's easy, but how to brake if R=0.5 or even R=0.1?