Whether disc or rim brake, braking is a balance of three factors: wet braking, dry braking and heat build-up. These all work in tandem and affect the “feel” or modulation of braking. Some systems excel at certain aspects and others less so. For example, disc brakes are excellent in wet, sloppy conditions, but can be prone to building up heat.
In terms of modern wheels, the main topic, other than disc brakes, is braking on carbon clincher road wheels. These wheels have a small volume, clincher tire on a bike that can hit speeds in excess of 50 mph. When the brakes are applied they generate heat and that heat does two things: it heats the air in the tire/tube causing an increase in pressure and also it heats up the brake sidewall of the rim. If the temperature of the rim sidewall gets hot enough, it could exceed the glass transition temperature of the resin in the carbon fiber (the glass transition temperature is the temperature at which the “glue” in the carbon fiber starts to get soft). The higher tire pressure exerts higher force on the rim hook bead and could cause the rim hook bead to bow outward under pressure.
This issue has dogged carbon fiber clincher rims for the last decade and this is why we developed our testing for all of our wheels. Below is a simplified version of how we approach braking on carbon clinchers.
First of all, carbon clincher rims are typically built using a higher Tg resin (resin with higher glass transition temperature) to resist the heat build-up. Our goal is to minimize heat while maximizing braking power and modulation. This is done via brake track base material, brake track coating and brake pads.
We use a combination of tests in excess of industry standards to ensure we excel.
- Dry brake performance based on ISO 4210
- Wet brake performance based on ISO 4210
- Long application brake heat based on ISO 4210. 300W held continuously for 15 minutes performed 10x. This is 150 minutes at 300W of braking. This is the equivalent to someone dragging the brakes for a long time.
- Excessive heat application. 1200W for 5 seconds, 10 seconds off. Cycled 5 times.
- Ride and race test.
Technique: Proper braking technique is extra protection whether it is our wheels or anyone else’s. So it is on a car going down the mountain, so it is on a bike. You can’t drag your brakes all the way down without risking damage to the brakes and just like in your car, pulsing the brakes (on hard to scrub speed and release, on hard to scrub speed, release…) is the best technique. Even a short release drops temperature significantly. This can be seen in the temperature profiles in our testing.
We recommend hard braking for short duration to scrub speed and then release as opposed to applying the brake and holding it. Some people prefer to alternate front are rear brake which also works. Either way the concept is the same: brake in short bursts and release.