19/07/2017 12:45pm
In recent years this style of disc has become very fashionable. Their manufacturers and promoters have worked hard to make a sales argument and claim they are an improvement over round discs. So, is it a better disc? The manufacturers claim they are lighter, stronger, cool better and that the cutting edges of the discs ‘clean’ the pads.
Ok, so let’s take a look at this. First you take a round disc and then cut out 20% or more of the surface area. Then yes, we agree, all other dimensions being equal it will indeed be lighter. However, this means that you have removed 20% of the surface area contact between the pads and the discs. You have therefore reduced the available friction by 20% as well. How do you make friction when you are pushing a brake pad against fresh air? So the available friction will be lower.
Next the pad ‘cleaning’. Do pads need cleaning? Well no actually! Do you see Grand Prix and WSB riders getting beaten because there pads are not cleaned by the round discs? Er, no.
What is happening is that the pressure exerted on the caliper pistons is trying to force the brake pad material into the cut outs on the discs and every time the cutting edge of the disc passes the pad it removes another little bit of the pad material. The result of this ‘cleaning’ action is massively accelerated pad wear. Go to a World endurance race sometime and look how many petal style discs you see in use. You will struggle to see any at all because the pad wear is so rapid that they need to change pads much more often than the teams with round discs and they cannot compete!
In our opinion the only benefit of this style of disc is an aesthetic one. Some riders prefer the way they look. That is just fine as long as they are not looking for excellent braking performance and are happy to pay for new pads on a regular basis. Other than that, we can see no real benefits and a host of negatives. What they are is an excellent piece of marketing. People like the way they look so they are convinced by the sales arguments that go with them because they want to be.
Some things are already the right shape. It doesn’t matter how many times you redesign it, the right shape for a wheel is round and it always will be! The same is true of brake discs. You have been warned!