This article originally appeared on BikeRadar.
Wheel brand Alto Cycling recently completed a destructive braking-heat test with Spark Wheel Works that shows carbon clinchers by Zipp, ENVE, Mavic and others failing, often in spectacular fashion. While Alto Cycling CEO Bobby Sweeting said the point of the test wasn't to call his competitors' products unsafe, the visual of rims blowing up wasn't reassuring for riders. BikeRadar talked to representatives for all the brands involved for their thoughts on the test, and on the safety of carbon clinchers in general.
Alto's carbon clincher heat test
In conjunction with Spark Wheel Works, Alto tested carbon clinchers from Mavic, ENVE, Zipp, Knight, Boyd, FSE, Bontrager and Roval as well as the brand's own product. The test consisted of running the one wheel from each brand on a drum at 1,200w, with a 7lb hanging load applied at the brake lever and a set of new SwissStop Black Prince pads used for each wheel. The wheels were run until failure, with the rim temperature measured constantly.
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Sweeting said the idea for the test came about as Alto researched new resins with high heat resistance.
Like all carbon cycling products, the carbon strands in carbon clinchers are held together with resin. To make carbon wheels, pieces of carbon fiber impregnated with resin are placed in molds and heated up, which effectively melts the resin. When it cools, you are left with a solid wheel. The issue with carbon clinchers is that rim braking generates heat, and, when pushed to extremes, can cause the resin to soften, which can lead to the rim bubbling or folding open. In worst-case scenarios, the rim can fail enough that the tire can come off or the inner tube can burst from the heat. Years ago, a few events like Levi's Gran Fondo in California banned carbon clinchers after multiple incidents on steep, winding descents.
Prior to the test, Sweeting said that he was often asked by customers how Alto compared to other brands in terms of heat resistance, and that he honestly didn't know.
Big brands' objections and responses
Bontrager
Knight Composites
ENVE
Roval
Mavic
Boyd
How big brands test for safety
Alto responds to critcism
What comes next
You can read more at Cyclingnews.com
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