An insider’s guide to wheel stiffness and other fun technology
3-12-07 // Online Exclusive: Mavic Tech Days 2007
Journalist endured cold and drizzly conditions riding bikes from Mavic's neutral support fleet to test wheel stiffness.
As for lacing patterns, the less the spokes are crossed, the higher the stiffness in both the frontal and lateral directions. The closer the spoke tension between the drive and non-drive side of a wheel, the better the wheel’s fatigue life—thus supporting the use of asymmetrical rims. Radial lacing increases stiffness but is bad for torque transmission, which is why Mavic advises against building a rear wheel with radial spokes on both sides. A radial drive side and three-cross non-drive side is 3 percent less stiff laterally and 10 percent less stiff torsionally than a radial non-drive side and three-cross drive side, but this still may be a favorable wheel design—see the Mavic Crossmax ST.
Any experienced wheel builder will tell you spoke tension is important, too. But there is one confusing fact about tension that fooled every journalist at the Mavic event. Spoke tension has a double-opposite relation to wheel stiffness. In other words, wheels with higher spoke tension are less stiff, more prone to buckling, and softer under load. That said, if spoke tension is too low the spokes can loosen, or rather come out of tension, and lose their ability to support the wheel. This can result in a pinging noise while riding and sometimes catastrophic failure.
With this aparatus Olivier measures the deflection of a wheel and fork when a lateral load is applied.
To drive some of these points home, Mavic sent us out of the classroom for blind A/B tests on road bikes (gasp!). We road several 3-kilometer laps that included cobblestones and out-of-the-saddle climbs using different wheels that appeared identical but had dramatically different stiffness, although their tension was about the same. On separate laps, we compared front wheels and rear wheels. In the end, even though the wheel tensions varied greatly, it was difficult for many riders to discern which was which. Actual wheel stiffness is very difficult to sense while riding, even for professional bike testers.
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Stiffness is so difficult to detect that many people mistakenly rely on brake pad rub to determine it. Devoted V-brake enthusiasts may experience brake-pad rub during out-of-the-saddle sprinting and climbing and assume it’s due to wheel flex. But Olivier demonstrated that wheels with lots of lateral flex between the ground and axle do not have any more flex between the axle and brake pad than wheels with minimal flex between the axle and ground. What that boils down to is this: Pad rub is usually caused by fork flex and not the front wheel and by the conbination of frame flex and the rear wheel deformation.
Mavic has done an impressive amount of testing and research to develop the products they put to market, and it was a privilege to learn about the science that backs up their wheel designs. The engineering principles are universal, so familiarizing yourself with the science can help you when purchasing a pre-built set or deciding how to build up your own pair of hoops. Because there are so many variables that affect a wheel’s performance, it’s impossible to find one with no compromises, but learning the parameters that influence wheel design makes it easier to find a wheel that suits your needs.
Mavic HQ is located in Annecy, France, a beautiful town about 45 minutes south of Geneva, Switzerland, and in close proximity to several ski/MTB resorts including the astonishing alpine town of Chamonix. Anyone thinking of taking a vacation in southeastern France, Geneva, or northwestern Italy would do himself or herself a favor to visit and enjoy the wonderful food and historic surroundings.
HI! I' don't write and speak english very well, but I try. ok?
I have a Mavic wheels, but one spoke is broken and I' like replace, can you tell me where I can buy o get them or wath can I do? Please answerme its very important. I wait your e-mail
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