Always Asymmetric
Rim asymmetry is essential to quality, high reliability disc brake wheels (and for all rear wheels, disc or not). The main benefit is in allowing for higher spoke tension of the non-drive side spokes of the rear wheel, and likewise the non-disc side of the front. Improved bracing angle of the spokes also results in greater lateral stiffness.
- Balanced Spoke Tension
- Improved Lateral Stiffness
- Longer Spoke Life
I built my first wheel set using an asymmetric rim, a rim brake pair, in the mid-90s. As a wheel building geek, I was blown away by the elegance of this solution to the relatively low non-drive side spoke tension that otherwise results from a conventional on center rim. I’ve since been frustrated that so few of the premium rims available for custom wheel building, including many of the top end carbon rims, utilize this design. Verum’s “Always Asymmetric” ethos put an end to my frustrations.
Rear hubs have long been asymmetric, with the drive side hub flange pushed in to make room for an ever-increasing number of cassette cogs. When Shimano hubs went to 11 speed, I took to wire tie and soldering the non-drive side spokes on virtually all my wheel builds in order to reduce spoke movement (and noise). Disc brake front wheels suffer because of the same type of asymmetry, with the hub flange moved in on one side to make room for the disc rotor. Assymetric rims are essential in clawing back the resulting imbalance in spoke tension and shallow bracing angles.
Asymmetric rims improve the balance of spoke tension on opposite sides of the wheel. In a rim break front wheel, because the hub and rim are symmetrical, the spoke tension on both side of the wheel are the same, creating an incredibly strong and reliable wheel. A disc brake wheel built with an on-center rim, by comparison, might only have only have 45-55% of the tension of the spokes in the drive side of the rear wheel. These low-tension spokes move more with every rotation of the wheel (and especially under braking load); they fatigue (work harden) and break much sooner than their much tighter counterparts.
Rim asymmetry also improves the bracing angle of the spokes attached to the farthest inbound hub flange. The greater bracing angle improves the lateral stiffness of both front and rear disc wheels. This is a real performance benefit with climbing or sprinting out of the saddle.
I could go on and on, but the long and short of it is that I can’t understand why anyone is building disc wheels with symmetrical rims. Okay, that’s not true… I do understand why, and it’s got nothing to do with building the best possible wheels.
-CW