Dear RC,
“I bought a pair of very expensive racing wheels (brand name left out) and after inspecting them, a Cat II racer whom I have great respect for said that the wheel bearings were too tight—that the axles should wiggle a little. Is that right?”
Look past the deep-section rims, and paddle-shaped aero spokes, and ignore the direct-pull hubs, because the largest potential increase in your wheel’s performance may be rotating much closer to the axle. When a wheel is first built, any free play in the bearings will cause false readings at truing stand’s run-out gauges when it is trued and tensioned (typically, digital or dial indicators that rub on the top and to one side). To eliminate this variable, the threaded hub adjustments are purposely tightened slightly order to prevent unwanted lateral play.
Many (almost all) wheels are then shipped in this preloaded condition, but when we take them out of the box and give them a spin, the hubs feel super smooth because the bearings are new and the balls and races are polished. When the wheel is installed, however, the compressive force of the quick release mechanism squeezes the axle and further overloads the wheel bearings. Racing mechanics know about this and they preset the wheel bearings with a tiny amount of free play. This compensates for the shortened axles and allows the wheel to roll noticeably smoother.
How much smoother? I received a pair of wheels from master builder Ric Hjertberg (Wheelsmith, FSA, www.wheelfanatyk.com) which were laced to Shimano Dura-Ace hubs. I threw the wheels on a bicycle that was in a stand to get the brakes dialed in and noticed that they didn’t just spin to a stop—instead; they rocked like a pendulum for quite some time. As a bike tester, I see almost every type of wheel—right out of the box—and it is rare that one spins as well as Ric’s pair. Most wheels will rock one or two times and then stop dead. Of course, he had re-adjusted the hubs, and they did have a minute amount of play in the bearings when I removed them for inspection.
The pendulum test is a standard method to test for bearing friction and, in this case, it reminded me of a regimen that I once did with every wheel I used. I would adjust the bearings a little at a time, and then put them in the frame and fork, close the quick releases and check for free play until the wiggle faded away exactly at the moment that the lever clicked shut. I also used the same amount of closing force on the quick release levers to insure that I benefited from those adjustments on the road.
Racing wheels cost a pretty penny, and much hype is made about the quality of bearings used by prestigious brands, but you will be throwing away bearing life and dramatically increasing friction by installing your already pre-loaded hub bearings on your frame and then squeezing them further with the quick releases. If all of the claims from ceramic bearing makers are correct—that smoother-rolling bearings can save you a handful of seconds a mile—you probably should use this simple tip to your advantage. Have your shop do this when you purchase your wheels, or adjust them at home. It’s free speed.
Feel free to support or dispute this or any claim I make at askrc@roadbikeaction.com
(And, while we’re on the subject, spin the rear wheel with the chain on and consider how much your cassette free-hub ratchet is slowing you down.)
That’s one of the big advantages of many of the wheels using press fit cartridge bearings (not cup and cone and not angular contact bearings). On my hubs (and may others) the skewer does not preload the bearings. There is a solid connection between the inner races and the axle so you can tighten the skewer as much as you want without doing any bearing adjustment. The outer race of the bearings are press fit in with the proper amount of preload and you’re done.
Ceramic bearings: On the hubs (not the bottom bracket where the contact seals are more aggressive) I am of the opinion that you get virtually nothing from ceramics. I sell a boat load of them (almost $50K so far this year) but, in my opinion, if one were to take the seals and grease out and just oil a standard Abec 5 bearing, you would be 99.9999% of the same rolling resistance and save a ton of money. They get virtually all of their performance increase from the low contact seals and light grease they use and there is nothing stopping someone from doing the same with their stock bearings. They would need to stay on top of the lubing but that’s not a big deal. Remember when hubs came with oil holes?
Thanks,
John Neugent: Neuvation Cycling
BALL BEARINGS: YES
For years I've been trying to make the point about leaving some play in the bearings so they don't get too tight when the skewer is squeezed down. Thank you for a good explanation. Referring people to your web page will be easier and perhaps more effective now than trying to explain it all again myself. My experience is that if the bearings are adjusted properly, they will last indefinitely.
Garth
Whittier, CA
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