Thursday, January 17, 2002

Rolling Resistance

By: Tom Cole Date: January 17, 2002
Every rear wheel drive car or truck on the road or racetrack uses tapered roller bearings in their front hubs. The reasons for this are simple, less friction and combined radial (perpendicular to the axial) and thrust (parallel to the axial) load capacity. So why are kart racers using ball bearings which are designed only for radial loads on their karts? I can understand why Jr. Drag racers don’t care about thrust load. They just go fast in a straight line. But kart racers go fast and turn fast. Usually, the one who gets through the turns the fastest wins. So again, why are so many kart racers using ball bearings? Endplay! Somebody has actually sold people on the idea that karts with tapered roller bearing hubs have so much endplay that you can’t set the toe-in. What a pile! How is it that those NASCAR and F1 boys can set the alignment on their cars? Never mind that endplay tolerance for a wheel with tapered roller bearings is only .002” (that’s half the thickness of a piece of notebook paper). How precise are the widths of the inner and outer races of a .65-cent ball bearing? How precise is the relationship between the inner and outer races? Are they parallel? Are they precisely on the same plane? How precise is the bore of the hub? Is the center sleeve exactly long enough? Well guess what! None of this matters if you use a properly installed tapered roller bearing. The guy beating you doesn’t give a rip how the wheel rolls on the rack. How the wheels roll on the track, in the turn under thrust load and down the straightaway under radial load is what matters in wheel bearings. And he is not going to tell you why he’s beating you.

All ball bearings roll on a “point” of contact between the ball and the races. A tapered roller bearing distributes the load over the length of the roller in a “line” of contact. This greatly reduces the friction coefficient allowing tapered roller bearings of the same diameter as comparable ball bearings to carry a greater load and achieve a much greater fatigue life. Simply put, it will roll easier than a ball bearing. The angle of the races along with the taper of the bearing rods allows a tapered roller bearing hub to roll equally well in the turns or on the straight-aways. Standard ball bearings DO NOT roll as well through a turn as they do down the straightaway, and they do not handle the demands of a kart racer as well as a tapered roller bearing.