ALL SHOOK UP?
BALANCING YOUR WHEELS CAN HELP
By John Copeland
An easy way to faster, more consistent lap times, and one that many karters miss, is to simply balance your wheels properly. Sure, it takes a few minutes, but the results are well worth it. Sprinters and even dirt racers will find it helps, and for enduro racers it's absolutely essential.
There are several different wheel balancers on the market, but they all follow two basic principles. The bubble balancer has a little bulls-eye level on the top. You simply slip the tire and wheel assembly, including a front hub, on the threaded shaft, spin on the retaining nut, and hang the unit on a piece of 1/4" keystock mounted horizontally in a vise or clamped to the bench. The balancer hangs on a hardened point and you can look at the bulls-eye level on the top to see how well balanced the wheel and tire are. By placing pieces of stick-on wheel weights (available at any tire store) around the perimeter of the wheel rim, you can eventually center the bubble in the middle of the bulls-eye. Now just carefully peel the backing paper off each bit of weight and stick it to the inside face of the rim. Cleaning the rim real well with Brake-Klean will help the weights stick better. And it's always a good safety measure to cover the finished weights with a strip of duct tape. Finally, recheck the wheel to make sure you got the balance just right. If it's off, even a little, try again.
More popular, and probably a little more accurate, are a variety of shaft balancers. These consist of a 5/8" shaft that slips through the wheel-tire-hub assembly, then mounts horizontally in a couple of precision bearings in some sort of support framework. This type of balancer comes a lot closer to approximately the way the wheel runs on the kart, obviously. And, although it may take a little longer, you can get the balance more accurate than with a bubble balancer. Once the wheel assembly is on the shaft and the shaft is in the support, the wheel will rotate until the heavy side is down. Then you just need to stick some weight on the high side and give the wheel a quarter turn and see if it comes back to the same place. If it does, you need more weight. It the weighted side goes to the bottom, take some off. It will take some practice, but eventually you'll be able to judge, by the speed at which the heavy side turns to the bottom, how much weight to add. In a pinch, it's possible to do this sort of shaft balancing right on the spindle of the kart. But, in general, the drag on the front wheel bearings is enough to make it quite a bit more inaccurate than a real shaft balancer. Caught without a wheel balancer of any kind, however, it's better than nothing.
One last thing; for those of you determined to get things exactly right, the optimal set-up is to evenly split the weight you add between the outer rim half and the inner half. That will improve the chances of having the correct dynamic (moving) balance. It's quite a lot more work, but for the truly retentive engineers out there, it's the best way.
Once you run your kart with balanced wheels, you'll wonder how you ever drove it before. In fact, losing a 1/4 ounce wheel weight on a high speed enduro track can be enough to make you pull the kart off the track before it shakes you to pieces. So get out there and smooth out your ride. You'll find it easier to concentrate on your driving, less fatiguing, and you'll probably go faster as a result. See you next month.