If you’re like me, you probably built your MRX Ultra, mounted up a set of fresh front tires on your favorite wheels, gave them a spin and was surprised to hear a rubbing noise. The reason for this is that the car was designed to be used with Atomic’s own wheels which have a fairly narrow inner bearing hub.
With other wheels, like those from Reflex, the hub is a bit wider and may rub on the ball cups. Here’s a picture below of a wheel rubbing on the bottom ball cup.
The fix here is pretty easy and that is to take one of the extra silver 0.5mm shims that come with the kit and put it between the knuckle and the bottom ball. You may also need to place a shim above the knuckle if you’re experiencing rub up there. You’ll want to check this with your wheels straight and when turning.
If your wheels spin freely, you’re done. If you’re still experiencing some rubbing, the bearings in your wheels are probably sitting down below the edge of the hub, causing it to rub on the knuckle and/or the shims you just put in.
To fix this, you’ll need to put a few 3 x 5 shims on the axle. The number of shims will vary depending on the wheel. I would start with about 0.2mm worth of shims and add a 0.1mm shim until it goes away. There is no exact science here. Even wheels from the same manufacturer have enough difference in tolerance that one set may take 0.2mm in shims and another 0.4mm. Just remember to put the same number of shims on both sides.