As mentioned above, just a few 0.1mm thick 5mm shims will stop the wheels moving, just ensure that you dont actually bind the axle with too many shims. I usually use only 1 shim between the pin and the bearing (then attach the alloy hex). I put the rest of the shims on the other side of the axle (inside) you will be surprised how few you need to reduce it. There is not that much problem with a bit of slop, it ensures the car is quite neutral. The less slop, the more precise the handling of a car, which is fine when you are on top of your game and can check for tweak etc regularly, but for more casual club racing it can give you a car that just changes how it feels every time you clip a barrier.