I have an aluminium replacement wheel with O-rings. It can slip on the first test stiches, especially if the machine has been unused for some time. The grip is fine after a bit of test sewing at high speeds, it has never been a problem. Common reasons for slipping are oil spills, dust, grime, or hardened rubber surface; you could roughen it with fine sand paper. A new wheel should not need it though. If you have the hand wheel off and just wipe it down with a cloth while it's running could be enough to sort out the problem.