Shooter wheel covering

[cad321]

Me and my team have been working ruthlessly over the past 2 weeks trying to make our shooter work the best we can. We are using a linear shooter with 2 andymark 8in rubber tread wheels on a mini cim each. We finally got it shooting decently(shooting from the back of the pyramid near the center of the field and only just making it into the 3pt goal) by putting surgical tubing around the wheels to make them like pneumatic wheels for grip and compression. This worked fairly well except that the tubing expands an awful lot and wears down to quicky. We have been experimenting with different ways of getting the same result as the surgical tubing that just doesnt wear as quicky but are at a loss, so we were wondering what you guys have been using on your wheels(if any)?