I rebuilt my starter rolls using two 100mm rollers and a foot activated switch it also stands on it's base so it takes up less room when not in use. I was going to wrap the rolls in tyre tread from my local retreader but with both of the rolls driving they turn over knobby tyres and have no trouble starting moto crossers.
The biggest problem is that I used a 9 inch angle grinder for power and with the starters size and weight it's only suitable for the workshop and the chain drive is very noisy.
I have drawn up a design for a more portable set powered by a starter motor and with a single belt drive connecting both rollers to the motor and also using 100mm rolls.
Anyone see any problems with it sometimes you can look at something and not see the obvious.
Workshop Starter Rolls
12 volt starter rolls
Zane