TU10 tape drive restoration

I have two TE16's, very similar to TU10. And on both drives the rubber of the capstan is gone. It was black, but now looks a sort of orange with white speckels ... Edward suggested to use a ring of rubber cut from the tyre of a bike. We have plenty of bikes in Holland, so that is no problem :-) I guess that friction is not a real issue either. The rubber will probably have sufficient grip on the tape. What is the real problem is of course the correct diameter, as that directly related to the tape speed when the tape moves along the head. I have not looked into it, but if the tacho is producing a slightly too slow or fast signal, because of the not perfect diameter, would there not be a trim point to adjust an amplifier that drives the reel motors? Even with the original capstans, there will be some tolerance in the production, and my guess is that there will be some pot that can change (within limits) the amplification, hence the tape speed. If you plan using the TU10 only to write tapes for yourself, so not worrying about interchangability, the correct speed is not an issue, as the tapes you write will be written on the same drive. just some thoughts, Henk.