Because I have no fear of living dangerously I’ve always used 18T on mine, the acceleration is rubbish but the drone as it gathers speed is great, and blatting thru town @ zero rpm always puts a smile on my face. I’ve never had rubbing wire probs, but I can see the concern, I just ignored it.
I made up a little calculator for this sort of thing you might like to play with, except you can’t upload xls files on here, so a couple of pics.
