10sp on 9psd?
 

I am looking to do warmups on my trainer before cross races and I have a powertap wheel from my 10speed...My cross bike is 9speed...Its just going to be used in the trainer..is it going to hurt it at all?

It won't shift well, unless you put a 9 speed cassette on the pt wheel. If you just leave it in 1 gear for warming up, that might be ok as long as the wider 9 speed chain is ok on the narrower 10 speed cassette. try it and see

I don't think it will set on the cog. Isn't the 9 sp chain width wider than the cog spacing on a 10 sp cassette?