farm equipment supply stores sell awesome idlers that are made for some major stress and speed. I bought one for a 8' chopper bike i made one time . It was a little overkill for what i needed it for but might be perfect for your dyno. For 20 bucks might be easyer than a skate board wheel, and made for the purpose. Can't wait to see the bike in the sun. keep us posted please.( I love roadsters)