You are correct John E, the diameter looks like about 1.75"; I'd have to take one off to get a more exact measurement. So a 13 would be about 6.5/pi=2" approx. Hard to tell if there is enough clearance for that. The question still remains on the table - do the extra teeth have a significant advantage or is it marketing hype?

Also any suggestions on brand of sealed bearing pulleys?
Thanks,
Raymond