you can run 17" TKCs 150/70 and 130/80, but you're better off with the 19" front for the gravel. i did run the 130/80 TKC on the front for thousands of miles of gravel and it does pretty darn good. here's one of the old bikes with a 130/80-17 TKC front parked at the gas pumps in Deadhorse. the 19" does better. the 17/17 wheel choice is fine for the SM setup, and i run the 150/70 and 130/80 Tourances when i have those wheels on the bike. there's a 130/80 Tourance on the bike in the photo shown in post #94.