Sup Big Dog!
Rodger at Trackside did a lot of testing with a 17.5. He found that he had to gear the motor STUIP tall. Much taller than our 13.5. So i would somewhere around a 4.0 ratio.
Hope that helps.
Team XRay, RCAmerica, Motiv, Gravity RC, Schacht Design Works.
Drive it, Dont slide it!