Go with the 18 height can be adjusted with a custom set of dog bones �25.00, gearing with a one tooth smaller front sprocket �15, once youve got an 18" rear wheel you can buy some serious offroad rubber, thats if you do a lot of offroading if not stick with the 17 it will be cheaper thats for sure, ive got a place that will lace up a 18" rim with stainless steel spokes into the original hub for �350, not cheap but an option