I am not sure if how stock your tecate is but I am running 13/38 gears with 22' turf tamers and I still have gobs of power with the wheel still coming off the ground relatively easy (mines alittle modified though). with 18" tires I think you would be closest to stock with the 15 cs which should put you around 65mph, and still leave you with some low end. As to your first post aking if a 38 will give you lowend grunt, the result will be the opposite, taking away low end and giving you more top end.
The problem with America is stupidity. I'm not saying there should be a capital punishment for stupidity, but why don't we just take the safety labels off of everything and let the problem solve itself?
85 atc350x ('05 christmas present to myself)
84 tecate (my baby)
84 honda 110 (lil buddy)
81 honda 70 (daughters ride)
86 lt250r (sold for parts) R.I.P.