it's time to get new tires and i just would like to known as far tires size work best along the proper gearing combo
on 400 scrambler 2x4,would like to gear a little faster but will have to fine tune the secondary helix then and i known it is a lot more testing to do then,thanks for the helpful inputs.

 

I'd keep the same size diameter if it was me. Alot easier to swap out a sprocket and play with gearing.

 

yeah,that what i tought also,maybe swap a 2 inches smaller tires in the front only...
i've messing with smaller rear tire with my old '96 scrambler,and always went back to stock size tire,speed was
higher with them...