with bigger tires you also have to gear down to compensate for the tires and in most cases smaller tires are faster because they are smaller and lighter allowing you to gear up to get the speed. Also make sure you you get the regular hb diffs http://www.rc-monster.com/proddetail...GY_DIFF&cat=47 and not the pro diffs. the pro diffs are truggy diffs and give you an ultra low gear ratio