i have itp 25 inch tires, I did the hauch upgrade and they sent me another spring similar to the epi clutch springfo rthe secondary pully and i didnt notice any difference at all, I put my 25 inch tires on the same time i did the upgrade but I honestly think mine might be slower, or exactly the same, not faster at all, mine used to do about 46, now im luck to get 42, definately not 60