Hi,
I have a PX 125 engine with a DR 177 kit on it. I know the gearbox is standard PX 21/67 primary but it has a 35 tooth 4th gear and basically is struggling to keep its speed up on any inlcine.
If I want to reduce or shorten top gear to make it rev more, and without taking the engine apart, can I do this by changing the clutch primary gear? If so do I want to go from 21 up to 22 teeth, OR from 21 DOWN to 20 teeth ?
you are welcome for the help.
there is a nice helpful gearing section and p-series gearing calculator at www.scooterhelp.com ( http://www.scooterhelp.com/tuning/gearing.html ). other good scooter info there too.
to shorten the gearing you want to go down to a 20 tooth.
what exhaust are you using? it seems like a DR177 should be able to pull and hold 21/67 even with a 35 tooth 4th gear. my stock Stella 150 2T (LML Star 2T) had 21/67 and when i put on a SIP road exhaust i also up geared with a 22 tooth and i have no problems keeping speed.
Thanks for this. I had guessed 20 tooth, but was a little confused working things out. The engine has a sito plus exhaust on it. I am not a lightweight either. It runs OK most of the time, but up long slow hills it loses speed. I just wanted to try down gearing it a little to see if the shorter gears helped it hold speed a little better.
many thanks for the help