Gear up

[ianmartin40]

Hi Folks, looking for a bit of confirmation, would I be correct is assuming that to make the gear ratio`s higher on my kitted PX125 motor I simply fit a 21 tooth clutch?
The motor is quick and pulls really well but is very revvy, I never use first gear as i am through it is 2 seconds so always move off in second gear which the motor is fine with, I just thought it would be more relaxed riding if the gearing was higher.

[mijapxman]

Ian, you are correct. Can't remember standard clutch gear tooth count on a 125 engine but go up one tooth on clutch to up gear or if you have enough torque, you may find 2 teeth more works. Have a look at mista freak mopeds you tube site, he has some videos on up gearing 😉

You can also have a play with this gearbox calculator, just enter your gearbox details and you'll see the difference.

scooterhelp.com/tuning/vespa.gear.calc.html



Mij☺

[ianmartin40]

Thanks Mij

[3narf]

Doesn't it have to be a special conversion gear? Unless you replace both primaries you might have problems as the gear modulus (effective diameter) will be wrong and it won't mesh properly... Just thinking back to smallframe gearing

[shaunbond]

Standard 20,21 & 22 clutch centres mesh with 67/68 primaries and 23 with 6. There are however others made by clever people which overcome this i.e. 23 / 67 by DRT

[ianmartin40]

I fitted a FA italia 21 tooth clutch which is now up and running fine and has made the difference I was looking for, no other alterations were carried out, apart from buffing down the outer edge of the rear clutch plate as it was hitting the casing!