Thread: Sprocket

What is the best tooth config. sprocket for my new 125cc 4 speed , 26mm carbu?

For road driving I like 16 front 35 rear

My engine will probably work with 18 front 35 rear, but I don't think those tops speeds are necessary for me

if you are going to change a sprocket I would change both and put a new chain on

they seem to wear together, and when you change just one the whole system wears out faster

Lots of different combinations of 125cc...I'll assume you are working with a small-valved bog standard china 125 motor.

That said, I think you could probably go with a 16 or 17 on the front and keep the stock 35 on the back. As stated, you should probably replace the chain and rear sprocket while you are at it. I'd only go 17 on the front with a bog standard 125 china motor if you weighed in under 170 and did most of your riding on the flat.

For me, I am am running a takegawa 124+r motor in my CT70...I'm running 17 on the front and 32 on the back and running a 12" wheel too. That is geared perfect for my weight (185) and for my type of riding (hilly street with periodic mountain crossings)

My other CT70 is running a YX177V2 motor in it. I run a 17 on the front and 29 on the back with a 120/90-10 tire. That is geared perfect for the same type of riding I do.

Ok more detail

my engine: eBay Motors: New 125cc SEMI AUTO CT70 CRF XR Z50 ATV MINI TRAIL (item 350190898331 end time Apr-22-09 1150 PDT)

on frame z50 1978 modified



Very heavy
Big tank 2.9 gallon
forks xl 250

Front tire: Monkey Bike UK 3.5 x 8 Heidenau Road Tyre
Back tire: Monkey Bike UK 4 x 8 Heidenau Road Tyre
wheel : Monkey Bike UK Low Cost Pair 8" Aluminium Wheels