This is where im getting thrown for a loop is the kit im looking at uses a 10t to 17t from the china girl engine to the jackshaft. Then gear on the right side of the jack shaft is a 10t gear down to a 36t on the pedal assembly. Then from the pedal back is a 44t gear.

These gear changing back and forth i guess is confusing me. From what i am seeing the jack shaft spins slower than the engine due to the slightly larger gear. But the other side has a gear the same as on the engine so in my view it is now spinning back like if it was connected straight to the engine. Then that is spinning a 36t sprocket that turns a 44t to the rear. That is where i am stumped.

I will be using a china girl 2 stroke on a gt2a grubee frame. I will also be getting a ported cylinder and piston kit along with a high compression head and a cheetha cdi. Im also looking at upgraded carb and exhaust.

My main goal is to have the bike capable of 40 mph as i want to have a useable speed of 25 to 35 mph. I probably dont need a shift kit but the videos i seen i do like the lower rpm the engines turn at speed.

Rusty, it's junior high school math.

Determine which sprocket drives the chain. That's the denominator. Driven sprockets are numerators. Work out each equation separately, then multiply them to each other.

The only odd ball where the driving sprocket is larger is the relationship between chain ring sprockets and rear wheel sprockets or cassettes.(Like a 24t chain ring and an 11-tooth cassette gear).

To solve your gear ratio, divide jackshaft sprocket by engine sprocket .

17/10=1.7:1.....

Divide 36t chainring by 10t jackshaft:

36/10=3.6:1.....

There's a built-in engine gear reduction of4.1:1.

Multiply 4.1 x 1.7. X3.6. =25.092:1

If you have an 11-34t rear cassette and a driving 24t chainring sprocket,

Multiply 25.092 by (11/24) = 25.092 x .45833333 = 11.50....

Divide that number by 4.1 to determine perspective rear wheel sprocket of 2.805:1, like a 28t in 8th gear.

Using the same formulae, you'll find that 7th gear is likened to a 33t sprocket. First gear is like a stump-pulling 87-tooth rear sprocket.

If you want 8th and 7th gear ratios to be like 31t and 37t rear wheel sprockets, change the10t JACKSHAFT sprocket to a 9-tooth one.

This should get you in the ballpark. The ratios in my shift kit are similar, and allow me pedal without engine assist.

Good luck in your gear selections.