Let's Talk About Gearing  By  captaincrunnk (Read 985 times)

captaincrunnk
hi, so you want a basic gears 101 lesson?
Then you're asking the right guy.

lets start off with the typical scooter gearbox setup.
your gearbox should look somewhat similar to this...

beedspeed.com/html-pages/diagram-final.jpg
here you see 2 sets of gears both converting lots of rpm with low torque into less rpm with higher torque
in order to calculate your gearbox reduction ratio you will need to divide the first and second sets of gears and then multiply the answers together
 for example if my gearbox goes 15 teeth to 47 teeth and then 13 teeth to 39 teeth,
47/15= 3.133 and then 39/13= 3:1 then the answers 3.133x3= 9.399:1
so there we have it. this gearbox has a reduction of 9.399:1.
that means when the driven shaft going into the box is turning at 9400rpm, the wheel will be turning at 1000rpm

so what does all this relate to in the real world?
you said you do a lot of high rpm riding. if you change the gearbox to give you a better reduction of about 8.xxx:1 then you will need less rpm to reach the same road speed, providing you have set your transmission up with heavier weights and your engine is giving enough torque.

it's like a trade-off between engine speed and engine stress, too much rpm will kill the engine from overheating or a valve collision, and too much strain on the engine will snap a connecting rod or destroy the crankshaft bearings. too much rpm will overheat the transmission and melt the belt, and too much stress will snap it.

on a stock engine, you should be able to run the engine a bit cooler with a bit more strain on the engine and transmission by reducing the gear ratio. but not by much.
doing this kind of mod is mainly for people with high rpm builds that want to use their extra rpm to get a smoother takeoff,
or high torque builds that would like to turn all that initial torque into wheel horsepower to get moving

If you want more top end speed with less RPMS the saying is go Taller on your gearing. Now you have to remember going to tall without providing more HORSES will effect your take off speed. But the rule of thumb for a stock motor in fairly good health going 2 up and 2 down works well. If you go more than that stock you will notice much slower times starting and getting up to speed.
My 350lb Trike pulls nice and strong with the 16/37 gearing from 13/40 stock but I added quite a bit of horses to the motor.
I have 18/36 gears ready to go in want to see how they work.
Here I took CCR's diagram and labeled the possible gearing changes.
Alleyoop

The most common gear changes Is #1.



My Gears: