Gear Ratio with Predator 212cc and jackshaft (2024)

Not quite sure where to post this but maybe someone with experience with this engine can give me a tip before I order the sprockets.

I bought the engine from somebody in this forum and he ran the following setup

13t clutch
22t JS in
9t SJ out
48t rear sprocket

I get a ratio of 9.026

He said he had around 50mph at 6700rpm

Now my goal is a good cruising speed of 50mph at a lower rpm

The website where I can order the jackshaft only offers the JS sprockets from sizes 10 to 18 and it would be great to order everything from one place.

So if I order the clutch with 12t then 18t in, 10t out and to a rear sprocket of 44t (which i still have around here somewhere)

I get a ratio of 6.600

If I calculate right, this would mean I can go same speed (50mph) with about 4904rpm. Which sounds perfect but then again I think it might be a little too long the ratio because of the start from dead stop.

Now from what I heard the engine got lots and lots of torque so here is the question:

Do you think this is a too long ratio for launching from dead stop?

Compared to my current bike with a slightly tuned (higher compression) 80cc running a 34t sprocket in the rear I can still perfectly launch from dead stop without paddling so im pretty sure with a monster like the Predator it should be no problem with this ratio setup. Or not?

The clutch I want to get engages at 2.000rpm

Can somebody explain me the different options they sell here and why you would either recommend a jackshaft or torque converter? And also - what rear sprockets are being used in the case of the converter??

take a look at his build thread most of your answers are here and its a sweet bike

he got it already race ready from another member and saved a boat load on it

governor is long gone look for buck0s videos he posted in the thread i linked

what kind of speed do you want is the key to all of this this is a bicycle still

all governors are set to 3600

and you need a 10:1 reduction from the motor since its a chopper you dont need the offset like the rest of us do but it may need to go the other way so you may still need a jack shaft
to work right it would be a 120T rear sprocket a 55t if you could make the power to pull that gear is something like 80-90 MPH the gear reduction is the other reason we use a jack shaft so we can use a 40-55T rear sprocket its taken up at the jack shaft

it idels at 2200 if your clutch in gauges at 2800 and the govenor is at 3600 that gives you 800RPM to use

the sprockets arnt hard to work out its division mostly if your clutch is 12T and your rear is 55T thats 4.58:1
with the suggested AGK jack shaft ratio 12T clutch 22T in 9T out and a 56T rear is 12.44:1
if you switch to a 44T rear or a 11T on the output of the jackshaft it brings it close to 10:1

your clutch wont work then the engine idles at 2200

top speed is determined by rim size and max RPM

if you set it up right you end up like this
http://youtu.be/JsKmNiie_J8