First post!

I have been trying to figure out this same conversion...

Some issues to consider:

Your QS motor makes 4400 rpm @72v with no load. Under load it will only make 75% of those rpm. So 3300 rpm under load.

3300 rpm with a final chain drive of 3:1or 42,14 teeth, will give a theoretical top speed of 75mph WITHOUT your belt reduction. With your belt reduction you are looking at about 25mph.

If you use a flux weakening controller it will help a little but not sure if its enough. They claim 6500 rpm....so 4875rpm under load. This translates to 111 mph theoretical and gives some room to reduce gearing there. But i doubt you will see 4875rpm, maybe 4k under load. These motors lose torque near the top. So maybe a reduction belt 25% at most. And it will be a pig off the line.

A CVT as an intermediate might work better. It would let you gear for speed and help off the line.

The QS motor you chose has 50nm of torque. That is about the same as a 450 4 stroke gas engine at peak. But the gas motor has 5 gears to help get it going and keep top speed potential. You only have 1 gear so you have to pick one....4th gear in the stock tranny is 1:1.

If you could output that motor through the stock transmission it would be a beast. More power from start than a 450f.

Or find a motor that has higher rpms. The Alta redshift motor goes to 14k and is gear reduced. Where can we source that baby?

So I don’t mean to throw a wrench in the works but i am trying to figure out the same problem. I haven't been able to find a suitable motor that has enough torque and RPM to work direct drive. Unless i pick something huge that weighs 60 lbs. That wont work for a dirt bike or supermoto. And a reduction of a smaller motor will make it slow. So really we need either a higher rpm motor for reduction or a transmission. A large diameter out runner would work but they don't really exist other than hub motors. This is why the Vector Vortex mounted a hub motor mid drive.

If you try to get rpm by increasing voltage to 100 i don't know if it will get you there. Will the motor handle it? Maybe? Your battery will start to get huge with any decent AH capacity at those voltages as well.

So when you figure it out let me know. I am still stuck.

Will be following your progress.