Need some opinions...Gearing

K

kite surfer

New Member
So I am about to start a custom non-kit build here.. I have some gearing questions and would like your opinions. The rider will be a 95lb girl on a 26" cruiser bike.

I have a lightly used ported 49cc Stroke with gearbox
This >>> (http://www.ebay.com/itm/49cc-Engine...ash=item5425ee7cf7:g:mTcAAOSw9a5XPl7Q&vxp=mtr)
It has the same gear box and the gear box is supposedly a 3:1 gear ratio, and I believe I have an 11 tooth sprocket on it.

Ive thought about useing this >>> (http://www.ebay.com/itm/49cc-X1-X2-...m257a189118:m:mRuRaoon97PC-c8mx7CVvVQ&vxp=mtr) But not paying the insane price this guy is asking of course.
It has a 7:1 ration on it, I can change the drive sprocket


What I want are your opinions on what you think I should use to drive this bike with a light weight rider to about 25mph, with a little pedal help at start if needed.
What transmissions would you use of the two listed and what front and rear sprockets size should I use? Also what size chain should I use?

Ive tried the calculators and im doing something wrong it seems.

Thanks for all of your opinions...
 
Kite surfer! I've done windsurfing always wanted to try the kite but never had the time. Or the money at the time.... My last board was a sinker I got for 20 dollars off some old guy.

Anyway I dunno about that cvt. I am pretty sure the internal ratio isn't 7:1. Your motor spins to what, 8k or so? I don't know. I'd say run a ratio of around 15:1 or so. Check out the ezm website they build the Qmatic transmissions for that engine. Somewhere on their website it says what the ratio is.

With cvts you want to set it up so your output sprocket is the same as if you were running single speed. Ie pretend the output sprocket is on the engine. For that motor and the wheel size you might still need another jackshaft to reduce the ratio if you run the cvt.

Your needs aren't difficult except for the large reduction required. Somehow gotta get that 15 or 16:1.
 
I'm running a similar engine in this build http://motorbicycling.com/showpost.php?p=627136&postcount=14

I stole the 3speed hub for another build and went to a direct drive, big mistake after having a 3speed, The practical ratio to be able to pull from a stop(this build has no pedals) and have a 25+mph top end was 22:1. I weigh 170 however. I initially started with an 18:1 and that really was hard on the clutch. An 18:1 might work for your 95lb GF with pedal assist starting. Probably a good starting point.

This bike worked so well as a 3speed that I have ordered another Nexus to put it back the way it was. It had plenty of power in the lower gears and hit around 35 in third.
 
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