Chainlube
Well-Known Member
The only reduction is the 6/44 sprockets.
Stupid idea!!! + -
- Thread starter Chainlube
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Sidewinder Jerry
Well-Known Member
So (6\44)>(9\27.5590551181)=22.4555263922\1 TR.
(7500×π×27.5590551181)÷(1056×22.4555263922)=27.3834586932 mph
If you don't have steep hills to contend with use an 8t sprocket.
(7,500×π×27.5590551181)
÷(1,056×16.8416447942)=36.5112782575 mph.
If you must use the 6t then change the 44t to a 32t for 35+ mph.
Chainlube
Well-Known Member
No, I don't want to go 35. 20-25 is fine.
I did find a couple 1 1/4" BMX pegs in my shop. Something else to think about.
Sidewinder Jerry
Well-Known Member
A 6t doesn't give your chain much to wrap around. You could run a 8\60 for a similar total reduction.
Are you talking about using the 1.25" BMX peg like an FD roller (1.25">700c)? That too would give you a similar total reduction like the 6\44>9"\700c
Chainlube
Well-Known Member
My idea is to have the engine centered on a rack mounted and the roller right underneath. I will run the chain from the little clutch, post #2, to a roller with the 44t on the end. All that on a 27.5" wheel. I just went and measured those pegs, they're 1 7/16".
Cannonball3
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A 2.8“ roller at 4500 will give over 40mph. I built a direct drive Lifan that ran well set up like that. So you have to balance with the smaller engine the reduction ratio, and the roller size. My recent conversion of the FD to a 5:1 gear box and a 10/44 final reduction (on a 24”) yields 26 ish at 7500. Nice cruise at 22 or so around 62-6500. This is on a 31cc 4stroke. The big 62cc should pull much higher ratios. I can figure roller speeds if you give me the roller sizevand max rpm.
Chainlube
Well-Known Member
The roller is a 1.4375" and the engine speed is 7500 max, probably more like 6500 cruise speed. The gear box on the engine has a 6 tooth and the drive gear on the roller is a 44 tooth, all with a 25 chain.
Cannonball3
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So, the reduction is 7.3:1. thats turning the roller only 1027rpms. The rollers circumference is 4.3”. 1027x4.3=3224”
Divide that by 12”=268’ per min or 4mph.
Either drive the roller directly for 30mph @7500 or run a much larger roller.
Divide that by 12”=268’ per min or 4mph.
Either drive the roller directly for 30mph @7500 or run a much larger roller.
Cannonball3
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It would take a 10” roller at your reduction rpm to achieve 30 mph@7500.;A large slower turning roller is better than a smaller fast one. However fitting such a large roller on a bike is difficult, though I have seem a pic of a build using a lawnmower tire.
Maybe raise the # of the reduction ratio (less teeth on the driven sprocket).
Maybe raise the # of the reduction ratio (less teeth on the driven sprocket).
Chainlube
Well-Known Member
Well, I was thinking of a little push me scooter tire, it has a diameter of 9 1/2". Or, I could just use the hub from the tire and have a 4" roller.
If I get 20mph I'd be very happy with that, don't need to red line the engine.
That engine is new, so I'm not sure what the rpms are. All have to go on is what they say in the manual. I'll have to fire it up again and hook up my tachometer.
