13.2:1 gear reduction - clutch killer?

GasX

GasX

New Member
I am running a 4-stroke with a 3:1 gear box spinning a 10T drive sprocket to a 44T pirate sprocket on the rear wheel for a total gear reduction of 13.2:1. I hit 29mph at not quite full throttle on my maiden voyage (as measured by a neighborhood speed monitor), so I know it is good for speed but it does vibrate noticeably when starting from a dead stop.

My best guess from readingna few threads is that I should be closer to 20:1. Am I just going to ruin my clutch if I don't change anything or am I alright as is? How would my ride change with a 56T sprocket?
 
Hit 32 mph today at full throttle going past the same speed trap. The bike really likes to move once it gets going and REALLY likes a slight downgrade. I definitely feel the gearing is too tall from a dead stop though. Rattled the exhaust so hard on the starts that it came loose. I can't help but feel a 48T or 56T would improve things...

Is there any science here or is it all seat of the pants?
 
It's physics. More reduction means more torque multiplication, less reduction means less.

Yes, your gearing is _way_ tall. According to the gear calculator, you would be going 40MPH at 6800RPM - the engine's HP peak!
Every tooth larger on the sprocket is worth a little under 1MPH. A 56T might be optimum for you - gear calc says 31.5MPH @ 6800.
 
I am building almost exact set up as what you have, including 44t sprocket.
Quite looking forward to your results with 56t sprocket.

Keep us posted!
Thanks.
 
I like the tall end gears on the ones I have build, just pedal assist from a dead stop.

Better yet, just jackshaft it and use your bike gears, that's my next 4-stroke project, SBP has 4 stroke kits for under $200, and the mounting plate beats the he|| out of the Grubee HS mount.
I have in inquiry in to Kings/Gasbike about a price for kits without the mounting bracket, BB & cranks, chain and sprocket assembly.
 
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