13.2:1 gear reduction - clutch killer?

GoldenMotor.com

GasX

New Member
Oct 7, 2011
277
0
0
Florida
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?
 

GasX

New Member
Oct 7, 2011
277
0
0
Florida
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?
 

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
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.
 

PieOnAir

New Member
Dec 29, 2011
10
0
0
Sydney, Australia
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.
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
57
48
Phoenix,AZ
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.
 
Last edited: