sprocket recommendation

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Mercman

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Dec 27, 2011
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Central VT
Guys,
What would be the best overall sprocket choice for a Trek 850/66cc build for running on both dirt and paved roads? Vermont is anything but flat with the exception of a 200 yard sprint here and there. Thanks for any feedback.
 
takeitez

takeitez

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Dec 19, 2011
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Clayton Missouri
It really depends on the weight of the rider and how much you will be pulling. Really if you are willing to do it the best thing would be a shift kit (I hear) I run a 36 tooth and It will pull me up all the hills around here but they are not super crazy. I weight about 130 and my bike isn't super heavy. I think a 44 tooth is good for most people. If you are trying to over come torque problems an expansion chamber can help give you some power. Btw I have the same bike and it has served me great.
 
The_Aleman

The_Aleman

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Jul 31, 2008
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el People's Republik de Kalifornistan
The stock 44T does work great for hills, from my experience. But it does typically limit your cruising speed to under 30. The engine will be spinning 6K RPM at 26MPH with a 26" wheel, and most 66cc engines aren't balanced very well. Spin em over 6K at your own peril! They typically need some work to do it often.

Each tooth smaller on the rear sprocket is worth roughly 1MPH. Hence, a 40T would put you around 6K @ 30MPH.
 
maniac57

maniac57

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Oct 8, 2011
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Stock gearing (44th rear) is pretty good for medium hills. If you plan any heavy climbing, I'd go smaller on the rear, like a 40 or a 38. Don't expect earth-moving torque from these motors. A tuned exhaust would help you pull hills as well, or even better, an adjustable mag to really wake the engine power up.
 
Last edited:
The_Aleman

The_Aleman

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Jul 31, 2008
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el People's Republik de Kalifornistan
maniac57 said:
Stock gearing (44th rear) is pretty good for medium hills. If you plan any heavy climbing, I'd go smaller on the rear, like a 40 or a 38. Don't expect earth-moving torque from these motors. A tuned exhaust would help you pull hills as well, or even better, an adjustable mag to really wake the engine power up.
Click to expand...
You have it backwards. A smaller rear sprocket increases speed, a larger one increases torque multiplication. A 44 climbs better than a 40 or 38.
 
2door

2door

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Staff member
Sep 15, 2008
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Littleton, Colorado
Think of it this way:
The smaller the rear sprocket, the higher the gear. A 44t sprocket is something like driving your car in 2nd gear all the time. A 36T sprocket is like you let it shift into drive, or third gear. If you go higher on the tooth count, such as a 48 or 56 T sprocket it will be like you leave your car in 1st gear. Low gearing= a larger rear sprocket. Gearing higher requires a smaller sprocket.

Hills? Gear low. A standard 44 or 41 T will do you well.
Flat ground, no load = a higher gear 36 or a 32T.

I'm in Colorado and flat terrain is hard to find. I run 41T sprockets on my bikes and they seem to perform well for most of the riding I do. I'm a light weight @ 135lbs. A few of the locals I ride with run 36T sprockets and they do the job also.

Tom
 
takeitez

takeitez

New Member
Dec 19, 2011
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Clayton Missouri
Another thing that I have been told is that for every tooth less then the 44 tooth it ads aprox one mph more. I haven't ever done the math for it but no one has told me I am wrong so far :D
 
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