Choosing a Rear Sprocket

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burnclouds

burnclouds

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Jun 17, 2009
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I'd like to know your experiences on 36T vs 32T rear sprockets. I'm looking at going to a smaller one. I have a stock 80cc on my MTB. There are some hills around here but it's mostly flat. I's like to keep up with most traffic around here (35mph), but the question is will the 32T be able to pull my 120Lbs or should I stick with the 36T? Any body with practical experience with the two please chime in.
.fly
 
Bikeguy Joe

Bikeguy Joe

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I will only say that you should stick with the 36T since the engine will not like pull you with a 32T. It barely pulls with a 36.
 
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Echotraveler

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Aug 25, 2008
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1+ bike guy...most people recomend 40t as a happy medium between torque and speed...120 pounds is so light!!! my MB is 280 and i can go 22 mph with a 44T.....i bet a 40t will give me 25 easy!
 
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Bikeguy Joe

Bikeguy Joe

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There is a big difference between the stock 44 and a 36, going to a 32 is pretty high.
I'd say 125 pound rider and good smooth tires, no hills it would be O.K., but the engine will be dogging at anything below 25 and it still won't go much faster than 40-ish.
 
burnclouds

burnclouds

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I just purchased a 36T from BGF with extra rag set (inc bracket and bolts) for 19.99 + $10 SH. I think the 36 should to it. Next I'll look at a larger carb jet and/or expansion muffler. But I really think I'll wait until i have my rotor brakes ordered and installed.

--My Father-in-Law had some good advice; "When making your toys go faster, First upgrade the brakes."
 
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Forbisher

Forbisher

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Dec 28, 2008
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Orange County, CA.
burnclouds said:
I just purchased a 36T from BGF with extra rag set (inc bracket and bolts) for 19.99 + $10 SH. I think the 36 should to it. Next I'll look at a larger carb jet and/or expansion muffler.
Click to expand...
When I designed my CNC 3 way mount sprocket I settled on 35 teeth
as the best compromise.......

44 tooth = 27.9 MPH at 6500 RPM and 26" tires
35 tooth = 35 MPH at 6500 RPM and 26" tires

35 tooth at 5000 RPM = 27 MPH
35 tooth at 5500 RPM = 29.6 MPH
35 tooth at 6500 RPM = 35 MPH
35 tooth at 7300 RPM = 39.3 MPH (~True redline on a stock 66 cc)

The Chinese 66cc 2 stroke engine does not have enough power to
pull a smaller sprocket than this without losing a lot of bottom end
and it won't go over 40 mph anyway cause it doesn't have enough HP

Speed is not the only issue with a smaller sprocket as you are dropping
1300 RPM at 28 MPH for a much smoother and comfortable cruise

My sprocket mounts with the small Grubee style rag joints and has
a larger center hole diameter of 1 11/16" that matches the rubber rings

It also mounts with the larger diameter PK / Raw rag joints or
can be Clamshell mounted by the large 3 holes

Reversible offset mount 1/4" thick light weight aluminum 7075

Sells for $29.95 for local pick up In Orange County and
$5.95 shipping & handling for 2 day Priority Mail envelope with bubble wrap

Can ship 2 sprockets for only $5.95 total

Buy three sprockets and get FREE Priority Mail shipping

PS: My CNC 35 tooth sprocket is 0.8 mph faster than your flat? heavy
steel 36 tooth BGF which has badly formed teeth :D
71
 

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Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
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up north now
Forbisher said:
The Chinese 66cc 2 stroke engine does not have enough power to
pull a smaller sprocket than this without losing a lot of bottom end
and it won't go over 40 mph anyway cause it doesn't have enough HP

Speed is not the only issue with a smaller sprocket as you are dropping
1300 RPM at 28 MPH for a much smoother and comfortable cruise.
Click to expand...
Words that should be required reading.
 
C

chrisme

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May 30, 2009
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Maine
burnclouds said:
--My Father-in-Law had some good advice; "When making your toys go faster, First upgrade the brakes."
Click to expand...
So true! I need to get better brakes on my bike. Having upgraded brakes in my car literally avoided a major crash last night. Someday upgraded brakes on the bike would be just as helpful.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
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Good brakes are a must. Learn the proper use of the front brake, as it is 70% or more of your braking ability.

Practice panic stops....you need to know what to expect in an emergency situation.
 
C

chrisme

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May 30, 2009
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Maine
I actually have a modified brake handle so both brakes are pulled by the same handle. But I spent a lot of time getting the adjustment right. So I can stop fast, but not go flying over the handle bars... Front brake is important as I learned from mountain biking...
 
Junster

Junster

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Jun 2, 2009
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Washington St.
I use a duel pull lever. It has a internal pivot to balance the pull. I have vee brakes front and rear. To get more brakeing in the front I set the front pads out as far as I can. The rears fairly close to the arms. It changes the leverage applied by the cable.
 
cyclepro101

cyclepro101

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May 13, 2009
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NEWCASTLE
Quote:
Originally Posted by Cabinfever1977
im hitting 35mph with my 44t sprocket so i guess i wont change anything.

If that was true you would be at 8150 RPM with 26" wheels

How are you measuring that 35 mph?
__________________
Click to expand...
I would like to know how u are measuring this too. 35mph with a 44t sprocket just does not add up. I have a 36t sprocket and can just ht 45km/h (32mph I think?)
Check your computer wheel circumference. I have even upgraded to the largest tyres I could find. K-RAD's 3.2 These bad boys give me a wheel circumference of 2092.

Steve
 
Cabinfever1977

Cabinfever1977

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Mar 23, 2009
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i was using my speedo and i double checked my speed with a friend in a car riding next to me. maybe you got a bad engine. if i put on a 36t sprocket on mine i could hit around 43-45mph. 32-35mph is the speed for a 44t sprocket not a 36t unless you are a big person.
 
cyclepro101

cyclepro101

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May 13, 2009
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NEWCASTLE
Thats 72.5 km/h. I would love to see that. I hit 55km/h today and the engine was running smooth but there is no way it could rev any harder, it was screaming. So I can't beleive that it could do another 18km/h. Sorry.
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
Believe it. I have gps'ed one of my bikes at 38 mph with a 44T. Another at 35.something, I forget. I have been paced by two cars at 40 plus, but that's not overly accurate.

I have only had one of eight that wouldn't break 30 mph.
 
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