Tooth sprocket question...

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ueyteuor

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May 28, 2010
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Hi there, I need some advice... I just purchased a grubee 66/80cc starfire kit... though i do not know how many teeth the sprocket it includes has...

Anyhow, what I am wondering is what type of sprocket tooth count would be right for my bicycle? Bicycle wheel is 20"!! So this is why I am wondering, since I don't see many motorized bicycle with only 20" wheels...

Another concern is that where I live there are many hills... which sprocket would be best for pedal-helped hills, and with the fastest speed, on 20" wheels...

Thank you!
 
corgi1

corgi1

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Aug 13, 2009
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Probebly a 40 to 44 tooth came with it,,,,that on a 20 inch wheel would possibly be able to climb trees,I don't know if they make a gear ,for 20 inch wheels,that would need pedaling help on hills,I'm thinking the smallest is 36 teeth.someone may know of others
 
bairdco

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
the smaller the wheel, the quicker the acceleration. you can get away with a smaller gear than the average 26" bike has. in theory, you'll need a smaller sprocket to get up to top speed, compared to a bigger wheel.

like, if a 26" had a 46 tooth, you'd need a 36 to keep up (i'm just guessing, i'm sure there's an equation somewhere that'll tell you actual wheel diameter + sprocket size = speed..)

there's people that claim a smaller bike won't be able to keep up with a larger wheeled bike at top speed, but in the real world, they're wrong.

with a 20", you could run a 30, or even a 28 and still climb hills, as long as your engine is tuned right.

i have a 24" with a 30 tooth, and i've run 30mph+ up 6% grades.
 
corgi1

corgi1

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62.83 inches per turn on a 20 inch wheel/
81.68 inches per turn on a 26 inch wheel/
about 25% less travel
40 tooth divided by 4 =10, x 3 =30 tooth ?
 
corgi1

corgi1

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75.4 inches travel on a 24 inch tire
12.96% shorter than 26 inch wh.travel
about 1/8 difference
40 tooth divide by 8 = 5,x 7 =35 tooth ?
 
corgi1

corgi1

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27 would be for more speed on the flat lands ,and less power on the hills,your weight will play a part,100-145 pounds 27 tooth,above that I would do the 30 tooth(or more w/cargo being carried),,,,,simi trucks dont hold 65 mph on hills and gear down (same as putting a larger gear on their rear axle) to climb the hills and use the power their engine has w/out boging down, slower speed "but works",,,,,,,,,,,,,
 
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ueyteuor

New Member
May 28, 2010
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California
Thanks! So I guess I should settle for 27t, I am a light person...

Do you know where I can get a 27t that's a direct fit? If not I would probably just have to find a 27t and have the mounting holes made custom...
 
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