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Sportster Motorcycle Transmission, Clutch, Primary & Secondary Drive Transmission, Clutch and primary or secondary drive problems, advice, and/or how tos.

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  #1  
Old 15th February 2012
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Default rear Chain sprocket size?

Im replacing my rear sprocket it is a 48 tooth and my front is a 21 tooth CHAIN DRIVE. bikes a 1988 883 with a 1200 conversion are these stock sizes? I do have high RPMS around 60-70 so could I change the rear sprocket to get lower RPMS would I need to go with less teeth or more teeth or should I just stick with the 48 tooth? would 1 extra or 1 less tooth make a difference?
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Old 15th February 2012
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You either have to go bigger on the front or smaller on the back. I think my 93 five speed has 23/48 which gives a 2.08 to 1 you have 2.29 turns of the front for one wheel rotation. This will reduce rpms by 10%.
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Old 15th February 2012
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I believe the 21/48 combo is stock on Sportsters with chain drive from the 1980's-on. One less tooth on the rear won't make much difference, but one (or two) more on the front will. I run a 23 front sprocket on mine, and it's turning about 3000 rpms at 60 mph.
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Old 15th February 2012
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Default front sprocket

so like a 49 or 50 tooth in rear wont make any difference? so your running a 23/48??
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Old 15th February 2012
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If you put a 49 or 50 on rpms will raise at highway speeds. Put on a 47 in rear or 22 or 23 infront.
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Old 15th February 2012
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I'm running a 23/49 on mine. Originally I just replaced the front sprocket with a 23 and still had the 48 on the rear. When I needed a new rear sprocket, I bought a 49 because the 23/48 gearing was just a little to high for the hilly area where I live. If I had it to do over again, I would have probably just bought a 22 front and 47 rear, because the 23 required a little grinding on the backside of the sprocket cover to fit without rubbing.
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Old 15th February 2012
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I did 22/46 on 1988 with 1200 conversion with ported head. Runs strong.
Nice on the highway.
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Old 15th February 2012
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Default rear sprocket

So if I use a 47 with my 21 I should be ok? the RPMS arent to bad I really never go over 60 or 70MPH so a 21/47 should work fine?
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Old 16th February 2012
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That will give you a 2.24 to 1 gear ratio. Divide the big by the small and you get the ratio. I matched mine to stock belt gearing when I made my choices. Your current setup is 2.28 to one which is not much of a change.
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Old 16th February 2012
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Im running a 23 front, 47 rear, i can cruise at 70 all day long at low rpm's.
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