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It'll read too high, just like going to a larger ring and pinion on a car. That's if the speedo sender is reads from the trans. final drive, like a car. Please correct me if I'm wrong. FIRST POST!
 

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MagnumRider is correct you will get a higher reading on your speedo when you put a b***** rear sprocket on your bike. (and remeber they read too high to begin with)
 

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hey wouldn't the speedometer read slower then what your going if you went to a larger rear sproket
 

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nope, the final drive out of the trans. will be rotating faster than before at any given speed in relation to the rear tire. Think shifting to the biggest rear cog on a bicycle, you pedal fast and go slow. For comparison's sake, the sender would be on the bicycle's bottom bracket and would gain input through the rotating pedals.
 

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MagnumRider said:
nope, the final drive out of the trans. will be rotating faster than before at any given speed in relation to the rear tire. Think shifting to the biggest rear cog on a bicycle, you pedal fast and go slow. For comparison's sake, the sender would be on the bicycle's bottom bracket and would gain input through the rotating pedals.
What he said... ;)
 

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it reads high,

a b***** rear sprocket is actually an "easier gear" basically. so if your speedo says 100 youre doin like 90 (just for arguments sake)
 

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Many bikes speed comes off the front wheel so like LifeLiberty says it will make no difference. So check on where the drive for you speedo comes from & then do some thinking.
 

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Smitty said:
Many bikes speed comes off the front wheel so like LifeLiberty says it will make no difference. So check on where the drive for you speedo comes from & then do some thinking.
+1...but if i doesnt come from the front wheel then the b***** rear sprocket could cause speedo to read higher but ive seen the speedo change from changing the front sprocket rather then the rear...i could see it happening if you go up 3 or more teeth in the rear...
 

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Agreed! I thought ALL motorcycle speedos were from the front tire. If so it doesn't matter what the rear sprocket size is. If you changed the SIZE of the front tire the speedo would read incorrectly.

Both of my bikes have the original OEM tire size yet both read 5mph SLOW on the highway. I've read that a lot of other manufacturers are like this too. Any idea why?
 

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BMW's take speed readings from sensor in differential on rear..
 

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All seedo's are off. If I remember right the manufacters have to do this because the speedo can't read slower that actual when stock, but they can read fast. This is to keep lawsuits off them so the include like a .2% error and the faster you go the greater the error.
 
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