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Anyone calculate speedo difference with a 21" wheel?

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Old Feb 26, 2010 | 03:39 PM
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Default Anyone calculate speedo difference with a 21" wheel?
Was just wondering if anyone has calculated how much of a difference the speedo is off with a 21" wheel?
 
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Old Feb 26, 2010 | 03:48 PM
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Heres a tire size calculator

http://www.miata.net/garage/tirecalc.html
 
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Old Feb 26, 2010 | 03:49 PM
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The speedo doesnt read off the front wheel, it reads off the tranny so a 21" wheel doesnt affect your speedo!
 
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Old Feb 26, 2010 | 04:02 PM
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Originally Posted by hog-doc
The speedo doesnt read off the front wheel, it reads off the tranny so a 21" wheel doesnt affect your speedo!
ditto!
 
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Old Feb 26, 2010 | 04:05 PM
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Originally Posted by hog-doc
The speedo doesnt read off the front wheel, it reads off the tranny so a 21" wheel doesnt affect your speedo!
Makes sense, it should still be off by about 5%
 
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Old Feb 27, 2010 | 02:20 PM
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Originally Posted by hog-doc
The speedo doesnt read off the front wheel, it reads off the tranny so a 21" wheel doesnt affect your speedo!
Didn't know that! Thanks!
 
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Old Feb 27, 2010 | 03:18 PM
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Originally Posted by hog-doc
The speedo doesnt read off the front wheel, it reads off the tranny so a 21" wheel doesnt affect your speedo!
Depends on how old your bike is. My 1990 Evo is front wheel driven. I don't know when Harley changed, possibly with the first TCs.
 
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Old Feb 27, 2010 | 03:51 PM
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Originally Posted by grbrown
Depends on how old your bike is. My 1990 Evo is front wheel driven. I don't know when Harley changed, possibly with the first TCs.
You are correct there, I was answering to his 09 model.

They changed some models in 99. 2000 and later are all trans driven speedos.
 
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Old Feb 27, 2010 | 04:01 PM
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Maybe I'm a little thickheaded, but if there is a tranny speed sensor that determines MPH, isn't measuring some rotational element of the bike to deptermine the MPH? And if so, and the new tires are a larger diameter and they cover more ground with a single rotation than the stock tires, isn't the speedometer reading still affected???
 
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Old Feb 27, 2010 | 04:03 PM
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Last time I checked Harleys aren't front wheel drive!
 
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