<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by John250R:
Simon,
I was under the impression that if you got the correct speedo drive for the wheel/tire combo the speedo should be right. I dunno, I think that they set them up to be a little "optimistic", even on an all original bike. I guess I'll find out soon, my wheel and tire swap it almost complete on my '86.
John<hr></blockquote>
The speedo driver only does one thing...tells the speedo the wheel is turning. The speedo is under the impression that each revolution equals what it is calibrated for. A revolution is a revolution but...an 18" wheel travels farther in one revolution than a 17" wheel. So the speedo thinks it traveled the distance of an 18" wheel...but actually it hasn't.
It's a similar problem for the newer gixxers. They measure speed from the countershaft. If you change the countershaft sprocket (your gearing) your bike will be at a different speed than originally factored. That's why everyone likes their Yellow Box's so much...it tells the computer in the gixxer your corrected speed.