[resonantfreq]

My bike came with 90 wheels and its an 85. The guy didn't bother hooking up the speedo drive. Do I need an 85 speedo drive or a 90 speedo drive? I'm getting a little tired of riding past cops not knowing whether they're gonna pull me over for speeding or not

 

[twinner]

The 90 driver will work fine. It's gonna make your speedo show your speed as faster than it really is...a good thing as it helps prevent getting a ticket...I had to use a '94 speedo cable with my '94 driver/wheel. You might have to do that with the '90 driver too.

 

[resonantfreq]

Thanks Simon. I don't suppose you know by how much faster it will show do you?

 

[twinner]

Around town it was off by only 1-3mph. It increases in deviation as the sppeds increase. I had a very accurate bicycle computer running in tandem to see how much it was off this summer...At 65mph on the cyclo computer on the highway the gixxer speedo was reading 69-70mph.

If you really wanted to calculte the variation you'd need a formula and some basic geometry. I'd try to figure it out but I'd rather be riding or playing with the gixxer.

 

[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

 

[twinner]

<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.

 

[John250R]

Oh, I was under the impression that the drive was geared much like the tailshaft where the speedo drive is in a car transmission.

John

 

[resonantfreq]

I think I can live with 5 or 6 mph on the highway. Now I just gotta find one. Thanks for the help.