Speedo question

[Guest]

It the gearing for the speedo done in the speedo or the drive gear on the wheel?
wish to know if speedos are able to be change from a smaller gs to a 1000 and vice verser

[quexpress]

It's the drive gear (matched to the associated wheel).
"All Japanese Motorcycles are equipped with mechanical speedometers of 2240 RPM= 60mph."
IMHO you can change speedos as long as the speedo drive remains with its associated wheel.

[cougar]

It's the drive gear (matched to the associated wheel).
"All Japanese Motorcycles are equipped with mechanical speedometers of 2240 RPM= 60mph."
IMHO you can change speedos as long as the speedo drive remains with its associated wheel.

so if I fitted a gs550 speedo to a gs1000 it will still read correctly ?

[Griffyn]

I'm having a problem where my speedo is reading quite a bit low (10%+1MPH) and I was wondering if a PO had done something stupid swapping parts around, or did I just have a bum speedo.

[Steve]

so if I fitted a gs550 speedo to a gs1000 it will still read correctly ?

Most likely, because they use the same size front tire.

I'm having a problem where my speedo is reading quite a bit low (10%+1MPH) and I was wondering if a PO had done something stupid swapping parts around, or did I just have a bum speedo.

What bike, and what size front tire?

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[Griffyn]

1980 GS750L with a brand new 100/90-19 Shinko 712 up front. I sized it down from the 110/90-19 Dunlop that the PO had put on.

[Steve]

The 100 will raise the speedo a bit, compared to a 110, and it should actually be quite accurate. Many of the smaller bikes came with a 90/90-19 front, and the speedo was a bit "optimistic". Installing a 100 usually removes the error. I just had a GPS on my wife's bike last weekend. At 60 mph on the GPS, the speedo was bouncing a bit between 60 and 61. Can't complain about that.

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[Griffyn]

That is exactly what I was hoping for, Steve. But when I tested it yesterday at 30, 40, 50, 60 and 70 MPH indicated speeds I found that my GPS unerringly reported 10 percent plus 1 mile per hour over the speedometer. I was hoping that a PO had put the wrong hub gear on it or something similarly easy to fix. The static 1 MPH off I'm quite happy with, but 10% is way too large an error.

[Steve]

I wonder if you might have a drive from one of the later E models with the 16" front tire.

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[Griffyn]

Thank you, that might be just the information i was looking for. Rule-of-thumb geometry says that a 100/90-16 would have a circumference of about 88% that of a 100/90-19. Which equates to a ~12% change and that is close enough to 10% that I assume the rest of the error is in my math.

Did these later E models run 100/90-16s up front? And if so, does anyone have a spare 19" aluminium wheel speedo hub to aid in the experiment?