97 ZL600 speedometer reading 10% high

10% makes it easy to do the math while riding, but would still like a more accurate speedometer. my ZL600 has an 18" front wheel. From E-bay images it looks like a speedo drive from a 600 Ninja, that has a 16" front wheel, would fit.
So would the Ninja drive be geared differently, or are they all geared the same regardless of wheel size.

They aren't all the same, check out stereordinary's recent post for the calculations

Here’s the thread (starting at the third post):
www.kzrider.com/forum/5-chassis/621661-p...nd-conversion#912953

Stereordinary wrote:

Here’s the thread (starting at the third post):
www.kzrider.com/forum/5-chassis/621661-p...nd-conversion#912953

So it looks like I would need a speedometer drive with a 22 or 21 tooth gear. Probbally not going to happen unless there are Kawasaki motorcycles with front 14" wheels.
I don't think reducing the reading buy 4% will be enough. Just makes the math harder. 

AI Overview
Motorcycle speedometers are required to show a speed that is never less than the actual speed but can be higher. Because of this, most manufacturers design them to read about 7% to 10% higher than the true speed to ensure they comply with regulations. This is a common requirement in many regions, though specific rules may vary by location.  

All vehicles read “high” not only to meet regulations but also to avoid litigation claims from convicted speeders 

It may be possible to remove the needle and reposition it. Some of the ZRX folk have done that. Evidently It is also possible to strengthen the magnets to improve accuracy.
You could also build a 10% reduction gear set to install between the cable and the speedometer.

1997 zl600. partzilla. speedometer gear = 25T. pinion = 9T.
1986 zx600. partzilla. speedometer gear = 24T. pinion = 9T. 

assuming a swap can be done. either the speedometer gear or the entire gearbox. the 24T will improve the accuracy by about 5%. 

edit: 2005 ex500. speedo drive gear = 23T.  pinion = 9T. if anything swaps. this would get you even closer.

Wookie58 wrote:

All vehicles read “high” not only to meet regulations but also to avoid litigation claims from convicted speeders 

I think that's the official line. The real reason is motorcycle manufactures want us to believe our bikes are faster than they really are.