Speedometer accuracy

Okay so I had my girl do 30 on main road and my bike was reading correctly but when I get to top of gear im reading 70-75. Are speedometers inaccurate sometimes at high speeds ? Its probably something else but I was curious about this anyways

Are your tires larger than what came on the bike? Lubricated the speedometer cable lately? If you have a GPS on your bike, I think that's the most accurate way to measure speed.

spedo has a fluid damper that helps the needle move correctly and smooth....sometimes the fluid dries up, leaks out. this will FUBAR the needle reading. I have gone though 2 and the best one I have is jumpy.

you can get a brand new one for about $160......its not a Kawasaki part.

www.z1parts.net/product/kawasaki-z1-900-...1000-speedometer-mph

Road tests in the 70s reported in general that Japanese speedometers erred on the high side and usually by a percentage so that the higher the speed the larger the error. Do you feel that yours is under estimating speed ? Could be just old, cobwebs, dust or dried up oil as suggested.

As mentioned, GPS way to go but with a Buddy ride next to you, compare speed measurements...

Another method for ball park.... What's your tach informing you...?

Example on my build:
Originally due to ZX636 conversion to KZ 630 chain, had hard time finding rear sprocket in 35 tooth.
Wanted faster off the line/low end torque, decreased high end.... 15/37 gearing.
Recently found/changed rear sprocket to 35 tooth....

Stock gearing 15/35 gearing @ 70mph = 4500 rpm (4500 + 1500 rpm difference = 70mph)

2 up on the rear gearing 15/37 @ 70mph = 5000 rpm (5000 + 2000 rpm difference = 70mph)


One of the nice features of Acewell electronic speedo, can adjust wheel circumference on the fly thus adjusting speed measurements in comparison with another rider (ne digital speedo or GPS)... Dial it in for +/-1 mph accuracy....

Just some thoughts...