easy to use tyre size comparison tool which gives speedo error factor.

 

http://www.miata.net/garage/tirecalcold.html

that is really cool :lolcry:

or the new version http://www.miata.net/garage/tirecalc.html woo!

 

Gets tricky when youve got the diff and wheel ratios changed.... i.e. the Silvias got a 4.4 diff and larger rims so the speedo reads slightly funny...but its not too far out. 4.1 diff on the way but :lolcry:

yep...gotta love the bmw magnetic pickups on the diff to measure speed. my '84 had one.

Irokin: could you get a cable or end gear off a car with the diff ratio you have?

yep...gotta love the bmw magnetic pickups on the diff to measure speed. my '84 had one.

Irokin: could you get a cable or end gear off a car with the diff ratio you have?

 

Nope, gearbox never came with a 4.4 diff. But its even easier than that to change the speedo. Drop down to jaycar and buy a "Digital Speedo Corrector". Yay for electronic speedos :lolcry:

Well it was definately wrong for mine. My speedo is to fast by about 20ks and that said it was to slow by 10ks. Haha does that mean i need a new speedo cable or what?

Need a new gear drive in your gearbox that goes onto the end of your speedo cable.

Need a new gear drive in your gearbox that goes onto the end of your speedo cable.

 

Thanks brother.