can someone tell me what the std rolling radius of the z32 is? i.e with std wheels and factory recommend tyres....

 

The question i have is if my rolling radius is LARGER will the speedo be showing FASTER or SLOWER than i am acutally going and how much difference does it make in mph per cm increase/decrease.

 

I am actually running a HUD with digital readout taken from the ECU but i guess the same rules apply as it takes the factory rolling radius when it calculates the speed from the wheel rotations.

 

Just want to know so i know i am safe when going through speed cameras!

if you increase the rolling radius of your wheels, the speedo will read lass than what your actually doing.

The speedo is reading what your speed is at the shafts and presumes 16" diameter. but if you increase the diameter, you'll be covering a larger distance per rotation of the wheel. Hence making the speedo read slower.

HTH

the second page on this has a tyre calculator,

http://www.carbibles.com/tyre_bible.html