I just bought a set of 18" rims with rubber.

The stock S0-2's rotations per mile are (F/R) 833/840.

The Ecsta Supras are 824/825.

Now since I am travelling the same distance, however, the wheels are actually revolving less, does this mean that my speedo will be reading low. ie I am travelling faster than what is actually being read.

I realize that the error is small and probably negigible, but I want to understand this.

Thanks!

 

It's the rear wheel/tire diameter that affects your speedo since this is what the speedo sensor is picking up (the final drive coming out of your tranny). So if stock is 840 and your new ones are 825, you will be showing "slower" speed than before or about 1.8% less on your speedo at the same road speed. Putting it another way, if you are travelling at any given speedo reading, your actual road speed will be faster (you'll be speeding).
Putting it YET in another way, you have effectively reduced your diff gearing from 4.10 to about 4.01, REDUCING the mechanical advantage of your drive train by about 1.8%.

 

Thanks Xviper that is exactly what I am looking for...once these tires are done (came on the rims ), I will be looking for stickier tires closer to the OEM.

 

can you say N1's??????

 

Yep, they will be my next set .

 

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

shhhh dont tell them that u used it...they might get mad

 

bridgestone canada swapped my rear MBZ's for N1's.....GRATIS!!!

i'm set....just waiting for spring now!!!!

 

TKG 26 shorthand again.
What's the N1?

 

Porsche equivalent of our SO2s in larger sizes.