spare tire size for 225/45-17 ?

[wiratorn]

My car has 205-50-16 wheels from factory with
T135/70D16 spare tire.
But i have changed the tires to be 225/45-17 on STi wheel.
from the manual, the spare tire to match is T135/70D17.
Do I have to order T135/70D17 to replace my T135/70D16 ?
Any problem if i use the D16 with my new 17" rims ?

thanks

[PlatinumPRM]

I'm not 100% sure here, but...

When you upgraded to the 17" wheels and 225/45 tires you increased your wheel diameter by 1", but you also decreased your tire sidewall height by about the same 1", keeping the overall diameter close to stock.

This type of change is called "Plus 1". (If you had gone to an 18" wheel, it would be "Plus 2").

Therefore, I would think you'd be OK using the stock spare tire if necessary. (At least that's what I thought when I got my 17" Prodrive wheels.)

I'm sure someone will correct me if I'm wrong.

[z0s0]

The following site will probably help here.

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



Tire Size Comparison

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
135/70-17 3.7in 12.2in 24.4in 76.8in 825 0.0%
225/45-17 4.0in 12.5in 25.0in 78.5in 808 2.2%
205/50-16 4.0in 12.0in 24.1in 75.6in 838 -1.5%