Tire size for 18 inch wheels [Archive] - SaabCentral Forums

: Tire size for 18 inch wheels

30th March 2004, 05:31 PM
Ordered the 18 inch BBS CH's today. I'm at odds over which tire size to run. 225/40/18 or 235/40/18. I've seen cars set up with both. I think that the hirsch is running 235's. Any advice?

Going on my 2002 9-5 Aero

30th March 2004, 05:47 PM
Ask the people who are supplying you the wheels, they should be able to tell you.

30th March 2004, 08:27 PM
For your speedometer & odometer to remain accurate, the best size is 225/40/18.

If you go with 235/40/18, then the new overall diameter will be 10.9mm bigger than stock. This means that when your speedometer is reading 30mph, you are actually going 31mph.

Now, I'm not sure if Tech II will allow you to adjust for a new wheel-tire size combo. Does anyone know?

30th March 2004, 10:23 PM
In January I got new rubber for my car. The factory standard is 215/55/R16 and the new rubber I put on my car is 225/50/R16. I'm lso wondering by how much this will affect my speedo reading too.

As for DriverEd, whats the difference in price between the 225 and 235?

31st March 2004, 07:38 AM

Your 225's are 11.5mm smaller in diameter than the stock 215's. When speedo reads 30, actual is 29. When speedo reads 90, actual is 88.

235/50/16's would have been closer to stock (1.5mm smaller) - negligible speedo difference.

Over time, your odometer will indicate that you've driven more mileage than you actually have, so keep that in mind if you're counting mileage (ie. on a lease).