Tire size question

[schwank]

Actually the 225 and 245 are the width of the tire.

Tire sizes work like this

225/40 - 18

tire width (millimeters)/tire sidewall height (% of width) - wheel diameter (inches)

So a 225/40 is 20mm narrower than a 245/40.

Each tire has a sidewall 40% of the width.

So 225/40 = 90mm sidewall height
and 245/40 = 98mm sidewall height

HERE is a link with more explanation, or just google 'tire size explanation'

Heres the size

Size: 18x8 front/ 18x10 REAR

Offset: +48mm front/ +40MM REAR

[schwank]

I have the 18" factory option turbo twist rims on my S. I just ordered a new set of Bridgestone 960AS Pole Positions from TireRack in the following sizes:

F: 225/40-18
R: 265/35-18

As you can see the sidewall height number drops down when using a wider tire. But if you do the math, the sidewalls are less than 3mm variance since that number is actually a ratio.

Hope that helps!

Originally Posted by schwank

I have the 18" factory option turbo twist rims on my S. I just ordered a new set of Bridgestone 960AS Pole Positions from TireRack in the following sizes:

F: 225/40-18
R: 265/35-18

As you can see the sidewall height number drops down when using a wider tire. But if you do the math, the sidewalls are less than 3mm variance since that number is actually a ratio.

Hope that helps!

So will F 225 40 18
R 265 35 18 which i think im going to order will fit my rims??

[jmatta]

ET40 on the rear may cause some outside rubbing if you go wide on the tire. You may need to increase negative camber to offset or roll the fenders. My rears are ET47 with 275/40/18 with neg 2.5* camber.

Originally Posted by jmatta

ET40 on the rear may cause some outside rubbing if you go wide on the tire. You may need to increase negative camber to offset or roll the fenders. My rears are ET47 with 275/40/18 with neg 2.5* camber.

So can you give me the new tire sizes for the front and rear, what you said just confused me.

[blackONblack]

Originally Posted by blkboxster

So can you give me the new tire sizes for the front and rear, what you said just confused me.

For your rear rim being so wide, so smallest width you can use that will stretch and fit is 265/35. If you increase the width (275-285) then you will have to decrese the sidewall hieght (275/30 or 285/25). But as I stated before if you go much wider in the rear you will have fender/strut rub issues. Your front rims are the same width as stock rims so there is no difference there. 225/40 front will fit fine and fill out the wheel well without spacers.

Front 225/40
Rear 265/35 or 275/30.

[mtch]

Originally Posted by blackONblack

For your rear rim being so wide, so smallest width you can use that will stretch and fit is 265/35. If you increase the width (275-285) then you will have to decrese the sidewall hieght (275/30 or 285/25). But as I stated before if you go much wider in the rear you will have fender/strut rub issues. Your front rims are the same width as stock rims so there is no difference there. 225/40 front will fit fine and fill out the wheel well without spacers.

Front 225/40
Rear 265/35 or 275/30.

I have an 03 S with the Carrera wheels (8x18 & 10x18). I replaced the rears (265/35 stock) this summer with 275/35 tires with no problems. No camber adjustments, everything else stock. I live in the mountains, and have done 2 DEs at VIR so I've driven pretty hard many times since the change. No issues with that size.

One thing to consider is the front / rear size difference balance. I noticed the difference that came with the increased front to rear offset. Rear held tighter, (more oversteer at speed) which is good in most cases but not as good in a few isolated instances. Just something to consider.