jfort

Went to Dayton. Picked out what I wanted. Went again to pick them up. Met the guy who made them. Had them ceramic coated. Couldn’t be happier.

Petza914

They're awesome. Love my Forgelines too!

woozylv

Hi Brandon,

Did i get it right, rears should be with lower profile than fronts? You were saying i should be looking at 235/30-20 fronts and 305/25-20 rears, wouldn`t that look odd fronts 30 and rears 25, or it is not that noticeable on car? Sorry it`s my first time buying wheels and tires for car which has different sized wheels, a bit frustrated

alaris

The second number in a tire size is the height of the sidewall expressed as a percentage of the tread width. Since the rear tires are significantly wider, the sidewall height is taller than the higher percentage front.

235/30 and 305/25 are fine but they have a very thin sidewall. I run PS4S in 245/30-20 and 325/25-20 on my 20x9 20x12 setup and those sidewalls are pretty thin but larger than the former.

Next time around I’m going with 255/30-20 in front as the 245s/325s are a bit stretched. I’d also go with 335/25-20 if the PS4S were available in that size but they aren’t.

Petza914

First number in tire size is the with on mm, 2nd number is sidewall height as a percentage of width. In order to heep the rolling circumference the same for the front and rear tires, the wider rear tire needs a lower aspect ratio (percentage of width).

Busta Rib

You are trying to plus-size (go bigger) than OE spec with the 20" wheels you just bought. Ideally, you want to maintain the same aspect ratio and rolling diameter of the OE wheels/tires from the factory. Use this calculator to figure out the closest spec tires that will get you to OE aspect ratio: https://www.calculator.net/tire-size-calculator.html

The calculator will tell you how close to original 19" factory spec your new 20" setup will be and how it will affect your speedometer reading. I suspect you will not be able to get exactly to OE but you can get close. Good luck.

Petza914

For anyone with an AWD car (4, 4S, Targa, Turbo, etc) it's critical that the front and rear sizes selected are within 2% of each other or you'll destroy the AWD transfer case as it tries to spin the different size tires at the same speed, and you'll have PSM and ABS system issues.

alaris

Factory C4S sizes are 2.86%, closer to 3% than 2%. On my setup with 245/30-20 and 325/25-20 I’m actually at a lower differential of 2.37%.

Jeroen//997

Thanks, the 2% bandwidth is that a number from Porsche that you know? I would like to go from 305x30 to a 315x35 to have a little less stretch on my 12J wheels. That´s 0,9% difference in circumference, so no issue. Is closer to the original size better for the transfer case, or doesn't it matter as long as you stay under the 2%?

Petza914

I don't believe 305 width was ever factory spec on a Carrera. It is on the GT3 but that's a RWD only car and on a 12" rear wheel, which is a width also not offered on a Carrera. A normal 235/35-19 & 295/30-19 is a 1.9% differential. Now, lots of us have run the 235/35 F with 305/30 rear and not had issues, so maybe within 3% is the critical factor, but I don't think Porsche ever used that combination on an AWD car.

Petza914

You can go to a 315 on a 12" rear, but you can't run that with a normal size front - the difference would be like 8%. You also shouldn't run a 315/35 as the overall tire will be huge with increased width and larger aspect ratio.

To run a 315 rear width, you need a 245/30-19 front and a 315/25-19 rear and that puts them within 1.64% of each other.

On my car with 12" rear, I run a 255/30-19 F & 325/25-19 rear and those sizes are within 1.47% of each other.

Apex Wheels

Yes, those are the correct sizes. They are chosen for their heights and to match the wheel widths you will be working with. For context here are the OEM and 20" heights outlines below:

OEM 19"
235/35-19 - 25.5"
305/30-19 - 26.2
The rear tire is ~2.7% taller

Narrower OEM 19"
235/35-19 - 25.5"
295/30-19 - 26"
The rear tire is ~1.96% taller

20" setup
235/30-20 - 25.6"
305/25-20 - 26"
The rear tire is ~1.56% taller

As you can see, the heights are very close to the OEM setup and as close as we can get with your wheel width when going to 20" and looking at tire availability.

Edit: Added the 295 rear OEM tire option specs

- Brandon

alaris

295/30-19 is not the factory size for the AWD cars except for winter tires. From the .1 manual:

Jeroen//997

Thanks. I was thinking about a 315/30-19. Indeed then I need to go up to a 245/35 upfront.

SSMOKE-U