I have a set of 325/25/20 Continental Extreme DW and need some front tires. What is the correct size? It had 245/30/20 before, but looking at some tire size calculators, it looks like a 255/30/20 is a closer match?!?

These are going on a 2007 997 Turbo, if the 255 is the right tire, will I have rubbing issues?

Thanks in advance,
Jayson

 

245/30/20 is the most common size to mate with the 325/25/20 to avoid any issues with the AWD dif.

I've not run the 255's but definitely not something i would want to experiment with and end up costing yourself in the long run.

 

I agree, I see those sizes together most often, but if you look below, the 255 is closer in diameter than the 245. I used this calculator: https://tiresize.com/calculator/

Do you know the spec? What % difference is safe?

Tire Size..........................Equivalent Diameter
225/30R20 25.3X8.9R20.....25.3"......-2.7%
235/30R20 25.6X9.3R20.....25.6"......-1.5%
285/25R20 25.6X11.2R20...25.6".......-1.5%
245/30R20 25.8X9.7R20.....25.8".......-0.8%
295/25R20 25.8X11.6R20...25.8".......-0.8%
255/30R20 26X10R20.........26".........Equal
265/30R20 26X10.4R2-.......26"........Equal
305/25R20 26X12R20.........26"........Equal
225/35R20 26.2X8.9R20.....26.2".....+0.8%
325/25R20 26.4X12.8R20...26.4".....+1.5%

 

The tough part about your question is that there really isn't a "correct" size, as Porsche doesn't recommend a 20" wheel for the 997.

I think your best bet is to read the comments of people who have installed 20" wheels and go with the size that seems to create the fewest issues. It looks like Kricci has identified that size in the post above.

 

I've seen it somewhere before, there is a certain % that the overall diameter has to be within to not damage your transmission. That's the spec I'm looking for.

 

Got it. I know for the 996 cars the front to rear diameters had to be within 3% of one another. I'm not sure about the 997 turbo cars as they utilize a different AWD system.

 

I believe the 997 is 3-4% from what I have seen and read.

I would err on the side of caution once again and stay as close to 3% as possible. But again not something I would feel comfortable experimenting on and finding out I fried the awd diff in the process.

Good luck!!

 

As folks have said, the 245/325 is the right choice. Based on the stock sizes, you want the rears a little less than an inch larger diameter than the fronts.


Also, 245 is probably wide enough for street traction. On my track 18's I'm going to see if I can squeeze a 265 in front. Neg Camber and wheel offset will play an important part. Cheers