Specifically I have a 997.2 and am curious what the OE wheels (5 lug) will support in terms of tire width. I'd like to go with a "Plus Zero" (245-35 -19 x 325 30 19) fitment but has anyone else done this?

I'm asking because I want to know how it affected the handling compared with the OE sizes. I suspect the handling might be a bit more sloppy as the sidewalls would allow more flex (sidewall buldging) on the narrow(er) wheels.

I really want to go with a 325 rear section without having to upgrade wheels. The car really needs more "meat" at the rears for better traction... lol

 

I ran 245/325s on my 4s. I will be putting those on my turbo next.

 

Just make sure you do proper research before buying - here's some info that's interesting:

https://www.6speedonline.com/forums/...5-s-rears.html

 

315's are not a plus zero.

 

I been racing AWD cars for years. Changing height of tires front to back will only kill the driveline. Even an 1/16 of an inch.

 

As have I. The safety margin has always been to stay within 3% rolling diameter.

235/35-19 to 245/35-19 is 3%

305/30-19 to 325/30-19 is 3%

As long as the relationship between the front and rear diffs are the same, the tire size is irrelevant.

 

Can you post a picture? I want to see how much it sticks out past the rim.

 

Hope these help. I couldn't tell that they stuck out any more than the 235/305's

 

I say go for it. The diff is only 9k or if you are lucky maybe 3k used. A tranny is what 10-15k. The look is worth the 20k risk.

FYI Porsche .2 cars at least the non turbos 11+ will kick a sensor if you have a rolling diameter that is wrong. Guy had about 10k on the car, ran over a nail and had to replace one tire. He got an error and running the code it was the rolling diameter. So while some AWD cars are fine the Porsches are very sensitive.

Like I said though its only a 15k-20k fix if it goes to **** on you.

 

You're (and other like minded people) missing the point. It has nothing to do with the rolling diameter when the front and rears are the same rolling diameter.

It has everything to do with when there is a DIFFERENCE between the front and rear rolling diameters. If you run a front and rear tire with DIFFERENT rolling diameters is when you run into issues. And when you'll get mechanical damage to the diff and possibly transmission.

For AWD cars, when the front and rear tires spin at different rates relative to one another because the rolling diameters are different is what causes the damage. When the front and rear tires spin at the same rate relative to one another, there is no issue.

The only issue you will see is a slight decrease in revs per mile when comparing the OE sizes to the sizes I listed (Plus Zero). The revs per mile (rotations per mile) difference between the OE size and the "Plus Zero" size I listed in my original post is 10 REVS per mile for BOTH the front and rear. So there are NO issues because the front and rear tires are spinning at the same rate, just like they do with the OE size.

You also need to read the tire rack article that spells out exactly what I just said..... albeit better written.

http://www.tirerack.com/tires/tirete....jsp?techid=18

 

I have a 997.1 TT and have been considering dropping to an 18" wheel for track tires. Better selection, less expensive, etc. and have been "told" that a 245/40 R18 and 315/35 R18 will work fine.

Using the following Tire Size Calculator (http://tire-size-conversion.com/tire-size-calculator/ ) the oem 235/35/R19 revolves 792 times/mile and the 305/30/R19 revolves 770 times per mile. This means the front tires rotate 2.86% more than the rears.

Similarly, the 245/40R18 will revolve 784.6 times/mile and the 315/35/R18 will revolve 756 times. That is a 3.78% differential.

Assuming that anything less than a 3% differential is okay and anything more than that is not, it would appear the 18" package described above is a no-go.

Am I thinking about this correctly and/or is there some other measurement besides the revolution/mile that really is the gold standard? I'm not interested in taking on a potential Big Dollar repair to change wheel size if in doing so it puts me into the grey zone or worse. Thanks,

 

^ Compare the overall diameter.

Oem size in 19 has a 3% delta

18" in 245/40 & 305/35 has the same delta and safe to run and also NT-01's are avaialbel in this size

 

".....18" in 245/40 & 305/35 has the same delta and safe to run and also NT-01's are avaialbel in this size."

Thanks, and yes, the Nitto's seem to be the tire of choice. Now they just have to start making them again. Have also heard the Kumo Ecsta is very good albeit with a short lifespan, ie, about 10 heat cycles before significantly falling off.

A couple more questions: (i) In going to 18's must the car be realigned and re-corner balanced? (ii) Can I continue to use the 19's on the street - mostly just toodling around - or do I just need to stick with 18's for everything? (iii) In going with a 245/40/18 and 315/35/18 setup, are 9" fronts and 12" rears the way to go? Anyone have an idea what the wheel offsets should be? Thanks,

 

Thanks for the lesson. Its just you roll into a dealer with that and dont expect Porsche to even think of helping you.

So what do you need the meat for? Not enough grip? and you want more understeer?

 

From experience, I will never stray from the factory specs on wheels/tires. I bought a pre-owned 997TT Tiptronic with 22k miles that required a new diff/tranny because previous owner ran 305 25 20 instead of 325 25 20. Looked great with more rim showing but total repair was over $25K.