I want to start a thread that would make this as simple as possible without getting into complicated equations.

What can be safely run besides the stock 225/40/-18 295/30-18 setup??

 

I would imagine would also depend on 18s, 19s, etc.

235/315 is another safe setup.

 

Sorry, no can do. (though the equation isn't complicated...)
The rolling diameter of front and rear have to be very close
in order to be safe for the viscous differential.

Sorry, but if I picked and chose different tire brands, I might
be able to find a particular 225-40-18 and a different 295-30-18
that would not match, and could hurt the car.

If you want simple, stick to OEM. Porsche already checked things
out for you. If you want to go wider, taller, different, you (or
someone else) must check the actual rolling diameters of the
tires, by reading the tire spec sheet.

If it suits, we can make this thread into a list of tried, successful
combos (each listing would have to have the tire brand, model, and
nominal size.)

I run Yokohama Advan Neova AD07s in 265-35-18 front, and
295-30-18 rears, but those are not on stock wheel sizes...
Joe

 

I think all you really have to do is go to the Tire Rack website and enter your car's specs by year, make, and model, and it will give you a listing of the various brands that will work for your particular application. You can set it up by stock or custom wheel specs. I'm running 315's mine so I get back a customized list according to the criteria. As you know, it's critical that AWD vehicles get tire circumferences from front to rear that are the same in order to keep from burning out the front differential. It's not complicated and it saves off your info for future use.

***I didn't see Joe's explanation before I wrote mine...and he explains the viscous information much better.

 

235-??-?? and 315-??-??

I can guarantee I can find some 235 tire and a 315 tire (same brand,
same model) that won't work, eg: 235/50ZR18
which is going to have a diameter much bigger than
any 315-35-18.

The basic truth is that we have to be careful and informed. It can't
be easier if you want to step away from OEM.

 

Sorry for the Hijack....Joe are you on stock 18 wheels and offsets. Do you use spacers front or rear? Thanks

 

Actually, that's an important question. I'm on 9.5x18 fronts, 11.5x18 rears.
In the OP's interest of simplicity, we should stick to stock wheels for this
discussion.

 

235/40-18 and 315/30-18 PS2s...no issues, and more importantly the front to rear size difference is 0.1" (same as factory pairing of 225/40; 295/30).

The difference in revolutions per mile is actually closer to zero with the 235/315 than it is with the factory sizes. (819/817 versus 829/832)

Stock rims too, although these are the GT2 tire sizes and will work on GT2 size rims (8.5" & 12" as I recall).


A

 

Must keep the Rolling Diamter the same......Figure out what stock is and go from there. You can advance but only certain tires will work!!!

 

I'm running 245/30/20 and 315/25/20 without any issues just to give you a heads up. Not the exact same diameter but close enough. I think within 5% is ok for 996TT...997TT is different though.

 

But without saying which brand/model tire, you don't know what the
real diameters are. The '245/30/20' nomenclature does *not* exactly
define the real tire diameter. See this:

https://www.6speedonline.com/forums/...referrerid=582

 

Most manufacturers allow a variance of 2% from the stock rolling D. It will slowely tear up your Diff.....Be careful because the dealer can blame your tires for a drivtrain failure!!

I deal with this issue with my SRT Jeep....

-AZT

 

I would ask Tym for Switzer since he builds very fast AWD turbos?
Robert

 

That was the idea I had Please also mention what is the sizing of wheels if not stock.

 

reference the "specs" section for the tire sizes and check "overall diam." to make sure its the same or really close. its interesting that there is quite a bit of variation in their recommendations...

looking at stock sizes, ADVAN NEOVA AD07's come in at 25" and 25.1" respectively. Only one was exactly the same at 25.1" front and rear and that was Hankook Ventus S1 EVO's. I've seen as much as 0.4" of variance between front and rear from the Bridgestone Potenza S-02 A's as recommended by them. I would avoid those anyways...

So there you go, Its as easy as looking at a chart. If Tirerack doesn't have the info, the manufacturer's website usually will. Shooting for 25" will only keep your speedo accurate, the real importance is keeping the diameter the same front and rear to keep the diff from working itself to death out of confusion.