Kevinmacd

Dell not irrelevent, but know how manufacturers design and implement. Whether you want to believe it or not, manufactures use molds based on measurements and calculations. It's not an approximation, it's a true design feat to provide mesurements within a certain tolerance level. You seem to want to discount this over and over. Since you seem to be so stubborn on this I challange you to go take a multiple manufacturers of multiple tires within the same size and see if the circumference and diameter are not within a tolerable spec between them.

BTW here is the test procedure required by the DOT to conform to the size measurements
S6.1.1.2 Test procedure.
S6.1.1.2.1 Measure the section width and overall width by caliper at six points approximately equally spaced around the circumference of the tire, avoiding measurement of the additional thickness of the special protective ribs or bands. The average of the measurements so obtained are taken as the section width and overall width, respectively.
S6.1.1.2.2 Determine the outer diameter by measuring the maximum circumference of the tire and dividing the figure so obtained by Pi (3.14).

So there cannot be too much variance inorder to comply with the size measurements as outlined by the DOT

PAULUNM

I don't know... Yet... I just bought a set of GT2 wheels, and will be going with GT2 tire sizes. I think the rear offset on the stock turbo wheels can cause rubbing on the inside fender liner.

Worst case scenario- I'll have my fenders rolled, and MAYBE buy GT2 fender liners if necessary, but I doubt it will be.

You can fit a 315 on a 11 or 12" rim, but I would not fit a 295 on a 12" rim

LVDell

Kevin, please refer back to post 19 and 29 to shed some light on your blinders.

Now that this horse has been beat to death...............

Kevinmacd

So lets see I go to the manufacturers site for the tires posted by Doubleurx, which by the way a few are in error.( Tire rack seems to post incorrectly)
BridgeStone Expedia S-01 = 24.9
Michelin Pilot Sport 2 = 25.1
Michelin Sport Cup = 25.1
Dunlop SP Sport 01 = 25.1

The calculator shows 25.087
So from this point of view the calculator is well within the manufacturers statements
Hoosier you can't count since they are not street tires, and a few do not meet DOT and is stated so by Hoosier

Sorry can't see the point! All the tires that were mentioned in previous posts are within the calculator range, excluding Hoosiers which came in at 24.8 which is pretty close to the calculator.
None of these differences are significant enough on the front to rear spec needed to meet the 996 requirements.

Enuff said!

SSST

It's basically an extra 1/4" vertical clearance, and 1/3" horizontal. Since my car isn't lowered, that shouldn't be a problem, but I will double check when I get home.

Thanks for the info. I did manage to pluck what I needed out of the discussion.

LVDell

So long story short, the calculator is an estimate of what the tire specs are in reality. Shocking.

I believe this thread has run it's due course........

doubleurx

FWIW, tire rack physically measures the tires mounted on specific rims which is the basis for their data - not just what the manufacturer states.

Not all 235's are exactly 235 mm in width. Therefore their respective aspect ratios and resulting diameters will be different.

doubleurx

No it hasn't - DOCK where are you?

Kevinmacd

Wanna buy som swamp land???? LOL

doubleurx

???
Are you saying all 235 tires are exactly 235 mm wide?

PAULUNM

As long as they are Porsche Approved, N spec- of course!

z99

235 40 18 with 305 30 18 and 245 40 18 with 315 30 18s should work with most tire brands.

Another P

I was looking at some beautiful rims but apparently Tire Rack told me to not use the 315s on the 12" rear rim. Nixed that deal just in time. Boy the price is right, but....

jellonailer

I went with what paulunm says. Ditched the 19's for 18's. There's a bit of a gap which is why I'm looking at x73 or pss9 or 10's.

With my light Fikse's they are great.

l8tebr8ke

Hi I just purchased my first P-Car, 2003 996 TT X50 and it came with 997 19" wheels with 235/35/19 f and 305/30/19 r. I check the mfg spec for diameter and the f are 25.5 and r 26.2. When I did the ppi the shop mentioned I need to have an alignment done specific to the 19". from what I am reading here there is more to it than that. Will running the 19"s as is damage the diff? Any help for this newbie much appreciated.