tx targa he meens Carrera Sport wheels...they are 8.5x19 fronts and 11.5x19 rear. However 305's will fit fine on 11" rears anyway.

 

From the 997.2 Tequipment catalog,

Carrera Sport Wheels like Dan's are spec'd 305s Rear NB/WB - summer only.

All other 19s' are spec'd 295 Rear NB, and 305 Rear WB - summer tires. Winter tires for all cars are 295 Rear for C C, C S II, and C IV wheels.

The only difference in the WB and NB wheels is the offset, so 305s should fit either wheel.

But I read about people doing all sorts of other offsets and wheel/tire combos that don't fit that.

 

Simple, Wide Body cars, C4, C4S, Turbo came with 305, while C2, C2S came with 295. Exception was Carrera Sport wheels on C2S which came with 305 as they are wider (11.5"). People however have swaped to 305 on C2S without any issues.

 

wouldnt the ride height increase by approx 1/4 inch???

 

10mm per side (both tires), or 20mm overall width increase in friction surface.

 

For PZero 295's and 305's are rated at 26.1".

 

I plus sized to 305's for one set of tires, and then switched back while they are "slightly" wideer as others have pointed out, while not huge, I certainly noticed the understeer. I think the standard "S" car on 19's drives better with the OEM 295s. Also, the 305's are more $, so why waste it there?

 

Since they are 30 series tires, the wall height would theoretically increase by .3x(305-295)=3 mm. which is just over 1/10 of an inch.

 

Correct. The diameter would increase by 6 mm (1/4") but since only the radius matters for ride height it's 3mm (1/8")

 

Looking at tire calculator it makes sense to me to use 235/295 or 245/305 for front/rear tires. It will keep same difference between front/rear axle hight.

 

i dont get it is my math off?

295/30/19= 295mm * .30 *2 = 177mm. converting in inches = 6.97in +19in = 25.97in
and
305/30/19= 305mm*.30*2=183mm. converting in inches = 7.02in +19in = 26.20in

thus the difference is .23in or 5.84mm.

 

Your math is correct, but remember it's the overall diameter that increases by 1/4". That means it's 1/8" for the radius which is the ride height increase.

 

On my first tire replacement I went from 295 to 305. I immediately noticed the additional sidewall flex - the rear end was just not as stable. On the next replacement I went back to 295 and the car is back to its original stability. In terms of looks, the 305 protrudes just a little, especially when viewed from the back. While I like a full wheel well, it doesn't relly look any better.

 

remember all brands are different.. ive seen 285's wider than 305's just depends on what brand each is... ;-)

changing a size with same brand/model will yield change in handling..

changing a size without same brand/model is impossible to tell.. too many variables.

that being said i run 245/305 on my 911 non S .2 because the tires ran a lil narrow and i wanted to keep same bias as stock.

 

I have a nice set of widebody Carrera Classic for sale with Michelin PS2. Will sell set as a whole or might be willing to swap the rears for narrowbody rears + cash. PM if interested...