305 rear tyres to replace 295??

[9hellheaven]

Will it be ok to replace my Pirelli 295x30zr19(100y) N1 Tyres with 305x30zr19(102y) N1 Michelin Pilot Sport? It states in the book 11J x19h2 for the 295 size, and 11.5J x 19H2 for the 305 size. I have looked at the wheels on my car and they are stamped near the valve stem 11J 67. Is this a problem??
Thanks guys.

[wildoliver]

What I would advise and what I would do are two different things.

On my car it wouldn't bother me put it that way.

[9hellheaven]

Thanks wildoliver..I am thinking well the only difference is that the Michelins are 1cm wider at the tread than the Pirellis ie 295 vs 305 but then I think whats the (100) y verses the (102) y on the Michelins.
I just dont want them to be A dangerous and B make the car handle like crap.
Maybe someone will advise further. I am a on matters of tyres!!
Thanks 9HH

[damianc4s]

Extra width at the back can lead to increased understeer.

[Merritt]

Increasing the width will also increase the profile and hence the rolling radius and diameter (albeit by a little bit). The profile i.e. 35 is the percentage of the tyre width so a tyre of 305/35 R18 has a profile of 35% of 305mm.

You might encounter wheel arch rubbing problems and possible handling differences so I would advise not changing them.

Steve

[Pork_n_Beem]

There isn't a direct size of wheel wrt stickered tyre width.

I have two identical stickered tyres, 315/30/18 one from pirelli and one from yokohama, the yokohama requires a smaller wheel width, which i do not have.

I have run it, bit its not ideal.

Michelin should give a recommended wheel size for the tyre, if its only 1/2 inch you may get away with it, like i am at the mo.

However you also have a taller tyre which alters gearing.

Cannot u get the Michelins in the smaller size?

[ChrisW.]

I have fitted 295/35 18's on my GT3 in place of the 295/30 18's.

The rolling radius is idetical to the 305/30 19's and I have had no rubbing issue in the wheel arches.

(I was on the canvas and could't get the 295/30's I needed)

However, I do find the ride a little more compliant which is good on the road --- though the gearing is now also a little higher.

[9hellheaven]

I have spoken with the guys at local OPC (WILMSLOW) it would seem that while you can get away with running 305 instead of 295 on a 11J rim its not ideal.
The car (9972s) was set up to run on 295(my car) which is what it came with new. The issues relate to gearing and also traction control/electronis issues. As I understand it can be also something as simple as changing one of the two rear tyres that are fairly worn for a new one will create warning lights (traction/psm) due to smaller radius. Both tyres should be changed on each axal at the same time. They even advise in the book to stick to the plastic valve caps, I am guessing for weight reasons. Anyway I am going to get the 295 and stick to the factory formula.. Thanks everyone. 9HH

[ATHEY997S]

alright
not sure if anyone has mentioned this, but (having been caught out in the past) this would be classed as a Modification and you would need to inform yr insurance company! Just be wary about this! When you come to claim for a 50K plus car the insurance company go over it with 16 very fine tooth combes....

Den

[9hellheaven]

Thanks Den..I am looking a bit further into this. It does say in the manual both 305 and 295 are standard equipment so that covers the insurance. What I cant get to grips with is Porsche say not ok 0n 11J with 305, and Michelin say its ok on 11J and 11.5J. I am intouch with Michelen today just to clarify..we will see!

[ATHEY997S]

9hellheaven said:

Thanks Den..I am looking a bit further into this. It does say in the manual both 305 and 295 are standard equipment so that covers the insurance. What I cant get to grips with is Porsche say not ok 0n 11J with 305, and Michelin say its ok on 11J and 11.5J. I am intouch with Michelen today just to clarify..we will see!

Ask one of the GT3 onwers? I know the 305 tyres are standard fit on a 997 GT3...be interesting to see if same Rim size, but i doubt it! Do you think you'll gain anything, and are they more expensive? I know OPC wilmslow quoted me last year 330 + VAT for a year Michelin, but found them for £250 + VAT
Den

[anglebox10]

Pretty sure the 997 GT3 has 12" rims at the back

[Pork_n_Beem]

i would believe michelin, if opc say it needs a 11.5 and u have 11 and mich say 11 ok - go with it.....

e.g.

For a yokohama 315/30/18 - the specified rim width is 11 inches.

The permitted rim sizes are 10.5 - 11.5

I have them fitted on 12 inch standard rims with the tyre size being also standard - i.e. OK for Pirelli tyres of that size but not Yokohama.

Confusing isn't it

[Erik997]

9hellheaven said:

Thanks Den..I am looking a bit further into this. It does say in the manual both 305 and 295 are standard equipment so that covers the insurance. What I cant get to grips with is Porsche say not ok 0n 11J with 305, and Michelin say its ok on 11J and 11.5J. I am intouch with Michelen today just to clarify..we will see!

I always thought it was 295 for the C2S and 305 for the C4S? Could be wrong.

[IanHug]

Don't know whether you've seen this:

www.porscheclubgbforum.com/tm.asp?m=195805

Ian