225 vs 235 on TT

[Kiko]

On a clear attempt to reduce understeer and to comply with the GT3's "N" rating of 235's I'm thinking about fitting 235 fr and 295 rear. The calculations say the rolling radius diferences are...

Brand new 235/295 = 1,7%

New 235 and worn 295 = 2,6%

New 225/295 = 0.5%

I think I read somewhere the max admisible difference on a 4wd would be 3% if this correct the 235/295 shouldn't present a problem on a TT...

Loren,

Whats your opinion on this one?

Best Wishes to you all

Francisco

[Loren]

I don't see a problem with 235's. Porsche does not set a spec (since the specify only one tire size for the TT). They only mention that the differences should be as little as possible.

[Kiko]

Thank you once again for your input , Loren. I'll give the 235's a try and will dial as much camber as I can on OEM set up and see how it goes...

[ar38070]

From the PCA website tech section:

http://www.pca.org/tech/tech_qa_question.a...B-D7E57E43B5DA}

[JonasGranlund]

Hello!

I have just bought a 996TT wich have 245x35 R19 at the front and

275x30 R19 at the rear, is this something critical so I have to change tires?

They are almost new so I would prefer not to change them.

Best regards

Jonas

[ar38070]

Measure your tire diameters or check the manufacturer's or tirerack's website for the numbers and see if they are within Porsche spec.

[Kiko]

The 245 is 2054.91 and the 275 is 2034.49mm so there 1% difference between them which is fine and a maximum difference of 2,11% from the OEM 295/40-18 which is fine once again. Any time you need to calculate perimeters go to:

http://www.carbibles.com/tyre_bible.html

[ar38070]

It is still best to check the manufacturers specs as one manufacturers 245/35 is not necessarily the same as anothers. Things such as tread depth will effect actual diameter, albeight slightly.

[JonasGranlund]

Thanks alot for the help guys!

All tires are new and when I measure them they are very close to what they say in that URL.

[damianc4s]

On a clear attempt to reduce understeer and to comply with the GT3's "N" rating of 235's I'm thinking about fitting 235 fr and 295 rear. The calculations say the rolling radius diferences are...

Brand new 235/295 = 1,7%

New 235 and worn 295 = 2,6%

New 225/295 = 0.5%

I think I read somewhere the max admisible difference on a 4wd would be 3% if this correct the 235/295 shouldn't present a problem on a TT...

Loren,

Whats your opinion on this one?

Best Wishes to you all

Francisco

<{POST_SNAPBACK}>

HI Kiko,

I've been running with 235 on the front for quite a while now with no problems. I've always run Pirelli Corsa & Corsa System (N6) (for the winter/wet) which is the standard tyre for the GT3RS.

This tyre change combined with a geometry setup to increase -ve camber and reduce toe-in has reduced/minimised the understeer characteristic.

Damian

[Kiko]

Thanks for your input Damian, even if theory and numbers show alot the practical experience is the ultimate test for everything...

Would you like to share with us your experience withose tires and on the alignment topic give us your set up?

[Kiko]

Just fitted 235/40 in the front but it messes with ABS/PSM to the point of kicking in mid turn just by touching the brake pedal due to the increased turning radius. I already ordered a set of 225's...

Edited April 24, 2006 by Kiko