Cup2 thread dept

[fredt]

Have one tyre goosed by a nail on the Gt2, now the previous owner couldn't get 315s quick enough when he needed tyres so put on 295s.

I was thinking to change both to get the correct size, but the good tyre still have near 5mm left. What is the thread dept of new Cup2 tyres?

I can't imagine they are more then 6-7mm new so maybe I just get one 295 and change both to 315s when they are closer to the limit? I can't see it will make a massive difference to me..?

Thanks

[fredt]

5.4 mm

Staying on the 295s for a season.

[TB993tt]

fredt said:

I can't see it will make a massive difference to me..?

Putting 295s on the driven wheels of a turbo charged 911 designed for 315s........ seriously, you don't think this may be a little dangerous ?
I personally think it is reckless and dangerous, illegal etc, but I suppose if you are just cruising round for the next 5mm of tread it will probably be OK

[SFO]

TB993tt said:

fredt said:

I can't see it will make a massive difference to me..?

Putting 295s on the driven wheels of a turbo charged 911 designed for 315s........ seriously, you don't think this may be a little dangerous ?
I personally think it is reckless and dangerous, illegal etc, but I suppose if you are just cruising round for the next 5mm of tread it will probably be OK

you may have your insurer declining liability too

[TB993tt]

SFO said:

you may have your insurer declining liability too

That was the "illegal" bit !

I suppose one could argue that GT2s are specced with 295s as winter's so there is a level of approval from the manufacturer.

[Magic919]

Which law does it break?

[TB993tt]

Magic919 said:

Which law does it break?

I guess if you fishtail into another car under acceleration and the Police decide that it is because you have the wrong sized tyres on the back there may be some laws broken ?
Certainly in Germany this would be very illegal.

[Magic919]

What law though? Germany is a poor example as they different laws to UK.

[TB993tt]

Magic919 said:

What law though? Germany is a poor example as they different laws to UK.

I can see how you've got 11000 posts

Quick google gives site below which says law requires correct sizes - don't know the exact law tho', do you ?

http://www.carblog.co.uk/car-tyres-do-you-know-the...

[Magic919]

I don't believe there is one in the UK.

[fredt]

Must say I didn't think of the insurance/law point of view. I'll have to look into this.

From a safety point of view it's not really an issue. You really have to provoke it to get any sort of movement in good conditions, more then I would do on the open road for sure.
And on anything less then ideal conditions I am super careful whatever.

But maybe I am being a bit stupid for the sake of couple of hundred quid...

For winter tyres the Porsche spec is 265/35/18 at the rear.

Edited by fredt on Thursday 25th February 09:23

Edited by fredt on Thursday 25th February 09:25

[TB993tt]

fredt said:

For winter tyres the Porsche spec is 265/35/18 at the rear.

That's interesting, the 997GT2 is 295s, I wonder if the 265 for 996 is because the 295s weren't available in the late 90s when the 6GT2 was developed ?

I remember an anecode during the development of the 997GT2 where Walter Rorhl spoke about needing to increase the rear tyre size from 315 to 325 because of twitchiness when testing at the ring. Particularly from the late 90s Porsche have really embraced the latest tyre tech, the GT2RS got special compound compared the regular 997GT2 despite there being very little difference in the cars, the fantastic new Michelin rubber, the Cup 2 Porsche took great pains (lots of work on the rear end) to fit the 918 spec rears to the new GT3RS because the tyre was so phenominal.
I just had new Cup 2s fitted all round last night (hence this thread piqued my interest), these are now the recommended tyre for the 7GT2s and enjoyed slip sliding my way to work this morning

[s_mcneil]

TB993tt said:

I just had new Cup 2s fitted all round last night (hence this thread piqued my interest), these are now the recommended tyre for the 7GT2s and enjoyed slip sliding my way to work this morning

What sizes and where from? I can't get hold of 295/30/18, Michelin have had no stock since Dec '15.

[BertBert]

really? 3% difference in size. Probably much less in contact patch.

TB993tt said:

Putting 295s on the driven wheels of a turbo charged 911 designed for 315s........ seriously, you don't think this may be a little dangerous ?
I personally think it is reckless and dangerous, illegal etc, but I suppose if you are just cruising round for the next 5mm of tread it will probably be OK

[SFO]

fredt said:

Must say I didn't think of the insurance/law point of view. I'll have to look into this.

insurers will find any excuse not to pay

IMO, if you fit tyres in an incorrect size/width from that set by the manufacturer, you are giving the insurers a golden opportunity to blame an accident on the incorrect tyres

[9e 28]

TB993tt said:

fredt said:

For winter tyres the Porsche spec is 265/35/18 at the rear.

That's interesting, the 997GT2 is 295s, I wonder if the 265 for 996 is because the 295s weren't available in the late 90s when the 6GT2 was developed ?

I remember an anecode during the development of the 997GT2 where Walter Rorhl spoke about needing to increase the rear tyre size from 315 to 325 because of twitchiness when testing at the ring. Particularly from the late 90s Porsche have really embraced the latest tyre tech, the GT2RS got special compound compared the regular 997GT2 despite there being very little difference in the cars, the fantastic new Michelin rubber, the Cup 2 Porsche took great pains (lots of work on the rear end) to fit the 918 spec rears to the new GT3RS because the tyre was so phenominal.
I just had new Cup 2s fitted all round last night (hence this thread piqued my interest), these are now the recommended tyre for the 7GT2s and enjoyed slip sliding my way to work this morning

They need a bit of heat before hitting the loud pedal in your 900bhp dd lol! You'll be amazed what they can do on track - there is so much cornering G available it feels like the car is going to rip itself off its driveshafts! Amazing tyre and Michelin have done a really good job on this one. Not bad at all in the wet either for a trick tyre.

OP I'd go back to 315 asap just so you can be on the best tyre available. Makes an amazing difference to any car but on a car like yours will give you a lot of confidence to press on when you have some heat in them.

[Magic919]

SFO said:

insurers will find any excuse not to pay

IMO, if you fit tyres in an incorrect size/width from that set by the manufacturer, you are giving the insurers a golden opportunity to blame an accident on the incorrect tyres

That's rubbish.

[gtsralph]

This might help on whether the tyre width is appropriate for the wheel width

http://www.tyresizecalculator.com/tyre-wheel-calcu...

[TB993tt]

BertBert said:

really? 3% difference in size. Probably much less in contact patch.

According to tirerack the Mich PS2 N4 has an inch difference in tread width between 295 and 315, about 9%

9e 28 said:

They need a bit of heat before hitting the loud pedal in your 900bhp dd lol! You'll be amazed what they can do on track - there is so much cornering G available it feels like the car is going to rip itself off its driveshafts! Amazing tyre and Michelin have done a really good job on this one. Not bad at all in the wet either for a trick tyre.

Im, the difference between these and my pretty worn PSSs is incredible, the traction is so much better even in the current cold conditions, I'm quite shocked, should've changed bloody months ago !

gtsralph said:

This might help on whether the tyre width is appropriate for the wheel width

http://www.tyresizecalculator.com/tyre-wheel-calcu...

Its not really about what's "appropriate" although I guess from a legal perspective you are probably right, it's about giving the widowmaker an excuse to do its thing

[9e 28]

TB993tt said:

BertBert said:

really? 3% difference in size. Probably much less in contact patch.

According to tirerack the Mich PS2 N4 has an inch difference in tread width between 295 and 315, about 9%

9e 28 said:

They need a bit of heat before hitting the loud pedal in your 900bhp dd lol! You'll be amazed what they can do on track - there is so much cornering G available it feels like the car is going to rip itself off its driveshafts! Amazing tyre and Michelin have done a really good job on this one. Not bad at all in the wet either for a trick tyre.

Im, the difference between these and my pretty worn PSSs is incredible, the traction is so much better even in the current cold conditions, I'm quite shocked, should've changed bloody months ago !

gtsralph said:

This might help on whether the tyre width is appropriate for the wheel width

http://www.tyresizecalculator.com/tyre-wheel-calcu...

Its not really about what's "appropriate" although I guess from a legal perspective you are probably right, it's about giving the widowmaker an excuse to do its thing

You'll be amazed when the weather warms up mate. In the hands of someone like WR on those tyres and the built RS engine you have sub 7 min Nurburgring GT2 right there even with rear seats etc. I think you'd pip a 918. Ur new tyres making the greatest contribution to those quicker lap times by the way. Enjoy