Moochier

Just make sure you lock it up well tonight John!

John McM

If I had my tools with me I'd bring the seats inside

pcarplayer

...and he had them priced at 1200 a couple of days ago

John McM

What size are they? That seems to limit the selection. I run Hankooks on my Fuchs and am very happy with them. Only $1,000 fitted at Megatyre.

racoguy

The rears are a bit over 10" and the fronts will be around 9 / 9.5 once done, I'll end up rolling the front guard lips also.
I read something a while back about Porsche running a stiffer sidewall? (or that you should, something to that effect anyway)

John McM

Don't mention the 'N' word. There has been a lot of debate over the Porsche tested 'N' rating for approved tyres. Apparently they have stiffer side walls. Are you running 18"? The rears would be 265/35 if on a turbo. No idea for the fronts. That's a lot of meat on the fronts. I hope that Mercedes pump can cope!

nzskater

My vague understanding is that stiffer sidewall relates to the extra strength/durability in run flats, and Porsches use of them (for a period of time, do they use them anywhere these days?).

Either way, I use Michelin's that are neither N rated nor run flats, and the world hasn't ended. I'd ask the question on the 964 sub section, am sure you'll get a wealth of information (alongside a significant number of annoying posts and a few arguments!). I just priced up Hankook RS3's through Mega Tyre, very tempting when compared to importing Michelins.

John McM

Brands aside Brian at Mega Tyre is the man. His machine is touchless and he takes his time. Your rims will be well looked after if he does the change for you. I think Pete found him first.

996tnz

Turned this over a while back. N rated tyres normally have higher load ratings (stiffer sidewalls - often with extra reinforcing layers or stronger fabrics) and also typically wider rain grooves (at least the primary circumferential grooves) than their same tyre model non-N equivalents.

Never seen any proper explanation for this but my take on it is that it primarily stems from the nearer to 33-66 than 50-50 weight distribution of cars like the 911, relatively wide tires (spelling there for searches), and higher than average speed capability and usage.

In the wet, weight on an axle helps grip but our front is lighter than most cars and with wider tyres. So the bigger rain grooves compensate for the inherently higher chance of the front aquaplaning, especially at track speeds. With the cars weight back on a longer lever, 911s can also apply more braking torque to the front wheels than most without losing traction. This helps give us our great 100-0 braking performances (low 30 metres) but puts big demands on the front tyres, hence their beefier construction, which also supports the 911's snappy steering feel (with the bigger influence being the polar moment of inertia - think centre of mass - lying both low and back towards the rear axle pivot point).

At the other end, the rear is heavier than the back of most cars and carries its weight low so generates big lateral forces under hard cornering, and also massive forces when hundreds of horses are unleashed during a hard launch. The same long rear-weighted lever that helps with straight line braking also acts in corners, but this time it generates a big lateral rotational moment around the front axle - ie the car is trying really hard to step its backside out when cornering hard. So you can see why the rears need to be beefier too, with higher load ratings through stiffer sidewalls, and bigger rain grooves to help keep the rear in place when pushing on in the wet, or at least give the driver a fighting chance of recovering if it lets go.

As stated, the above is how I understand it and I'm happy to be corrected.

For specific applications of course (wet track, dry track, road mileage, fuel economy etc) there will always be non-N rated tyres that outperform the N spec all-rounders but just be aware of their weak spots in other areas.

FWIW it's worth, I've run non N-rated tyres for over 4 years but I'm not under the illusion that they will outperform the Porsche tested and tailored items for all-round road/track, and wet/dry use.

Those 300 tread wear Sumitomo HTRZIIIs are yet to last their natural life on my car. The first set's rears died with big palm-sized interior sidewall bubbles after a dry track spin at half life and the second ones had big chunks of tread coming off, failing their warrant of fitness when only half worn. Having been left with two pairs of half worn fronts, I've recently bought a third pair of the Sumi rears but had them shaved down from 10mm to 8mm to minimise heat buildup from tread squirm on track and hopefully give them a longer life.

They may be my last set of Sumis actually - unless I restrict them to road duties only - but I did take comfort from seeing Doug's N-rated Pirellis chunked up even worse (sorry Doug) so who knows whether I'd just be destroying $2500 sets of tyres instead of $1200 sets.

I'm not aware of any run-flat options for the 996/997s but know they were standard (and usually hated) factory fit on many BMWs in the noughties.

Macca

Walt is a nice idea but you forgotten aero which makes a big difference on requirements of sidewall stiffness and of course Cayman shares same front tyres as other 911 models yet weight distribution differs.

I havent re visited this for years but more recently have a friend who put Ferrari rated MPSC2 on the back end of his 991 GT3 for some track work. Hes a very experienced and hardcore track guy and got a sensitive bump. His bum and telemetry concluded that the Ferrari tyre of same spec and dimensions broke away earlier than the N rated equivalent (out of stock at the time) and even after pressure adjustments his conclusion was that the compound was the difference. Not sure but perhaps the clue is the compound as after all the sidewall rating is noted by the manufacturer in the spec sheets so is obvious for all to examine as is the tyre construction. Just a thought.

My conclusion on tyres for an older car like 964/993 was that the newer tyres with more modern tyre construction and compounds were at least as good, almost certainly better in the performance stakes than the OEM tyre back in the day (unless its been superseded or up graded which is rarely the case as the N rating is expensive to achieve by the manufacturer).

If buying in NZ off the shelf then Japanese/Asian brands provide the best value for money. the Koreans have come a long way in last 10 years. Dunlop is also worthy of consideration. In terms of the European brand and self importation there is only one brand I would personally consider for a road tyre and that is Michelin. All IMO :-)

996tnz

Matt's P1 is about the only car around here running enough aero to potentially impact tyre construction, the odd race or hillclimb special aside perhaps.

For example, at 200kph, Sport Auto using the Daimler wind tunnel at Stuttgart University were reportedly the only ones in the world other than Porsche to test lift and downforce and CDxA. For the 911 for instance they found a while back that net lift is close to zero for the GT3RS (and for the TT):

GT3RS
Front: - 19kgs
Rear: 25kgs
Net: 6kgs of downforce

996TT:
Front: - 7Kgs
Rear: 6kgs
Net: -1kgs lift

Most cars generate front axle aero lift instead but still the figures are peanuts compared to the 400-800 odd kgs of mass on those axles. And especially at normal road speeds.
The rake changing as the car pitches on braking and acceleration would probably have a bigger effect but I can't find figures for that. Different when you get to GT3 Cups running 7 degrees of wing of course but that's outside the N-rating discussion.


When talking tyre contruction, the 911 and cayman weight distributions are both still heavily rear weighted compared to the vast majority of cars out there, ie the front engined, FWD cars that most stock non-manufacturer rated tyres are designed for.

Toyota Camry F/R is 60:40

compared to:

911 996T 38:62
Cayman 46:54
BMW 540i (e39) 53:47

More here about how that and how the balance changes dynamically under braking and acceleration: http://www.caranddriver.com/features...11-gt3-feature

Yes, the tread compounds may sometimes vary I suppose, but I've only ever come across the construction varying in articles I've come across over the years. Construction can measurably change performance though.

Newer tyres are typically faster (though the Bridgestone S02s are still missed). This is seldom given credit when comparing performance figures and 'Ring times between generations.

I'd agree with that, though german Fuldas also rocked on my 750iL and were spectacular value for money.

993 Targa

Great pictures of the 575, thanks!

996tnz

Correction - I thought I'd previously saved some other testing data over a wider selection of speeds, and just found it. Bit dry, but they run the tests right up to 300kph in the MIRA test facility. Interesting how ride height and rake impact on drag: http://www.reverie.ltd.uk/Downloads/ReveriePorscheData.pdf


Much as we'd all like to think we this much aero, it's not much of a consideration for the tyres on our cars:



(pic via Chris Walrod).

pcarplayer

Anyone buying a pcar in Europe in May? Short notice but still taking reservations. Perhaps good for look in itself

http://www.porscheclubfrancorchamps....25799A0043E19E

John McM

Every moment reading about N rated tyres is a moment in my life I won't get back.