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PostPosted: Fri Mar 13, 2009 6:07 pm    Post subject: 993 Tyres, "N" Porsche Specification Reply with quote

The N Specification is a Porsche system of approved tyres, first introduced in the 1988 Model Year – it means that Porsche have worked with the manufacturer to produce an optimal road tyre for a particular model and wheel size combination, and tested it to their satisfaction at the time.

Whenever this process is performed for an individual set of approved tyres, the N spec number will increase. Often this will coincide with a model change, but can certainly occur within a model’s lifetime, and thus a bewildering chart of approved wheel and tyre combinations (for summer and winter use) is produced and published twice a year in Christophorus, the Porsche company magazine, and in TSBs issued to OPCs.

Importantly, Porsche recommendation is matching brand, type and correct N spec ALL ROUND.

Technical Service Bulletin Quote [TSB]

If new tires are to be mounted or the tires of one axle are to be replaced, tires of the same make, the same type and with the same specification code must always be used on each of the two axles. If tires are replaced on one axle only, the different tread depth from that on the other axle can cause a noticeable change in the familiar handling. This is especially the case if new tires are mounted on the rear axle.

This effect decreases with increasing tire mileage. When replacing a tire on an axle, make sure that the tread depth of the new tire does not differ from that of the other tire by more than 30 %. They are also rather proscriptive on getting a round result when fitting tyres. In order to optimize smoothness of rolling, it is appropriate - and necessary in individual cases - to mount the tire in a certain (favorable) position with respect to the wheel (matching).

Matching (uncontrolled and controlled) is explained below:

Uncontrolled matching: Turning the tire on the wheel by 900 or 1200 if necessary in order to achieve an acceptable value with regard to rolling smoothness (true running, imbalance and weight distribution of balance weights).

Controlled matching: With a balancing machine with matching program. In most cases, this produces an even better result with regard to the rolling smoothness (true running, imbalance and weight distribution of the balance weights) than can be achieved with uncontrolled matching.

Maximum permissible radial runout and lateral runout of the wheels < 0.7 mm. Maximum permissible radial runout and lateral runout of the wheels with tires < 1.25 mm. Values < 1.50 mm - ideally approx. 0.5 mm - are desirable.

The 993 options come down to 16”, 17” and 18” wheels, wide or narrow body, and manufacturers Bridgestone, Continental, Dunlop, Michelin, Pirelli, Toyo and Yokohama.

Not all manufacturers produce (or did produce) all sizes, and for the UK, winter recommendations are ignored, which are aimed towards countries with mandatory European winter driving regulations.

The last list for 993 was produced for MY 1998 but subsequently a couple of 993 TSBs have been issued, updating the list.

Manufacturers do continue to produce the same sizes in multiple N specs, although sometimes you have to search hard to get the correct one. Higher (and some lower) N spec tyres will not have been tested on the 993 (refer updates), although they may work well.

Sometimes manufacturers produce identical size / models with and without the N rating. The N spec tyre will be different in some way, compound, tread grooves, sidewall construction, whatever, but it may not be apparent.

So here’s the list by model and fitment – ‘summer’ use only.

Carrera Coupe 2/4, Cabriolet, Targa, Carrera S
17” x 7” 205/50
17” x 9” 255/40

The 2004 993 TSB recommends these in the same sizes ...
Bridgestone Expedia S-01 N1
Bridgestone S-02 N3
Bridgestone Potenza S-02A N4
Continental SportContact CZ 91 N0
Continental SportContact N1
Continental SportContact 2 N2
Dunlop SP Sport 8000 N0
Michelin MXX3 Pilot SX N0
Michelin MXX3 Pilot SX N1
Michelin Pilot Sport N2
Toyo Proxes F1 S N0
Yokohama A 008 P N1
Pirelli P-ZERO Asimmetrico N1
Pirelli P-ZERO Direzionale N2 /Asimmetrico N2 3
Pirelli P-ZERO ROSSO N3

Carrera Coupe 2/4, Cabriolet, RS
18” x 8” 225/40
18” x 10” 265/35

The 2004 993 TSB recommends these in the same sizes ...
Bridgestone Expedia S-01 N0 4
Bridgestone S-02 N1
Bridgestone S-02A N3
Continental SportContact CZ 91 N0
Continental SportContact N1
Continental SportContact 2 N2
Michelin Pilot Sport N1
Pirelli P-ZERO N0 4
Pirelli P-ZERO Asimmetrico N1
Pirelli P-ZERO Asimmetrico N2
Pirelli P-ZERO Asimmetrico N3
Pirelli P-ZERO ROSSO N

Carrera S, 4S and TT
18” x 8” 225/40
18” x 10” 285/30

The 2004 993 TSB recommends these in the same sizes ...
Bridgestone S-02 N1
Bridgestone S-02 N2
Bridgestone Potenza S-02A N3
Continental SportContact N1
Continental SportContact 2 N2
Michelin Pilot Sport N0
Michelin Pilot Sport N1
Pirelli P-ZERO N0
Pirelli P-ZERO Asimmetrico N1
Pirelli P-ZERO Asimmetrico N2
Pirelli P-ZERO Asimmetrico N3 4
Pirelli P-ZERO ROSSO N4

Porsche did all this testing for performance reasons, to ensure your car handles the way the factory intended, there are good guidelines here to follow.

If you change sizes at all, you (are on your own and) need to be aware of the change in the ratio of front to rear rolling diameters, because a significant change will screw up the ABS and/or the 4WD.

The logical calculation of rolling diameter from the tyre section / profile is not accurate in this regard, so be warned, you may need to check with the manufacturer.

FYI, the calculation for rolling diameter is Wheel Diameter (in mm) + Section*Profile*2, so for a 225/40 18, it becomes 18*2.54 + 225*40%*2, giving a logical RD of 637.2. As an example, an actual figure for a Bridgestone S02 in that size is 642.62 ....

The question about fitting WB tyres to a NB Car?

fitting 285/30 x 18s on the rear of narrow bodied NB 993s, may require 'rolling' the wing edges and may increase understeer. Do not assume bigger is better.

Notes

- Pre-96 cars need a steering rack brace fitted to run 18 inch wheels (refer to applicable TSB for non-approved VINs)

- 18" wheels were not quoted for use with Targa's but not disallowed so not quite as simple as that, check TSB's for details.

- The same tyres in different sizes are often at different N specs, which is a totally normal stage of the tyre development process.

The following is an update by Porsche on tyres for the Air-cooled 911

All you need now is the right tyre, by Porsche (2008)
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993C2S
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1997 Porsche 993 Carrera 2S

PostPosted: Fri Mar 13, 2009 6:15 pm    Post subject: Reply with quote

Great info, nice one!

Interesting info in the 2008 update as well - although I'm pretty sure Michelin don't do PS2 in 225/40 & 285/30 18s Question
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Joined: 22 Mar 2008
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1995 Porsche 993 Carrera 2

PostPosted: Fri Mar 13, 2009 6:43 pm    Post subject: Reply with quote

As usual Im lost Confused
I take it then all the tyres are still manufactured? Otherwise You would have to change all 4 all the time ! what
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PostPosted: Fri Mar 13, 2009 7:51 pm    Post subject: Reply with quote

993C2S wrote:
Great info, nice one!

Interesting info in the 2008 update as well - although I'm pretty sure Michelin don't do PS2 in 225/40 & 285/30 18s Question


Well what size do you run then, or do you have PS1?

Interesting in the wet the PS2's arent rated as well on the WB's as the Conti.

They could have provided a bit of detail. Whats the difference between 2 and 3 anyway, why not out of 10. E.g. breakaway speed under controlled conditions on a skid pan ...or something that would scientifically compare, or average lap times wet & dry etc etc.

I'm pleased that my personal impression of Contis both wet and dry is vindicated.

We should run our own real world test ...somehow Thumb
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993C2S
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Joined: 05 Aug 2005
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Location: Berkshire

1997 Porsche 993 Carrera 2S

PostPosted: Fri Mar 13, 2009 8:25 pm    Post subject: Reply with quote

Chris W wrote:
Well what size do you run then, or do you have PS1?


PS1 old and pretty much now obsolete (like Pirelli Asimmetrico)

PS2 not available in 225/40, 285/30

Leaves the Michelin Pilot Sport Rib N1s

I find the conclusions a bit sceptical TBH mate
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Tertius
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PostPosted: Sat Mar 14, 2009 8:48 am    Post subject: Reply with quote

993C2S wrote:

I find the conclusions a bit sceptical TBH mate


Me too.

Apart from anything else they make a big noise about how tyres are developed and optimised for the 911's unique layout/weight distribution, but the same tyre is apparently "approved" for both the 993 and the 968 ... Dont know
 
  
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993C2S
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1997 Porsche 993 Carrera 2S

PostPosted: Sat Mar 14, 2009 8:56 am    Post subject: Reply with quote

I'm inclinded to get some non-N rated tyres next time, top of the list are the Goodyear F1s, but they don't do them in 225 & 285 as far as I know frustrated
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2010 Porsche 997 GT3

PostPosted: Sat Mar 14, 2009 12:31 pm    Post subject: Reply with quote

993C2S wrote:

PS2 not available in 225/40, 285/30


According to Michelin - actually they now are (not sure if that is just non-N rated ones from their site, but have seen them listed as N elsewhere).

[ETA - oddly the 285/30 doesn't appear on the UK site, but it does for other countries such as the US]
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PostPosted: Wed Aug 29, 2012 10:51 am    Post subject: Reply with quote

Update 03/12

http://www.911uk.com/download.php?id=29236


More updates here (Posted in 996 FAQs, but documents are now whole range booklets):

http://911uk.com/viewtopic.php?t=51071
 
  
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