Question about tyre ratings

[simes69]

Having recently been told by my OPC during the car's service that the Dunlops on the 996 aren't N-rated (they're Z-rated), I wanted to know is the rating to do with strength of construction or grip? What do you get more of with a N-rated tyre?

[mymerak]

Hi

Z rating refers to the speed rating of the tyre

As far as I am aware the N rating is Porsche specific. For a tyre to be fitted as original equipment (OE) on a Porsche it has to be developed in conjunction with Porsche R&D engineers. When accepted by Porsche that tyre is then given an N rating.

Therefore, it is a badge of acceptance by Porsche. Ratings start at N0 and usually progress to N4

Howver, beware, an N3 tyre from Pirelli is not necessararily equivalent to an N3 from Bridgestone for example. I believe the number to be a reflection of the development of that particular tyre

Therefore, if fitting N rated tyres I would recommend the same tyre manufacturer all round and the same N number all round

Please see my article on p.28 and Pauls article (p13 first paragraph) in current AT

We have tried diligently to source the best knowledge on the subject of tyres for all

It is possible to fit the same tyre, in terrms of size, speed rating and loading rating etc., but without the N rating but that has already opened up a whole can of worms elsewhere, especially regarding insurance!

Hope this helps

[tr7v8]

Simon, you're talking speed rating, N rating is a rating applied by Porsche to manufacturers tyres they've tested. It only applies after 1990 when they started. The ratings are N0-N4.

The word from my tyre dealer is that if a manufacturer makes a Porsche N rated tyre in their range then he HAS to fit it. If not such as Goodyear then only the speed rating, size etc apply.
It does seem to be a bit of a grey area as to whether insurance Co's would refuse to pay out if you had correct but non-N rated tyres fitted.

Generally they seem to have stiffer side-walls but their maybe other differences.

[JW590]

Just my understanding of the tyre markings. This is not a recommendation, nor is it advice.

N1, N2 etc is not a manufacturer 'rating'. It is a Porsche rating which simply means that they are Porsche tested and approved. A quote from Porsche's national tyre expert, who works at Chester - "it means that we know that you can take your car, thrash it around on a track day, and then go back onto public highways and be safe". He went on to say that by 'being safe' Porsche simply mean that the tyre walls won't weaken if the tyres are used for track days. So generally, for those of us who don't do track days, the fact that the speed rating is correct is more important than the tyre having an 'N' mark.

He also told me that he recommends customers to run their tyres a couple of psi below the book figure because, and again a quote - "The book figures are fine for the billiard table smooth German roads, but running them with a lower pressure in the UK will give you a better ride and make your tyres last longer"

I have four x Michelin Pilot SX on mine, they have the N2 mark on them, and they cost me £300 all inclusive from Costco on one of their deals. They run at 34psi instead of 36psi and have been on the car for 22000 miles so far.

Hope this is useful to somebody!

[simes69]

Thanks for the advice guys. That's very useful. I recently fitted Dunlops on the rear to match the fronts, and was sure to ensure that the tyres were Z rated all the way around. I don't thrash the car so am a little reluctant to pay considerably more for a feature (being safer on a track day for example) I won't use.
Interesting comment about the pressure too - I inflate mine slightly above book as, when the pressure dips a couple of PSI (from 35psi to say 32psi) the steering feels a little numb. I've been tempted to inflate to 38psi simply because that means its a little longer before I need to add more air.

[JasonGibson]

I've been tempted to inflate to 38psi simply because that means its a little longer before I need to add more air.

Try inflating them with Nitrogen

Tyres filled with Nitrogen will maintain their correct pressure for longer, because Nitrogen doesn't leak through the tyre's structure. Normal compressed air contains Oxygen and water vapour, both of which permeate through the tyre casing.
Filling with Nitrogen will provide

Also it is an inert gas pressures are not effected by temperature

[Li Moo Bai]

I've been tempted to inflate to 38psi simply because that means its a little longer before I need to add more air.

Try inflating them with Nitrogen

Tyres filled with Nitrogen will maintain their correct pressure for longer, because Nitrogen doesn't leak through the tyre's structure. Normal compressed air contains Oxygen and water vapour, both of which permeate through the tyre casing.
Filling with Nitrogen will provide

Also it is an inert gas pressures are not effected by temperature

Air is largely nitrogen anyway (otherwise we'd be in bother). Inert just means it is very stable (un-reactive) in its elemental form. Temperature WILL affect pressure and with all gases. Pressure is dependent on the kinetic energy of the gas particles, not their reactivity!

[mymerak]

Hi

As Li Moo Bai states nitrogen is reactive and affected by temperature

Many consider it to be inert simply because it is used as an oxygen shield to prevent oxidation.

However, it is very slightly soluble in water

It you cool nitrogen to minus 195.8 degees Celcius it liquifies and so its voulume is greatly reduced, see the road tankers

It also reacts with oxygen to from N2O (laughing gas, used by dentists when I was a lad ) as well as nitrogen dioxide (highly caustic which in turn dissolves in water to form nitic acid, HNO3)

It's a main soursce of fertilisers in compunds such as ammonium nitrate (unstable and explosive in large compacted volumes).

It reacts with Iodine to form ammonium tri iodide (NI3) which is extremely unstable and explodes upon contact or when subjected to an air pressure wave

So IMHO stick to air in tyres for road and track use.

Also IMHO I see no benefit in running tyres other than at manufacturers recommendations for road use. Running them low will wear them out quicker which is no benefit to me!

The only exception would be a track day and then I would run them up to HOT and then lower back to manufacturers recommendation, whilst still HOT. Tyres are designed to be run at a temperature and a loading and so artificailly changing these parameteres cannot be helpful IMHO.

[tr7v8]

Understand the chemistry on the Nitrogen, however the idea of using it is that it is guaranteed dry.
The wet level means it behaves inconsistently when heated up in something like a tyre.
We used to pressurise Avionics with Nitrogen to prevent arcing at high altitudes.

This is the reason it's used by motor race teams.

[Li Moo Bai]

Mymerak

I spy a chemist!

Degree qualified myself but converted to engineering afterwards.

You forgot to mention N2H2 (rocket fuel), although IIRC that requires a fancy catalyst

Adam

[mymerak]

Hi tr7v8 and Li

Yes I agree about the moisture content but how much do you want to pay for certified "dry" nitrogen. If it isn't dry then to a great extent you have defeated the objective of using it

Avionics and F1 are in a different budget league to me. I can only afford a car!

Yes, I am also a degree qualified Applied Chemist and I also coverted to Engineering and now a retired Chartered Engineer.

Yes, I also love the Lake District (remember your note some time back)

Sorry about not mentioning the rocket fuel. I thought I was stretching it a bit with the ammonium tri iodide, but at least didn't let into how to make it. Good fun when impregnated into paper aeroplanes though! Here we go again with the avionics!

[JasonGibson]

My local charges £1.70 per tyre, free top ups


Actually he doesn't charge me

I've had two cars with nitrogen in, from my own tests I found that on a hot day and after a long hard drive that my pressures were as they should have been and on a cold winters day unused the tyres were still at the same pressure.
I also found that on my 928 I didn't loose any pressure over 9 months, of course if you've got poorly seated tyres or leaky valves it doesn't perform miracles

my friend ran his C55 AMG with one side std air and the other Nitrogen, to test on a good run in warm weather.
It did make a difference

Definitely not worth bothering for this reason on your shopping cart

Not really worth going out of your way for but if your local supplies it for very little cost and probably free with new tyres, then you might as well use it

[simes69]

Zzzzz....Zzzzzzzz.....Zzzzzzz.....