Tires

N-spec Explained

>> I contacted the factory last year regarding the Bridgestone SO-2s, as
>> they were not on the list of official tire recommendations, thinking
>> that this list might be outdated.
>
> I'm wondering: What is "N-spec?"

'Nx' (x = 0, 1, 2,...) is used to designate tires built specifically to Porsche
specs, determined by extensive testing. Any Porsche dealer will have a
list of tires that the factory recommends for a specific car and rim
size. As I pointed out, the Bridgestone S-02 is not recommended for
*16* inch wheels, but is OK to use with *17* inch wheels.

N0, N1, N2, and N3 are currently used, but I have absolutely no idea what the
significance of this differentiation is. Anyone?.........

......OK, I just called the factory, this is what I learned:

Back in 1985 the 'VR' was the highest speed rating, rated for speeds
of 210 km/h and above. Of course, when considering that an S4 will do
270 km/h or more, this rating might not be sufficient. The powers that
be (i.e. the government) then decided that you had to use specific tires on
specific cars (Porsche told me that this applies only in Germany and
Australia). These tires are specifically stated in the registration
papers (or in an update list from Porsche). Failure to use these tires
will get you in big trouble with your insurance when something goes
wrong, i.e. you might lose your coverage. It would also constitute a
breach of traffic code regulations, i.e. you won't pass TUV inspection.

Anyway, to make sure you use the right tire, Porsche and the tire
makers agreed on this extra designation.

The letter 'N' was chosen arbitrarily (it just stands for 'Nummer' or
'Number'). The numerals 0, 1, 2, etc. are used to designate updates within
one series of tires. Every time they change something in the
construction, the value is increased by 1. N2 is therefore the third
modification series.

ZR has since been superseded by WR and YR, which are rated at 270+
km/h and 300+ km/h, respectively. Still, speed rating is only one
factor in determining whether a tire is suitable for a specific
application, other factors include grip (wet and dry), tire noise,
ride quality, etc. The N-spec will therefore be continued to be used.

An N-spec tire will have the same outward appearance (tread
pattern, dimensions) as a 'regular' tire, but the rubber compound and
carcass construction will be different.

Porsche puts a lot of effort into testing tires and getting the tire
makers to produce tires to their specs. They might be harder to find
(depending on your location), wear faster and possibly cost more, but
I use them - at speed, the last thing I want to worry about is tires.

Testing tires is somewhat of an empirical science, depending on
weather conditions (obviously) and the tester himself (or herself).
For instance, Porsche (other makers might do the same) goes to the
trouble of testing all the winter tires for this year in New Zealand,
where they find suitable conditions in June/July.

Porsche continues to test tires for all models, albeit more frequently
for the current production cars. The current list for the 928 that Porsche
was friendly enough to fax to me is designated '7/11' and dates from
02/20/1998.

Hope this helps. (Are you still awake?)

Best regards,
Thilo Corts
'87 S4 auto mailto:corts@webx.de