[s-cars] Snow tire shopping, blizzak vs Nokian vs? thoughts?

[LL - NY]

My point comes from years of autocross, although in "spirited" street
driving, I suppose it could matter (although to go that far on the street
would be stupid).

Higher pressures = smaller contact patch.

Ideal pressure for max adhesion obviously will be greater than zero, pretty
well it MUST support the tire enough for all of the cornering to come from
the tire's tread (up to the shoulder) and not from other parts of the tire.

Most OE pressures are set with two things in mind 1) wear - customers aren't
usually too happy if their OE tires wear out before 30 K miles, especially
if it's from uneven wear from following mfgs suggestions and 2) (sadly) ride
quality. Performance is usually a distant 3rd. Hence, Audi's stupidly low
suggested pressures.

Why does raising the pressure seem to work? In the case of low ball OE
pressures for "spirited" driving, it helps keep the tire on it's tread. It
also feels much better, better response, better feedback, better
predictability.

The reason I cited the GRM Nov 2008 article is because they specifically
decided to test the issue of pressure and only one factor of performance,
skidpad grip.

They circulated the STS/SM2 prepped Mini Cooper with Hoosier A6 DOT-R's
around the skidpad, starting at pressures of 50 psi HOT and dropping 5 psi
retesting each time. Max grip was found at 30 psi and it dropped
signfincantly as pressures dropped below 25 psi (they went down to 20 and
killed the tires). The increase of grip as pressures dropped from 50 to 30
was steady on their graph, but the thing they noticed is the feel and wear
rate got worse and worse as pressures dropped.

That being said, I tend to run between 2 - 3 psi higher than spec on the
Saabaru for the street, 4 psi more on the UrS. For the former, it's to keep
the wear correct. For the latter, it's because it simply feels better (and
wear seems so far to be oblivious to pressure).

For performance, since I regularly autocross the Saabaru, I got some aid in
setting up, and after a number of tests/tuning and data tracking, I run 36
psi front/44 rear hot dry, a more balanced 38/42 wet and I dont have unusual
understeer issues in my SCCA Solo2 Stock car. The lower front pressures
really help kill understeer. On my last runs of last season, using up the
last of my DOT-R rubber (they're done, new ones next year) I tried dropping
in 1 psi increments the front pressure just to see if lowering pressures
would gain me any more time (I have enough consistency and repeatability on
course (typical variance within 6 runs is about 0.8 seconds, usually fastest
last unless I'm trying to test things) and I found the peak was at 34 psi
after which I started loosing time. As in the GRM test, the wear (on already
used up tires, admittedly) went up dramatically. So as a result, I suppose
in desparation I may use 34 psi on a last run to try to win an event, but
otherwise, I'll stick with my slightly higher (36 psi) pressure.

LL - NY
On 11/17/08, JC <jc at j2c3.com> wrote:
>
>  Agree completely w/ Larry - go easy on the extra inflation - I think I
> usually run 4-6 psi more, but certainly not looking to fill to max. spec.
>
> Re: tire pressure and steering I agree about the specific effects on the
> front, but disagree or perhaps some additional clarification on
> over/understeer - In most OEM cases you WILL see decreased understeer as the
> front tightens up while the rear of the car continues to pivot out a bit
> more on the softer tire pressures.  The limitation is (maybe this is what
> your'e saying?), if rear is very firm already, then the phenomenon may not
> occur to a noticeable degree, and in fact if you go too far you'll start to
> see the trend reverse as the front grip starts to decline again under
> overpressure.  However *at most 'OEM sticker' pressure starting points* if
> you pump up the fronts, while leaving the rears the same (or increasing to a
> lesser degree) the result will be less push.
>
>
> * ---- current ----
> 1995.5 S6 Avant
> ---- past lives ----
> 2006 A4 2.0TQA
> 1998 A6Q 2.8 PES G2
> 1989 200TQA SJM
> 1990 CQ
> 1997 A4 1.8TQ Wett
> 1987 4kCSQ
>
> * *John J. Cunningham
> jc at j2c3.com**
> US Mobile +1 (617) 750-5025*
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>
>  ------------------------------
> *From:* LL - NY [mailto:larrycleung at gmail.com]
> *Sent:* Monday, November 17, 2008 23:32 PM
> *To:* Mark Turczyn
> *Cc:* JC; Calvin Craig; Scar
> *Subject:* Re: [s-cars] Snow tire shopping, blizzak vs Nokian vs?
> thoughts?
>
> Don't go crazy with the pressures (see November 2008 Grassroots Motorsports
> Magazine for a skidpad test) until you see what the results are. The common
> suggestion is to change pressures 2 psi at a time until you arrive at the
> happy medium (in your case, even wear) that you are desiring.
>
> FWIW, higher front pressures (assuming adequate pressure to begin with)
> don't actually reduce understeer, they just improve response (at the
> potential expense of ride quality (which was Audi's concern) and potential
> center wearing of the tires) and predictability, which IMHO are the most
> important factors in street driving over ultimate grip. Of course even wear
> is also important. A side benefit of higher pressures is (slightly) improved
> fuel economy.
>
>
>
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