I don't know anything about these new Dunlops, but the pressure you're
using seems way high, as you confirmed by your center tire temp. I know it
sounds dangerous and hard on the tires, but I like to start very low and
go higher, looking for a center temp equal to or slightly lower than the
inside temps. Of course there are a lot of differences between radials and
bias ply, and caster and toe in makes everything weird too. But generally
speaking a bias-ply tire requires less caster than a radial will take, and
radials run best with the outer edge of the tire hottest.
Since most folks don't change caster much with the TR's after they get
their suspension put together, the biggest change you can make to suit
tire demands is pressure. Running tires soft has a similar effect to
adding caster (bigger contact patch) and it increases the edge
temperature. If you start a little soft you can see right away that you
need a little more pressure because the middle with be cold, but if you
start hard the lack of sufficient caster will mask the problem that you
aren't getting much tire on the ground. You'll see elevated center temp
and compromised handling (usually the car won't turn in well) but a small
decrease in pressure will get you close to the right temperature without
helping your handling much. Go really soft (like down to 20 pounds) and
see how the car feels and what you get for temps. Then bring it up slow
until you get the right center temperature. You'll probably be four or
five pounds lower than what you'd wind up with starting from too hard.
I learned all this on the Radical, where it's easy to set caster and you
can fiddle with everything. There I start with the lowest pressure that
will keep the tire on the rim (about 15 pounds) and feel my way up. The
odd thing is that the resultant hot pressure is nearly the same regardless
where I start when I run air. That's where I got all spun up on running
nitrogen in my tires (No, I don't want to start a thread on Nitrogen, dry
air, partial pressures and the flight velocity of unladen swallows again).
Despite less adjustability, all that has translated to Peyote where I've
found I can tailor the handling to the track to a large degree with a few
pounds difference in the tire pressure. It doesn't require huge
sensitivity to feel the difference if you start from low pressure and work
up, but I can't figure out what the heck is going on coming from the other
direction. I almost always wind up with a different pressure in each tire
(mostly because of my fat butt) even though I've corner weighted both cars
fairly evenly. Peyote doesn't permit much adjustment but it happens to be
closer to 50/50 side-to-side, front-to-back and diagonally I can adjust
the Radical, which is a bit light in the front but gets any static weigh
issues overridden with monumental downforce.
Anyway, I'm looking forward to trying these tires, though my Hoosiers are
lasting well and I really enjoy driving on them (slide, and slide, and
slide...). I bet your Hoosiers would have lasted longer if you'd used less
tire pressure. I'm running 21 to 24 pounds (for example, at PIR I think I
run 22 lf, 21 rf, 24 lr, 23 rr), though my memory sucks so bad I wouldn't
trust those numbers.
I'm the guy who has his pit crew running around with TWO tire temp
systems--a quick reading infrared gun with laser sighting, and a needle
type for once we get close. And software as well as seat of the pants and
lap times to interpret what's going on. What's it worth? Three seconds at
1:30 to 1:50 tracks, though probably in the process of paying attention to
handling in turns I'm also adjusting the largest problem any of my cars
have--the interface between the steering wheel and the seat.
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