New Tire Report (and some questions)

[Michael Spiers <mikes@specnet.com>]

Finally got around to installing my new tires.  Dunlop D40M2's, 215 45's on
17X6.5 Borbet Type C's.  Put 'em on Saturday night, Sunday morning I drove from
DC to New Hampshire for a New Years party, watched Penn State kick hell out of
Auburn, then drove back home.  1,000 mile round trip, gave me a pretty good
idea of how they perform.
The Pro's:
1.  Very quite, no different than the Pirelli's they replaced.
2.  Holly S%^&, can that thing corner!  Taking off-ramps marked at 25 MPH at
over 50 never squeeled the tires.  Quick lane changes at 80 were absolutely
effortless & quite stable.
3.  Dry road performance in unbelieveable.  Wet road is equally impressive,
although I never really pushed it, I wound up WAY too fast on a wet off-ramp at
one point in time & wound up in remarkable shape.  Snow, I can't really say.
 Although there was around 2 feet in New Hampshire, all the roads were
meticulously plowed, providing no fun to be had at all.  The only snow I
encountered was getting out of the driveway at my friends house, when I had to
go through the yard around an F150 in the middle of the driveway, but the Z34
behind me made the same treck as I did, so it apparently wasn't too slick...
4.  The huge 17" aluminum (no chrome here) wheels look quite choice on the
almost-black car.

The cons:
1.  If you live in New York, forget the 17's.  The difference between the 17"
and the 15" rims makes the car ride a tad rougher, which for the most part is
un-noticeable.  However, the Cross-Bronx Expressway damn near rattled the TQ to
pieces.
2.  Although the 17's look sweet on the car at close range, if you stand back &
look at it fromt a side angle, the low-profile tires look as if I should have
gold trim all over the car.  That part I don't much care for, and wish the
tires had a little more rubber on 'em, but hey...
3.  There may (I've got my doubts) be a problem with the ratio on the
speedometer now.  I had the cruise set at 81MPH (and my speedo has ALWAYS been
5MPH fast, so I should have been cruising at 76MPH) the entire way from DC to
New Hampshire, and from New Hampshire home.  Following a friend's Z34 from New
Hampshire to the New York line, he said he was showing 75, and I know I was
showing 81.  However, Barney Fife pulled me over at the Baltimore tunnel &
tells me I'm doing 89.  Asked to show me the radar gun, he tells me he'd been
following me for like five miles & was pacing me, (so no real proof) telling me
I'd gone from 85 to well over 90.  All this with my cruise set.  Sure.  So,
either:
a) he's full of s^&* (my personal opinion)
b) he's lying to give me a $265 ticket (my second vote)
c) his heap of garbage Crown Vic is a classic example of Ford engineering with
a faulty speedometer (aways possible, can we Americans make anything right?)
d) both the speedo in my TQ and my buddy's Z34 are WAY off base, and my cruise
was allowing my car to fluctuate speeds as much as six MPH and I was too
obliviuos to notice.  A trip to Audi later today will reveal any problems I
might have.  This raises some questions though:
i) If I truely was off by that much, like 13MPH (former true speed was 76, now
it's 89), I'd think my ABS would be all screwed up.  It works flawlessly, as it
always has.
ii)  If I truely was off by 13MPH, wouldn't I notice a HUGE performance loss?
 When I put 35's on my truck, my speedo was all screwed up.  I was off by
around 15 MPH at 75, so that's roughly the same margin of error.  I had quite a
power loss off the line, and had a hard time maintaining speed on the hills.
 Swappping in 4:56 gears fixed that problem.  I noticed zero power loss when I
swapped out my old tires to the Dunlop's on the TQ.
iii)  If I truely was off by 13MPH, wouldn't it have taken a much larger
difference in size of tires to produce the problem?  Now, when I had the speedo
problem in the Scout, I had gome from 205 70R15's (yes, truely small tires for
a truck) to 35 12.50 R15's.  I don't know how to do the math form the 205 size,
but standing the two next to each other was quite a difference in height.  So,
on the TQ, I went from a 205 60R15 to a 215 45R17.  Again, I don't know how to
do the math (although I have friends who can!) but I was told (and re-verified
this info with the Tire Crack) that the rolling diameter for the 205's was 24.7
inches & the rolling diameter of the 215's was 24.6 inches.  So, 1/10th of an
inch.  Granted, standing the stock wheels next to the new wheels revealed a
much larger difference in height, like around 3/4 of an inch, but we were
comparing BALD Pirelli's to never installed Dunlop's.  I imagine that's where
the difference was...

-- 
-Mike
mikes@specnet.com
mks107@psuvm.psu.edu
87 5000CS TQ
84 5000S (2,000 miles away and a mile high)
90 80 (sibling's mode of transportation I get lynched into working on)