Cooper in the trunk

[PDQSHIP@aol.com]

In a message dated 95-11-28 11:21:57 EST, you write:

>
>This was real news to me: I was told by the comp. dept of British Leyland,
ow
>Rover/BMW, that the reason why we went to narrower section tires on our
>competition Mini Coopers was precisely to prevent the effect you say is
>caused
>by the narrower tire. The theory was that the wider the section, the greater
>the weight dispersal and hence the less force being used to displace water,
>crud, mud and snow. It therefore was no surprise to me that when I bought my
>4000 CSQ in 86, the winter quipment option had the narrower section tires.

Sure, however my point was in reference to the float caused by the higher
sidewall not the narrower tread, this is chassis to tire float reference not
a tire to crud reference..... In fact, my post referenced the scirocco as
having too much float on a "wide" 185 tread tire, so you must have missed my
float reference........
  And the post was a 195/65 vs a 205/60, and for the 3 tenths of an inch, you
will notice little, if any difference in crud float, but you will notice a
big difference in sidewall float....

>This
>is the case still as it was the Audi marketing theory that most Q drivers
>would
>think themselves bullet prrof in the wet etc, so they were given the best
>equipment option. Since the quatrro has enjoyed little real advantage on
>unimpaired dry roads, this was not something Audi dealers were trying to
>optimize except for those who demanded it, and expected to replace their
>tires
>in the winter.
I'm not sure I give either arm of audi that much credit.......
>
>So can you explain what you mean about causing the sidewall to float... I
>understand that the narrower section tires have sidewalls which are not as
>STIFF as their wider counterparts, promoting roll under and distortion at
>10/10. But this only ocurrs in the dry. In the wet you loose traction long
>before this happens?

No .....  you lose control quicker with a narrow section high sidewall
tire.....  The problem is that the hi sidewall makes the tread pattern
inconsistent at the contact patch.  The more sidewall the more flex, and the
more flex in the tire, the more you will have the tread pick up the inside or
outside edge of it's own footprint, and footprints are key to control, wet,
dry, snow or ice, and given the size of the contact patch with the narrower
tire, just a little (as in way before 10/10ths) pick up can be
catastrophic.....  I refer to this as time delay syndrome.....  If you take
your summer tires and go 60 mph, and do lane jumps quickly, you can
eventually get the tire behind the steering input.....  If you do this with a
higher sidewall summer tire you will notice that the tire falls almost a
whole input behind the steering, that is the definition of tire float on
sidewall......  A stiffer sidewall can "help" but not eliminate the problem,
cuz it's just rubber and flexing steel belts after all, you have a height to
weight problem.....

A Minicooper or my 1988lb scirocco can go with very narrow tires cuz they are
very light cars, and are much more sensitive to width than height, not enough
weight to crud push, sidewall stiffness is plenty for the weight...........
 The audis OTOH, are big pigs with too small a wheel/tire combo from the
factory......  They tend to be sensitive to the sidewall more than the tread
width (and we are talking tenths here) becuz of weight, a 225 tire on a
3500lb car can prolly push the same amount of crud as a 165 on the mini, but
the 3500lb teetering on a 70series tire is asking for control trouble for the
audi, and little to  none for the cooper....

You can eliminate some of the sidewall problem with wider wheels/narrow tire
combo, but the sensitivity to height is still there.....  And in fact, I know
that there are some stiff narrow tires on the market, but the height still
gives you a control disadvantage, and it's before the car reaches it's 10/10
point in any conditions.....  You want the tires to follow your steering
input as accurately as possible, low traction almost more than hi traction
conditions, cuz low traction makes the steering and tire outputs crutial for
maintaining the contorl of the vehicle.....  You are comparing the apples to
oranges with the pocket rocket.....  Portly is the nice word for the
audis.......   So, your argument is well founded for a 195/60 vs a 205/60,
but given the MPS (that's miss piggy syndrome) of the audis, I doubt you'll
notice any difference unless driving 10/10.....

Scott