Jay Mitchell wrote:
Sorry if I'm late, but digest only for me!
>Uhh, no. Take a look at the skidpad figures achieved by various
>BMW, Mercedes, Jaguar, Lexus, etc. boats in magazine skidpad
>tests and compare them with the same figures for much smaller
>cars. You might just be shocked to see how well the barges do.
Some folks have mentioned that skid pad figures are primarily a
function of tire design/compound and size. Bigger, heavier,
expensive cars tend to have nicer tires and wider wheels. A huge
generality I realize, but until we try skidpads with IDENTICAL
tires/wheel widths we really don't know, do we?
>>While it's true that a tire generates more grip with increased
vertical load,
>>that relationship is decidedly non-linear - the rate at which
grip increases
>>with load diminishes with load, and the rate that rate changes
is very much a
>>function of individual tire construction.
>See my comments re the optimal load range for a tire. Within that
>range, its Cf doesn't vary by nearly as much as you seem to
>believe.
But doubling the mass is a fairly significant change. So from DG's
initial model, I'm assuming he meant equal tires and equal tire
sizes. If this is the case, then the doubling of the mass sends
the CF waaaaaay non linear.
Ever wonder why "wider wheels/same tire compound" always gives
higher skid figures? It is due to the non linear ness of the CF figure.
Which is why everyone tries to run wider wheels in SP over stock. It
is also why a CP car with HUGE tires and horsepower pulls higher G's then
Stock wheeled lotus cars with slicks. And why drag racers try to run super
low
air pressures - all in an effort to get more contact patch to the
ground in an efficient shape.
This is also why another goal is to get the weight as LOW as possible.
In a corner, the loewr the weight the less weight gets moved from
the inside tire to the outside. If the CF were truly linear then there
would be no advantage to a low CG on a skid pad. But the CF is not
linear.
Weight is still king. lose weight and you effectively increase
acceleration/deceleration capabliities and increase max G's in the
corner. Not to mention transitional issues. A no-lose deal.
All of my ideas are hopefully the restatement of that guy Milliken who wrote
that big thick grayish book...
-Doug "still thinks ackerman in autocross is good" Miller
|