Doug Miller wrote:
> 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?
That's correct.
> But doubling the mass is a fairly significant change.
Yes, and doubling the mass would reduce a car's steady-state cornering
capability. I never said otherwise. I DID say it wouldn't reduce the
car's capacity in direct proportion to the increase in mass, and that's
a correct statement.
> 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.
If you start with tires that are much larger than optimum for the car's
mass, the effect of the nonlinearity may still not be that great.
> Ever wonder why "wider wheels/same tire compound" always gives
> higher skid figures?
Always? I've seen the opposite happen (admittedly in rare
circumstances). Depends on the car's suspension geometry, the tire
design, wheel size, etc.
> 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.
Ever hear of "steering response?" That's as strong a motivation to go
wider/lower profile as steady-state cornering. Autocross has relaitvely
few steady-state features and lots of transient maneuvers.
<snip>
> If the CF were truly linear then there
> would be no advantage to a low CG on a skid pad.
As I pointed by implication out earlier in this thread.
> Weight is still king.
No argument there. However, it is not true that a car's cornering
capacity decreases in direct proportion to increases in weight, even if
the tire sizes are the same.
My autox car weighs 1330 lbs and has 8" rims with 225/45 tires, and I've
gone to quite a bit of trouble to get it as low and as light as
possible. Over the winter, it's getting lower still.
Jay Mitchell
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