I'd been holding off weighing in on this, but I can't any longer.
Derek Butts said:
> I have driven this van before. We used to have one as a parts van.
> If autocrossed it will end up like an upside down turtle....
I have both autocrossed my Previa and been up on two wheels in my GTI.
My Previa is an Altrak, with a rear sway bar, good shocks, and slightly
lower than stock due to low profile tires (215/60-15). It handles better
than a lot of sedans. I autocrossed it once at an SFR event (at Alameda
NAS about 4 years ago) and my time put me in the top 80% of the entire
field. Beat a Porsche, a Vette, and a Tiger among others. Look it up.
My GTI was running in ES on BFG R1s at another SFR event. My co-driver
sawed the wheel trying to catch a spin and got us up on two wheels.
I couldn't tell, but Katie Elder and other reliable witnesses said they
saw air under the tires. I did not like this. I lowered the car 1.25",
beefed up sway bars and moved to DSP. The car is now totally
uncompetitive, but is safer and a lot more fun to drive.
What's the point? That vehicle/tire combos that roll with some regularity,
such as race rubber clad but otherwise stock VWs, BMWs, and various
econoboxes, are allowed to run events, but others that *may* be even less
prone to rollover provoke a knee jerk reaction like, "A Previa is not an
acceptable vehicle for Solo II"
My suggestion: you can't easily measure CG during tech, but you can
measure outside dimensions. CG height can be conservatively approximated
as the midpoint between ground clearance (C) and height (H). Divide the
estimated CG height by the track width (T) and use that ratio as a
stability index.
C + H
----- = stability index
T
Pick a cutoff stability index that would exclude vehicles already known
to have a propensity to turn turtle (VWs, 3 series BMWs, etc).
And encourage vehicles over that ratio be excluded by the safety steward
on stability grounds, unless the vehicle is classed in the rulebook.
Perhaps my Previa could have been excluded on under this rule. So be it.
Note that lowering a vehicle reduces both C and H. This correlates well
with what we all know intuitively.
I'm not claiming this formula is perfect, but I think it's better than
excluding vehicles based on appearance.
/Bill
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