A quick word about slip angle: A tire will offer the best cornering, not
when it is pointed directly where you want to go, because it will always
slip (a sort of push/understeer) a little. So, slip angle can be from a
couple degrees to 6-ish degrees angled more than where the car is
actually going to go. So, to get the best traction from all four tires,
the car would probably be a couple degrees sideways. (Not necessarily the
slip angle of the tires, but probably a bit less, since the rear wheels
don't turn. The slip angle thing wasn't all that important anyway. What I
did want to point out, is that cornering force is independent of the
radius of the skid pad circle. Don't think of it as a speed the car can
reach, but rather the time to get around the circle. If the radius is
larger, there is more ground to cover, but the car can go faster and
lateral g's will be the same. I'm going to check on the proper formula to
calculate lateral g's later and get back to you.
Second, I never said difference in weight makes no difference, just a
very minute one (at least until you get to extremes). I'm going to get that
straight before I say anything else about it, but it's simple vector
distribution. Also, if weight is distributed farily evenly above and
below the center of gravity, roll should not change, only if a lot of
weight is added high up, and a decent suspension geometry should minimize
camber change through suspension travel. An example: the BMW M3. R&T or
C&D did a $35K+ car test or something like that a month or two ago. The
M3 has a staggering amount of roll, but excellent suspension geometry
that allow it to corner as well as, if not better, than anti-roll bars
with engines like an F355. In fact, it had the best overall handling. So,
roll really isn't an issue.
And one more time: best way around a skid pad is at constant speed. As
long as the speed is attainable by the car (I've never had any problems
reaching 30 or 40 mph in my Alpine), torque, hp, etc. is irrelevant.
Age
On Fri, 24 Oct 1997, Jarrid Gross (Yorba Linda, CA) wrote:
> Adriano and alpine skidpad freaks,
>
>
> >Well, a properly timed skid pad would be run as follows: you have two
> >circles connected at a point, basically making a figure-8. The car
> starts
> >at the center where the two circles meet, goes right first and goes
> >around that circle twice: once to get up to speed, and the second time
> >around as the actual timed measurement, then the car would go around
> the
> >left circle, once to settle in, and a second lap to be timed, then
> leave
> >the skid pad at the center, opposite where it started and it would be
> >timed from the center point, where the circles meet, so again, power
> >wouldn't make a difference.
>
>
> You said in your post yesterday, or at least my interpretation to that
> effect was, that the car will make best Gs at the raduis where the slip
> angle of the tyre is at the apppropriate angle for its load.
>
> This would mean that the two circles would have to have been
> painted with prior knowledge of the correct turning radius for that
> car.
>
> In magazine road tests, the radius is gererlally specified, or at
> least written in the report, and interestingly it seldom changes
> from car to car to car.
>
> While this may not yield true peak G numbers, it does appear
> that it is a standard test, perfomed in some painted lot.
>
> If the radius is to large, an underpowered car may not be able to
> attain the required velocity to generate the same level of Gs
> that it could have produced at a lower radius. This is especially
> true of short wheelbase cars like the alpine.
>
> The original 1961 road test had some specified skidpad radius
> or diameter, which unfortunatley was not variable as should be.
> The alpine didnt make enough torque to the rear wheels
> in third to attain the velocity required to make peak Gs.
> Second gear probably wouldnt have gotten your there
> without over revving, so they condluded that a 4.22 rear
> instead of thr 3.89 unit, would have gotten them the much
> needed torque to pull the car at the needed higher velocity.
>
>
> While I do not argue any of your technical points, I do know
> that more mass means more centrifugal force, which the
> tires, suspension geometry, power of the vehicle ECT must
> overcome to maintain a given radius on the pad.
>
> Centrifugal force, is the same thing as performing constant
> acceleration, only the acceleration is lateral. More mass
> running at a given speed means more force required to
> maintain the same speed.
>
> Your statement that weight is not a factor in attaining Gs
> may hold true in a racecar where you have nearely unlimited
> tire traction capabilites, and tunable suspension, but in
> a production car, more mass means more roll ECT, which
> means that when you put the stickiest tires you can buy,
> and have given yourself about as much camber as your
> suspension will give, you are at the mercy of the weight of
> your car.
>
> Shave off a few hundred pounds on the same car, and it will
> make more Gs "assuming you didnt disturb the weight transfer".
>
>
>
> Jarrid Gross
>
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