>Phil Ethier wrote:
>
>> http://www.visi.com/mac/icerace.htm
>> This is Philip N. "Flip" Shockley leading Peter Kitchak through a
>> left-hander. The interesting thing is that both cars are in an
>> oversteering attitude and the front wheels on the two cars are pointed
>> in opposite directions. This illustrates a basic difference between
>> FWD and RWD when ice racing.
>
>Yea verily, it is interesting. And yes, it is a wonderful and graphic
>demonstration of fwd vs rwd chassis dynamics on a low grip surface.
>
>> Both cars are in an oversteering attitude
>
>Hmmm?
>
>Well... I don't get that. To me, the Saab seems to be understeering,
>and the Porsche oversteering.
>
>At the risk of opening yet another can of worms, here is a definition
>of understeering and oversteering that I dimly remember:
>
>Understeering:
>When the grip angle at the front (i.e. the angle between the plane of
>rotation of the front wheels and the velocity vector) exceeds the
>grip angle at the rear (i.e. the angle between the plane of rotation
>of the rear wheels and the velocity vector).
>
>Oversteering:
>When the grip angle at the rear (i.e. the angle between the plane of
>rotation of the rear wheels and the velocity vector) exceeds the grip
>angle at the front (i.e. the angle between the plane of rotation of
>the front wheels and the velocity vector).
>
>According to these definitions, I believe the Saab is understeering,
>and the Porsche is oversteering.
>
>Am I missing something obvious to the contrary?
>
>Regards,
>Erik Berg
>
>PS> Boy, does that ice racing look like fun, or what...
>
>
I agree with you, Eric. I say the Saab is in an understeering four wheel
drift. That is, all wheels are sliding but, in order to maintain the
drift (stretching the definition a bit), the steering wheels are
understeering (steering into the turn).
I do see Phil's point though about the totally different philosophies
between fwd and rwd required to get the cars around the turn on slippery
surfaces. The reason I think the definition of a drift is stretched a
bit for what the Saab is doing is that the rear is where it is only
temporarily, because of the use of momentum on entry. If the turn would
be long enough, this effect would dissipate, leaving no drift and pure
understeer. In the case of a rwd car in a drift, both front and rear are
controlled more directly (IMO).
Rod
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