[DeTomaso] <detomaso at realbig.com>Re: Oversteer/Understeer

[Mark McWhinney]

Hi Göran,

Thanks for the info.

I have made a few changes to improve handling including a installing a
larger rear sway bar, shock compression/rebound adjustments, rear camber
changes, and tire pressure adjustments.  The car feel more neutral now, but
I suspect the real reason for the improvements is that the driver is better
at handling the dynamic over/under-steer forces with steering inputs and
throttle position.

Mark



-----Original Message-----
From: detomaso-bounces at realbig.com [mailto:detomaso-bounces at realbig.com] On
Behalf Of Göran Malmberg
Sent: Tuesday, August 28, 2007 1:22 PM
To: detomaso at realbig.com
Subject: [DeTomaso] <detomaso at realbig.com>Re: Oversteer/Understeer

Allright, we talk about the same language. Resentley I heard a discussion 
about
passenger cars where  over-under steering tendency was reffered to as some
sort of turn-in or feel in the steering wheel effect. Pleas let me explain 
my way
of looking at it.

If for example the rear wheel is l

If we drive the car on the 200f diameter skidpad slowley building up speed 
and
the front wheel is the axle that is loosing its grip first, the car is said 
to be
understeering. Ok, if sideway acceleration is 1G the car is speeding 44 mph.
Lets say we use a bigger diameter skidpad so that the car has to speed 144 
mph.
then we need some 300 rwhp to propell the car. Now the car is probabley
badley oversteered since a lot of the tire grip is used for maintaining 
speed.

Now, is the car in general term to be named under or oversteered?

Myself I am in to that the car should be described as under-oversteered from

only
lateral acceleration, which mean that the slower diameter circle should be 
used
and that we should use almost zero trottle when the brakes loose to see what
happen to grip balance.

Also, as speed builds up on the skidpad we should note the steering wheel
position. If steering input needs to be greater to keep the car in the 
circle at
an increasing rate that ends up with the frontwheel is loosing all of its 
grip,
the car is understeered.

Even if the car is oversteered it will need a little amount of increased 
steering input
during speed buildups, but as slip enter the picture a more sudden loss of 
rear wheel
grip will take place.

So, in the first part of speed build up we couldnt tell for sure what the 
steering
tendency of the car really is. What it comes down to is that in a dynamic 
situation
the car is never really neutral since it is under influence of more forces 
than the
steady state skidpad cornering situation. Therfore I have a term of my own
i call "average neutral", which means that the car is set up to neutral seen

over
the whole lap around the track. Which means that the car is not true neutral
in any situation around the track. Excuse me for using a racing track for an
example, but how do we handle the neutral situation on the street?

I am not saying that hte car not could be said to be more or less "neutral" 
or a better
or worse driver, what i am telling is my way of looking at this problem.

Goran


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