rec.autos.simulators

A car goes around a certain turn at 50 mph.  Predictably, weight
transfers to the outside tires.  At steady state cornering, the OF and
OR tires are carrying a certain constant load.

Now, say the OF spring rate is lowered by 10%.  The same car then goes
through the same turn at 50 mph.

Will the load on the OF tire at steady state cornering be higher, lower,
or the same as it was before?

I have some experimental data that gives me an answer.  I'd like to hear
what others think.  There are surely some guys working on sims that
could pull actual numbers off of their computer.

Thanks!

Pat Dotson

I believe the way it is supposed to work is that the
outside weight transfer should be the same in the
same conditions. (Sum of front and rear)

Since you have reduced the roll resistance of the front,
the proportion of the load transfer at the rear will be
larger (just like tightening a rear roll bar, or loosening
the front.) So the answer is the outside front tire with
the reduced spring rate should show less load
after the change.

- Matt

According to the data I use on a Late Model Coil Over car pulling 1.3G's in
a turn it would reduce the weight in Steady State cornering 1lb on the RF
and LR and increase the weight by 1lb on the LF and RR.

If you don't already have these books:
Race Car Vehicle Dynamics by William and Douglas Milliken
Fundementals of Vehicle Dynamics by Thomas Gillespie.

They do a very good job covering this topic.

The other answers you got are right in principle, but I'm in a nitpicky
mood. ;o)  What's the weight distribution?  How stiff is the chassis?  How
much more does the chassis roll as a result of the spring rate reduction?
It is conceivable to me that for a car with a heavy front end, not much
chassis stiffness, and not much roll stiffness to begin with, that the
answer could be the opposite from what you would normally assume, i.e.
higher instead of lower.

We discussed this last year, but I had forgotten.

I guess the load on the RF will be lower up until the point of roll over.

Try this; In steady-state cornering, when a car or kart is at the point
of bicycling (all of the weight is on the right side), then the load
split between the RF and RR tires will be equal to the static front/rear
weight bias.  Does that sound true?

So, say the static weight on the RF is a lot lower than the RR.  Then
initially you will get a higher rate of weight transfer onto the RF.

On Sat, 01 Mar 2003 13:38:23 -0500, Pat Dotson

I tried it in Racer (although it's still suffering from a few small WT
bugs):

Car, mass about 600kg, turning at 0.5g, regular suspensions:
   front
1957   1010  (Newtons)
2118   2072
    rear

Then lowering the front-left spring rate from 19300 to 10000 got:
1929   1035
2122   2072

Doesn't really look that ok; I tried before and I think I saw diagonal
weight jacking, but in any case, the RF tire became lighter. ;-)

Ruud

Ruud van Gaal
Free car sim: http://www.racer.nl/
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