1. The vertical loads on the tyres change dramatically
as we drive the race car. So weight transfer
considerations should be our main weapon in balancing and setting up a race car.
the wheels lock, we hit oil, or the tyres leave the road over a bumpy section of track,
all this goes
out the window.
2. For steady state cornering it is
relatively simple. We would only have to be concerned with
relative roll stiffness between the front and the rear of the race car. (Add aerodynamic
effects, if applicable.)
3. But steady state cornering is only a
very small fraction of lap time. In some corners it is effectively nil.
Getting into and out of the corners is the main game. Therefore my over simplified
but interesting combined roll and pitch examples apply. There is very significant
de-wedging effects going on here. (Contributions to understeer and oversteer.)
4. We havn't done a warp (or twist)
with cornering example because I think it can be considered
as a pure diagonal weight transfer between two wheels. The wheels on the other
stationary - do not change weight. (This is the assumption used by Neil Roberts in
his shock tuning article.) There is no other wheel pair
to allocate a part of the weight transfer to. So all
the weight just goes off one and on to another. To work out what's happened to
consider whether the weight movement increases or decreases inside rear weight percentage
compared to the front. In fact, our "LH Turn With Acceleration" example
has got nearly all the weight transfer going from the LH front to the RH rear.
Weights on the other diagonal are not
changed much from the static load. So this example is really diagonal load transfer.
But we need
to break it down into roll and pitch so we can tune it.
5. These examples are only snap shots
in time. What about the transients - accelerating and
de-celerating the various masses to cause the load transfers? How important are
they? Transients are what happen most of the time, and are the reason why shock
absorbers have been the focus of race car development in the 1990's. See shock tuning for a discussion on this.
6. They say the driver feels intuitively the
various net accelerations as they affect tyre loading, and
this sounds about right to me. (He also feels front tyre load through the steering wheel,
and perhaps yaw angle to a lesser extent). So we had better get the transients right
so he can do his job. Carroll Smith talks about making the race car responses linear
in all his books..
7. Consider what a large affect
driver inputs have to the transients. He's got to build the loads and
let them go constantly. It explains why a good driver can sometimes drive around a
handling problem and still be quick. On the other hand, a driver and car set up may
be so much in the groove that a lap record time may come in the course of a race, without
balls out driving,no sweat at all.