Lets play with power sliding through corners (v. long)

[gnt@nhm.ac.uk (Graham Thackrah)]

Dear Berthann,

I have been reading a good book of a friend of mine that tells you all about
front/rear/all wheeldrive handling and racing/fast driving technique. As far
as I remember it the best ways to cope with four wheel slides is to plan for
them in the first place. In other words if you find the car loosing grip
when you are not expecting it then simply back off the gas, this'll result
in the car turning in sharper esp in a front wheel drive car and
understeering all wheel drive car. This may lead to a tendency for the back
to loose traction and opposite lock to be applied quickly to avoid a spin,
the solution, basically for saving a rear wheel drive car when the rear lets go.

To anticipate the loss of grip it is best to set the car up to slide around
the corner in a controlled slide, obviously easier on loose or poor surfaces
and almost certainly safer as the speeds involved in sliding on tarmac as
compared with snow are clearly greater on the former. The set up is to
lessen the weight on the rear tyres such that they loose traction and can be
controlled using judicious use of the throttle. On corner entry a flick to
opposite lock briefly before turning in can begin a pendulum motion (you
must have seen rallying cars do this) and a touch of left foot braking will
serve to transfer weight to the front of the car to aid turn in and secondly
to allow the rears to loose traction in conjunction with their sideways
motion, see below. On the turbo cars this also serves to keep boost up, as
the throttle is still depressed, to avoid lag on the exit of a corner. 

All the above are in order for all wheels to go beyond what is called the
slip angle and begin sliding (the maximum angle between the attitude of the
tyre footprint and the wheels direction of travel, once exceeded the tyre
begins sliding) this is easier the narrower the tyres as the transfer
between slipping and sliding is quicker the wider the tyre. The amount of
traction a  tyre has is more or less constant, when cornering the forces
acting on the tyre are not only in its direction of travel but also
perpendicular to this. for an equal amount of power from the engine, this
explains why the tyres loose traction when cornering. The forces from
cornering are added to that from the engine. It also may explain why
swinging the rear out aids the controlled loss of traction from the rear wheels.

A four wheel slide is thus a balancing act between the force produced from
the engine, from cornering and the relationship between this, the amount of
available grip and the slip angle of the tyre. What this means I am not
sure, if you read a book by a guy called Frere it explains it using some
fairly complicated diagrams and equations, much of this reply could be found
in that book (I will find out the title tonight and post it tomorrow this
time). 

Disclaimer, I have only just begun to try out a few of the things (I have
not succeeded in having the back hanging out yet but it is tricky on a long
wheelbase front wheel drive car on the public highway, not to mention
dangerous) it mentions in the book and am sure a session on a race track
with a suitable tutor would be far more beneficial but until I can afford
that.....

Any comments on the above gratefully recieved.

Hope this helped,

Graham.