How-To Section: Race-tune your handling
Understeer – Front of car heads towards outside
of turn. Can be less dramatic than oversteer, so therefore easier
to not notice.
Oversteer – Opposite of understeer. Rear
of car heads towards outside of turn. Usually dramatic therefore
gets your attention more!
Camber – negative :- viewing car from front
on, wheel attitude has them outwards at the bottom. Measured in
Esky Standard = buggerall to 1.25 degrees neg
Castor – positive :- Viewing car from side,
the angle in degrees , that the strut is away from the vertical.
Standard has the top of the strut towards the rear of the car.
Esky Standard = 1 to 2 degrees
Toe-in : Viewing car from above, the distance from
one wheel to the other, with the dimension at front, less than behind
wheel centreline ( wheels pointing in at front ), measured in mm.
Standard = 3mm
With the nature of front engined rear wheel drive
cars, they are prone to understeer, either by manufacturers design
or the fact that the engine is over these two wheels- read heavy
Because of this it is important to reduce understeer,
although it is a balancing act, front to rear. The front is the
most tortured due to the weight imbalance.
For anyone in competition it is a matter of finding
what works best for your vehicle/driver style, which means testing
Remembering that the stop watch is the ultimate
With this in mind I jotted these notes, collected
from various publications to help pinpoint things to reduce understeer
better tyres e.g. wider, softer, lower profile
braking too hard and too late ~ driving style
tyre pressures front to rear
not enough negative camber ~ outside of tyre will
be hot and wearing
front roll stiffness too high
too much front toe-in
too much front spring
front track width too narrow
insufficient front shock absorber bump resistance
front roll centre too low or rear too high
too much toe-out in bump steer
too much toe-in in bump steer ~ rear
So, where to start…..with an Esky?
Re-drill track control arm mounts in crossmember
to give increased negative camber this will be from 6mm out and
up, approx. 1.5 degrees to 8mm out and up, 2 degrees approx., or
purchase adjustable track control arms ( T.C.A. ) Too much negative
camber will affect the braking performance of the front tyres, but
I feel this is when you use much more camber than as above.
Using other strut tops, other than Esky, can give
you a means of adjustment, but this is less dramatic than modifying
TCA. However, these can be used to adjust castor. Castor is there
to provide stability, mainly in a straight line, adding more than
the standard setting will produce ~ better initial turn-in, more
negative camber in turn and higher input from you to turn the steering
wheel! The best way to understand this is to grab a spare tyre /wheel
and strap on ( tape ) a tube or wooden stake to it to simulate the
strut . Then hold upright and turn left/right while watching tyre
contact patch on the ground. Repeat with tube/stake angled back
Corty MKII GT strut tops have a smaller outside
diameter, therefore these can be moved around in standard body strut
top hole. New holes in body inner fender will have to be drilled,
for the mounting bolts
K-Mac sell a 24 and 27mm sway bar with threaded
ends to allow for castor adjustment. I guess a street car could
have a 24 and a race car a 27mm. A cheaper way is to obtain a MK
I and MK II bar ( they should be different diameters ) and cut the
ends off, then make up some clamps to clamp on the extra bar below
the existing one, then try out the two.
Front toe in, is there to allow for flex in all
the front end, including the bushes. Therefore a good start is to
replace all the bushes with urethane type. The standard toe setting
is 3mm in at the front. With the new bushes , you will need something
closer to straight ahead. While we are on the subject, you might
want to experiment with toe-out, as this can give you better initial
turn-in, into the corners. This should only be done on a race car
as it will become " darty " e.g. will be difficult to
hold in a straight line…..just hold on.
Start with 30% stiffer front springs and go from
there. Standard is front 95 – 135lb per inch, depending on
model and accessories etc. I noticed in a magazine recently that
they used 600lb per inch front and 450lb per inch springs on the
rear of a MK II race car. Therefore that gives the two extremes,
I guess. Spring rates are fairly easy to calculate, especially when
comparing one to another, unfortunately they need to be off of the
car. Have your moderately sized friend stand on the spring and measure
compressed and free length, then weigh person. Calculate:- spring
travel ( free – compressed length ) , then person weight divided
by travel. Same for leaf springs, stand on diff mount area only
whilst spring is inverted. Best to do this on some nice hard ground
e.g. concrete. This is as accurate as you and I can get without
Front track should be as wide as possible. Purchase
wheels with widest offset or try wheel spacers. Front track needs
to be wider than rear.
Shocker resistance can only be checked via testing,
however count on resistance improvement being in line with percent
Roll center changes usually require suspension
redesigning, however the easiest way to change this is to raise/lower
the relative ends of the car. This can have a big influence on car
Toe-out in bump, when the suspension moves up/down
the steering rack arms act to change toe settings. Relatively simple
jig needs to be built to check this, spacers for rack mount and/or
tierod – strut connectors need to be bent.
As rear axle moves up/down, especially in roll
( going around a corner ) one of the wheels will move forward more
than the other, effectively steering the rear of the car, especially
if you have de-arched springs. Difficult to adjust, however maybe
better to use lowering blocks than de-arcing springs.
One of the better ways to see what’s happening
is to take a picture of your car cornering. A lot can be revealed
from this. With this in mind lets look at this famous esky .
One of the first things I notice is how fashion
just goes around and around [sunglasses]
Next is that car is in understeer mode. Front left
wheel is off of the ground , no weight on it, so car is three wheelin,
would corner better with 4 wheels on ground.
Right front tyre, closest to you, has the majority
of weight on it, the tyre wall is buckling under, therefore would
seem to need more negative camber to corner faster. This is the
reason for negative camber , to keep the tyre tread flat on the
track surface, however it is always a compromise. The rear is doing
a fine job. He’s probably about to bury the throttle pedal
and bring the back round anyway!
There is probably lots of things that I have missed
, therefore I suggest you read the following publications :-
Escort Performance – Dennis Foy
Escort Rally preparation – Charles Reynolds
Race and Rally Car Source Book – Allen Stanifoth
Engineer to Win – Carroll Smith
Tune to Win – Carroll Smith
Drive to Win – Carroll Smith
Race Car Engineering and Mechanics – Paul
Advanced Race Car Suspension Development - Steve
I don’t profess to know everything, just
passing on my experiences.
Hope it helps…..where’s my next beer!