Qu. How do i set up suspension on my car?
SUSPENSION – SPRINGS & DAMPERS - DO NOT
CONFUSE SPRING RATE AND POSITION OF ADJUSTABLE SPRING
The spring rate is measured in lbs/inch. Thus a 500 lbs spring
will compress 1/2 inch if a load of 250lbs is placed on the spring,
1 inch with a load of 500lbs, 2 inches with a load of 1000lbs and
The length of the spring will control the ride height. If the
ride height is low then screwing the spring seats up will raise the
ride height. (The spring rate cannot change) as you move the spring
seat up the body the tube in the shock absorber extends. The load
on the spring has not changed (the weight of the car is unchanged)
and the length of the spring does not change. The position of the
spring seat has changed and as the spring length has not changed
the position of the top mount has moved up.
If you run out of adjustment on the spring seat then a longer or
shorter spring can be substituted but keeping the same rate.
This analysis fails if the damper runs out of length. A simple
way to check that the damper has sufficient travel is to remove the
spring from the damper, fit the damper to the car and with a jack
lift and lower the car observing how the damper travels. Ideally on
full bump the bump stop on the damper should prevent the chassis
from bottoming on the road. On full droop the damper has sufficient
travel to allow the wheel to fall to a reasonable position. Ideally
on full droop there should be some pre-tension on the spring so
that it does not rattle loose on the seats.
On full bump if the bump stops do not prevent the chassis from
bottoming it is possible to position the bump stop with 3mm nylon
shims that clip on the damper piston.
If on full droop the spring does rattle loose helper springs can
be fitted. These flat section springs have a very low rate and as
soon as the weight of the car settles on the spring the helper
spring collapses to a flat coil. Without the weight of the car the
helper spring exerts just enough load to keep the main spring and
seats in place.
As well as controlling the ride height the position of the
spring seat also affects the load on that corner of the car. This
is why competition cars have their corner weights adjusted either
on corner weight scales or with a corner weight checker.
The weight on each corner needs to be a proportional spread of
the total car weight.
SUSPENSION – CORNER WEIGHTS AND HOW TO
As already discussed the position of the spring seat controls
the ride height. It is possible to adjust the spring seat such that
the ride height is greater on one corner. This means that this
corner is carrying a greater proportion of the car weight. In fact
what happens is that diagonal corners carry a greater proportion of
the weight and the other diagonal corners a lesser proportion.
If the proportion is unequal the car is not balanced and may not
brake in a straight line and may corner better in one direction
better than the other.
Correctly adjusting the corner weights will remove the
First the weight on each wheel is measured. This can be done
with electronic scales or a corner weight gauge. The anti-roll bars
must be disconnected when taking these measurements.
Total TW = LF+RF+LR+RR (LeftFront + RightRear etc)
% Front = (LF+RF)/TWx100
% Rear = (LR+RR)/TWx100
To check %front + %rear = 100
%Right = (RF+RR)/TWx100
%Left = (LF+LR)/TWx100
To check %right +% left = 100
Then calculate what the ideal weights should be
LF = TW x %Front x %Left
RF = TW x %Front x %Right
LR = TW x %Rear x %Left
RR = TW x %Rear x %Right
It is not necessary to measure the weights in any particular
unit, all that is required is a comparison.
The spring seat positions are then adjusted to give the
calculated weights. When this has been done the ride heights can be
adjusted by moving equal turns on the adjuster seats. The corners
have to be adjusted in pairs, either side or front or rear to keep
the proportions correct. (not diagonally)
Finally the anti-roll bars can be reconnected ensuring that they
have no preload.