kits worth having cost about £600 upwards, to many of us that is
more than the base car cost! But there are some budget options.
The basic change needed to any road car for circuit racing is to lower
the centre of gravity and increase roll resistance so that the tyre is
in full contact with the road over its full width. Usually this has to
be compromised a bit because of roll and constraints of the base car design.
So, lowering the car is usually the best starting point. Spring kits for
some cars can be reasonably cheap, but beware of very cheap parts because
the spring rates can vary wildly and upset the cars balance. Best use
a brand that other racers of your sort of car go for.
Don’t be tempted to make the springs too hard, Graham Chapman is
said to have worked to the principal ‘softly sprung – firmly
damped’ in order that a wheel can move effectively and freely enough
to do its job.
As a rough guide to rates (as seen at the wheel, so the actual spring
will have a higher rate depending on where it is fitted) a standard road
car might be 100 lb/in, a sports car about 150 and the old British Touring
Cars were in the 300 range at the front. Rears tend to be a lot lower,
possibly half the front. My old Rover SD1 ran 300 in the front struts
and 100 in the rear coil-overs that used the old damper mounts which are
more outboard than the original spring mounts, and it handled beautifully.
Real racing springs are surprisingly cheap, about £10 each depending
on size. They come in two main diameters; 2.5 inch or 1.9 inch so you
need to do some modification to make them fit. If you have struts then
you can weld on threaded tubes, usually about £20 each, which have
adjustable spring seats so you can vary the ride height and set each corner
up precisely. If you don’t have struts then you would need coil-over
dampers, which are very expensive and you end up spending a similar amount
to if you had bought the full suspension kit but with the benefit of full
Another spring option is to cut a coil off the standard springs, although
this does have problems. Cutting one coil off will lower the car significantly
and also make it stiffer (going by ratios; if it had 10 coils and you
cut one off then it will be 10% stiffer), but the cut end must be profiled
to sit in the spring seat properly and this is where the problems start.
Most springs are flattened at the end and bent so as to form an even surface,
spreading the load across the spring seat. If you just cut one coil off
you end up with a point loading on the seat which can damage it and lead
to failure. Also any heat applied during the cutting will change the spring
stiffness, so if you are not carefull you can end up with different rates
on each side of the car. But using a hack saw and a file some people have
achieved reasonably acceptable results. Alegedly.
Another option is using standard springs off a different model, on my
V12 XJ-S I used the ‘Sports Pack’ springs off the six cylinder
model. So look at what other models used the same type of suspension.
Which ever way you choose to lower the car, there will be an optimum ride
height, most car suspension changes camber as it moves so if you go too
low the wheel will be tilted too far over and you loose grip. As ever
the best starting point is to ask other racers what ride height they use.
Dampers are obviousely critical, much more important than the springs.
Adjustability is nice but comes at a price, far more important is consistant
reliable operation. Because dampers get hot when used their performance
changes, cheap adjustable dampers should be avoided as should second hand
ones, you just don’t know how worn they are. A good starting point
is to use quality non- adjustable dampers, most brands do a ‘sports’
damper for about £40 each.
Of course some times you can grab a bargain from someone elses misfortune,
unfinished projects come up for sale far too often and can have lots of
nice new bits nailed onto a rusty shell, so keep a look out.
As for rubber bushes, you may be tempted to replace them with polyurethane
performance items, but beware as cheap bush sets are very poor quality
and can fall apart when used in competition. Decent bush sets will cost
above about £150 but new standard rubber items are surprisingly
good. Some bushes have a gap or ‘void’ in them to reduce noise,
sometimes these can be fitted in a different orientation it stiffen things
up, for instance my Jag has void bushes in the trailing arms that link
the rear hubs to the chassis, rotating the bushes 90º moves the voids
from front/back to left/right and so acceleration and braking forces are
transmitted to the chassis more directly. Don’t be tempted to remove
all the bushes and make solid ones, most suspension relies on some compliance
to avoid locking solid, plus the fact that a little give in the suspension
will help prevent things bending when you hit a kerb.
Off road racing
Similar rules apply, you need to get as low as you can but still maintain
a safe ground clearance, particularly when landing after a big jump.
For Land Rover based racers there is a huge range of standard springs
available, from the massive springs of a 130 Defender hi capacity crew
cab to the light spring from and original Range Rover. Other manufacturers
also have a range of springs from different applications.
Dampers for off road racing get a hell of a hammering and so get very
hot indeed, I used Fox 2.0 dampers on my Tomcat and they were too hot
to touch after just a few miles of competition, bigger dampers with remote
reservoirs are better but then costs just get silly with each damper costing
about £200 upwards. A better budget option is to use quality standard
dampers (about £40) but doubled up, or in extreme cases use three,
thus sharing the work and heat between them. Obviously this needs some
mods to the axle and chassis but they are usually not too difficult. Again
see what other racers in your chosen class do.
Which ever way you go the secret to good off road suspension is long wheel
travel, the art is to keep all wheels on the floor no matter what shape
the terrain is. This makes anti-roll bars problematical, it is usually
better to engineer in a reasonable amount of roll resistance into the
front suspension, but keep the back end supple enough to drop into big
holes or off side slopes without causing a front wheel to wave in the
air. This can be done by running higher spring and damper rates at the
front but also suspension geometry can help, for instance the Range Rover
style front ‘hockey sticks’ bind up in roll giving inherently
high roll resistance and so firmer bushing will increase this.