Tuning
SuspensionLast
on February 15 20102009 Update
New for 2009, a range of front and rear suspension kits, developed by Karl Hacken of Kustom Engineering based in the USA, are now available for the Mk1 Fiesta. These kits are for the four / five speed Mk1 Fiestas, and are of the very highest quality, drastically improving the handling, and performance of any Fiesta.
Rear Kit:
Kit includes:
-2 Lower Links with hardware
-1 Panhard Rod with hardware
-Links construct from swedged 6061-T6 alloy
-Rodend bearings are 7075-T6 alloy
-Entire kit weighs 38.5 oz
$250 Shipped to UK
Front Kit: (5 speed)
-2 4130 Chromoly control arms
-2 Swedged alloy Tie bars
-2 Tie bar Brackets
-All necessary hardware: bolts, nuts, rodends, clevises
-Links construct from swedged 6061-T6 alloy
-Rodend bearings are 7075-T6 alloy
-$450 with 2 chassis braces shipped to UK
Visit www.kustomengineering.com for to place your order!
Making a FWD car go round corners
Since a FWD car is nose heavy, it must be setup to work the front tyres as evenly as possible. That means it must corner with the inside rear tyre very lightly loaded or airborne. We trade away lateral grip at the rear to gain more at the front, where we need it. We also gain drive traction on the inside front wheel. This is important in a FWD car, because we cannot use limited slip differentials that lock too firmly or abrubptly, unless the driver has great tolerance for steering fight.
It is important to note that once the inside rear wheel is airborne, the rear suspension has contributed all the anti-roll moment it can, and any further roll resistance has to come from the front. Up to the point of rear wheel lift, rear load transfer builds faster than the front load transfer. Beyond that point, rear load transfer is 100%, and front load transfer builds rapidly. So does roll angle. So does understeer.
As a general rule, to get a car that has good consistency as grip varies, we want the inside rear wheel to lift just a little in steady state cornering, when grip is good. If it lifts more than that, we are likely to have a relatively loose car when grip is poor and a much tighter car when grip is good.
Nov 2004: I am toying with the idea of fitting a softer front anti-roll bar to complement the rear.
Now compare this picture with the one shown below, taken the year before, and you can easily see the difference in the body roll and the behaviour of the rear axle. Look at the gap between the rear tyre and the top of the wheel arch. The addition of the stiffer springs and rear anti roll bar have made the biggest differences. The -ve camber rear axle helps too.
Finally, another picture showing the behaviour of the stiffer rear suspension, this time at Shelsley Walsh hillclimb, July 2004. The rear tyre is off the ground as the car approaches the top S at full speed.
How to make your Fiesta handle
Its all about preventing the shell from rolling too much, and trying to keep as big a contact patch at the front at all times (so you can keep the throttle pedal buried and get round corners even faster)
I'll start at the rear of the car.
Rear suspension
The tubular rear axle on the Mk1 Fiesta is a traditional design, shared amongst many manufacturers. Using a Panhard rod to keep the axle square to the ground, the system works quite well. Linked with an uprated rear anti-roll bar however, considerable improvements can be found, in keeping the car straight and level when cornering hard. I wanted to give the rear wheels some negative camber, and had thought about bending the axle, or cutting it in two, and using a steel sleeve, welding the axle back together, with a preset amount of negative camber.
What I settled on was a system that joined the two halves of the axle back together, but allowing adjustment of the camber and toe-in, in situ using two wedge shaped aluminium rings. The trick is machining the rings so when they're bolted back together, and sandwiched between the two halves of the axle, the resultant angle gives -1.5° negative camber on each wheel.
This picture shows the end result. I also had the axle and all parts powder coated whilst it was away. And all fastners are 12.9 grade steel for added strength and safety.
My Fiesta also has an adjustable and rose jointed Aluminium panhard rod, supplied by Kustom Engineering (USA). And it has a pair of Aluminium adjustable and rose jointed rear trailing arms, again supplied by Kustom Engineering. All the rose joints add up to a very noisy ride, but the suspension is completely adjustable and the settings cannot drift once adjusted.
Since fitting the modified rear axle and anti-roll bar, I've adjusted the anti-roll bar drop links so that they are vertical when the car is sitting on all four wheels, which reduces the risk of the links binding and causing the rear end to lock up when cornering. I've also shortened the bar. As you can see, with five holes, the bar is rather close to the axle. By shortening the bar, I've reduced the number of adjustments available, but I still have from 5 times to 8 times the stiffness of the original XR2 anti-roll bar.I'm using SPAX gas adjustable rear shock absorbers. Together with 450 pound shortened rear springs, and the anti-roll bar set on 5 times the stiffness of the standard anti-roll bar, the handling has been transformed. As you can see from the photograph below, the Fiesta now has a tendancy to lift a rear wheel on hard cornering. This is, believe it or not, to some extent desirable (read on...)
The front suspension
This section will be updated as soon as I have the new Kustom Engineering setup installed.