Let me explain the Abarth 500 suspension for both road and competition; I have been asked many times what improvements can be made. 

What we need to remember is that the original floorpan design was for the Panda and Punto 2 which were at that time fitted with narrow 13” wheels.  By far the most important thing with any car suspension system is the geometry and the relationship between the centre of gravity and the roll centre at each end of the car.  With the rear beam the roll centre is a bit imprecise as the Kinematic centre usually overrules the mechanical centre, however simplest is to assume the height to be the height of the beam pivot points, so lower the car an inch and the roll centre comes down an inch, the roll moment (the force rolling the car) remains the same. 

The front roll centre is simple and purely mechanical, a line from through the bottom arm pivot points extended to meet a line perpendicular to the top of the strut, and then a line back to the base of the tyre and the height at which that crosses the centre line is the roll centre.  With a standard 17” wheeled 500 the front roll centre is roughly at ground level.  Lower it by an inch (25mm) and the roll centre drops by 55mm.  So assuming the centre of mass is 500mm above ground the roll moment goes up by just over 10% and therefore the car will try to roll 10% more at the front which increases the rear weight transfer and therefore reduces the understeer. 

If we watch BTCC cars we see that the quick ones are always lifting the inside rear wheel, that is to give maximum rear weight transfer and therefore minimum, rear grip allowing the driver to put ever more power through the front wheels without understeer.  The clever guys alter the rear droop from circuit to circuit depending on the grip level and then play with the rebound on the rear shocks to alter the point at which the wheel picks up as they turn-in – more rebound means that the wheel picks up earlier as the car is rolling into the corner. 

The change to 17” or 18” wheels to make suitable tyres available has actually messed the chassis up, it has raised the car by 2”, but to stop the car looking like a 4x4 the suspension has been dropped and if you are following this you will see that the back roll moment has gone by 10% but the front has gone up by 20%.  To counteract the tendency for the car to oversteer, something that motor manufacturers don’t like as it ‘might cause the car to crash’ the front anti-roll bar has been thickened and the lever arms shortened.  On my own car I use a Panda anti-roll bar arrangement with the drop links on the front of the strut as against the back – I hate understeer – and I’m on 15” wheels. 

Above is standard Abarth Essessee rear springs/damper & below is the shorter kit we developed.

So, what to do with an Abarth 500 for the road?  Abarth, Koni, Bilstein etc all make excellent kits that do a fine job of keeping the car safe and making it go over undulations without spitting the car off the road.  My road car list is very simple, sort the bushes in the front wishbones to make the steering more direct, fit shorter rear dampers and maybe stiffer rear springs. 

I have always assumed that the ‘go-faster’ spring kits for the Abarth 500 from Koni, Bilstein etc have rear springs that are short and stiff to give good handling. 

I bought a car fitted with a cheap kit and was appalled; it didn’t handle. I played with springs from the various kits and found that the rear springs were all much too soft. To get the low rear ride height with standard length dampers and not have the springs come loose at full droop, all the springs that I have tested are very soft. Bilstein have two lengths of rear damper but their springs are half the standard rate at full droop and only come up to 30% softer at ride height, it just equals massive understeer. 

I have had some springs made that are 50% stiffer than standard, fit the production mountings and give a low ride height where the wheel fills the arch nicely. They give mega handling, just a little understeer but lift off and the car slides nicely. The snag is that they fall out at full droop with standard dampers. I got my friends at AVO to make super short rear dampers to stop the springs coming loose, and they are adjustable without being removed so that the handling can be tuned, plus the stiffer spring needs more rebound. Keep the dampers soft and the car is good to take the bird to the pub; arrive at a circuit, stiffen them up and big smiles.  Unfortunately AVO have gone bust, so watch this space. 

Essesse with our shortened damper/springs at the rear

The front wishbone has hardly changed from the Panda, the outer upright pin in thicker and both inner bushes have been made a bit stiffer, in the case of the big rear bush there is an aluminium insert in it to stiffen it up (not on a Cabrio) but that gives a problem with the bush failing quite quickly if the car is driven hard.  I was involved with the development of this bush and I’m afraid it wasn’t put through long distance testing! 

We fit a spherical bearing into both the wishbone inner pivots.  We have a pair here that have done over 100k miles so life isn’t an issue and road salt hasn’t attacked the stainless steel of the balls.  With a softly sprung car we raise the rear pivot point to get some anti-dive and have to raise the steering rack by 6mm to keep the bump steer correct. 

Powerflex make an excellent poly bush but trying to be clever and making the caster adjustable has made them almost useless as 99% of people, including me, can’t set them up properly and the steering becomes worse not better.  They do a simple polybush, but in my opinion it isn’t as good as the production bush. 

One of the issues with upgrading the rear bush is that we have found four different diameters and two thicknesses for the bush and hence have to manufacture and fit specifically.  It isn’t an issue as the housings that we carry in stock are for the biggest diameter hole in the wishbone, so we just have to turn the housing to the right diameter.  It takes me a couple of hours to fit the bearings in their housings , so we can return customer wishbones very quickly. 

Wishbone fitted with our upgraded bearing kit

The rear beam flexes – it is designed to – but with big wheels it flexes in the wrong way.  We have done two mods, both of which have good and bad points to help make the back end do what we want it to.  The first is to fit a thick tapered spacer to get more negative camber and keep the top of the rear tyre in the standard position.  Doing the famous ‘ELK test’ with negative at the rear is chalk and cheese when compared to the standard car.  A thin spacer does the job, but, I don’t like the thought of the stub axle not having the spigot in the axle, hence my 15mm thick design with an extension for the spigot, plus it keeps the top of the tyre in the original position. 

For the race cars we have now stiffened the rear beam by welding in a piece of heavy angle iron just at the back of the spring pans, it gives exhaust and spare wheel well clearance issues and I don’t know how long the welds will last before they fatigue.  The race cars are now on 8” wide 15” wheels and to get them under the rear arches we cannot use the tapered spacer so we machine the stub axles to get the 4½0  negative that they need all round. 

I could write a long article about front struts, the salient points are that bump travel is severely restricted due to the chassis having been lowered at least 2” since being designed and so relatively stiff springs are required to stop it crashing through over bumps.  On the race cars we recommend something between 350 and 500lb/in front springs depending on the tyres and circuit.  As a rule of thumb the rear springs will be the same rate as the front for good neutral handling when the front roll centre is at ground level (wishbones horizontal).