| Escort Cosworth Suspension. Updated 9th of January 2005 Updated 15th of September 2002 |
| The bare facts of the Escort Cosworth suspension can be found on the suspension specs page. On this page however I'll discuss the suspension layout with its strengths and weaknesses, and how to improve it. |
| Front Suspension The standard front suspension on the Escort Cosworth has a few shortcomings. The number one problem is that the original suspension bushes are too soft. There are 3 pairs of suspension bushings in the front suspension: One pair where the anti-roll bar is attached to the chassis, one pair where the anti-roll bar is attached to the lower track control arms (TCA) and one pair where the TCA are attached to the front crossmember. The soft suspension bushes allows the lower track control arms to move: When braking the arms rotate backwards in relation to the chassis about the point where they are attached to the front crossmember. This doesn't lead to any noticeable problems. When accelerating on the other hand the consequences on the soft bushes are much more noticeable. There are a number of reason why the consequences are more noticeable when accelerating. When the the throttle is applied the front wheels will try pull forward in relation to the chassis. As the suspension bushes are soft the bush where the anti-roll bar is attached to the lower track control arms will be compressed by the front wheels trying to pull forward. The anti-roll bar also has the purpose of holding the TCA in their correct position to retain suspension geometry. When the front wheels try to pull forward the anti-roll bar will also be pulled forward and thus compressing the bushes where the anti-roll bar is attached to the chassis. The deformation of these two pairs of bushes leads to the front wheels creeping forward when accelerating. This leads to intermittent changes in the suspension geometry. The most noticeable being the toe-in changing from (hopefully) zero to quite a bit of toe-out. While this is bad enough the car also has what is known as ackerman steering. This allows the inside wheel to turn in more than the outside wheel in a turn. The result is that when accelerating through a turn you get a lot of toe-out, and as the power is fed to the front wheels the inside front wheel will go a bit sideways and scrub the inside of the tire. If you drive a bit fast on some twisty road you will soon enough notice that the inside of the front tires will be worn down awfully quick. The second problem the soft bushes can lead to is the front juddering when applying the brakes, but that can be warped brake discs too. To minimize the problems associated with soft suspension bushes changed them for polyuretan bushes or Group N rally bushes. Here it is worth noticing that some polyuretan bushes are harder than others. It seems like the bushes sold by Graham Goode are quite a bit harder than those sold by Powerflex. And in this situation harder is better (when performance is concerned). I myself have Powerflex bushes but although they are a lot stiffer than original bushes they are not the best. But I have planned replacing them with bushes from Graham Goode. Polyuretan bushes will improve things quite a bit but if you want to fix the problem for real then you'll have to rebuild you car to rally-specs. Read on to know how the rally-boys go about with the problem. |
| Rear suspension: The rear suspension of the car is probably better than the front but it may still be described as simple compared to what exists on some of today's cars. The problem with the soft suspension bushes remains though. The rear of the car has four pairs of suspension bushes: One pair where the anti-roll bar is attached to the chassis, one pair of big bushes where the crossmember or tubular subframe is attached to the chassis and then two bushes for each trailing arm where those are attached to the subframe. There are two problems that can occur with the rear suspension. The tubular subframe can be bent if subjected to unusual loads such as hitting something sideways. This is not easy to detect but if it's bent enough you should notice it on the cars handling. The other problem is the big rubber bushes that holds the subframe the the chassis. Those are too soft, something that can be felt when going through a turn with bumps. Then it feels like the rear of the car slides around sideways while the tires still have grip left. This will improve if polyurethan bushes are installed. The standard bushes that holds the trailing arms to the subframe are stiff enough as those are metal-to-metal bushes. |
Lowering:
Lowering the car has two benefits: The first is that the car gets a lower
center of gravity and that increases its stability (most noticeable through turns),
the second is that many people think the car looks better when lowered.
There are mainly two possible solutions when lowering the Escort RS Cosworth. The
first is to replace the original springs with shorter aftermarket spings. The
second is to install coil-over dampers.Simply changing the springs for shorter ones will mostly improve looks but it will lower the center of gravity too. The big gains in performance doing this can be had when installing stiffer spring and harder dampers. Quality lowering springs are available from Eibach, Graham Goode and Bilstein. Stiffer dampers worth mentioning are made by Koni and Bilstein. A new setup with adjustable Koni shocks and Eibach springs is probably what most people would want if they got to try all available setups. The will give a nice firm ride while not being too harsh for everyday use. When lowering it is not recommended to lower more than 30mm or so. Lowering more than this will affect the suspension geometry more than what's good. The second option is to install coil-over dampers. Coil-overs are dampers with springs that's attached to the body of the damper, and an adjustable platform that screws up and down the damper body to increase or decrease spring preload, in effect making the ride height of the car lower or higher. In addition most coil-over dampers have adjustable dampening characteristics, some with only one way ajustment while others have separate adjustment for compression and rebound. Coil-over dampers was basically intended for race use only but fortunately they can be valved for any type of driving you want. From as soft as your standard car to full-on touring-car hard. Springs can also be changed quite easily. When installing coil-overs there is also a very good idea to install a rear strut brace as the coil-over dampers will increase the load on the shock towers a lot. The rear strut brace will have to be custom fitted and mounted. A front strut brace is probably also a good idea, but not nearly as necessary as the rear one because of the wall that runs across the engine bay just to the rear of the front shock towers. When you have decided you want coil-over suspension on your car the problems begin: What make of coil-over shall you buy ? There are at least four or five manufacturers that makes coil-over dampers for the Escort Cosworth. Öhlins is the best (and most expensive). Proflex might be about the same quality, but not that expensive.I think Reiger makes coil-over for the Escort Cosworth but I am not sure. Leda also makes coil-overs for the Escort Cosworth and they are a lot cheaper and have only one-way adjustment, but then off course; not the same quality. At last there are AVO.... Cheap. But considering the price of Öhlins and Proflex most people don't have much choice. I have AVO myself and they are a lot stiffer than the original setup but not really what I would have wanted if I had more money. They are stiff enough for normal road use but for track days they are too soft on their hardest setting. I would also have liked to have independent compression and rebound dampening. So, my advice is to get coil-overs and get the most expensive ones you can afford. Spring rates I would recomend for mainly 1 or 2 persons in the car and no luggage is 200 lb/inch rear and 350-375lb/inch front. |
| Race suspension: The suspension of the Ford Escort Group A cars have some similarities with the standard road car, but many differences too. The rear suspension of the WRC cars on the other hand is almost completely different. The group A cars still used a trailing arm suspension in different layouts. There is the 'standard' group A suspension that used a modified main rear beam, and adjustable trailing arms different to the road car. Along with this they used an adjustable blade-type anti-roll-bar. This setup has many of the weaknesses of the standard roadcar's suspension. Bump-steer among others. Then there is a wide-track version that uses a different rear beam altogether. It is made of box-section steel and is quite an improvement compared to the old bent tubular main beam. At least as far as strength and simplicity goes. It is also much easier to see whether the beam has been bent. This layout uses modified and adjustable versions of the standard rear trailing arms. Still it is a trailing arm setup that retains the same weaknesses. On the Escort WRC cars this is remedied by a total change of suspension-type. Getting rid of the the trailing-arm layout altogether and replacing it with a McPherson-strut/multilink system. This system uses two front uprights, and a sort of rectangular rear subframe that holds the rear diff and all the pickup-points for the suspension. This consists of two lower arms and an rear steering arm. The dampers, of coil-over type, are mounted to adjustable top-mounts making the suspension fully adjustable. This layout is a wast improvement both in performance, weight, and adjsutability compared to the trailing arm layout. The group A and WRC front suspension are basically similar and retains the McPherson strut layout while there is an additional compression strut and a relocation of the anti-roll bar. The compression strut is an adjustable-length bar that's attached to the lower track control arm and then to the chassis, both places with a rose joint (metal to metal universal joint). Then the anti-roll bar is changed for a blade-type adjustable one and relocated to the front of the suspension making it leading instead of trailing. The blade-type anti-roll bar consists of one straight stiff bar across the car, on each side of this there is attached a flat piece of metal (blade-shaped) that connects the bar to the lower track control arms (which also is adjustable and rose-jointed). This is also done with rose joints. The blades are adjustable; making the anti-roll bar stiffer or softer. For a soft anti-roll bar as one would want for gravel or snow the blade is rotated so that the rotation of the bar bends the blade about its weakest axis. (As with a plastic ruler which is very soft when bending it when lying it flat over the edge of a table and very stiff if you put it on it's edge and try to bend it.) When you want a stiff anti-roll bar the blade is rotated 90 degrees in relation to the softest position. And off course it can be adjusted infinitely between these two extremes. The anti-roll bar is attached to the chassis with metal-bearings. All the other bushes in the suspension is also swapped for rose-joints. All this leads to a suspension where the geometry is adjustable and doesn't change when accelerating or braking. The downside of this suspension is all the noise the rose-joints translates into the car. Almost unbearable in a normal roadcar. |
