The following rhetoric shares my experiences during past work on my Seven's suspension. I make no claim as to its technical accuracy and, in fact, hope it stimulates some alternative views that I can then try out.

As is documented elsewhere in this site I run a Seven with Vegantune twincam engine. This is somewhat up from the 1600cc Kent with 110bhp as fitted to the original Eugene.

It was the hike in power that showed up the inadequacies of the original suspension. Like many people I had not thought much about the suspension, concentrating instead on the engine and how to get more power out of it. It became obvious that its no good having the power if it can't be put down on to the road. Therefore I decided to attempt to improve the cars handling and road holding.

In the same vain as the way the rest of the car was built (on the cheap) any improvements needed to be within a strict budget (Sarah has a lot to do with this) and without too drastic alterations to the basic '84 specification. This was pre the last re-build and I still had the original '84 chassis.

The obvious starting point seemed at first to be the springs and dampers, which at the back were the originals and at the front at least five years old. The idea of adjustable platform dampers also appealed, enabling corner weights to be set. Additionally, the original spring rates of 75-lbs. back, 105-lbs. front were on the low side, making the car run more on the dampers than the springs.

Before any decisions were made I decided to talk to those in the know, including Jim Whiting, Arrowstar, Red Line and Caterham. Initially, this was in as much an effort to find the cheapest components as anything else, but as usual there was no shortage of alternative ideas from all those I spoke to.

What their suggestions added up to was a three-stage approach to improving the cars handling and road holding.

The first stage, surprisingly to me, had nothing to do with springs or dampers. Unless the dampers are leaking badly, or the springs collapsed on to the bump stops, changing them would bring little improvement on their own. What would make a difference would be to improve the geometry of the front suspension to prevent it altering during cornering.

The second stage involved finding new tyres to suit the improved suspension and to replace the existing Goodyear NCT'S, that were close to the legal limit.

The third and final stage is where I intended to start and involved new dampers and springs with increased spring rates, but to compliment the other changes rather than to cure the initial problem.

Stage One - Top link & anti-roll bar.
The basic '84 spec front suspension harked back to the original Chapman concept of using the anti-roll bar as half of the upper wishbone. While fulfilling the Lotus ideal of keeping weight to a minimum the increasing engine power of today's Sevens and cornering forces of new tyres has increasingly shown up the limitations of the original design.

The old top link and anti-roll bar setup allowed the top link to move in it's mounts, allowing the upright to twist during cornering. This had obvious affect on the stability of the car. To overcome these problems Caterham evolved the Chapman design through a couple of stages to the present full double wishbone layout with independent anti-roll bar. This setup also includes the benefit of the top links being adjustable, enabling front wheel camber angles to be set.

The idea, therefore, was to incorporate the latest top link and anti-roll bar into the existing '84 lower wishbone and upright.

The first potential problem was that the taper of the new ball-joint was different to that of the original Triumph upright/hub carrier. Caterham have developed a new unit complete with lower rose-joint replacing the original trunnion, but replacing all this can get expensive and is money better spent elsewhere. In reality the tapers were close enough that ensuring a 'tight' nut on the ball-joint enabled the new and old to work together. A thought here is that Midas Metalcraft make traditional top links that are adjustable. I wonder if the thread is the same as the Caterham wishbone as this would give the correct taper?

Fitment of the new components was easy enough, except for the radiator fan which needed spacing to move it away from the larger diameter anti-roll bar and the recesses in the nose cone which needed enlarging, also to accommodate the bar. The only other part requiring some thought was the holes that have to be cut in the body panels to accept the new front wishbone mounts.

First impressions are important and the first was a crisper turn-in that appeared to respond quicker to initial movement of the steering wheel. Mid-corner control again seemed more precise with fewer tendencies to drift, either into or out of the bend, requiring less corrective input at the steering wheel. The overall stance of the car through the corner was also flatter with less body roll, inspiring additional confidence.

Negative aspects included the car being more 'twitchy' in a straight line due in part to the improved response of the steering and the fact I had set a smaller camber angle than previously. A second and somewhat less desirable result of the change of anti-roll bar was a less composed ride over rough or uneven surfaces. Its not so much a rough ride as would be caused by stiffer springs, but a rolling or jerking motion caused by an inverse reaction of the anti-roll bar to the wheels becoming uneven.

Anti-roll bars work well at increasing roll stiffness without increasing spring stiffness, preventing straight-line suspension from becoming too harsh. The problem occurs when hitting a bump or a pothole displaces just one wheel. Under these conditions the anti-roll bar attempts to keep the wheels level, which is obviously impossible, resulting in the car body rolling to compensate. Not a desirable aspect, especially if its mid corner. For racing cars, where track surfaces are smooth, this is not a problem and thick anti-roll bars can be used. Having said that, its worth remembering that when an anti-roll bar is twisted during cornering it attempts to untwist itself and the suspension with it. As this is impossible there is a resultant transfer of weight from the already lightly loaded inner wheel to the higher loaded outer, which causes understeer by reducing the available grip at the front compared to that at the rear.

Its interesting to note that the original Lotus Elan, one of the best handling cars, had neutral cornering and was designed without the inclusion of anti-roll bars.

For this reason, and at the suggestion of Jim Whiting, I've used the 5/8" bar, up on the original 1/2" but not as large as some of the alternatives. It seems to be the correct compromise although I would like to try a 1/2" if there was one available.

Its also worth thinking of wheel camber angles here as well. Caterham recommend 1 degree negative at the front for present road cars and use up to 2, possibly 3 degrees in race cars, all round, except for cars with crossply (bias belted) slicks which run 1/4 to 1/2 degree. The large camber angle is intended to increase grip by leaning the outer wheel into the corner.

This 1 degree or more camber may be correct but experimentation with my car suggested otherwise. Reducing the camber to virtually zero degrees gave an appreciable decrease in understeer which at first is difficult to understand. The reason, after discussion with Reg Price, seemed to be due to the NCT tyres in use at that time. They were of a fairly flat profile and consequently with less camber angle more of the tyre tread, of both the outer and inner wheels, was in positive contact with the road during cornering. Combined with a zero degree of toe this seemed to be the best setup for that car/wheel/tyre combination. When I moved to a more rounded profile tyre, as with most Yokohamas, an increase to 1 degree camber proved beneficial.

It cost around £200 for the parts and second to the money spent on the engine has been the best investment so far. Much like the enhancements to the engine it has had a measurable effect on reducing A to B times.

Stage Two - Tyres.
When it comes to tyres there are a bewildering array of possibilities. From race-bred rubber to those more at home on a touring car.

When I first bought my Seven it was shod with Goodyear G800 185/70/13, which seemed very capable as a first experience. At about the same time Caterham started using NCT'S, so when replacements were due I changed to them. The difference was amazing. More grip, better handling and they looked better too! But time moved on and now Caterham started using Michelin MXTs, which they said were better again (but they looked like saloon tyres!).

Tyres come equipped with a variety of information moulded on to them, which went through a change of description so the following breakdown may be of use but may now be dated.

Take a 185/70 R13 86H for example:

185Tyre section width in mm
70Relation of section height to section width in %
RConstruction (R = Radial)
13Rim diameter in inches
86Load index (Max load, 86 = 530kg)
HSpeed symbol (H = 13Omph) M+S = Mud and Snow (On a Seven?)

Rim markings (Drop centre rims). Example: 6J X 13 H1
6Rim width in inches
J Rim flange height
XOne piece rim
13Rim diameter in inches
H1Number of humps (used to keep tyre in place

A secondary reason for changing tyres was the possibility to alter the cars overall gearing by changing the rolling radius of the tyre. The mph per rpm can be found with the following calculation;

Engine rpm multiplied by 60 (revs per hour), divided by gear ratio divided by axle ratio = Number of wheel revolutions per hour.

Wheel revs per hour multiplied by rolling circumference = inches travelled per hour. Inches per hour divided by inches in a mile (63,360) = MPH

Therefore, the information needed is engine rpm, axle ratio, gearbox ratios and tyre rolling circumference. For my car that was;

Max engine rpm = 6,800 (although I regularly go to 7,400!)
Axle ratio = 3.636:1
Tyre rolling circumference for 185/70 13
881 revs per mile (taken from data book) = 72 inch circumference
Tyre rolling circumference for 185/60 13
954 revs per mile (taken from data book) = 66.5" circumference

Giving the following gear speeds for my car with 4 speed Escort Sports box and both 70 and 60 profile tyres:


As can be seen, 127mph top speed is slightly over-geared for regular use, although tests on Greenham Common have proved it to be possible with the Vegantune engine.

Therefore, changing to 60 profile tyres from 70 can give a more realistic maximum top speed with an associated improvement in acceleration. Negatives include a reduced road clearance of about 3/4" and the need to select 3rd gear prior to hitting the magic 60 mph.

I contacted the major tyre manufactures to find out their suggestion for Sevens and in return got an interesting cross section of varying information, which is impossible to list here. Interestingly the hardest information to obtain is compound type and carcass stiffness.

At the end of the day the tyre type needs to be chosen for the job in hand. For the primary road use that I do the Yokohama A510's seemed to fit the bill, bred from race rubber but with a good wet performance as well, unlike the A001 R tyre which is more race than road. The alternative Goodyear and Michelin tyres are more road by comparison, although they probably offer a less harsh ride due to softer side walls.

Having said that, I decided that I wish to keep the 70 profile tyre size and maintain the gearing. For long distance touring where maintained high speed is required the lower gearing could get a bit wearing on both the car and the occupants. Therefore I went for 185/70/13 Yokohama AOO1R's. Yes, they did come in 70 profile, as did the A008's. Not sure if you can still get them. However, the gist of this article is the theory not the actual tyres.

One other possible alternative was Avon who were about to produce a crossply tyre for Formula Ford that may just have been road legal! I never did check them out.

Stage Three - Springs and Dampers.
Springs and dampers are in theory a much more complex issue, except for the fact that there are only a limited number of options available.

Spring rates on all but race-only cars can't be set too high as they would give an unacceptable ride. However, they need to be stiff enough to prevent too much body roll with its associated weight transfer and centre of gravity migration. Both these affect the cars road holding.

Dampers affect roll during the transitional stages and prevent oscillation of the spring/weight combination. They cannot, on their own, prevent roll, only alter the frequency of response to the change in attitude of the car. Ideally this needs to be different for bounce and rebound with rebound being stiffer than bounce.

Another major factor that affects car road holding is unsprung to sprung weight. In its simplest terms this affects the wheels ability to follow road surface changes. Therefore a light wheel/tyre/suspension combination and relatively heavy car can give some impressive handling capabilities. The limiting factor here is the tyres ability to grip the road, which eventually diminishes with applied weight. While most Sevens have a relatively low unsprung to sprung ratio their overall lack of weight more than makes up for this making the tyres limits hard to find under normal circumstances. That's not to say savings in unsprung weight shouldn't be sought if possible, hence why some dampers are mounted in what looks like an upside down position.

The chassis also affects the apparent spring/damper rates by acting as a large torsion bar. It transfers weight, or better still roll, from one end of the car to the other, causing the suspension at the opposite end to work harder than if it were isolated. For example, a car that rolls more at the front, due to a heavy engine as with the Seven, will transfer some of that roll to the back because of the stiffness of the chassis. This causes the rear outer suspension to be compressed by a greater amount than the rear weight alone would require. Knowing this, suspension can be modified to incline the cars roll axis to increase the weight transfer during cornering, increasing or decreasing oversteer/understeer. Spring rates can also be altered to have a similar effect. See the more in-depth handling and roadholding article elsewhere.

Looking at the individual corners of the car it should also be apparent that the weight applied to each wheel under static loaded conditions will be different if nominal suspension set-ups are used. This affects each wheel's ability to supply grip under similar conditions. Therefore adjusting the individual spring rates can set up equal corner weights and hence grip. This can be performed by adjusting the spring seat heights while measuring the weights.

This should give an idea of the possible complexities associated with springs and dampers, but as most of the possible variables require re-locating suspension mounts or re-engineering the chassis, we are left with the springs and dampers themselves.

Without breaking the bank the real options were sensible front to rear spring weights of about 140/210 lbs front, 100/120 lbs rear and adjustable platform dampers all round. The options on dampers were the original Spax or the newer Bilstein. Spax were easily adjustable for both spring seat height and damper value, while the Bilsteins required shimming for seat height with no damper value alterations. Having said that, the Bilsteins were designed, in collaboration with Caterham, to have the optimum setting for Sevens. Obviously, since I performed this work there are a number of newer dampers available and probably offer better alternatives. Checkout The 7 Workshop for some ideas.

At the end of the day, when it comes to suspension set-ups unless you have the time - and money - to experiment, its best to go to one of the specialists and gain from their knowledge. Talking to Jim Whiting and Pippa from Arrowstar the information they supplied was very similar. The main difference was spring rates with Pippa's suggestions being slightly harder than Jim's and Pippa suggesting the fitting of an LSD.

All I can say is it was fun playing and there were many points I could not look at.


Eugene - upclose and personal

Is it the the one who dies with the most toys or the best toys that wins?!