In 1978 from July-September Cars & Car Conversions magazine did a series of articles on improving the handling of the TR7. I found it very interesting & only slightly confusing so here it is:
<font face="Verdana">July 1978
To me the name Triumph remains obstinately synonymous with pleasant, if hairy, sports cars. Comfort was sacrificed for taut handling, good road manners, air-in-the-hair motoring and FUN.
The latest Triumph, born of BL parentage, is hardly a classic of the marque, and is really a GT car designed for American highways. Comfort is the keynote, which allied to flamboyant styling, sells the TR7 on the other side of the Atlantic.
For the UK, with our tight, twisty country lanes, we need a car with responsive handling to enable us to set good cross country journey times in safety. The TR7, despite having very good road holding capabilities, lacks the sort of handling that I look for in an enjoyable road car. This series of articles is intended to show what can be done to the marque in the first instance for road use, and secondly in different forms of competition, culminating in the specification of the factory prepared rally cars.
Those of you who read CCC regularly will know that last year I raced a 7 in Production Sports and had a lot of fun, having done quite a bit of development on how to get a standard specification car round a circuit as quickly as possible. The work that we did on that race car isn't really relevant to a road or rally car, as the objectives are to get the car as low as the rules permit, and as stiff as possible to reduce roll. The damper settings for racing produce a ride which gives me a headache after 50 miles, and the amount of understeer needed to make it come out of a bend quickly on full power would be lethal on a wet country lane. So for these articles it was back to the drawing board.
We borrowed a couple of TR7 road cars from Dunham and Haines who own SAH, the leading Triumph tuners. One was a standard demonstrator from their Luton distributors and the other was a mildly tweaked development car from SAH in Leighton Buzzard. The modifica¬tions to the latter amounted to a pair of 2 inch carbs, a free flow exhaust manifold and system and a road rally camshaft to make it quicker in a straight line, but the things in which I was more interested were the front spoiler to see whether it affected high speed handling by reducing front end lift; the Spax rear shock absorbers; Koni strut inserts; and stiffer front springs.
The Basic Car
As with all modern cars, the big compromise in design is cost, and so the TR7 suspension is very very simple with a minimal number of chassis attachment points. At the front is a MacPherson strut controlled at its base by quite a long strut control arm and held in a fore and aft direction by the anti-roll bar. Rubber, to give compliance, is fixed at the top of the strut on the inboard end of the TCA's between the TCA and the anti-roll bar, and where the anti-roll bar is fixed onto the front subframe.
In practice the amount of compliance in these rubbers is very little, giving basically good wheel control. However, it is all spoilt by the front sub-frame being mounted to the body on four horrible bungy rubbers.
The rear suspension is the now almost universal cheap and cheerful system of live axle, four trailing arms and coil springs. Its big advantage lies in the fact that all the suspension loads are fed into the bodyshell in front of the wheel arches, allowing the use of relatively thin gauge metal for the back of the bodyshell. This gives a weight saving and allows for good rear end deformability to comply with modern legislation. The side-to-side axle location is controlled by the top arms being angled ins at approximately 45 degrees, and this gives a rear roll centre at the point where the axis of the arms intercept. The coil springs are fitted between a cup on the chassis rail at their upper end and a small pan on the top of the lower arms, which are parallel. For NVH reasons (noise vibration and harshness) the rubbers at the ends of the suspension arms are big and bungy and allow plenty of axle movement which we will go into in greater detail later.
The geometry is such that the front roll centre with two people on board is at 3 1/2 inches above ground level and the rear roll centre is at a massive 13 1/2 inches above ground level. The spring to wheel ratios are 0.918 at the front and 0.765 at the rear which allied to the 88 front and 165 lb per inch rear spring rate gives wheel rate of 80 front and 125 rear.
If, by the way, you don't understand my terminology and such things as what a roll centre is, I suggest you go back to CCC of March 1 975 where it was explained in words of less than one syllable, or alternatively obtain a copy of J. R, Hartley's Question and Answer Book on Automobile Steering & Suspension, printed by Newnes Technical Books.
The high rear roll centre and relatively high rear wheel rate compared to the front would, at first sight, indicate that the car is a very heavy oversteerer. However, the front anti-roll bar is very stiff and the rear anti-roll bar, which goes between the bottom links is frightfully inefficient which brings a certain amount of balance back to the beast.
Testing
For our initial testing the Triple C/DAD entourage ambled through the Sussex countryside to Goodwood, a circuit which al¬though not used at all these days for racing and thus neither Gordon or myself had visited before, proved ideal as our test track. The road surface has presumably deteriorated quite a lot since the circuit was used for racing and had sufficient undulations to give us a good idea of the sort of ride we would get on a normal road. The parts we had available were three sets of Bilsteins with various settings from Leyland ST, the struts having an adjustable platform enabling us to play with front ride height, 50 per cent stiffer front springs, 240 lb per inch front and rear springs and a set of Koni strut inserts and rear shock absorbers. Knowing the TR7 I had also made up a pair of rose jointed top arms for the rear suspension and we had hard rubbers for the bottom rear arms and the front track control arms.
For the second part of our test we used our usual test facility where we were able to quantify the car's roadholding by driving round a 45 metre circle and from the time taken work out the average lateral G-force. In practice we found this to be an excellent test giving very sensible results and very similar results with different drivers.
The Standard Car
In recommended production trim our notes were as follows: understeers heavily on throttle. Tightening on lift off on high speed corners and moderate oversteer on tight corners. Docile behaviour displaying high G levels - 0.765 G. Feels very under-damped, even on the straights. Diagonal pitching behaviour "in corner" due to the lack of damping control when kicking off the bump stops. Over responsive around the straight ahead - ? rear end compliance.
Next month we will tell you how we sorted it all out.
Andy Dawson
CCC
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