Bespoke Handling

Suspension can be tuned for ultimate performance or ultimate comfort. Somewhere between those two extremes lies a compromise that can tailor the car's handling so that it fits your style like a made-to-measure suit. As Eddie Evans explains, the key is in knowing where to modify and to what extent. 

Essentially, handling improvements are about cornering ability and straight-line stability and these characteristics show themselves through the steering. We also steer partly with the accelerator - putting power down to nose the car into bends - so it follows that the engine's state of tune and responsiveness will also have an apparent effect on handling.

Before deciding how the car should handle and which defects to eliminate, we must have a true picture of the car's standard handling characteristics and this can only be seen if the suspension is in reasonable condition. Front and rear suspension checks have been covered in previous issues of Triumph World but as a minimum, brakes and dampers need to be serviceable for a true appraisal.

It is important to understand which suspension components produce which effects and what the likely outcome will be if they are modified, remembering of course, that modifying one aspect will affect the performance of the other components in the system. So we need to consider the whole of the front and rear suspension together when implementing changes.

STEERING

Most suspension changes will affect the steering characteristics by either promoting understeer (running wide on bends) or oversteer (where the car turns tighter than you expect). So modifications can, for example, reduce the understeer caused by the GT6's heavy engine, or the oversteer experienced when backing-off the throttle on an early Spitfire in a tight bend.

The chassis is designed with inherent, slight understeer for safety reasons and this should be retained, though the amount can be adjusted to preference; remembering that good throttle usage will also counter understeer.

Steering modifications will not affect these characteristics, but a high-geared competition-designed 'quick-rack' will increase responsiveness.

GEOMETRY

Front and rear wheel alignment, or toe-in, must be kept within tolerances. Aim for zero toe-in at the rear, but a rear-wheel drive car must have slight toe-in at the front to help stability.

Castor angle and king pin inclination are steering features and, in general, neither need to be modified unless ultra-wide wheels are being fitted for track work. Our particular interest is camber angle - the amount by which the wheels lean in or out at the top. A positive camber leans out at the top, negative angle leans in.

NEGATIVE CAMBER
Negative camber is desirable so that as the car leans into a corner, the outside wheels, which take most of the weight, transmit their load directly through the tyres to the road rather than trying to drag the tyres sideways. On the minus side, when travelling straight ahead, some stability and braking efficiency may be sacrificed because the tyres will not be quite square to the road surface. For this reason most vehicles are set up with slight positive camber which, by way of suspension geometry, varies into negative camber as the wheel moves up under cornering load.

This tendency towards negative camber can be increased at the front by fitting extra shims between the bottom wishbone brackets and the chassis - or on cars with MacPherson struts, by inserting shims at the bottom of the strut. Increased negative camber at the front can produce oversteer, so although the car may corner better, it won't necessarily feel as if it does. A similar camber angle at the rear will tend towards understeer, somewhat neutralising the combined effect.

Rear camber variation is a well known problem on Herald derivatives, though the Rotoflex and pivoting spring systems fitted respectively to the Vitesse, GT6 and Spitfire cope admirably. Earlier models can easily be converted to a Spitfire swing-spring, though the spring will be rather weak if carrying four people in the Herald or Vitesse. Alternatively a conventional, but de-cambered, rear spring can be fitted.

LOWERING AND STIFFENING
Lowering the centre of gravity of a car reduces body roll, so there is less lift on the inside wheels when cornering. Adhesion is improved, making the car feel tighter and giving the driver a more accurate impression of what is happening at the vital interface between rubber and tarmac. Lowering invariably means shortening the springs. This stiffens the spring rate but also reduces the suspension travel and hence the amount of camber angle variation during cornering. For this reason, lowering may need to be balanced with camber modifications as described above.

Fitting short springs which retain the standard spring rate goes someway to help. Stiffer springs of standard length will also give a reduction in body roll, but any stiffening will reduce comfort. Another point to consider here is that the shorter suspension travel will reduce the wheels ability to follow undulations in the road surface, with a potential loss of tyre adhesion.

Lowering the front end will further increase understeer, but this time its a tyre problem. The energy that would otherwise make the car's body roll has to go somewhere and the tyres take the full rap. In extreme situations they will slip, allowing the front to run wide on bends. this calls for wider tyres (and preferably lower profile ones so that the sidewalls don't deflect as much) keeping the tread flat on the road. Alternatively, the increase in understeer can be countered by stiffening the rear suspension.

The transverse leaf spring cars can be lowered approximately half an inch (12mm) at the rear by fitting a de-cambered spring, otherwise a one inch (25mm) thick spacer block - machined for an exact fit - can be installed between the spring and the differential and this will produce a half degree of negative camber.

ANTI-ROLL BARS
For normal road use, adding a front anti-roll bar (or a stiffer one if already fitted), will produce a similar effect to the shortened, stiffened springs. It increases stability by reducing cornering body-roll and especially the rebound roll experienced when driving rapidly through a succession of bends. Even better, the anti-roll bar only comes into play when you need it - when cornering - leaving straight line performance and comfort uncompromised.

Stiffness of the anti-roll bar has to be chosen carefully because it will effectively increase the overall spring rate and also tends to induce understeer. But this can be countered by fitting another anti-roll bar, or harder springs, to the rear axle to give an opposing oversteer. This front/rear balance can be fine tuned by changing the anti-roll bar link bushes for harder or softer material to increase or decrease their effects.

Generally, it is advisable to install a rear anti-roll bar if the front one has been upgraded and/or the spring rate or height altered. A rear bar will produce a very marked improvement on the Vitesse, GT6 and Spitfire.

DAMPERS
Adjustable dampers provide a quick and easy way to tune the suspension. Dampers only control the spring's rebound movement and not its initial movement when going over a bump or leaning into a bend, so ride quality need not be reduced for the sake of improved control.

Damping rates can also be adjusted to counter the effects of understeer and oversteer in the same way as spring rates, but an excessively high setting can overload the suspension and restrict its movement.

Uprated non-adjustable dampers should always be bought with matching springs.

BUSHES
Harder bushes reduce unwanted suspension movement during braking, acceleration and cornering, giving a tight feel and accurate feed-back to the driver. But the harder they are, the more road noise and shock they will transmit. Again the compromise is a personal choice.

Bushes are a particular problem on the rear suspension of the TR7 and Toledo/Dolomite range. Even new bushes can allow sudden, transverse movement of the rear-axle under hard cornering, so it is imperative to fit harder bushings to the rear radius arms.

Hard bushes will also help to eliminate rear axle torque-twist, which is prominent on Stags when changing gear under hard acceleration. This problem also occurs on the swing axle TRs and the 2000/2500 saloons and can also be reduced by fitting modified axle shafts such as those offered by Chris Witor, Monarch and others.

WHEELS AND TYRES
The large camber changes and castor characteristics of Triumph suspension systems were never designed to keep a wide, non-flexing tyre in contact with the road, so extensive modification is needed before fitting anything in excess of a 6J wheel width, and then, only for the race track.

Tyre pressures offer the last tweak in honing the handling. A lower pressure in the front tyres will give a slight increase in understeer, while in the rears it will promote oversteer - and vice versa. But keep tyre pressures within manufacturers limits.

STATE OF THE ART
Much of the Triumph's character is to be found in the way it handles. And whilst some serious modifications will change the car's personality, the elimination of vices can make driving more enjoyable - and even safer! The shortcomings have not gone unnoticed by the specialist suppliers who have put much effort into designing and testing new systems, components and modifications. The result is that all the parts are now available to make your Triumph handle exactly as you feel it should.


Article featured in August/September 1998 Triumph World magazine


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