Locost Handling.
 

What I mean by the term handling is not ultimate road holding and the ability to go round comers as fast as possible. Handling is about the balance of the car, how it feels to drive. Good handling is a result of compromise, personal preference and what you want from your car.

If you want road holding, fit a set of wide wheels and tyres, clamp everything down and eliminate as much suspension movement as possible. Fit high rate springs and dampers and replace all those rubber bushes with something a lot harder. Great if you are one of our Locost Racing Series friends who just wants a race car. Not so good if you want to prevent your body, and more importantly that of your passenger, being pulverised to a mush on that summer evening drive to the local hostelry.

Racers want to minimise movement and reduce the variable effects of changes in the suspension geometry as the car is pushed to its limit around a circuit. Always try and keep in mind what you want the car for, change one thing at a time and maximise the benefit from the change before moving on to the next thing.

In the best Locost tradition spending money is no guarantee of success, you could even end up with a car that less to your liking than when you started. I'm sure that they won't thank me for mentioning it, but if Mercedes can spend millions on their A Class and still get if wrong then there's hope for us all.

There is a considerable amount of nonsense talked about the handling and set-up of cars. For most of us achieving the 'perfect' settings for camber, spring rates etc. will not be an issue. Mild bump steer will not be noticed on our country drives nor will that understeer which appears when trying to execute a right turn off a roundabout at 85 mph. However sensible changes can be made to improve your car and make it just that little more enjoyable for you to drive.

Static Handling.

This might seem a strange idea, but good handling starts with weight distribution. The total weight carried by the tyres will always equal the total weight of the car and contents. While changing the total weight of the car is not an option, and here Locost builders have an advantage, you can affect the distribution of weight. However, and here is the first compromise, are you setting up with a full tank of fuel and two passengers or just the driver and half a tank?

Gauges for measuring the corner weights are available although you might be able to get away with two bathroom scales and a suitable cross member. A Locost, driver and half a tank of fuel will typically weigh 500 to 600 Kg in total so you are going to need a range up to about 250 Kg to weigh each corner. Remember that if you are weighing each corner in turn you need to chock under the other wheels to keep the car level. Ideally you want to achieve 25% of the total weight on each wheel, failing that the corner weights should be equalised across each axle.

To achieve the weight distribution some items can be positioned favourably during the build. Consider fitting fuel tanks and batteries on the passenger side to help balance the weight of the driver along with wiper motors, heater boxes etc.

For those who have splashed out on a set of shock absorbers with adjustable spring platforms, corner weights can be set by raising or lowering each spring seat. While remembering that keeping the ride height of the car as low as practical is an advantage, raise the spring platform to increase the weight on that wheel, lower it to reduce the weight. Don't be tempted to try and achieve an equal weight distribution across the wheels by having the shock absorber mounting brackets in different positions on each side.

Dynamic Handling.

Once on the move the way a car behaves is as a result of a set of complex interactions between the various elements and components which connect the car to the 'road'. These will change depending on the way in which the car is being driven and the 'road' it is being driven on. How the car stops, goes and steers come down to the performance of the four tyres at the point where they are in contact with the road. The effect of any changes that are made to the suspension system and components must be considered in the context of how they affect the way the tyres do their job.

The ability of a tyre to perform is related to the 'grip' it can generate. If what we are asking of a tyre is less than the grip available then there is no problem. Demand more grip of any or all four of the tyres than is available then you have got a problem.

The grip available from a tyre is related to the area of the tyre in contact with the road and the weight being carried by that tyre at the time. Of course the road surface plays a big part as well but we generally have little or no control over that The dynamic handling of the car comes down to the way in which the weight carried by each tyre changes as the car is driven (remembering that the total weight must stay the same).

A characteristic of tyre performance is that the grip from a tyre increases as the load on it increases. However this effect is not linear. Doubling the load does not double the grip, the increase in grip is less than doubled. Similarly halving the load means that the tyre has more than half the grip. Spread the load more evenly around the four wheels or between wheels on the same axle and you will have more overall grip. Making changes to help even out the weight distribution, especially when cornering, will help improve handling.

The basic design of a car is the first factor which has a fundamental effect on the way weight is redistributed during cornering etc. and this is related to the car's centre of gravity. Here the Locost is a winner before you start. As you go around a corner weight is transferred to the outside wheels, the amount transferred depends upon the height of the centre of gravity and the width of the track. Low wide cars transfer less weight than tall narrow ones, back to the Mercedes A Class here. The Locost being more like a Formula 1 car than an A Class has the advantage. This advantage can be increased by keeping the ride height as low as practical and by mounting the engine and gear-box fuel tank and driver as low as possible in the chassis.

Once your car is finished the options for altering the way weight is transferred and thus the handling is limited to component changes and adjustments within the suspension. Ron's Locost design does not in include anti roll bars, these being different to roll bars (cages) to save your head if you turn over your pride and joy - so the briefest of words. Anti-roll bars, front or rear, effectively connect the two wheels on one axle together. They are designed to reduce the weight transfer to the outside wheel by moving the inside wheel in the same direction, i.e. as the outside wheel raises relative to the body the anti roll bar causes the inside wheel to raise also, effectively levelling out the body and reducing weight transfer.

Turning to the changes and adjustments which are available within the Locost design, changing the rates of the springs fitted to your car can also be used to alter the weight transfer when driving. Fitting a higher rate spring (stronger) to a wheel will increase the weight carried by that wheel, a lower rated spring will reduce the weight carried. Higher spring rates will result in a harsher ride which is why car manufacturers prefer softer springs with anti roll bars.

While the attitude of the car is changing e.g. as it enters and leaves a corner, shock absorbers can be used to give the same affect as springs. Stiff dampers will reduce the rate at which the car reaches its roll angle and equilibrium. Until equilibrium is reached the stiffer shock absorber will like a higher spring rate. Adjustable shock absorbers allow you to after the rate at which the roll angle and equilibrium is reached.

Suspension Geometry.

Fitting wider tyres increases the area of tyre on the road but could make the steering unacceptably heavy. Before you go for wider tyres, and probably wheels as well, it would be better to ensure that you have the maximum contact area from the tyres you have got

When the car is not moving you will maximise the contact area by having the wheels vertical. However you want maximum grip, not when the car is standing in the garage but when cornering. On road cars the suspension is not solidly attached to the car. Rubber bushes are used to reduce the level of shocks, vibration and noise transmitted to the body which inevitably leads to some movement of the components when subjected to a load.

When cornering the forces/load on the outside wheel will have a tendency to lean out at the top, this is called positive camber. Setting a negative camber (the wheel leaning in at the top) when the car is static will allow the wheel to move to the vertical (zero camber) when under dynamic load when cornering.

The movement of the suspension up and down will also affect the camber angle of the wheel, here we see how complex the relationship between the various elements of the suspension can be. The spring rates affect the ultimate angle of body roll, the dampers the speed at which the angle is reached which also depends on the centre of gravity and the weight transfer. The suspension geometry, the movement in the suspension and the static camber angle will affect the camber of the wheels during cornering as will the size of the tyre, the speed of the car and the tightness of the corner. Change one of these and you can affect all the rest.

Toe in or toe out is another adjustment like camber. A static setting of toe in on the front is set on rear wheel drive cars. Under driving conditions movement in the suspension normally results in the front wheels moving towards zero toe.

Oversteer and Understeer.

Oversteer and understeer are much used terms in the motoring press. A well balanced car should be neutral and display neither, however manufacturers seem to consider that understeer is more desirable in the safety stakes than oversteer - neutrality under all conditions cannot be maintained.

Oversteer is where the car turns more than the driver expects from the amount the steering wheel has been turned. In terms of the tyres it means that the front tyres are gripping more than the back. Under these conditions the car will tend to spin round - at least you won't be able to sea what it is you are crashing into.

Understeer is the opposite, the car turns less than expected and feels like it wants to go straight on rather than round the corner. The front tyres have less grip than the back and will skid first, you go off the road forward and benefit from grandstand seats for the ensuing accident.

For good handling a set-up which gives neutral handling under most conditions tending to slight understeer when pushed is considered the ideal. The following table might help you sort out a handling package that meets your needs.

Having made a component change, an adjustment may be required to the front wheel camber or toe to maximise the benefit. In general wider tyres on the front will increase the forces on the suspension requiring and increase in negative camber and toe in. Fitting uprated (harder) springs, dampers or bushes will reduce suspension movement and mean a decrease in negative camber and toe in is possible.

Whatever you do, have fun experimenting to get the car just as you want it but please no tyre smoking, brake squealing, massive oversteer power slides in Sainsbury's car park just to see that +1 deg. Camber change has done the trick

Rory Perrett April 99