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Citroën A-Type Tuning

Brakes and Handling

© Copyright: J.Cats.

Disclaimer: This page only provides information based on the personal opinion of the author. The author can't be held responsible for damage in any way that could result from modifications mentioned here.

Contents of this page:

Selecting and improving the brakes

It's no good having a powerful car without some decent brakes to get the thing to stop. So upgrading the brakes is called for. There are 2 objectives when upgrading brakes:

  • Increase friction
  • Reduce fading
Increasing friction

On disc brakes the friction area can be improved by fitting bigger pads (covering more of the disc). This can become a disadvantage when the disc can't get rid of it's heat due to the bigger pads. Bigger diameter discs with appropriate pads and calipers can be fitted to increase friction area. Friction can be reduced by glazing of the pads or brake dust getting trapped between pad and disc. In this situation grooved discs can help to brake up the glazing and improve getting rid of the brake dust. But remember that grooved disc have a smaller affective surface for braking then non grooved discs.

On drum brakes wider brake shoes (with a wider drum) can be fitted to increase the friction area. Another option is a bigger diameter drum with appropriate shoes but for a reasonable increase in area the drum needs to be a lot bigger. Drums can be grooved as well to improve getting rid off brake dust.

Reduce fading

Fading is caused by overheating of the friction material. Fading is dangerous because it can lead to boiling of the brake fluid. When the brake fluid has been boiling, air bubbles are created in the brake lines. Next time you press the brake pedal you are compressing air bubbles instead of moving brake fluid so you don't have any brakes.

Fading can be reduced by improving the cooling on the brake components. The first thing to do is feed cold air to the discs and pads, but prevent rain from going the same route. The discs can be drilled to provide additional cooling, this also prevents glazing but reduces the friction area. Another way of cooling the brakes is fitting ventilated discs. A ventilated disc is essentially 2 discs put closely together but with enough room between them for air to flow through. In order for ventilated discs to work at their best a cold air feed is required. Ventilated discs can be found on the Citroën Axel. These discs and calipers will fit straight onto all Ami Super/GS(A) gearboxes. They can be made to fit on the 2cv gearbox, as done on the 24h 2cv racers. The Axel brakes use red DOT fluid and for a green LHM car the calipers need to be rebuilt with GSA rubbers. For some cars finned drums are available for improved cooling, however, I've never come across finned 2cv drums. Fading can also be reduced by fitting brake pads or shoes with a harder material. A disadvantage of using harder material is that the brakes need some heat in them to work properly. This means that after a driving a long distance without using the brakes, the first time the brakes are pressed, they are not very effective.

Wheelhub mounted front brakes

With all the engine and gearbox swapping being done, some people have considered fitting the brakes to the wheelhub as do most cars. This is not a good idea on a Citroën A-type. Because of the forward and downward facing front suspension arms, when braking with this modified setup the chassis tends to rise and go "over" the suspension. This means reduced stopping power because there will be less traction from the tyres. I've seen this setup on a few cars, all with very heavy engines, and the cars were pretty undriveable.

Rear brakes

A-types are very light at the rear, therefore be careful when upgrading the rear brakes. The brake balance can be easily upset, causing the rear brakes to lock up prematurely. This can be countered by fitting a brake limiter. A limiter of some sort is used on 2cv vans and the Ami (Super) breaks. However this one doesn't work very well because it limits according to the position of 1 suspension arm. A better solution is a proper brake pressure limiting valve as used on race and rally cars. But these are usually for DOT (red) brake fluid only. There is the option of fitting rear GSA discs and calipers if this should be required.


Handling

Most people define handling as the level of confidence they have in a car when cornering hard. This confidence (or the lack of it) depends on 2 things:

  • predictability, how much warning the car gives before a change in attitude.
  • responsiveness to changes in steering and/or throttle.
But confidence isn't handling.
Handling is 3 separate but related qualities:
  • cornering performance
  • predictability
  • response

Handling is a compromise between these three. Improving one doesn't necessarily improve one of the other two as well (usually another will deteriorate). Now we look at some different aspects of a car and how they influence the handling.

Weight

The weight of a car and it's weight distribution (front to rear mostly) are basic to any handling discussions. Heavy cars require more cornering force from their tires then light ones. Weight also penalizes response; more work is needed to change the attitude of a heavy car. Weight helps predictability. Nothing happens very suddenly in a heavy car (because of the work needed to make it happen). Weight distribution front to rear determines which tires (front or rear) have to do the most work in a corner. The weight distribution of a normal 2cv is about 55% front to 45% rear. Fitting a heavier (4 cylinder) engine obviously makes the car even more front heavy. The front tires on a front heavy car will tend to lose grip first (understeer). The height of a car or more accurately, the height of its center of gravity is also very important to handling. A higher center of gravity results in more weight being transferred to the outside tires which therefor slide sooner. Cornering performance and response suffer from a high center of gravity. Predictability is improved however because it takes more time for the car's weight to transfer. Adding weight, then, even to improve the weight distribution (bag of cement in the boot) is generally a poor way to improve handling. Removing weight is quite difficult in the already light A-type. A good place to start are the windows (heavy glass, high off the ground) by replacing them with Perspex. Lowering an A-type to lower the center of gravity, seems quite easy at first. "Just" loosen the suspension tie rods. Apart from the fact that loosening the tie rods to much can make them break out of the eye, there are other problems. If the springs are not at least slightly compressed when the car is lifted, the car will tend to "fall" heavily when going over bumps, making it unpredictable (and not only when cornering) and reducing cornering performance. Therefor with the car jacked up under the chassis and the wheels of the ground, there should still be some tension on the tie rods. Also unwanted is any modification that reduces the suspension travel. Reducing the suspension travel increases the change of bottoming out the suspension (riding bump stops). Bottoming out the suspension reduces predictability and cornering performance because all load is transferred to the outside wheels. The reason a 2cv won't fall over is it very long suspension travel. Reducing the suspension travel, and the inside wheels will be lifted off the ground. All load will be transferred to the outside wheels and the car will either slide out of the corner or fall over.

Tires

Tires are the biggest single improvement you can make on your car's handling. Big tires are a unique handling improvement in that the help all 3 handling qualities. A bigger tires (greater cross section and tread width) will improve both the cornering performance and the response significantly, with some improvement in predictability. To gain the full benefit of larger tires, wider wheel rims should be used. At least as wide as recommended, sometimes even wider. The idea is to get the tire wall as near vertical as possible. Different tire sizes front and rear are frequently used on racing cars to compensate for excessive oversteer or understeer. A practical problem on a road car could be the carrying of only one spare. Different tire pressures front and rear, while unable to compensate as much as different tire sizes, do provide a simpler solution. If more cornering force is desired at the front of the car, to reduce understeer for example, increase the front tire pressure and reduce the rear tire pressure. Under no circumstances should you set tire pressures below those recommended and it's not advisable to exceed recommended tire pressures by more then 0.7 bar. Within sensible limits, increasing the tire pressures improves the cornering performance and response of the car, but reduces predictability. A noticeable increase in ride harshness will also result from high tire pressures.

On 4J rims (with 125 or 135 tires fitted standard), up to 145 tires can be fitted without problems. Contrary to popular believe, the Ami Super rims are 4J like those on other A-types and not 4.5J as found on the G-series. On 4.5J rims (GS(A) rims with 145 tires fitted standard), up to 165 tires can be fitted without problems. On the 4.5J rims 125 tires can be fitted to increase the side wall stability. On a 2cv, anything more then 145 will not clear the rear body work and 145 rims already foul the front steering. Anything over 165 will need special wheels or widened rims. Special rims are available from most 2cv specialists. Widening of rims can be done by many wheel specialists.

When changing rims the offset has to be looked at. Offset is the distance between the bolt face on the rim and the inside edge of the rim. Normally wheel offset is designed to distribute wheel loads between the two wheel bearings according to their capacity. A change in wheel offset will overload one of these bearings. Another problem (on the front) is the kingpin. When the offset is changed additional strain will be put on the kingpin, making it wear much faster. When using 4.5J GS(A) rims look out for different off set between the different type of rims. The most modern GSA rims (with full plastic grey hubcaps) sit a bit further inward which gives clearance problems.

Spring rates

Higher spring rates are needed when the type of driving you do is liable to bottom out the suspension, particularly if the suspension bottoms out as a result of the car leaning to much in corners. When bottoming out occurs, not only is it very hard on suspension components, but severe understeer or oversteer will result, depending on whether the front or rear suspension bottoms out first. Generally, high spring rates reduce cornering performance and predictability, and improves response. When higher spring rates prevent a previously existing bottoming out condition, all three qualities are improved. Increasing the spring rate at one end of the car while leaving the other side of the car alone, will increase the tendency of that end to break loose. Generally unless a change in the understeer/oversteer characteristic is desired, spring rates should only be high enough to prevent bottoming out. Anything more not only reduces cornering performance and predictability, but also increases ride harshness.

Shock absorbers

Shock absorbers are designed to damp oscillations which the springs would normally make after the wheel hits a bump. The stiffer the springs, the stiffer the shock absorbers must be to damp these oscillations. You can feel inadequate shock absorber control under several conditions. If the car feels like it is floating or feels imprecise at high speeds, inadequate shock absorber control is probably the reason. Stiffer shock absorbers have an effect on handling similar to stiffer spring rates, a reduction in cornering performance and predictability, but increased response and ride harshness. Like spring rates, therefor, shock control should only be increased to the point where the springs are adequately damped. There are several types of adjustable control shock absorbers on the market.

Anti roll bars

An Anti roll (or anti sway) bar is a torsion bar linking the left and right suspension arm on an axle. If one moves, the other wants to move as well. Anti roll bars are another means of preventing suspension bottoming out during cornering. An anti roll bar increases stiffness only when the car is cornering. Anti roll bars are attractive means to reduce lean (and the resulting possibility of the suspension bottoming out) because while stiffer springs will also reduce this leaning tendency, the anti roll bar doesn't increase spring rates except during cornering or a one wheel bump. Harshness is reduced because lower spring rates can be used. Otherwise Anti roll bars and higher spring rates have the same basic effect in handling. Anti roll bars have a disadvantage however, when used with an independent suspension as on the A-types. In effect they tend to reduce the independence of action between the two wheels. They tie the wheels together, more or less, depending on how stiff the bar is, and partially defeat the original purpose of independent suspension: to allow one wheel to hit a bump without disturbing the contact patch of the other wheel. Anti roll bars are often used as a chassis tuning aid. Since like stiffer springs, the anti roll bar generally reduces cornering performance, it can be used to increase understeer or oversteer. If used on the front the anti roll bar will increase understeer, if used on the rear, oversteer. Front anti roll bars are common because understeer is basically a more instinctively controllable and therefor safer attitude then oversteer. Anti roll bars were fitted as standard on the Ami 8 (front) and Ami Super (front and rear). They are also available from 2cv specialists. Basically any anti roll bar can be used, it doesn't have to be a Citroën one. When driving a light anti-roll bar equipped A-type through a corner, the anti-roll bar can be felt working. This is not a pleasant feeling since it gives the impression of the car being unstable. Therefor, only fit anti-roll bars when necessary. On public roads, twin anti-roll bars are never needed.

Suspension geometry

The considerations which affect suspension geometry design are many and quite complex. Any modification to the original suspension geometry by someone who isn't thoroughly familiar with suspension design are foolhardily. One of the problems with the 2cv suspension is the front kingpins. On 2cv racers an extra upper arm is welded to the standard arm and connected to the hub carrier. This relieves the kingpin to some extend. Excessive lowering can result in unwanted castor angles (the kingpin leans back too much). The car will start leaning over when turning the steering wheel (even with the car is standing still) and the steering will be very heavy. On the 2cv racers, this is fixed by cutting the end of the arm, turning it until the right castor angle is achieved and welding it back on. Before you start cutting off suspension arms, on most cars heavy steering is due to bend chassis. To make sure everything stays straight during the welding, special jigs are used. However welding on suspension parts is not easy and is best left to professionals. The original castor angle is 15 degrees. When modifying 5 degrees is the practical minimum. Castor (positive castor, the king pin leaning back) provides the force that tends to center the steering as you drive. Less then 5 degrees positive castor and the car won't drive in a straight line any more. If you do a lot of hard cornering you may want to set a degree or more negative camber. A good way to judge just how hard you drive is to look at the side wall of your tires, or if you are running high tire pressures, the outside edge of the tread. If the amount of wear indicates that the tire is rolling under, then you can probably use more negative camber. Remember however the objective here is to use the whole tread when you are cornering. So don't go too far or you'll just start wearing out the inside edge of the tread.

As you can see, handling is a fairly complex business, full of compromises. The engineers who designed your car were much more familiar with these compromises then you are liable to be, and they have weighed them carefully. You should be equally thoughtful before you make any of the more sophisticated changes mentioned here.


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