Monthly Archives: July 2011

VW Wheels and Tyres

Both in visual terms and for the sake of handling and roadholding, the first move you should make when tuning your car is in the wheels and tyres department. A nice set of alloy wheels with low-profile tyres really sets a car off even before you get involved in uprated suspension and body styling. The difference is instantly visible when you compare the car to a standard one of the same type, and the low-profile rubber gives you better handling, grip and braking, making your car safer as well as more satisfying to drive.

The larger the wheel, the lower the profile the tyre needs to be to maintain the same gearing and rolling radius (important for speedometer calibration). A larger wheel looks better and helps to fill out the wheelarches visually. It also exposes the brakes to better airflow and thereby aids brake cooling when the car is being driven hard. For early cars which came on 5.5J x 13in wheels, the natural upgrade was the so-called Plus One conversion. Using 185/60HR14 tyres on 6J x 14in wheels, this provided the same rolling radius as the 175/70HR13 standard rubber but put more rubber on the ground. The Plus Two system was 195/50VR15 rubber on 6J x 15in alloys. This was the largest size that could be accommodated under standard arches. The use of this tyre size with 7J x 15in alloys is possible, but on some cars the wheelarches have to be radiused or contact will be experienced over big bumps or when the car is loaded.

The very latest trend is to 16in diameter wheels as with the Nothelle package for the Golf Rallye, but only a car with as much wheelarch clearance as the Rallye can use these wheels without arch modification. The tyre size in 205/45VR16. When going to such wheel sizes, always bear in mind that the larger the wheel and the lower profile the tyre, the greater the chance of wheel damage on rough roads. Large potholes have been known to bend expensive alloy wheels, so if you live in an area with badly made roads, both ride comfort and your wallet may dictate no more than a Plus One wheel and tyre package. Also, when you are considering putting more rubber on the road, remember the law of diminishing returns. A 20% increase in tyre width gives you a 10% increase in grip – but only up to a certain point. Complications like over-sensitivity to changes in road surface such as patches and white lines, and a sharp deterioration in grip and steering feel under difficult conditions – when there is standing water on the road, for example -can set in if you pursue the wide tyre philosophy too far.

VW Suspension Tuning

Following wheels and tyres, the next priorities in modifying your car to make it perform better are suspension and brakes, again before you touch the engine. You will find that with more cornering power at your disposal, your point-to-point times will be quicker anyway, as cornering speeds will begin to be limited only by visibility, by the need to retain the vital ability to stop safely within the distance you can see to be clear.

You will also find that a car with better suspension control is more comfortable to ride in as it does not roll so much in corners or give that uncomfortable wallowing sensation when driving on bumpy roads. Again, you can go too far. A car that is made too stiff in its suspension settings can be most uncomfortable. It is jiggly, you can leave the seat over big bumps and you will have less traction in bumpy corners as the car takes off over undulations. And it is skittish in the wet.

Ride and handling are thus a compromise, and VW in fact set a very high standard with the stock fuel-injected cars. The Mk1 cars are slightly under-damped and prone to rock-roll slightly in fast bumpy bends but the Mk2 car is superb straight out of the box. That is not to say that the Mk2 GTI cannot be improved. Far from it. To understand fully how the various suspension tweaks improve a car’s handling, let us look at the forces acting on a car when it is driven on the road or track.

Roll: a by-product of cornering, roll takes place along the longitudinal axis and in a softly sprung vehicle tries to lean the car excessively to the detriment of comfort and cornering ability. The more a car rolls, the greater the slip angles of the tyres and the less of the useful tread area is doing work. The primary component that will reduce this condition is the anti-roll bar, or swaybar as it is called in America.

Pitch: occurs on the transverse rotational axis and causes a car to dive under braking or squat under acceleration. In the absence of anti-dive, anti-squat geometry being designed into the suspension by angling the lower arm locating points, the springs and dampers play the major role in reducing the amount of pitch. Good progressive suspension prevents harsh oscillations.

Yaw: a force that provokes body motion around the vertical axis, yaw affects all the suspension components. In an ideal situation, a vehicle’s suspension should provide completely neutral handling, but most cars are designed to provide mild understeer which allows the front of the car to go wide in corners. This is a safe characteristic to keep the average driver from getting into trouble especially when braking or suddenly decelerating in a bend where a neutral vehicle could then move into oversteer and perhaps spin. If you stiffen just one end of the car at a time, you can induce severe yaw conditions; stiffening the rear induces oversteer while stiffening the front only creates understeer. Suspension development is very much a question of balance.

Diagram showing the forces on a car during road or track driving
When driven on road or track, a car is subject to varying forces which try to rotate it around the three major axes, causing roll, pitch and yaw.

Modifications: to save customers a lot of time and trouble, aftermarket suspension manufacturers have developed kits for various cars providing just uprated springs, or dampers, or matching springs and dampers (which is better), as well as upgraded anti-roll bar kits to be used with the stock suspension or in conjunction with the spring and damper kits. The European manufacturers, like Bilstein, Koni, Sachs, Spax and others, favour the spring and damper kit approach while the Americans, with a more conversion-orientated custom-car background, tend to go the whole hog with upgraded anti-roll bar kits and better quality locating bushes as well.

Bushes locate suspension components to prevent metal-to-metal contact and provide isolation from road shock and noise. They are used in all moving components in the suspension and steering in modern cars and if a manufacturer is over-generous with these rubber bushes, the car can feel rubbery in its handling and ride. Too much lateral movement in suspension bushes does not help accurate suspension location and makes a car feel woolly in corners. Conversely, the metal or metal and nylon rose joints used in racing suspension are too hard and direct for road use and would destroy themselves in short order. Upgraded high-quality road-car bushes made of polyurethane, like the AutoTech ones, will keep the suspension components in check while maintaining adequate comfort. Polyurethane steering bushes will sharpen up the GTI’s steering, which has a slightly dead feel about the straight-ahead position.

AutoTech in California are US distributors for Hor Technologie parts. Hor are an original-equipment manufacturer who supply suspension, exhaust and other components to German car makers like BMW and VAG but who do their own range of aftermarket parts too. AutoTech are also agents for the excellent Japanese-made Tokico adjustable shock absorbers which match up well with Hor springs. The UK agents are Steiner Engineering.

AutoTech's polyurethane steering bushes tauten steering response and stop the rack moving horizontally in its mountings.
More polyurethane bushes. From left to right these are for the Golf/Jetta Mk2 lower front suspension arms; rear shock absorber top mounts; 15mm front anti-roll bar (standard GTI size); and 18mm front anti-roll bar (Jetta and Corrado).
Adjustable dampers are available in Europe from Spax and Koni. With the Dutch-made Koni set, shown here, the rear spring-pan height is also adjustable. Note the progressive-rate coil springs.

Amongst the European suspension manufacturers, you will find that each of the kits you can buy has different characteristics and so will please customers looking for different kinds of performance. The Koni suspension has adjust-ability of damper settings as its strength. You can raise and lower the rear spring pans to adjust ride height and the dampers can be tailored from soft to fairly hard settings if you want to commute in the week and then do club events at the weekend. Koni now have another damper design with a semi-active electronically controlled system – the normal kit is user-adjustable from the shock towers.

First on the scene as a complete suspension set was the famous Bilstein Sportpak.

The Bilstein Sportpak was the first kit on the market for the original GTI and gives a firm ride but brilliant handling. It may be too firm for those who live near less-than-smooth roads, and the gas filled dampers are not adjustable. The kit for the Mk2 is more supple and was the last of the three Europeans to appear.

While Sachs were last on the scene with the Mk1 GTI kit, they were at the head of the queue with the Mk2. Their Mk1 kit strikes a good comfort/handling balance for most people but may still be too soft for really press-on drivers. The Sachs Mk2 kit, on the other hand, is well-nigh perfect, with very little comfort lost over the standard suspension, and it also gives very progressive handling on the limit. All these kits lower the ride height by about an inch which helps stability.

Of the three kits for the Mk1 cars, the Sachs offers the best ride quality but may be too soft for heavy-duty work.

It is not unusual for road testers in different countries to form slightly different opinions of a given car, especially in ride and handling terms. There are several reasons for this, not least of which is that suspension settings are in fact often tailored to the country of destination. The Americans like a softer-riding car despite the good quality of their roads and enthusiasts then complain that the car does not handle properly. Grip and tyre noise are affected by the content of the road surface and this varies from country to country. Thus, a Pirelli P6 manufactured in the UK for local use may turn out to be different from one made at Pirelli’s German factory or indeed one made in the home market of Italy. Suspension, wheel and tyre tuning must thus be done for local conditions and, on that score, companies like Automotive Performance Systems (APS) in California specify different damper settings for their Bilstein kits from those that you would find in Europe. By the same token, a German-bought set might prove a touch hard for use in the LK. Caveat emptor…

Anti-roll bars: the suspension design of the Golf and Golf-derived cars allows the inside rear wheel to pick up under hard cornering. While this is safe in practice, it is indicative of a very severe roll attitude. The solution is to increase the roll stiffness of the chassis without affecting suspension travel and thus ride comfort adversely. The AutoTech front anti-roll bar is a direct replacement for the factory original and comes with all the fitting hardware. The rear factory bar is part of the torsion beam assembly and thus upgrading it means adding an additional external bar. Such an external bar will have different pivot points from the torsion beam and, once the beam is deflected, this would cause the anti-roll bar to push or pull the end of the beam out of alignment. AutoTech’s rear bars use a clever sliding end design to allow the beam to move properly and yet be usefully acted on by the anti-roll bar.

AutoTech front anti-roll bar kit comes complete with all fitting hardware for non-GTI models. You can use the factory brackets with Auto-Tech polyurethane bushes on a car already equipped with an anti-roll bar.
To prevent the rear anti-roll bar and the torsion beam axle fighting each other under deflection, AutoTech designed this 'popsicle' mount which uses the lower damper bolt as a locating point.It allows the bar to move in and out of the link to prevent binding, ensuring light loadings on the mounting points and linear geometry changes. As the rear anti-roll bar on Mk2 cars is integral with the torsion beam, an additional bar has to be used to increase roll stiffness, rather than a replacement as on the Mk1. This is located under the torsion beam and connected to the damper bolts by drop links. (Lower Image)

Stressbars: when a car is cornered hard, the forces produced by the act of the tyres gripping the road transmit high loadings back through the suspension to the monocoque bodyshell. Even though the mounting points are reinforced, the shell still deflects. A hatchback car with its large rear aperture is less rigid than a saloon, a convertible potentially even worse. When the shell deflects, it affects the suspension geometry, the accuracy of which is vital for good handling and grip. The Golf Mk1 shell is much less rigid than the Mk2 and the Cabriolet even weaker despite substantial bracing to compensate for the loss of the roof. The Cabriolet also has a higher centre of gravity and so benefits even more from suspension bracing and uprating.

Although you can use a single bar to brace the front lower suspension arm mounts, a greater increase in stiffness is provided by a triangulated subframe like this one from AutoTech.
An upper shock-absorber tower brace for a Mk2. This looks after the structural integrity of the front end.

The weakest point of the Mk1 chassis is the lower front and the car benefits tremendously from a lower brace to stabilize the lower wishbone mountings. This has been done in more than one way by various manufacturers. The normal after-market European brace is a single bar which attaches to the front joints of both lower wishbones via the retaining bolts and then has two further bolts which attach it to the floorpan. Realising the weakness of the chassis, the factory developed a similar brace for the Scirocco 16Y and this used a wholly tubular design with four mounting points which did the same job. Techtonics market a brace for the Mk1 cars which they admit is a direct copy of this.

The most comprehensive lower strut brace is the triangulated, fully adjustable one from AutoTech which is really a subframe. This connects the front and rear mounting points of the lower wishbones for maximum bracing and is then triangulated between front and rear bars. It is fully adjustable to take in the production tolerances of individual cars.

A lower brace is more effective than an upper one on all Mk1 floorpan cars, i.e. Golf 1, Scirocco 1 and 2 and Jetta, but an upper shock tower brace is icing on the cake. The improvement in turn-in and cornering stability is instantly felt with the lower brace and steering becomes more positive. In the long term, the continuous loadings on the suspension strut towers weaken a car’s structure. The upper stressbar helps to prevent this fatigue and staves off squeaks and rattles in higher-mileage cars. The Mk2 has a rigid front subframe from the factory- and only needs a top stressbar.

As the rear torsion beam twists, so the loadings are transmitted to the bodyshell. A simple adjustable bar can be used to join the tops of the towers and this is easily removed when you need to use the car’s full luggage earning capacity. For more serious high-speed work, a multi-link triangulated set up is available from APS (Neuspeed) which has permanent fixtures in the bodywork via aircraft type Nutserts. The crossbrace, however, can still be removed.

©Ian Kuah. This article was published with explicit permission from author Ian Kuah

VW Brakes

For owners of right-hand-drive Golf, Jetta and Scirocco cars with the Mk1 floorpan, brakes are rather a sore point. Because RHD was something of an afterthought, RHD cars retained their brake servo on the left-hand side of the bulkhead and the pedal action was transmitted via a bell crank linkage system with no less than eleven pivot points! This was somewhat less effective than the system used by Ford with their Escort or by BMW in their contemporary cars, and left VW owners with a rather dead-feeling pedal and brakes that seemed inadequate for the car’s performance. Although you could take up the slack in the linkage, it soon loosened again and you would end up adjusting it every three months or so. Various solutions to the problem were tried. GTI Engineering would tighten up the linkage and fit Mintex M171 racing pads in the early days. This offered some improvement but the linkage would loosen with time and the racing pads, while they worked well when cold, unlike the Ferodo DS11s , would glaze-up easily in slow driving, made dreadful graunching noises when used hard and inevitably wore out the standard discs more quickly. At one point, GTI Engineering even tried grafting Ford Granada discs onto the Golf and these worked quite well but could only be used if you had 14in or larger diameter wheels fitted. It was also an expensive solution.

In 1985, the Italian brake manufacturer Tarox came on the scene with a replacement ventilated disc that was also slotted for better cooling and wear characteristics. With their own matching pads, this brake set worked very well and gave good stopping power, better pedal feel and superior fade characteristics. Tarox also make a set for the Mk2 Golf and, with the already satisfactory four disc Mk2 set-up, this gives a GTI exceptional braking ability.

The Tarox slotted vented disc kit, a direct replacement for the standard front discs, im-proves pedal feel and reduces brake fade in hard driving. Unlike most competition-type brakes, it works perfectly from cold and does not make unpleasant noises.
The ultimate in braking power, if you are prepared to go to 1 Sin diameter wheels with 25 to 30mm offset, is provided by this APS/ Neuspeed 11 in vented disc kit. These are essentially the G60 brakes, with all the parts you need to upgrade a Mk2 GTI or Jetta.
The APS/Neuspeed big-brake kit fitted to a Golf with Bilstein suspension. The kit includes a larger master cylinder and brake lines in Teflon and stainless steel.

Grafting the rear discs from a Mk2 onto an earlier car is not a straightforward task. The hubs are different for a start. If you can find a crashed Scirocco 16V, it is easier just to swop the rear axles and, of course, the brake proportioning valves have to be changed too.

While the initial idea was to get better pedal-feel and retardation by fitting larger discs to RHD cars, if LHD cars had satisfactory anchors with the same equipment, did it not make more sense to attack the problem at source? Autocavan certainly thought so and this British VW tuner sensibly brought out a stiffer, braced brake bar that fitted to the bulkhead and reduced the linkage pivot points to just two.

BR Motorsport’s Brian Ricketts came up with a large servo conversion kit that raised brake line pressure considerably and gave a vastly better pedal feel. He also developed a bigger disc conversion. With both these modifications in place, he effectively put paid to the old joke, ‘Why is a GTI like an Exocet? Because nothing will bloomin’ well stop it!’.

This did not mean that LHD markets were entirely happy with their brakes. When they uprated their engines, the American tuners sensibly looked for better stopping. AutoTech and APS offer big disc conversions for early and late GTI-based cars. Their latest kit uses the front discs from the G60 Corrado to stop the 170bhp turbocharged, supercharged or 2.0-litre cars they sell to clients. Buying a kit like this from these firms is very cost effective because not only do you get all the parts you need, and even Aeroquip braided hoses if you specify them, but, because of the quantities they buy from original equipment manufacturers, these tuners are able to offer the kits for about two-thirds the price you would pay if you assembled all the parts yourself from your local VW dealer.

©Ian Kuah. This article was published with explicit permission from author Ian Kuah