CHASSIS TUNING GUIDE
Go on a Diet!
If your car has 280 bhp and weights 1300 kilos it will accelerate, brake and corner in a particular way. If you remove 300 kilos, you car will have the same power, but that power has to accelerate, brake and corner much less weight. The result is that you car will now accelerate, brake and corner faster! In a fully trimmed road car, consider removing the heavy sound deadening materials, carpet, trim, seats, headlining, stereos, heater matrix (think about demisting windscreens first though!). Swapping electric windows for manual ones, glass windows for plastic and fitting lightweight body panels will also see the weight coming down.
Wheels and Tyres
Some wheel designs are very heavy adding weight to your car. Too larger diameter will give longer gearing ruining performance. Narrow wheels means narrow tyres giving smaller tyre to road contact area hence less grip reducing you car’s acceleration, braking and cornering performance. Consider a wide, low weight motorsport wheel when choosing wheels for your car.
Your car’s tyres are the only contact your car has with the ground. When you think about it, it’s a very small contact area so you can imagine how important your tyres are when your car is accelerating, braking and cornering. In order to be able to put the power down without wheel-spinning, brake harder without the wheels locking and corner more quickly without sliding, try to use the widest stickiest tyres you can fit without rubbing on your arches or suspension. If you intend on modifying and improving your engine, brakes and suspension, having the stickiest tyres available will maximise the benefit of these upgrades. Remember though, sticky road legal track tyres will have great grip in dry conditions but the offset is often poor grip in the wet, their softer compounds will also wear out more quickly so maybe not ideal for a daily driver. For s dual purpose car, consider a dry tyre, a wet tyre and a road tyre as the ultimate solution.
Brake Upgrades
Good brakes will transform the performance of your car. They will help you reduce lap times by allowing you brake later for corners, which means you spend more of you lap accelerating and going faster! There is huge competitive advantage in being able to outbrake your competitors and sneak up the inside for an overtake!
The first line upgrade is generally uprated discs and pads as the lower cost solution. However, the greatest increase in your car’s braking performance will be seen with a big brake conversion kit, available for most of the popular track-day cars and in 4 or 6 pot design. These kits will slow your car down much more quickly, great for competition but also offering more safety in emergency braking situations on the public roads.
Anti-Roll Bars
On a road car, the job of the anti-roll bar is to resist body roll. The use of anti-roll bars allow manufactures to stiffen the suspension during corning whilst allowing them to use softer springs for a generally more comfortable ride. On our track day car, an uprated (stiffer) anti roll bar will help us resist body roll still further whilst allowing us to use a softer damper setting in order to maximise traction.
Steering Racks
A “high ratio” steering rack or “quick rack” will allow you to physically turn the front wheels of your car with less movement on the steering wheel resulting in faster steering inputs. A real plus in motorsport situations where large movements on the steering wheel reduce your cars steering response times. Many high ratio racks are made of alloy and are lighter than the OE part!
Suspension Bushes
Most manufacturers use rubber bushes in their suspension joints to maintain comfort and reduce noise. As these bushes age they become soft or crack and the suspension components are allowed to move about and hence your suspension geometry settings will move. Your cornering will become inconsistent and grip will be reduced. The most cost effective solution is to fit polyurethane bushes that remove most of this unwanted movement thus sharpening up your car’s handling and grip.
The ultimate improvement comes when you replace the bush with a race-style metal ball joint (often called rose joints). These have no play in them at all and give the best “feel” although you will get a slightly harsher ride.
Coilover Suspension Kits
The job of the shock absorber is to damp body movement of the car. We want some movement in the suspension so we do not unsettle the car during hard cornering where bumps in the road or track may make the car jump off the road. We also want the dampers hard enough to minimise body movement and weight shift. The job of the spring is to help control the damping effect. They also affect body movement and vehicle height hence the best suspension solution is a matched spring and damper combination.
Converting you car’s suspension to coilovers is the most effective form of suspension upgrade. The best kits are height and damping adjustable (whilst the suspension is still on the car) giving you the ability to change damping and height settings for optimum performance. Most full kits consist of uprated adjustable dampers matched to uprated coil springs and a ride-height adjusting spanner. The fitment of coilover due to their compact size often means wider wheels can be fitted to your car.
Many manufacturers make road kits and track kits. The track kits are generally better specified and of lighter weight, they are designed to perform more consistently over the duration of a race without their performance fading off. Road biased kits can be used with success in racing conditions if you are building on a lower budget, but talk to your specialist about springs rates for your application. Often a higher initial outlay for the track designed kits pays dividends in the later part of the season when your own new found driving abilities overcome the abilities of your road biased setup!
A word on ride height! Many customers want to know the maximum drop a coilover kit will allow them. Well, most kits will get you down 100mm or so (depending upon what model you have within your car’s range). However, it is worth noting that most cars designed for racing will have their bodies just millimetres from the ground whilst also offering a good deal of suspension travel in order to damp the body effectively. Most road cars will loose suspension travel upon lowering and the more you lower, the more suspension travel you will loose. Whilst having you car sitting on the floor looks great, having no suspension travel when entering a bumpy corner at speed is likely to result in a visit to the scenery! Road cars will always be a compromise and hence most suspension manufacturers talk of drops of 60-65mm being the optimum for fast road use!
Suspension Setup - Alignment
Once you have your coilovers (or lowered/uprated dampers/springs) fitted, don’t skimp on the geometry! Have your car laser aligned and any necessary adjustments made. Your options will generally be a standard, fast road, race, drift, drag geometry set-up. If it possible, adjustments will be made to tracking, camber and castor. Tracking (also known as toe settings) affects initial turn in and under/over steer, camber affects your car’s cornering grip and castor affects the steering self-centering action. All are critical settings both on the road and on the track in terms of safety, tyre wear and improving suspension performance.
It is worth noting that, depending upon your vehicle, you may need to invest in extra parts such as suspension top mounts that adjust camber and castor in order to get the correct geometry for you application. Adjustable suspension arms are available for a wide range of vehicles and allow greater adjustment of camber.
Suspension Setup – Corner Weighting
Having your “car corner weighted”, especially after fitting coilovers, will give you considerable benefits in handling. Your car will weight different amounts at each corner front and back. “Corner weighting” involves measuring each corner individually and adjusting height settings to even out the weight differences (taking driver and fuel into consideration also) and is an inexpensive job handled by specialists. Handling characteristics can be dialled in/out and the feel of the car can be totally transformed. To get the most even corner weights, you may even want to move components within your car, fuel tank and batteries are commonly moved if regulations allow! |
