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Racing Secrets Revealed

Weird Ways to Make FWD Cars Fast - Part 1

by Roger

My first ever track car was a 98 Nissan 200sx. It was a 2-door Sentra 1.6, complete with a cast iron 115hp GA16DE motor, 14" wheels and a curb weight under 2300 lbs. On paper, it's the perfect base for a nimble, lightweight handling monster.

But for some strange reason, I couldn't get it to handle. My beloved Nissan was easy enough to drive, but getting the car to turn was a constant problem. After three years and dozens of suspension mods later, I finally realized that the advice I received from books and online setup guides were missing some key points in how to set up front wheel drive cars.

Here's what those books and guides are missing:

 

Know the two major setup philosophies

The first thing you need to know is that there are two major schools of thought when it comes to setting up production based front wheel drive cars, and the difference is in tyre size. One school of thought uses the same size wheel / tyre combination in the front as the rear. The other uses a larger wheel or a wider tyre in the front.

This seemingly small difference makes a huge difference in how all of the other pieces fall into the setup puzzle. A larger front wheel and wider front tyre will naturally reduce the amount of understeer the car exhibits through every corner. You can run stiffer front springs, run less extreme alignment settings, and the car's behavior won't change as much when the tyres heat up. But it also means that you can't swap wheels front to back, and that you will need to really work with the brake bias to keep the small rear tyres from locking up.

In contrast, most FWD club racing cars and street-driven track cars in the US use the same size wheels and tyres on the front and rear. Along with the economic benefit of being able to use the tyres all the way around, this approach will give you more setup freedom in the rear end of the car. The downside is that the added rear grip will make the car difficult to rotate and you need to rely on stiffer rear springs and stiffer rear anti-roll bars to make the car turn.

There are tons of fast FWD track cars on both sides of the fence. But it is important to understand that these differences exist, especially if you plan to use coilover kits or anti-roll bars with off the shelf rates. A coilover kit with super-stiff front springs is probably not what you want if you plan to run the same 245/40R17s on all four corners of your car.

 

Make the rear springs significantly stiffer than the front

What a lot of people don't realize is that most passenger cars (FWD, AWD, or RWD) come with higher rate springs in the back than they do in the front.

One reason for this is to help with ride comfort when driving over big bumps. By making the rear spring stiffer, automotive engineers can make the front and rear settle from a bump at almost the same time. This reduces the amount of bouncing the passengers experiences and gives the perception of a better ride. However, making the rear springs too stiff would make the ride jarring. So car manufacturers will use progressive rate rear springs to maintain a supple ride while keeping the advantages of a high rear ride frequency for when drivers hit potholes or speed bumps.

Another reason for installing a stiffer rear spring is that the rear suspension of most passenger cars are designed with a higher motion ratio than the front. Look under your car and see where the springs mount to the control arms in the front and rear of your car. They will be further inboard in the rear than they are in the front. The further inboard the springs, the higher the motion ratio, and the stiffer the springs need to be in order to achieve the same effective rate at the wheels.

Because progressive rate springs are difficult to engineer and produce, most aftermarket coilover manufacturers will use linear rate rear springs that are somewhere between the softest and stiffest rates provided by the factory rear springs. Generally, this is a mistake. The spring will be too soft for the car to handle, while simultaneously being too stiff for a comfortable ride. If you are setting up your car for performance, install a significantly stiffer spring in the rear than the front.

So how much stiffer should the rear be? A good way to approach this is to calculate the motion ratios of the front and rear suspension on your car, and look at how different the front and rear motion ratios are. The bigger the difference between the front and rear motion ratios, the stiffer your rear springs need to be.

If you are just starting out or aren't confident in your abilities, find out what kind of spring rates racers use for your car, and lower both the front and rear spring rates proportionately.

For a detailed explanation of motion ratios and how to calculate them accurately, head to:

http://alison.hine.net/cobra/tweaks/motionratio2.htm

 

Dial in as much front camber as you can

For some reason many track day enthusiasts don't put enough camber in the front of their FWD cars. Some people seem to think that even 2 degrees is too much. They will claim that it would cause uneven tyre wear or that it would increase braking distances.

What these people don't realize is that modern R compound tyres are designed to work with a minimum of 2.5 degrees of negative camber. Even the latest generation of high performance street tyres are so sticky that they need extra negative camber just to keep a flat contact patch under hard cornering.

At the last SCCA March Lion test weekend, I had the pleasure of meeting a friendly gentleman who was testing out a new acquisition - A 4th gen ITS Prelude Si very similar to my own. His primer-grey Honda had the weirdest looking setup of any ITS car I've ever seen. It must have been 5 or 6 degrees of negative camber in the front, and the ride height was so low it looked like an early 90's Super Touring car. Definitely not something you would expect from a club racing car running DOT R compounds.

But you can't argue with results. Within 15 minutes of hopping in the car, the driver had belted out a 1:16.5 on NJMP Lightning. That's within a second of the ITS lap record. When he broke out the tyre pyrometer, it read a perfect even gradient across the tread.

If you have a track driven car and want to run R compounds, I would recommend starting with at least 2.5 degrees of negative camber up front. Adjust your rear camber based on the front, and fine tune both sides using your pyrometer. FYI, I run 4.25 deg negative camber in the front and 2.25 negative camber in the rear.

 

That's all for part 1. Check back soon for part 2, with more weird setup tips for FWD track cars.