by John Comeskey of SPS and James Walker of scR motorsports

Like anything else, improvements to the handling of your Saturn should begin with the weakest link in the chain. Without question, this infers that tires should be the first improvement to the Saturn chassis for improved handling and braking.

Unfortunately, many enthusiasts underestimate the value of tires and fall victim to the temptation of first spending money on more "glamorous" upgrades instead. Of course, other chassis upgrades also play an important role in creating an athletic Saturn, but the effectiveness of those other upgrades is severely limited by the stock tires. We hope that an understanding of the very important role that tires play within the chassis system will prevent you from making the same mistake.

Tires are the Most Vital Link in the "System"

If you have ever driven on pure ice, then you know what happens when friction is reduced between the tire and the road surface: the car becomes difficult – if not impossible – to control. This is because the tires depend on friction against the ground to transmit forces from the chassis.

Imagine that your car were suspended in air upon a giant air-hockey table. In this scenario, your car would literally not move. As you pressed the accelerator pedal, your tires would spin, but having no friction against the ground, you would remain at rest. If the car were set into motion from an outside force, you would not be able to turn or stop – even though you could turn the wheels and press the brakes. Friction against the road surface must exist in order for a car’s controls to function properly. And it is the tire that employs friction against the road surface in order to transmit chassis forces.

Put simply, a car depends upon the tire to transmit every force generated by the chassis. As a result, the capabilities and limitations of the tires will almost always define the limits of acceleration, braking, and cornering.

Stock Tires are the Weakest Link in the "System"

Fortunately, in the real world, even the worst tires on the worst roads have more friction than the air-hockey table scenario. But do common tires have enough friction to handle the performance potential of even a stock chassis? In most cases, they do not.

If you have ever spun your tires under acceleration, skidded under braking, or slid when cornering, then you have witnessed the limits of your tires. Even a stock Saturn is capable of overwhelming the stock tires when driving aggressively. So what happens when you add more power, stronger brakes, or upgraded suspension components to a car with stock tires? Does the car perform better? As a general rule, the answer is no. If a stock Saturn’s performance is limited by the capabilities of the original tires, then a modified Saturn is still limited by the same threshold established by the stock tires. Without a change to the tires, there is no net gain in performance - it only becomes easier to reach the performance threshold and to overwhelm the tires which leads to more spinning, more skidding, and more sliding.

To understand this in another way, imagine that the tires’ capabilities are represented by a one-gallon bucket and the forces generated by the rest of the chassis are represented by water. The only forces that the car can use are those that stay in the bucket. So as soon as the suspension generates more than one gallon of force, the excess spills over the edge and is wasted. In order to use more than one gallon of "force," we must find a larger bucket. Only then can we benefit from the extra forces generated from the rest of the chassis.

The conclusion: better tires are like a larger bucket. Start with tires to expand the performance threshold of your car!

Choosing a Better Tire

Choosing the proper tires for your car is often like choosing the proper shoes for your feet. Most of us have a favorite pair of shoes that we use for "hanging out." But for optimal performance, we almost always have several pairs of specialized shoes that are made for specific functions – running shoes, court shoes, golf shoes, dress shoes, hiking boots, etc. And the specialized shoes usually do not cross over well into other applications. (Can you imagine wearing your golf shoes to play basketball? Ouch!)

Tires are much like shoes in the sense that many types of tires are made to meet the diverse needs of an equally diverse set of consumers. Rubber compounds and tread designs vary among these tires in order to create products that work well under a narrow set of performance guidelines. Seldom do you find a tire that claims to be all things to all people - and a wise enthusiast is skeptical of those that do since the "magical formula" has yet to be found. In fact, there are generally a series of trade-offs that create a multidimensional array of tire characteristics.

On one end of the simplified array are high-performance tires. Tires on this end have unusually large degrees of traction on warm dry roads. But in exchange for performance, they generally bring lower lifespans, reduced fuel mileage, poor cold weather performance, higher levels of road noise, harsh ride qualities, and higher costs.

On the other end of the spectrum are conservative passenger tires that offer less grip at the road surface. But, in exchange, these tires usually offer longer lifespans, better all-weather performance, less road noise, better fuel mileage, smoother ride, and lower costs. In between the extremes are a large number of tire designs that offer many combinations of the potential advantages and disadvantages.

When auto manufacturers choose the original equipment tire for a car, they must choose just one set of tires that will fit the "average" driver in a wide range of uses. They do not have the luxury of providing a "closet" full of "shoes." The result is a tire that can perform a range of tasks suitably, but is unable to perform any single function particularly well.

As a performance enthusiast, you probably enjoy a more spirited driving style than the "average" Saturn owner. In order to accommodate this spirited driving style, you are willing to accept many trade-offs in the pursuit of increased performance capability – especially those involving costs and comfort. (If not, then you have chosen the wrong hobby!)

The conclusion: you should choose a tire on the high-performance end of the spectrum.