A number of readers have requested articles on improving driving skills. Well, we aim to please. Here’s a look at what separates a good driver from a great driver written by Chief Driving Instructor Van Svenson for the fall 2009 edition of the Air Cooled Advertiser.
What separates good drivers from great drivers? The answer is: smoothness. Perhaps you’ve heard this from an instructor, perhaps from a race commentator on TV or perhaps from a buddy in the pits. It’s true – speed comes with the ability to drive smoothly. What exactly is “smooth driving”? Before tossing out a definition, let’s first review some basic race car physics.
The car has four tires. As each tire touches the pavement, it deforms a little bit, making a “contact patch”. The “traction” a car can make, or, more specifically, the friction generated between the rubber and the road, is dependent on how large the contact patch is and how much force is pushing down on that contact patch. Wider tires yield a larger contact
patch and therefore have the capability to produce more traction. Fine tuning the car’s alignment and suspension can also help define the size of the contact patch, yielding more traction. However, we’ll make those topics a discussion for another issue. Putting a wing on the car, to generate aerodynamic down force, will push the tires against the road more, generating more traction. However that’s impractical for most cars, except the most dedicated race cars (and it won’t make you a better driver). So, the key here is: what can you do as a driver to change or manipulate the forces pushing down (or pulling up) on tires.
As a car changes from accelerating to braking to turning left to accelerating again, and so-on, it goes through a series of transitions that change how much weight is pushing down at each tire. To answer the original question, “what is smooth driving?” I am ready to tell you the answer. Smooth driving is controlling weight transfer in transitions to maximize traction of the tires.
How this works is probably best illustrated through examples. Let’s start with a turn at the end of a straight – accelerating down the straight will transfer weight towards the rear of the car. The car will literally “rock” backwards (kind of like going up a hill) which will make the rear wheels feel more weight and the front feel less weight. If the car weighs 3,000 lbs, and it has a 50/50% weight distribution, there will be 1,500 lbs on each axle.
Accelerating aggressively can transfer several hundred pounds – yielding 1,300 lbs on the front wheels and 1,700 lbs on the rear wheels. Taking one’s foot off of the gas pedal and coasting will transfer weight back to the front. Applying the brakes will transfer more weight to the front. Again, we’re accelerating down the straight, transferring weight to the rear of the car. Now we brake and transfer weight to the front of the car – while we’re braking we start turning a little bit. If we haven’t reached the absolute traction capacity of the tires with our braking, we’ll have some traction available for turning. As we turn, weight is going to transfer to one side of the car.
Let’s say we’re turning right. If we’re braking and turning, our left front wheel is going to have the brunt of the car’s weight on it. This will also give this tire the most traction, but two things might happen. We might exceed the traction available to us and that wheel will start sliding towards the outside of the turn, or the left rear wheel, which doesn’t have much weight on it, but which has to help support the car against the sideways push caused by centripetal force, might start to slide because it does not have enough traction.
Quick action by the driver to get back on the gas might cause the opposite scenario. The weight transfers back, and the front tires no longer have enough traction to keep the car turning – the car starts to go straight. The idea of smooth driving is to transfer weight and load tires progressively. I once had an instructor tell me: if someone comes up to you and quickly shoves you, you might fall over; but, if that person starts to gradually push against you, you’ll start pushing back– pushing progressively harder.
Cars have mass and it takes time for that mass to move, so there’s a little delay between when you ask the car to do something and when it does it. Braking is more effective when it’s done progressively so the pressure on the brake pedal increases as the weight transfer to the front of the car increases. The increased weight on the front allows the tires to provide more traction, thus providing more braking force. Easing up on the brakes as you start to turn the car will give the front wheels added traction to initiate the turn, but weight has to transfer rearwards so both outside tires can provide maximum cornering force.
If you’ve selected a good line (remember how important it is to drive the right racing line?) you’ll be able to progressively apply the throttle mid-way through the turn which will transfer weight away from the front wheels and reduce their steering ability. If the line is chosen well, the car can gradually transition out of the turn to the next straight at maximum acceleration.
Driving smoothly, meaning, with a focus on transitions that do not upset the balance of the car and giving care to ensure weight transfer maximizes the traction of each contact patch will increase your enjoyment, reduce the stresses on your tires and car, and ultimately make your lap times lower. I’ll meet you at the apex!