The Track Experience 3: What You Learned From Your First Track Day
by Graham Chandler
The previous article covered a typical first track day and presented a series of photographs that illustrated how a car is positioned to negotiate the turns on the track. This article builds on those concepts...
Your first track day was a lot of fun wasn’t it? You may not have experienced everything covered below. For the sake of completeness the following will be discussed in this installment.
• Vehicle Dynamics
• Anatomy of a Turn
• Types of Turns
• The Straightaway
• Car Control
When discussing vehicle dynamics, we are really talking about the behavior of the car ; how it handles in given situations. The grip of the tires, weight distribution, and suspension design are three factors that govern handling. For the purposes of this discussion, let’s focus on the tires. We can talk about the weight distribution and suspension in another article when we might want to make some adjustments in these areas.
Tires are designed to provide traction for acceleration, braking, and cornering. To obtain the most traction for acceleration, the car should be moving in a straight line like a car on a drag strip. The same applies to braking. We should always apply the brakes in a straight line for maximum effect.
So what about cornering? First, I want to address a very important vehicle dynamic. Cars can become extremely unstable if the brakes are applied in a turn, so let’s adopt a golden rule right now. Do not apply the brakes or lift off the gas in a turn. To ignore this rule invites immediate loss of control. For example, if you are using 80% of the tire grip to accomplish a turn and you attempt to use 30% more for a combination of braking and lifting off the gas, you have just overdriven the tires. A spin is almost inevitable due in part to overdriving the tires and also because of the weight shift off the rear wheels.
To understand the correct cornering technique, let’s look at a simple example of a turn in the next topic.
Anatomy of a Turn
An example of a simple turn is a 90 degree constant radius turn preceded and followed by straightaways as shown below in Diagram 1.
Diagram 1 - A Constant Radius Turn
Because all cars brake faster than they can accelerate, we need to find a way to provide more acceleration space onto the straightaway so that we enter it with the most speed. To achieve this extra acceleration, we should approach the turn with the goal of turning much later and sharper than you would normally think about doing, and then accelerate in an almost straight line through the apex. This “driving line” is shown in diagram 1.
First of all, because we accomplished most of the turn earlier by turning sharper means we can squeeze the gas pedal earlier. In effect our next straightaway now begins before we even reach the apex. We also saved some time by turning in as late as possible so that we preserved our inbound straightaway speed as long as possible. The effect of these techniques is dramatic. I was amazed by how effective these techniques are while I was under instruction some years ago. I try to get all my students to do this and those that do really move on rapidly to the next level in the sport. Moving up is a topic of a future article in this series.
The very instant that you turned the wheel into the turn, the tires took a "set." The sidewalls moved so that the tread was set in a different position relative to the rim. We only want the tires to do this once so it’s important to get the turn angle right the first time. A common mistake with novices is to “saw at the wheel” trying to find the right turn angle. Assuming you got this right; the car changed direction and headed for the apex. Next you unwound some of the steering input as you can see in diagram 1. This “flattening” of the turn removed some of the grip requirements from the tires so you were able to accelerate without overdriving the tires.
In contrast, the following diagram shows an incorrect technique. This technique, shown as a red line, is what many street drivers do when they try "cutting the turns" or "straightening the turns."
The turn into the corner is much earlier and we are only half way through the turn when we clip the apex. The car is also pointed at the outside of the track instead of pointing down the track. This driving line also carries some risk if the speed is too high. Look at the exit point, the car could depart the track. The other downside is that acceleration cannot occur until the car straightens out because the car is still using most, or even the entire available tire grip for turning. You can see that the car is in the turn for a longer period of time and consequently this is a slower technique.
Types of Turns
Obviously not all turns are the same on a road track. The fact that the turns vary so much is what makes road tracks so interesting and technically challenging to drive. The types of turns fall into 3 main types:
1. Constant Radius
2. Decreasing Radius
3. Increasing Radius
These types can vary also in degrees of turn from a basic kink to a 180+ degree carousel. Then there are elevation change and track camber variables. I have already covers the Constant Radius turn above. Here are some diagrams that show my suggested line for the other types of turns:
A decreasing radius turn is particularly challenging because it forces you to slow down the further you go into the turn. As before, there is a normal braking zone but after releasing the brakes for the turn you will need to slow down some more as the turn tightens. In this case, you are not using the brakes to reduce speed; instead you use the drag of the tires to slow down. This avoids upsetting the car’s balance and allows you to have a smooth transition to acceleration through the apex.
Diagram 3 - Decreasing Radius Turn
Here we are waiting longer to turn in and then seeking and following a tightening line to the apex which is all the way around the turn just before start of the straightaway. Notice how far down the inbound straightaway we have to wait before turning in. That’s how we can preserve speed going in by leaving our braking much later than you might expect. Then see where you can squeeze the gas pedal again. Again, before you reach the apex.
This type of turn is generally easier that the decreasing radius turn although sometimes the track designers will try to slow the turn down by having an uphill exit or an adverse camber. So although the turn looks easy from above, driving the line might be a challenge. The idea is to again preserve speed down the inbound straightaway, then turn sharply for the apex and squeeze the gas. The exit path should be as straight as possible so that the car can accelerate as quickly as possible.
Diagram 4 - Increasing Radius Turn
Next up in diagram 5 is the carousel. This turn is really challenging because it tests your patience. Just start out turning in really late and work your way into the late apex almost all the way around the turn. This is a real test of car control. The fastest path through here will be on the edge of lateral traction. You must feel this through your senses ¬¬– balance and feel. You can detect G forces through your sense of balance and you can feel the tires grip (or slip) with your hands. Maintain speed with the throttle maximizing the G force without losing sideways traction, a delicate balance! Guide the car to the apex and then unwind the steering input while applying maximum throttle. The car should slingshot out of the turn headed for whatever comes next.
Diagram 5 - The Carousel
The Complex is a series of turns with no intervening straightaway’s. The Complex, shown in diagram 6, forces you to find a line that works for the entire set of turns. Not, as you might imagine at first, the ideal line for each turn. We want to be in this complex for the least amount of time and exit from this complex with the most speed.
Diagram 6 - Turn Complex
In this situation, it is the first and last of the turns in the combination that matter the most. Ensure that your entry line into the first turn makes the most of the preceding straightaway. That means a late turn in and a late apex as before. Then optimize your line through the last turn to be able to achieve the earliest acceleration point onto the next straightaway. You may have to give up the optimum line for the turn or turns in between.
If any of the intervening turns follow the same turn direction, then you have another opportunity to save time. Try to reduce steering inputs and make the multiple right or left turns one turn. Linking turns together will save a little time because the tires only have to adjust to the turn once. Here is an example of this type of situation:
Diagram 7 - Linking Turns Into One
A straight is just a way of getting to the next corner! Well, there’s a little more to it than just that. For many of us the straightaway means many things. For some, it’s a place to satisfy that “need for speed.” For others, it’s a place to pass a slower car, or a place to let a faster car pass. What else is there to do?
Well, it all starts with the last turn. How did the brakes feel at the last turn? Were they firm or spongy, or somewhere in between? How was the pedal travel? You are going to want to know the answers because you have a big slowdown coming up at the end of this straightaway. It’s also a comfort to know that the brakes will be cooling down now.
A good entry onto the straightaway means lots of early acceleration through the apex and unwinding of the steering as soon as possible to reduce tire drag. Even to the point of unwinding early and using the entire available track rather than keeping the wheels turned longer than really necessary. Every second that the wheels are turned unnecessarily, you are losing time.
Now handle any passing maneuvers correctly as you have been taught. Check the mirrors for cars you may have not seen behind you when you were in the turns. Determine if anyone is gaining on you.
Make sure you are positioned correctly for the next turn, also look for your braking and downshift points. Always brake before downshifting to ensure you don’t over speed the engine. Last of all, make that all important late turn in for a late apex at the turn, then prepare to get on the gas as soon as possible.
See! There’s more to it than you’d think. But, there is a kind of “calm before the storm” feeling when you’re blasting down the straightaway at 130! Many of us track folks crave the turns over the straightaways!
This topic is really about what to do when a car behaves a certain way. I mentioned in the first section of this article that the car depends mostly on its tires for traction and that the weight distribution and suspension also have a part in the traction equation. Let’s also take into account the drive system in this discussion. Let me introduce some terms with which you may already be familiar.
First there is understeer. When a car enters a turn there can be a sensation felt by the driver where it seems as though the car resists the turn and wants to run wide. This understeer tendency can be described as pushing towards the outside of the turn. Most, if not all front wheel drive cars are set up by the manufacturer to understeer as a safety measure. In a street situation understeer tends to want to make the driver slow down. In fact, if the driver lifts off the gas the resulting engine braking on the front wheels will tend to make the car “tuck” back into the turn.
On the track however, the driver must not brake or lift in the turns because the car is much closer to the limit of traction than on the street—a spin could result. Instead the driver must tighten the turn and stay on the throttle to avoid running wide. See diagram 8.
Diagram 8 - Understeer
An understeering car can still be made to go fast in the turns by adjusting the driving line to be tighter and allowing the car to drift out with speed. Not really ideal but there aren’t really any surprises so long as you don’t lift once you are committed to the turn. As I said earlier, if you lift after pushing the car hard into a turn, a spin can result. This is because the rear tires in the turn will want to slide out under front wheel engine braking especially with the front wheels turned. So the rule here is to understand what understeer is and don’t lift.
Then there is oversteer. When a car enters a turn, the driver may feel the rear tires beginning to slide outwards and the car will point more into the turn than desired. Many rear wheel drive cars exhibit this tendency depending on weight distribution. A 50/50 weight distribution between the front and rear wheels will mean that the car should be neutral in its handling—its weight is evenly balanced and there is neither understeer nor oversteer. However, most rear wheel drive cars have more weight in front and the rear is lighter and tends to slide around more.
If you lower the tire pressures in the rear and raise them in the front, you should find the car handles better. To correct a car when the tail steps out with oversteer, you should use opposite steering inputs. While turning right and the tail steps left, apply left steering input and vice versa for a left turn. See diagram 9.
Diagram 9 - Oversteer
If you are at all uncomfortable with either of these handling tendencies or you just don’t know how your car will handle at speed, you should practice on an autocross course. This type of event will help you quickly discover your car’s handling tendencies. Anything you learn at the autocross will transfer to track driving. It’s worth the inexpensive entry fee, trust me.
Above all else, car control is about smoothness. Any rough handling of your car will cost you time. Rough downshifts, uneven braking, jerky steering inputs, missed apexes—all will add time to your laps. So, strive for smoothness and speed will follow.
I have presented a lot of material for you to put into practice all at once so let’s get some track days organized and practice. The next article in this series will assume that you have achieved some good consistency and a reasonable level of smoothness. I will then address some advanced techniques that will help you go faster while continuing to maintain all of our safety goals.