Sequence For Improving Lap Time
Published: July 31, 2013; updated: October 25, 2014
This essay will cover my approach to corners on a road course that is optimized for running lowest lap times. We will first consider corners independently of one another, and later look at tying corners together for a complete lap.
Late Enough Apex And Appropriate Throttle Application
We can separate decisions involved in driving through a corner into a list like the following:
- At what point to begin braking.
- How hard to brake.
- When to get off brakes.
- When to turn in.
- How much to turn and at what speed, which also determines the apex point.
- When to begin unwinding steering.
- When to get on throttle.
- How much throttle to apply.
On most tracks time spent on straights dominates time spent in corners, and as such corner exit speed is generally much more important than corner entry speed, how hard the car is braking or how fast (or slow) it is in the turns. The more power a car has, the more important exit speed generally is. This sentiment is popularly expressed as "slow in, fast out".
Practically speaking this means that the first iteration of driving through a corner would employ conservative braking, meaning the driver would brake early and more than necessary to achieve comfortable corner entry speed and permit giving most attention to corner exit - getting on throttle as early as possible while still fitting into track and applying as much throttle as possible.
At this point I am looking to be applying at least some throttle at the apex, increasing the amount of throttle applied through corner exit, and trying to be full throttle as soon as possible after the apex. In most cars applying throttle requires unwinding steering, as such I would be adjusting my line going into the corner to enter later and perform more rotation prior to apex, which permits flattening the line after the apex to achieve throttle application goals.
Signs that you have not properly executed this step:
- You wait until you are completely tracked out to get on throttle.
- You get on throttle halfway between apex and track out point.
- You get on the gas but then get off the gas while still exiting the same turn.
- You add steering input after the apex to keep the car on pavement.
The next step after early throttle application is braking hard and late. It is crucial to maintain exit speed while working on braking harder and later, as it is quite easy to overslow the car under hard braking. Predictive lap time, or more accurately, realtime delta is extremely helpful in braking hard but not overbraking.
- First, hit the same peak deceleration in all corners that call for hard braking.
- Second, ramp up braking at the same rate in all corners which call for harf braking.
- Third, try to brake at the same deceleration in corners which call for light to moderate braking.
Braking late requires reference points, and the ability to adjust them in small increments. For braking zones that have brake markers, 1/4 of a brake marker is a good resolution. For shorter braking zones which do not have brake markers you might need a resolution of 1 foot.
Remember to keep the exit speed high while working on braking - realtime delta (people often call it "predictive lap time") is incredibly helpful for this.
Solid braking and acceleration with a sufficiently late apex produces approximately 8.5/10 pace through corners.
You may also note that braking and acceleration improves time on the straights rather than through the corner itself. In fact, apexing late compromises time in the corner to gain a greater benefit on the following straight.
Apex Speed, Or Minimum Corner Speed
The next step is to improve time spent in the corner itself, and this is done by examining the minimum speed of the car in the corner.
Minimum speed is usually achieved somewhere between turn in and apex. Generally speaking, the closer the minimum speed point is to the apex, the better. Reason for this is combined G force achieved by the vehicle.
As you know, tires are able to generate a certain amount of grip. This grip can be used for deceleration, cornering or acceleration. In the braking zone for the corner 100% of the grip is ideally used for deceleration. At some point you are completely off the brakes, and at that point you want to use 100% of the grip for cornering. Because exit speed is important, you want to be on increasing throttle as of the apex at the latest, which means you cannot be using 100% of the grip for cornering at the apex. This means, in turn, that the point where most lateral G is achieved is between turn in and apex.
As you are not on throttle in the instant before you get on throttle, that is the point at which you should be using 100% of the available grip for cornering. Geometry dictates that this point should ideally be the apex (but for safety we run slightly later apexes than ideal). Therefore the point of 100% cornering just precedes the apex.
Up until that point, you should be decelerating. Which means your speed significantly before the apex should be higher than your speed just before the apex.
From here we can derive a corollary: if you are on power from the turn in forward, that is, your apex speed is significantly higher than your turn in speed, your turn in speed is too low. Suppose your turn in speed is 50 mph, your apex speed is 55 mph and your exit speed is 60 mph. Chances are you can enter at above 55 mph, drop down to 55 mph at the apex and still accelerate back to 60 mph at corner exit.
The minimum step speed is figuring out at which point in the corner you achieve your minimum speed, and move that point closer to the apex by entering the corner faster. Trailbraking will help in many corners.
With the correct line and speed, the next step is to look at whether the tires are sliding in the corner. DOT tires generate the most grip at roughly 5 degrees of slip angle, which means for the lowest lap times that is how much slip angle you should have in the corners.
Typically, to achieve nonzero slip angle you would enter the corner faster and carry that extra speed through the entire corner.
We have not talked about compromise or combination corners, but it should be obvious that the simple guidelines above would need to be adjusted for more tricky corners.