Traction Sensing

Published: June 8, 2013

Traction sensing is the art of feeling how much of the available grip the car is using.

Traction sensing is different from using logic to reason that "I have not gone off track in this corner, therefore I can drive through it faster".

I believe I first saw the term in Ross Bentley's Speed Secrets books, but the concept is very broad and to some extent is practiced by all advanced drivers. It is my opinion that to drive at 9/10ths or above, traction sensing is required.

Benefits

If you have never done it, what does traction sensing offer? Consider the case of a driver jumping into a car they have never driven before and going out on track.

On the first lap, the driver would start with conservative estimates for braking and turning points, usually based on the school line. They would run late apexes and start braking early. During this lap, the driver would note, in each corner, whether the car is trying to understeer or oversteer, and generally how "planted" it feels. In braking zones the driver would start braking early but press on the brake pedal harder while in the braking zone and note whether the deceleration is proportional to the amount of braking effort supplied. Exiting the corners the driver would note whether the car tends to understeer or oversteer again.

On the second lap, knowledge gained through the first lap would be obtained to shorten the braking zones to eliminate obvious coasting. In corners where the car handled neutrally the driver would enter faster. In corners where the car understeered the driver would try trailbraking. In corners where the car oversteered the driver would try widening the line. The driver would try to get on power earlier and harder, and would try to floor the throttle exiting at least one or two corners where they did not on the first lap. While experimenting like this, the driver would continue to evaluate the car's attitude in every corner, paying attention to whether the car transitions from understeer to oversteer or vice versa or remains doing the same things it was doing on the first lap. On each subsequent lap the driver would try to push a little harder in one or a couple of corners at a time, constantly evaluating the feedback they are getting from the car.

If you are a novice or an intermediate driver, traction sensing is what allows experienced drivers or instructors to drive your car faster than you are driving it. Experienced drivers do not magically know what your car is capable of; rather, they are constantly evaluating the feedback they are getting from the car. When said instructor is sitting in the passenger seat, they are still performing traction sensing, and are telling you where you can go faster based on what the car is telling them (although they are getting less feedback as a passenger, not being in contact with the steering wheel).

Novice And Intermediate Drivers

They may not realize it, but novice and, to a lesser extent, intermediate drivers have their instructors performing traction sensing for them. Some examples of traction sensing by instructors are:

Solo drivers, lacking instructors, need to develop their own traction sensing skills to continue advancing their driving. Even with instructors, 8.5/10th is typically the practical limit for what a driver can achieve without doing traction sensing. While an instructor can traction sense at 9/10ths and above, there is so little margin for error at those driving levels that a driver cannot safely drive that fast while not having an idea of how close to the limits of the car they are.

The better you are at traction sensing, the closer you can get to 10/10ths while still being reasonably safe.

Traction Evaluation

Traction sensing is, again, judging how much of the available grip the car is using.

In its purest form traction sensing is relative. The amount of grip that is available at any given moment depends on the car, the setup of the car, track conditions starting with dry/wet but also ambient temperature and how many other cars are running in the same session, down to tire wear. True traction sensing is taking whatever car and track happens to be and using the most of them.

Drivers with a lot of experience driving particular types of cars and tracks eventually develop a memory of how much absolute grip a certain class of cars has at a particular track. They can then jump into a car and put it in a "grip level bucket", short-circuiting traction evaluation partially or completely. Technically this is not traction sensing.

Doing It

A good way to start traction sensing is to evaluate the car's attitude one corner at a time (as opposed to, for example, considering corner entry, mid-corner and corner exit separately). Evaluation should be performed as soon as the car finished each corner.

Decide which of the following applies the most after every corner:

  1. Car was overdriven (driver exceeded available grip);
  2. Car was underdriven (there was available grip that was not being used);
  3. Car used approximately all of available grip.

While there are objective criteria of overdriving and underdriving (car leaving pavement despite driver's attempts to keep it on pavement, and car not using full track width, respectively), at 9/10ths and above the difference between underdriven and not is "the car tracked out because the driver chose to put the car on that line" and "the car tracked out because the driver had no choice but to allow the car to follow that line". This is what traction sensing is all about.

Out of 10 or 15 corners that a particular road course might have, after some laps you are going to find that some corners are at 2, some corners are at 3 and hopefully none are at 1 intentionally. Work on corners that are at 2 and try to judge how far the 2 corners are from the 3 corners to avoid jumping from 2 to 1. As your traction sensing abilities improve, you will find that some of the 3 corners really are in the 2 corner category, and some of the 2 corners advance into the 3 category.

As you gain experience, traction sensing will become less of a binary option (under/over) and more of a scale. A sliding car is slightly over the grip balance, but how far over it is would dictate whether a correction is necessary or the car will fix itself. One example where this comes into play is sideways exits out of corners, especially when wet. As lifting costs time just as being sideways does, being able to tell whether lifting is necessary is a good skill to have.

Advanced Traction Sensing

Beginning traction sensing is evaluating what the car did in a corner after that corner is finished. With more practice you will be able to evaluate what the car is doing in the corner while the corner is still being driven. For example, you will be able to tell at the apex whether you braked too much and therefore were going slower at the apex than you could have been.

Similar things will start to happen in the braking zones; you will be able to tell whether the car is decelerating enough to make the turn way before you start running out of track, which will for example allow you to correct the line to enter the corner earlier or later.

A notable milestone that I observed was ability to correct trailbraking/trailing throttle oversteer on corner entry twice in a single corner.

Lines As A Function Of Traction Sensing

As you practice traction sensing more and get better at it, you will start to develop your own driving lines which are based on traction sensing rather than following lines that someone gave you that may or may not be appropriate for your car and driving style.

The school line is generally based on a single premise that corner exit speed trumps everything. More advanced DE/Time Trial lines try to keep apex speed and entry speed up while maintaining the exit speed. Traction sensing can validate or disprove lines that someone suggests are "best". If you are on a line where you feel that the car is not using all of the available grip, this is probably not the fastest line; a good example of this situation is going from a school late apex line (on which you brake before turn in but are unable to accelerate until apex) in long but slow corners to a trailbraking line (on which you are braking until the apex, carrying higher entry speed as a result).

Rain Driving

It should now be apparent that drivers that can traction sense enjoy driving in the rain, for it provides ample opportunities at traction sensing in conditions that are typically infrequent. Traction sensing drivers learn a lot in rain sessions.

Similarly traction sensing drivers can find rain lines much quicker because they are able to immediately evaluate the grip difference between rain lines and traditional lines.

Learning

Try these feel learning exercises next time you are on track.

Tagged: intermediate, advanced