Using AIM Data Acquisition To Improve Driving Technique

AiM SportsAs we’ve discussed in a previous blog post on the days leading up to a race, one critical piece of the preparation as a driver is to elevate your driving technique from being good to great by using data acquisition.  We use such a system by AiM, the MXL Pista.  Other than analyzing our driving technique, this system also gives us important data about the car itself, such as the health of the engine, engine RPM, temperature, oil pressures, throttle position, and lateral G-forces to name a few.  I won’t go into these sources of data here, but needless to say, our AiM system is clearly a critical part of our race team.  For this article, I won’t get into the installation of the AIM system.  If you have more technical questions about the AIM system itself, please visit the AIM web site.

AiM MXL

AiM MXL

One great opportunity for drivers to learn in our series comes from the fact that each car has at least two drivers at a given event.  While the conditions can change between laps from one driver to the other (changing tires from old to new, the track can gain or lose grip from temperature change, suspension changes, fuel load differences, etc.) you’re still driving the same car.  Since it is rare for two drivers to drive the exact same for every corner on a track, therein lays the opportunity to learn: You can analyze the effects of those subtle differences between driving styles to see what technique or driving line is faster.  From there the slower driver can adopt the technique that was faster.  With drivers of relatively similar speed, both drivers will greatly benefit from data analysis because one driver will usually be faster than the other somewhere.  You can likewise compare variations between laps made by a single driver to self-refine technique.
There are five key areas that you should think about when looking at data to improve your driving: braking, throttle application, steering input, shifting, and going slow to go fast.

 

Braking

Braking… What a deceptively complex part of driving.  It’s my personal opinion that braking is the most critical and subtle part of road racing technique that is the last thing a racing driver learns how to perfect.  Looking at the brake application leading up to a particular turn, there are four key things to look at:

  1. Braking point.  This is the location on the track where you start applying your brakes.  This point is critical because it determines everything else that follows from your entry speed to even when you are able to get back to power.  Many turns on race courses have numbered signs leading up to the turn which makes it very easy to find a reference for your brake point.  If you feel that your braking point was too early or too late in a given turn, you can simply adjust your braking point to a new spot relative to these signs.  Lacking braking point signs, you can use discolored patches of the track, speed bumps, references along the track that lie outside of the track itself, etc.
  2. Initial brake pressure.  An optional sensor that you add to your data acquisition system records the hydraulic pressure of your brake system.  In other words, you can measure how hard you’re pressing the brake pedal at a particular moment in time.  An initial brake pressure that is too high could cause the tires to lock-up and cause flat spots on the tires, or send the car out of control.  For most ABS-equipped cars, too much initial brake pressure can engage the ABS (anti-lock braking system) which actually cuts out brake pressure.  Due to the nature of ABS, the brake pressure pulsates when it notices lockup – which by its nature means the tire has lost grip.  This pulsing leads to under-maximization of the tire’s grip. So, it is better to keep the tires at the point just before lockup and the engagement of ABS.  Some ABS systems are much better than others, but in most cases, the car will decelerate better if you just ‘tickle’ the ABS, barely engaging the ABS system.Our #61 ROUSH Performance Mustang uses a Ford Racing ABS system that is slightly different than the stock ABS.  However it’s similar to the stock ABS in that braking works best with a moderate initial pressure where the pedal will sink down and then push back against your foot once the system is ready to take more pressure.  If you try to pounce on the brakes with too much pressure in our car, the ABS will activate and assuming that you’re panicking.  It will pulse the brake pressure which you will feel in your pedal to prevent lock-up, and your braking will be less effective.On the other hand, too little initial brake pressure will cause you to start braking too early, and you’ll spend more time than necessary getting the car slowed down (and lap times will increase — that’s not what we’re looking for). The higher the speed, the harder it is to lock up a tire, and the more initial pressure that can be applied (and the quicker the lap time).
  3. Brake pressure through the braking zone.  What I’m referring to here is the braking that truly gets the car slowed down.  Remember that the higher the speed, the harder you can press the brake pedal; but as you slow down, it becomes easier to lock up a tire. (Try spinning a bicycle tire slowly and stop it with your hand.  Now spin it faster –it becomes harder to stop the faster you spin it).  As the car slows down, you must modulate and ease off the brake pressure accordingly to avoid lockup or engaging ABS excessively throughout the brake zone.  Keep in mind that ABS is very hard on brake pad wear and brake temperature.
  4. Trail braking – brake release.  This is the most difficult aspect to perfect and is defined as simply the release of the brakes during the corner-entry phase of the turn while keeping the tires at their maximum level of grip.  While you are braking at 100% of the tires capability, you cannot turn the wheel.  The goal is to keep the tire at 100% of its ability at all times and in trailbraking, you ease off of the brakes while you are adding steering input.  (To ride the “traction circle” rim by seamlessly going from 100% braking and 0% turning to: 95% braking and 5% turning to: 75% brakes and 25% turn to: eventually 0% braking and 100% cornering. Simply put, we must give up braking ability as we introduce cornering force but must blend the two seamlessly to keep the tire at a combined 100% maximum of its grip ability at all times).Depending on the balance of the car and the type of turn, the rate of this release will vary from car to car and corner to corner.  Some scenarios will require trailing the brakes down to the apex (ex: a decreasing-radius corner), while other turns might require the car to be more settled in order to handle quick transition from one direction to another and will have little to even no trailbraking (ex: a highspeed chicane).  The ‘classic’ or ‘club-racing’ technique that is taught of doing all your braking in a straight line then turning-in to the corner off the brakes and throttle, or even turning into the corner on throttle is the safest and a very slow technique in most corners.

Braking is the most difficult aspect to master but the concept of utilizing 100% of the tire’s grip at all times and riding the rim of the ‘traction circle’ is the primary goal of driving a car fast.

Figure 1 - Braking

Figure 1 – Braking

In Figure 1, you can see Driver A (Blue) had a later initial braking point than Driver B (Red).  Due to an ABS-equipped car which a high initial spike of brake pressure engages ABS, Driver A had a quick squeeze of brake application to a high initial pressure and a very nice modulation and reduction of brake pressure throughout the brake zone which trailed off into the corner, keeping the car out of ABS the entire time.  Driver B was forced to an earlier initial brake point due to a lower initial brake pressure which cost driver B 0.05 seconds in the first quarter of the brake zone alone due to under maximization of the brakes.  The brake modulation was okay but the higher spikes of pressure later in the brake zone resulted in more weight on the front of the car which took away from cornering grip during trailbraking on corner entry which led to a slower entry-speed and more time lost totaling 0.25 seconds.

 

Throttle Application

It can be a hard thing to overcome your testosterone and not stomp on the gas as you approach the apex of a turn because the result may not be what you’re looking for.  As you apply throttle, the front tires become unloaded, reducing front grip and making it more difficult to get the car to turn.  Step on the throttle too early in a turn, and you will be pushed out wide with understeer at turn exit, forcing you to lift the throttle so you don’t go off the track.  If you stomp on the throttle too aggressively, it can induce wheel spin, which also would require you to lift off the throttle in order to get the tires to hook back up.

Figure 2 - Throttle Graph

Figure 2 – Throttle Graph

The best throttle application for most turns is one that is earliest where you can keep the throttle down and won’t have to lift.  This is often much later than most believe and is perfected by trailbraking and rolling more speed through a corner allowing the car to get more of its turning done.  It is also important to roll on to the throttle rather than stabbing it.  This is another area where AIM data can help.

As you can see in Figure 2, Driver A (Blue) brakes less efficiently than Driver B (Red) and has a slower entry speed.  Driver A goes to throttle and gets to full throttle very early but since he did not get the car turned enough when he went to throttle (due in part from a slow entry), the tires did not have enough grip to accelerate and turn as much as he needed and thus he had to lift at the exit.  While he gained almost 0.1 seconds by getting to throttle early, he lost well over 0.2 seconds by having to lift.  The longer the following straight the more time he will lose.

Steering Input

Steering input data is another useful thing to look at as a driver.  It simply tells you in what direction and how much steering input is given at a particular instant in time.  In most cases, turns will require a gradual initial turn in that increases as you get closer to the apex.  Once maximum steering angle and cornering force has been reached, you’ll want to hold that angle until most of the turning is complete.  It’s also worth noting that at this time, you will also want to be completely off the brakes and throttle allowing for maximum cornering power of the tire.  Once the car is rotated and is close to pointed down the next straight, you will want to unwind the wheel as you are rolling on the throttle.  This is similar to trailbraking and blending the two to keep the tire at its maximum grip through this transition.

Figure 3 - Steering Graph

Figure 3 – Steering Graph

Figure 3 provides a great example of two different driving styles.  Driver A (Blue) brakes earlier and lighter but rolls more mid corner speed with less steering input but struggles to get to full throttle as early as Driver B (Red) and gets oversteer at the exit of the corner.  Driver B brakes later and harder, adds more peak steering input on a tighter radius (which is possible by a lower mid-corner speed), gets the car pointed sooner, and gets to full throttle much sooner.  While slower on entry and the middle of the corner, Driver B gains on exit and nets a time gain down the next straight.

 

Shifting

Shifting sounds pretty straight-forward but often there is a lot of time to be gained here.  Looking at data makes it very clear when you’ve had a quick shift and when it could have gone better.  On long straight-aways, a slow shift can cost a lot of time.  It’s not just the delay in the shift that costs you.  It’s the shift in the acceleration curve along the remaining straight-away.

While there is time to be had here, you can damage your synchronizers in efforts to quicken the shift.  You want to complete each shift as quickly as possible but there is a quick way that is efficient, and there is a common way that damages your transmission.  It is important to know how synchros work and respect them and use very little force when shifting quickly.

Another shifting dilemma that you will run into is whether you should up-shift or not as you run out of RPM right before a corner or brake zone.  Depending on where you are in terms of RPM vs. your power curve and where your RPM limiter is set, it may make sense not to up-shift right before a turn but rather lift slightly just enough to not bounce off the RPM limiter for the short period of time before the brake zone or corner.  It is important to try this and try upshifting both in the same session to later look at data and compare the two laps to see which one was quicker.

Figure 3 - Shifting Graph

Figure 3 – Shifting Graph

Similar to knowing when not to up-shift, there are also times when not down-shifting heading into a turn may make sense.  The down-shift itself will take some time as will the corresponding up-shift.  Depending on the power and torque of the motor, the RPM the engine will be at in the middle of the corner in each gear, and the exit speed, the higher gear may provide enough torque to power you out of the turn and avoid the excessive shifting.  Another thing to note is that higher gears tend to make the car more stable with variations in throttle because the motor will be less responsive at lower RPMs, which will make a high-speed corner more comfortable.

In Figure 4 Driver A had a much slower shift than Driver B for both shifts; losing 0.1 seconds on the first shift and almost an additional 0.25 seconds on the second shift.  On this one lap on this one straight, Driver A lost over 0.3 seconds from shifting alone.

 

Going Slow To Go Fast

Our final point to discuss here will be one that is hard to grasp as a driver, but it is very important.  It is very common for amateurs and professionals alike to go into a corner harder than the guy in front of you, gaining on him as you enter the turn.  This is fine but the real question is, while you were faster getting into the corner did you kill your exit?  You’ll find out quick because if the car ahead of you leaves you in the dust after the apex, there’s a good chance that you drove in too hard.  Many people blame their competitor having more power when in fact they ruined their exit themselves by being too aggressive entering the corner.  If you’re still gathering the car up after the apex or if it’s pushing badly and you are missing the corner, or even running out of room at corner-exit, that’s a major warning sign.  However, there’s a fine line between going into the corner too fast and just right.  The common saying of “slow-in, fast-out” is a great starting point and teaches patience because in fact the exit of a corner is far more important than the entry.  But for me, I say the goal is “fast-in, fast-out” but you must perfect the exit before working on your entry and since your entry determines your exit, once you mess up the entry, you ruined the entire corner rather than the more conservative slow-in, fast-out gives you room to play with learning how to perfect the exit.

Figure 5 - Fast In Fast Out Graph

Figure 5 – Fast In Fast Out Graph

Figure 5 describes an example of the three most common ways corners are taken.  Driver C (Black) takes the classic “slow-in, fast-out” driving line.  He loses almost 0.4 seconds on entry of the corner but gains on exit to net a 0.3 second time loss in this corner.  Driver B (Blue) overcharges the entry to gain 0.1 seconds but loses over 0.4 seconds for a net loss of 0.4 seconds+.  Driver A (Red) takes the corner “fast-in, fast-out” while braking almost as late as driver B, and getting as good of an exit as driver C, Driver A gains on both drivers by almost half a second.

Driver C only has to work on improving his entry by braking later while Driver B needs to brake earlier and find the optimum exit, which is more work.

 

Conclusion

In closing, these are the fundamentals of how to analyze data to improve your driving.  Having a professional drive your car to set a benchmark is very helpful in analyzing the areas where you need to work on and the areas where you just need to keep your consistency.  Data analysis can be a can of worms because there are so many subtle factors to analyze to further improve even the best of drivers.  There are many details that can be over-analyzed or misunderstood, but by working and focusing on these five fundamental key areas and focusing on the corners where you are losing the most amount of time first, data analysis is a crucial tool in driver development.

-Written by Billy Johnson and Jack Roush Jr.

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