GHIT extra: everyone sucks at racing

I was recently interviewed on the Garage Heroes in Training podcast and they asked me a lot of really interesting questions. I want to follow that up in a series of posts on YSAR where I get into a little more depth on a few topics.

I suck at racing

Guess what? I suck at racing. Most people do. There simply isn’t enough money to get the track time to be really good at it.

How many hours do you think it takes to become good at any of the major sports like basketball, tennis, football (either kind), etc? Playing 2 hours per day for 300 days per year for 5 years sounds like a good start. That’s 3000 hours, which includes some mixture of unstructured time, coaching, drills, and games. How many racers do you know that have even 1/10th of those hours on track? Very few. How many of those hours feature coaching? Next to none. Drills? Nope. Wheel-to-wheel races? Some. If you’re a basketball player who plays h-o-r-s-e and shoots free throws a few weekends per year, you probably aren’t going to do very well in the neighborhood pickup game much less any kind of league play. But driving is different from basketball because you drive to work every day, right? Not so much. Biking to work every day doesn’t prepare you for riding a half-pipe any more than driving to work prepares you for track driving.

Good news

Since everyone sucks at racing, it doesn’t take much dedicated work to be better than average. Racing isn’t usually measured against some absolute criterion. You don’t have to be the best, just faster than the next driver. The good news is that you can be the fastest driver on track and still suck at racing! So how do you move from the lower levels to the higher levels of suckiness?

  • Knowledge
  • Skill
  • Confidence

Knowledge

Racing is a complex activity because it involves optimizing the driver, the vehicle, and the interplay between the driver and vehicle. If you want to get out of suckville, you need to understand what driving data looks like. It doesn’t look like a stopwatch. At a bare minimum, you need to be able to understand what a speed trace is telling you. Is the driver braking too much? Is the driver fighting understeer at the exit? You can ask and answer these questions and many more with a speed trace.

GPS-based data loggers are not that expensive when you consider the costs of track time or car parts. It’s one of the best investments you can make to improve your driving. Should you get a dedicated unit (e.g. AiM Solo) or use a phone app with a 10Hz GPS antenna? Up to you, but using your phone without an antenna doesn’t give you enough resolution. If you have a modern car, your car is spitting out data for throttle position, brake pressure, wheel speeds, steering angle, etc. Capturing these requires a more sophisticated data logger that connects to the CAN bus (e.g. AiM Solo DL). These extra channels are really helpful, but also a little confusing to the novice. So start with the speed trace.

Video is also very useful because you can see driver activities that don’t show up on a graph (e.g. hand position while steering). The best place to put the camera is on the roll bar so you can see the driver’s hands and legs. If you don’t have a roll bar, a camera mount that attaches to the head rest works well. The picture below shows a mount I made from some box section aluminum, j-hooks, and a RAM connector.

Bottom line: if you’re not using data to improve your driving, you will keep driving around suckville for the rest of your life.

Skill

You’re not going to make it out of suckistan unless you can drive a car near the limit. And by limit I don’t mean your limit. Everyone drives their limit. In the speed traces below, you can see that the red driver and blue driver have very different ideas about what the limit is. In most corners, the blue driver thinks it’s much lower than the red driver.

Regardless of whose limit is higher, the real question is if your limit is close to the actual limit. How do you know the actual limit? Math. Find the radius of the corner and the grip of the tires (from data) and you can estimate the corner speed. Well, that only works to a degree because the real racing line doesn’t have a constant radius (see previous post). But a little math is good for the brain and will give you some feeling for what should be possible.

The very best way to measure your skill is to compare yourself to dozens of other people driving the exact same cars with identical setups and weather conditions. This is generally impossible in the real world, but is trivial in the virtual world. In other words, sim racing is the best way to compare your technique to other drivers.

Bottom line: If you’re not using data to compare your skill to other drivers, you might as well start buying real estate because you’re never leaving suckistan.

Confidence

Most drivers enter fast corners 10-20 mph too slow. Look at the speed trace above. The minimum corner speeds are the same for slow corners but not fast corners. Why? Because people fear losing control of the car at high speed.

Exiting a corner on the limit is like walking on a tight rope. Entering a corner on the limit is like jumping onto a tight rope blindfolded. — Mark Donohue

Walking a tightrope takes bravery/confidence/commitment. Jumping on blindfolded takes more. And yet this is what it takes to drive a car at the limit. If your confidence isn’t the equal of your skill, you will enter corners 10-20 mph off pace and your lap times will suffer. On the other hand, if your confidence is much greater than your skill, you will probably wreck your car.

If you’re not driving the limit because you lack confidence, you will always suck at racing. However, I’m sure your loved ones appreciate your extra margin for safety, so don’t feel bad about it. Also, no matter what you do, you will always suck at racing anyway, because there isn’t enough time and money not to. So lighten up, be safe, and have fun out there! There’s a lot more important stuff in the world than how fast you drive around a race track.

GHIT extra: racing lines

I was recently interviewed on the Garage Heroes in Training podcast and they asked me a lot of really interesting questions. I want to follow that up in a series of posts on YSAR where I get into a little more depth on a few topics.

The Racing Line vs. the line you drive while racing

Several of the questions were either directly or indirectly related to the racing line. When most of us think of the line we imagine the path we take through a corner that optimizes our lap time, and in the typical 90° corner this would be the standard outside-inside-outside late apex line that we all know and love. However, in an amateur endurance race, this is almost never the line you want to take. When there are 100 cars on track, there are much more important things to think about than optimizing your lap time.

Grip, line, awareness: pick two

When I’m racing, awareness is always at the top of the list. The only time I’ll let that go is if I look behind me and I can’t see any cars at all. But as soon as I’m in any kind of traffic, my mind set is “how do I position myself in case the drivers around me do something unexpected?” If I’m optimizing awareness, it means I generally can’t drive the typical racing line as I’m positioning the car to avoid potential disaster. But wherever that line happens to be, I’m driving near the limit of grip. Ultimately, when racing, I almost always throw away the line and optimize the other two.

Does the angle at the apex matter?

Another question I was asked was if I thought the angle at the apex was important or was it just good enough to be at the apex. The angle is critical. In the picture below, both cars have reached the apex. Car #1 is going to have to do a lot of steering in order to finish the corner. Car #2 may have to make some steering corrections to prevent itself from spinning. In other words, Car #1 is understeering and Car #2 is oversteering. The angle you arrive at the apex determines how much throttle and steering you can use in the 2nd half of the corner.

If Car #2 doesn’t spin, it will win the race down the following straight. Car #2 is ready to go to full throttle very soon. Car #1 will have to wait a bit. If Car #1 gets impatient and adds throttle too soon, it runs the risk of understeering off the exit.

Most novice and intermediate drivers position themselves like Car #1. Why? Because in order to position yourself like Car #2, you must have oversteer in the first half of the corner. Not throttle-on oversteer, but throttle-off oversteer. Most novice and intermediate drivers spin under such conditions. Because spinning will earn you a black flag and the humiliation/penalties that go along with it, intermediate drivers may find themselves perfecting a driving style that prevents the rear from stepping out. You can be a pretty fast and safe intermediate driver but unless you learn to drive with oversteer, you won’t be as fast or safe as the advanced drivers.

It’s easy to see why driving with oversteer can make you faster, but why safer? Because shit happens on a race track. Shit you can’t foresee, like being forced off track, having a tire blow out, getting hit, or driving through oil. When shit happens, your car control skills save you, not your work-arounds. If you’ve learned how to drive a sliding car, your muscle memory and experience will help you navigate a perilous situation. However, if you’ve learned how to avoid sliding at all costs…

FWD Drifting 101

So let’s say you have a front wheel drive vehicle because that made sense at some point. Actually, there are a lot of reasons FWD vehicles make sense.

  • Lighter
  • Cheaper to manufacture
  • Better fuel economy
  • More compact
  • More interior space
  • You got one as hand-me-down

RWD vehicles have several advantages too, but let’s be honest, the only one that really matters is power-on oversteer. Burnouts are good, dumb fun and drifting is a visceral mixture of beauty and savagery that is so instantly compelling that even non-car-enthusiasts find it engaging.

Oversteer

Sadly, you’ve got a FWD econobox and you can’t join the fun. Or can you? One of the common misconceptions about FWD vehicles is that they are a bucket full of understeer. With 65-70% of the weight of the vehicle on the front tires, FWD vehicles actually want to oversteer. They just need a little encouragement sometimes. Here are some of the ways you can do that.

  • Lift – Lifting off the throttle shifts weight forward. Ideally, all you need to get a FWD car to rotate is to snap your foot off the throttle in the middle of a corner.
  • Brake – Braking is an even more aggressive form of weight transfer than lifting. Brake too much and you’ll get understeer as the tires are using all their traction for deceleration instead of cornering.
  • Hand brake – Not only does the handbrake transfer weight forward, it also changes the brake bias so that the rears do more work. Even if the rear tires aren’t locked, they will have less lateral grip because they are using longitudinal grip for deceleration.
  • Flick – The Scandinanvian Flick is a dynamic way of swinging weight around. Not only are you decelerating as you turn, you’re also throwing weight to the outside.

Things that work in RWD but not FWD.

  • Throttle – Adding throttle will not overspin the rear tires. Instead, it pulls you out of a drift! No, no, no. Don’t do it.
  • Clutch kick – Spinning up the engine and then engaging the transmission is one way to reduce  traction as the wheels suddenly get power. In a FWD vehicle, that just makes you look like a chump.

2 Keys to FWD Drifting

The best way to create imbalance is to start with imbalance. Yes, FWD vehicles have more traction in front, but if it’s worth doing, it’s worth over-doing. The first key to FWD drifting is to put sticky tires in front and slippery tires in the rear. This is such an effective oversteer formula that it would be dangerous to drive on the street. It’s not quite skid plate racing, but it’s on that spectrum. If you drive around in a circle, progressively gaining speed, your rear tires will reach their adhesion limit before the fronts and the back end will start chasing you around. Alternatively, try braking as you enter a corner. Get ready to countersteer because you’re about to swap ends.

Getting the rear out isn’t hard, but keeping it there is. In a RWD car, you use a mixture of throttle and steering to hold a slide. In a FWD car, it’s steering plus brake. The second key to FWD drifting is managing your finite supply of momentum. The critical word here is finite. You can’t build momentum. All you can do is spend it. If you’re wasteful and spend that momentum all at once, you may pivot or spin, but you won’t drift. If you want a long drift, you need to bank a lot of momentum so you can spend it gradually throughout the drift.

  1. Enter the corner at high speed. No, even higher speed. This is your momentum bank.
  2. Use a mixture of light steering and light braking to create oversteer. You shouldn’t need the hand brake.
  3. Make steering corrections to prevent spinning. The corrections need to be fast, and possibly large.
  4. Go back to step 2 a few times.
  5. Finish the drift by yanking the car out with throttle. Bonus points for getting all 4 tires smoking.

If you can drift a FWD car, you can also drift a RWD car. The reverse isn’t true.

Just 1 mph faster

I think most people who read this blog would like to go just a little bit quicker around a race track. In fact, that may be your New Year’s resolution in a couple weeks. Rather than trying to make a huge leap, like 5 seconds, focus on something more realistic, like averaging 1 mph faster. How much faster is that in terms of lap times? It depends on the car and track. For example, in the Global MX-5 Cup at Laguna Seca, lap times ran about 1:40 in the ND2 Cup car. That’s a nice round number because it’s 100 seconds. Anyway, it turns out that 1 mph amounts to about 1.3 seconds.

As a complete aside, if you’re wondering how much faster the ND2 MX-5 is compared to the ND1, both models are raced in the Global MX-5 Cup (in different classes of course), and the answer is about 2 sec at Laguna Seca. That’s a pretty significant gap, but there’s a lot more gap to be found among the drivers. The top ND1 driver runs about the same speed as the middle of the pack ND2 driver. The difference between the two cars is 26 hp. It’s kind of amazing that even among very good racers, some drivers are effectively 26 hp better than others. Among HPDE drivers, the gap can be huge.

So back to that 1 mph faster. How are you going to go about averaging 1 mph faster? It turns out there are two ways.

  1. Enter the corner with more speed
  2. Enter the corner with more yaw

1. More Speed

For most people, more entry speed is the low lying fruit. That’s because most people brake too much and enter the corner several mph too slow. To go 1 mph faster, just enter every corner 1 mph faster and everything should sort itself out, right?

Let’s take a look at some real data from my team at a Willow Springs race a couple years back. The driver on the red trace is braking way too much, on the order of 8-10 mph in T1 and T2. That results in a lower speed all the way to the next corner and a lot of time lost. You might think the red driver is a novice, or this isn’t his fastest lap, but he isn’t a novice and this is his fastest lap.

If you’re over-braking your corner entries, as do most drivers, then there’s certainly room to enter with more speed. But how can you determine if this is the case?

  • The best way is to compare your driving to someone in an identical car with identical setup and identical weather. That’s easy to do in the sim world, but hard elsewhere.
  • Have a coach or local hotshoe drive your car so you can compare data between drivers.
  • Compare your data to someone else driving a similar car. Perhaps you both have an GT86/FRS/BRZ.
  • Compare your data to someone else in a different car. If you’re on similar tires, your entry speeds should be similar.
  • Compare your data from different laps. You might find some laps you go in faster than others.

Perhaps you’ve noticed a theme here? You’re going to need some data acquisition gear and do some comparative telemetry analysis on the speed trace. Phone apps like Harry’s Lap Timer, RaceChrono, CMS Lap Timer, Track Addict, etc. work well enough. What if you can’t use a smartphone app? I’m not sure what world you’re living in where you’re worried about lap times and can’t use a phone app, but here’s my simplest advice.

  • If you can get to 100% throttle immediately, without any kind of maintenance throttle mid-corner, you probably entered too slowly.

One of the reasons people enter corners too slowly is that they’ve heard the phrase “in slow, out fast” too many times. Another reason is that going faster would scare the shit out of them. In any case, one of the problems of entering slowly is that being under the limit gives you an invitation to add a lot of throttle mid-corner. Here’s a pretty common sub-optimal control input sequence that’s very common among intermediate drivers.

  1. Mash brake pedal – leads to low entry speed
  2. Mash throttle – leads to mid-corner understeer
  3. Lift throttle – to prevent running out of room at the exit

One of the misconceptions of the intermediate driver is that they should mash the throttle mid-corner. That will get the car to rotate, right? Somewhere in their past the driver not only heard “in slow, out fast”, they also heard “loose is fast”. So they think mashing the throttle will get the car to loosen up. Spinning the rear tires isn’t the same as transferring weight to the front. Drifting greatly reduces the overall grip of the car. Transferring weight does not.

Too much speed

As you get better at optimizing your entry speed, you will eventually run into another problem: you can’t actually enter any faster. Let’s assume that 66 mph is the limit for a specific vehicle in a specific corner. What happens if you try to go 67 mph? The corner radius has to get bigger. The equation that relates speed, grip, and radius is: speed = sqrt(grip * radius). If you decide to enter a 66 mph corner at 67 mph, the radius of the corner will have to get larger to compensate because grip is a constant. In other words, you’ll fall off the track at the exit. If you don’t want that to happen, you’ll have to lift off throttle to tighten the radius and now you’ve basically done the corner backwards (in fast, out slow).

The intermediate level of driving is a mixture of too little and too much entry speed. In both cases, drivers are fighting understeer at the exit, but for different reasons. In either case, if you have to lift at the exit, you’re killing your lap time. The whole point of the typical late apex racing line is to optimize the power of the car in the second half of the corner. Lifting ruins that.

Even if you’re not lifting at the exit, you might still be in the “too much entry speed” category. Some drivers have enough discipline not to mash the throttle, so they don’t have to lift later. Instead, they spend a lot of time coasting in the mid-corner and are late on throttle. The time to add throttle is actually before the apex, but mid-corner coasters add throttle at or after the apex.

The high intermediate performance plateau

There is a very natural performance plateau associated with optimizing entry speed. Eventually you can’t go any faster and you learn the exact entry speed that maximizes every corner. If you accidentally enter 1 mph slow, you add a little extra throttle mid-corner, but not so much that you run out at the exit. If you accidentally enter 1 mph too fast, you coast a bit mid-corner, and end up a little late to throttle. This style of driving, where you modulate mid-corner speed with the throttle can be pretty fast and consistent. It isn’t actually the fastest or safest way around a track, however. Breaking out of this style of driving can be difficult, especially if you’re good at it. If you’re a racer whose been hard stuck 1-2% behind the front runners, this is probably the reason.

Brace yourselves, another tennis analogy is incoming…

One of the greatest tennis players of all time was Steffi Graf. She had a huge serve, killer forehand, tireless legs, and a consistent slice backhand. But no matter how good your slice backhand is, it is a liability against a serve-n-volley player who loves slow rising balls. In order for Steffi Graf to beat Martina Navratilova, she had to learn how to hit a topspin backhand. It’s a completely different stroke requiring changes as fundamental as how she held the racquet. Eventually she learned the stroke and the rivalry ended shortly thereafter. A similar situation existed with Ivan Lendl and John McEnroe. In case the analogy isn’t crystal clear, slice backhands are like intermediate driving. If you want to get to the advanced levels, you’ll have to learn how to rip a topspin backhand.

2. More yaw

The other way to lap 1 mph faster is to enter a corner with more yaw. There are two main advantages to this technique.

  • The front wheels do less steering
  • The drive wheels are pointed towards the exit sooner

Steering slows the car. The phrase “in slow, out fast” is not nearly as important as “the driver who steers less wins”. Having the drive wheels straight sooner leads to opening throttle sooner. Entering a corner with more yaw means less loss of speed and more gain of speed. It’s a win-win scenario. So why don’t more people do it?

  • Yaw leads to spinning

That’s reason enough. Spinning is dangerous. It wrecks cars, injures people, and gets drivers kicked off track. Lose-lose-lose. So why bother learning how to do it? Safety, paradoxically. A driver who can deal with yaw can deal with other adverse conditions such as rain, dirt, oil, and off track excursions.

How are you supposed to learn to drive with yaw when practice may endanger people or property? Thankfully there is sim racing. Your body can learn how to drive with yaw without breaking stuff. All you need is a sim rig and the motivation to unlearn your bad habits. But wait, what about that blog post a couple weeks ago where I was giving 12 reasons not to buy a sim rig? Those reasons are good reasons. But training your muscle memory to automatically correct for oversteer? That one positive is worth a few dozen negatives.

Tire pressures don’t matter

I remember reading a recent article comparing 200 treadwear tires and one of the initial concerns was setting tire pressure. Shockingly, they found that varying tire pressures had little affect on lap time. Whoa there! I did not spend good money on a needle pyrometer for no reason! Did I? Did I?

Clearly this is something YSAR needs to investigate. In theory, raising tire pressures does several things.

  1. Decreases rolling resistance
  2. Decreases grip
  3. Improves steering feel

I can imagine that these forces offset each other to some degree. Straight speed vs. corner speed: it’s 6 of one, half-dozen of the other. It makes some sense that tire pressures might not change lap time by much. But making sense isn’t the goal here. I’m a scientist by profession and passion, so I just have to conduct some experiments. Since I don’t have immediate plans for a semi-private test day, I’m testing this in simulation first. Later in the year I hope to revisit this study on a real track.  Let’s begin with the usual sim testing environment: Assetto Corsa, Brands Hatch Indy, NA Miata.

Experiment #1: Ideal tire pressure

In order to remove any human sources of variability, I’m going to let the AI drive first. Assetto Corsa sets the Miata pressures at 28 psi by default and allows a range from 15-40. I chose to change pressures in 4 psi increments. As you can see in the table below, 28 psi seems optimal. Interestingly, all laps are within 0.25 seconds using pressures from 24-40. If I had seen these numbers in real life, I would probably conclude that all lap times were roughly equivalent. But the AI drives each lap within hundredths of a second, so the differences are real, though small. Overall, I have to agree with the initial premise: tire pressures don’t affect lap time very much.

Front Rear Seconds
16 16 65.41
20 20 64.68
24 24 64.32
28 28 64.09
32 32 64.26
36 36 64.29
40 40 64.34

Experiment #2: Asymmetrical tire pressure

One of the things I like doing at the track is running non-square setups. I’ll mount completely different tires on the front and the rear. The two ends of a car are doing very different things, so there’s really no reason to run square setups. One of my favorite ways of goofing around on a skid pad is to mount sport tires on the front and all seasons on the rear. That’s a good way to train your oversteer recovery skills! Note that I said skid pad not HPDE session. I don’t think it’s a good idea to mess around too much in the presence of other drivers on a fast track.

So what happens when the AI drives a non-square setup? As it turns out, Assetto Corsa doesn’t allow you to have different compounds for the front and rear. But you can change individual tire pressures.

My first thought was to change the psi by 4 lbs on either side of 28. So 24F 32R and 32F 24R. The faster combination was to have more pressure in the rear. It wasn’t much of a difference, so I decided to go extreme and set one pair of tires to the ideal 28 psi and the other to 40. The result is sort of shocking. 28F 40R (64.04) is not only faster than 40F 28R (64.41), it’s also slightly faster than 28 square (64.09).

Front Rear Seconds
24 32 64.22
32 24 64.33
28 40 64.04
40 28 64.41

A stopwatch doesn’t give many details, so let’s load up the telemetry and take a closer look at what’s happening in Experiment #2. Green is 28-28 (because green is in the middle of the rainbow). Red is 28-40 (because oversteer feels red). Blue is 40-28 (because understeer feels blue).

For some reason, the AI chooses a different line on the square setup. The green line shows that the AI attempts to hold too much speed which results in being later to throttle. While initially faster, this ultimately causes the square setup to lose nearly 2 tenths by 1800 feet. It maintains that loss for a little while but then recovers most of it by the end. Apart from one bad decision in one corner, the square setup is actually faster everywhere else. This is why we don’t rely solely on the stopwatch.

What’s happening with the understeer and oversteer setups? The reason the oversteer is faster is that it’s able to use more mid-corner throttle, and it gets to full throttle sooner. It also has more yaw early and requires less steering effort in a few places. You have to zoom way in to see this. These are very subtle differences, but they add up to 4 tenths of a second by the end.

Experiment #3: Human driver

OK, time for me to drive. The first thing I did was run some square setups at a couple different pressures. There’s a little difference in the way they feel but not that much. I’d rather focus on what happens when you run different pressures in the front and rear.

Front Rear Fast Median M – F Cuts
28 28 60.93 61.25 0.32 0
28 40 61.80 62.26 0.46 1
40 28 61.25 61.36 0.11 0

The fastest was the square setup. That’s not really surprising. What is surprising was that the understeer setup was very close. The median lap was only 0.09 seconds off. If you look at the difference between the median and fast laps (M – F) you can see that the understeer laps have the most consistent pace. That was my impression while driving too: “oh well, another uneventful lap”.

The big shock is how bad the oversteer setup was. Its fast lap was 0.55 seconds slower than understeer and the median is even worse: 0.90 (some of the laps were not pretty). I was having to make steering corrections in nearly every corner as the back stepped out under braking and also under throttle. I also had one lap where I went a little too much off course and got a cutting violation.

In the graph below, the panels are speed, steering angle, throttle, and time. I have plotted the top 5 laps of each run. As you can see from the red steering angle trace, the position and magnitude of the steering corrections are quite variable. This indicates that an oversteering car is hard to drive consistently (and possibly also that I suck at racing).

Let’s take a closer look at the fast laps to dissect how understeer and oversteer affect driving style. I’ve zoomed in on the first corner (a fast, descending right-hander) below. Again, the panels are speed, steering angle, and throttle from top to bottom. The area under the blue steering angle trace is relatively large. I’m having to crank the steering wheel quite a bit because the front of the car is sliding (understeer). On the green trace, there is very little steering because the rear is stepping out just a little. This is what Paul Gerrard calls zero steer. On the red trace, the back has stepped out so much (oversteer) that I have to make a steering correction in the opposite direction to prevent myself from spinning. Note that the green trace also has a steering correction (it’s bowed down in the middle), but it is very mild.

Looking at the throttle trace (bottom panel) you can see the disadvantage of the understeer setup: it’s late getting to full throttle. So in addition to the loss of speed from scrubbing the front tires, it has an additional opportunity cost in throttle time. The oversteer setup should get to full throttle first because it’s pointed straight first, but I’m fighting the wheel so much I don’t manage it. A better driver could make this work better than me.

Here’s the whole graph. Note that the understeer setup isn’t always the last to full throttle. Sometimes the initial application is delayed. But once applied, the throttle can be used as an on/off switch. You don’t really have to balance the back end when the back end isn’t sliding. In contrast, the oversteer setup requires a soft foot and live hands to keep it on track.

Tire pressures do matter

The AI was relatively unfazed by non-square changes in tire pressure, but I was not. Having a loss of grip specifically on one end of the car or the other completely changed how I drove. I can sum up the driving experience as follows:

  • An understeering car
    • feels boring
    • requires a lot of steering effort
    • requires trail-braking to rotate
    • requires patience before throttle
    • may see you running off track at the exit
  • An oversteering car
    • feels exciting
    • practically turns itself
    • requires steering corrections to prevent over-rotation
    • requires throttle modulation
    • may see you spinning at the entry, middle, or exit

Why is the AI behavior (oversteer fast) so different from mine (understeer fast)? I’m not sure exactly what to take away from the AI driver. It’s several seconds slower than me and doesn’t even know how to trail-brake (data not shown). The AI sucks at racing. However, it is very good at controlling oversteer. Its steering corrections are always exactly the right amount. I don’t think we should read too much into the AI performance.

Although I set out to determine if tire pressures affected lap times, what I ended up focusing on was how tire pressures affected grip balance. Why? Because the handling of the car is what will ultimately dictate lap times. Too much oversteer not only results in a car that is difficult to control, it’s also slow. But what of too much understeer? It’s a little annoying but can be mitigated by trail-braking. Ultimately, it’s easier to deal with a little extra understeer than a little extra oversteer. For many inexperienced racers, the natural reaction to stuff going wrong is to lift off the throttle. If the car naturally understeers, the stuff is mostly understeer and lifting is the appropriate response. In an oversteering car, lifting is going to make matters worse.

Going Forward

All of the experiments here depended on the Assetto Corsa tire model. How accurate is that? No idea. I don’t think of these experiments as the end of anything, but rather the seeds for the real-world tests I’ll do later in the year. Stayed tuned (pun intended).

FWD Drifting: Part 2 and Cones in Practice

Last week I talked about some of the tuning and techniques for drifting FWD cars. Some readers may be asking “why bother?” Well, because it’s a driving skill. And if you can drift a FWD car, it will help you drift a RWD car. Inducing oversteer by dynamically changing the balance of the car is important regardless of which wheels are providing power. I shot the video below on the skid pad at Thunderhill between coaching sessions.

The first part shows an exterior view of some switchbacks. It’s sort of comical how slow I’m going and how little my car looks like a racecar. But even at slow speeds it will slide around corners. In the second part, the camera is inside the car. You can see that I don’t use the hand brake. The car oversteers by changing the balance of the car, not locking the rear wheels. It’s also set up with a lot less grip in the ear. The car has RE-71R tires on front at 26 PSI (cold) and Hankook runflats on the rear at 38 PSI (cold).

The next series of shots are what I’m calling point to point. It’s just going around two cones but with different turn radii. I start with a large radius and progressively shorten it. Which one do you think takes the least time? Back in December, I posted on this topic. See Cones in Theory. If you don’t want to read that whole post, here’s the short version: I make the statement that path A takes less time than B, C, or D. That’s the experiment I’m performing in the point to point videos above.

I timed the various runs and indeed, the tiny radius is the fastest (path A). It’s also in a very bad spot in the power band. I’m driving in 2nd gear the whole time, and there just isn’t as much power when driving the tighter radii. But it didn’t change the outcome. Path A is the fastest way around a brace of cones.

Oversteer overanalyzed: tuning

In part 1, we discussed that oversteer is caused by having more grip on the front than the rear. That can be accomplished by simply having a lot of weight in the front of the car (FWD), transferring weight to the front of the car by decelerating, locking the rear tires (hand brake or clutch), or smoking the rear tires. A car can also be tuned to oversteer. In the following video, look at how easily the car spins.

You might wonder how the builders achieved that. In a FWD car, it’s not too difficult because the weight is already forward. But does your street car spin every time you turn with the throttle off? No, because the designers tuned understeer into the car with the alignment. Setting the toe is a very effective way to tune handling. There’s a great article on a great website that does a much better job of explaining it than I could. Check this out: http://winhpde.com/track-alignment

Let’s watch another spin that is caused by tuning.

A car isn’t supposed to spin when decelerating in a straight line! Does the driver downshift? No. Does the driver grab the hand brake? No. The rear tires are locking up though, and that causes the spin. Why would this happen? There are several possibilities. Perhaps the rear tires are a different compound from the front and very slippery. A drifter might choose to do that, but not a racer. Another possibility is that the front brake pads are completely worn and the backing plates on rotors provide little stopping power compared to the rear. I think the most likely explanation is that the car’s brake balance was tuned incorrectly either with the use of a brake prop valve or by mixing pad compounds. A prop valve lets you dial in how much pressure goes to the front vs. the rear. It’s easy to use and makes a huge difference. But if set incorrectly, you can spin when braking in a straight line. You can also tune your brake balance depending on what brake pad compound you use. If you find that your front race pads are worn out and all you have to replace them with is OEM equivalents, you may find that your rear brakes are now overpowering your fronts and you’re entering spin city.

 

 

Oversteer overanalyzed: hands & feet

Last week we talked about weight transfer and the somewhat paradoxical notion that braking causes oversteer (by transferring weight and grip to the front of the car). So once the car is an oversteer stance (i.e. pointed into the corner more than necessary), what next? Well, if you do nothing, you will spin. The something you absolutely have to do is to open the wheel, which is often called counter-steering. Simply holding the steering wheel in the same place for too long will lead to a spin. In the following clip, the driver waits too long to open the wheel and spins.

How far do you turn the wheel in the other direction and for how long? It depends on how much you are oversteering and how much you are accelerating (or braking). Controlling oversteer requires a delicate balance between hands and feet. I’m sure I could come up with an equation for that, but it wouldn’t help anyone. Once you are in an oversteer stance, you have to control it with muscle memory. Thinking takes way too long. It’s got to be a habit born from hours and hours of repetitive training. In the next clip, the driver steps on the gas too hard and starts to oversteer. His lack of training is evident.

In both videos, the car ends up fish-tailing. In motorcycling, that’s called a tankslapper (because the handlebars slap both sides of the fuel tank). It’s such a great term that even car people also use it. What causes tankslappers? It’s a combination of extreme oversteer and late reactions. Even experienced drivers sometimes get into tankslappers when caught unawares, but the oscillations get smaller each side. Inexperienced drivers sometimes end up making matters worse as they try to recover.

So what can you do to prevent oversteer spins, tankslappers, and mass carnage? You could drive purposefully well under the limit of the car. That way it won’t oversteer. But what happens if there’s dirt, water, or oil on the track? What happens if you drop a wheel or 4 off track? It would be far better to learn how to control oversteer, right? Unfortunately, the only way to get that wired into your nervous system is by experiencing a lot of oversteer. There’s no amount of listening, reading, or watching that will make your reactions automatic. Talk about fun homework! I suggest simulation. I’d say it’s 90% as good as the real thing and virtual cars are a lot cheaper when you wreck.

Oversteer overanalyzed: weight transfer & brake bias

Whether you’re talking about drifting, e-brake turns, trailing-throttle oversteer, or Scandinavian Flick, oversteer looks awesome. It’s not always the fastest way around a corner, but it’s the coolest. Unfortunately, oversteer often leads to spins and crashes. Understanding oversteer will make you safer and faster, so that’s the topic for a few posts.

First off, let’s define oversteer. It’s pretty simple really. It’s caused when your tires are sliding and your front tires have more traction than your rear tires. Assuming your car has 50/50 weight distribution (half the weight on the front tires and half the weight on the rear tires), when you start to slide, the front and rear tires will slide equally. But this assumes you’re not accelerating or braking. As soon as you accelerate, weight and traction shift to the rear. This causes understeer. As soon as you brake, weight and traction shift to the front, which causes oversteer.

Wait-a-goddamn-minute, if accelerating causes understeer and braking causes oversteer, how the hell does drifting work? That’s totally different and has nothing to do with weight transfer. If you spin your tires really fast, the friction starts to disappear. The rubber begins to liquify and gasses build up at the tire-road interface. That’s some slippery shit. But even drifters initiate their turns with weight transfer. It’s the key to understanding oversteer.

So how does one add weight to the front of the car while driving?

  • Brake
  • Hand brake
  • Downshift (RWD only)
  • Trailing throttle oversteer
  • Downhill

Brake

Probably the most obvious way to shift weight forward is by pressing the brake pedal. But what isn’t so obvious is how much of the braking effort is being done by the front wheels vs. the rear wheels. Generally, the front brakes are designed to do more work than the rears because the engine is in the front of the car and the weight is also transferring to the front. Adjusting the brake balance between the front and the rear can make the front or rear tires lock up first. If the brake balance is too far to the rear, the rear tires will lock up first, which will cause additional oversteer beyond the weight transfer. How can you change brake balance/bias? That’s a topic for later.

Hand brake

The hand brake does double-duty for oversteer. (1) It transfers weight to the front (2) It causes the rear wheels to lock up. Grabbing a fist-full of e-brake is one of the most common ways to make a FWD car oversteer. There are a couple reasons for this. First, FWD cars can’t liquify their rear tires, so that’s out. Second, FWD cars have most of their weight forward anyway, so locking up the rears gets them to pivot very easily.

Downshift (RWD only)

Engine-braking a RWD car slows down the rear wheels only. This effectively changes the brake balance toward the rear. Downshifting and feeding out the clutch is therefore a good way to cause oversteer because the weight is transferring forward and the rear brakes are doing more work. A sudden pop of the clutch is a lot like grabbing the hand brake.

Trailing throttle oversteer

Driving at constant speed requires some throttle to counteract air resistance and mechanical friction. As soon as you lift off the throttle, the weight shifts forward. This is called trailing throttle oversteer (TTO). It’s basically a milder form of downshifting.

Downhill

If you’re driving on a downward slope, there is naturally more weight on the front than the rear. The car wants to oversteer simply because of the geometry of the track. Downhill corners are therefore the most prone to oversteering (and spinning).

Quiz

See if you can determine why these crashes happened.

Bad driving tip #7: drive (too) fast

Sports cars these days have ludicrous amounts of power. For example, a 2017 M3 has 425 HP. Modern sports cars tame that power with stability control, traction control, and anti-lock brakes. You can generally turn off some of these nannies, but even if you don’t, you’re driving an amazing machine that can exceed 100 mph very quickly. At that speed, you can get badly injured. Crash tests are performed at 35mph, not 100. Yeah, your car isn’t designed to protect you at track speed. At 100 mph, you’re experiencing over 8 times the kinetic energy compared to 35 mph.

Race cars tend not to have any nannies or airbags. This makes them more dangerous to drive. Even with full cages and safety equipment, you wouldn’t want to crash at 100 mph. In the video below, the driver is in a race-prepped Porsche 911 (996) at Willow Springs. He runs off track in T2 at about 85-90 mph. When he hits the dirt wall, he’s probably going 75-80. The crash breaks 4 vertebrae. That looks like it really hurt.

911s are notoriously difficult to drive and Willow Springs is a particularly dangerous track when you leave the asphalt. Driving it hard enough for it to oversteer in the middle of the corner is what you’re supposed to do if you’re an A-level driver (see the Skill page linked above). But if you’re a B or C driver, going this fast could get you in a lot of trouble. Once the car begins to oversteer, the driver’s reactions are slow, uncoordinated, and panicked. He loses control of the steering wheel and becomes a silent witness to his own crash. Oversteer recovery should be engrained in muscle memory, capable of retrieval without thought. Heres’ an important tip: learn to drive a sliding car at lower speeds and in safer environments. Get a first-generation Miata and drive it on all-season tires. Stay away from high speeds and sticky rubber until you’ve learned how to slide a car from entry to exit.