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).

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Stopwatch or it didn’t fucking happen

Probably like many of you, I sometimes watch car reviews on YouTube. I wish there was some way of determining ahead of time if the people reviewing the car were experts or poseurs. Here’s what one journalist says as he drives the Civic Si.

Chuck it into a corner like so… yeah, and you can feel that diff working up front, you can feel it pulling the car through the corner.

Now let your imagination fill in the scene… the driver approaches a tight corner at high speed… he brakes and throws the car in… the rear drifts around as the front tires dig the car out of the slide…

OK, time to click the link…

How embarrassing. The only thing he chucks into the corner is his credibility. He can feel the diff working… without any wheel spin? You fucking P-O-S-E-U-R. Apparently the 50k+ subscribers are tuning in for their sparkling personalities or handsome visages, because it’s certainly not the driving.

What about those reviews where the journalist gets out of the car for the track test? Hey Randy Pobst, can you take over? Pretty please. Drive the goddam car yourself. It’s literally part of your job description. Of course I understand why they do it. Professionals are more consistent. But the journalists should also post their lap times. If they’re 5 seconds off, I want to know that. It speaks to their credibility. Stopwatch or it didn’t fucking happen.

On the Physics of Racing

One of the first things I read on racing is a collection of articles called “The Physics of Racing” by Brian Beckman. This made a big impression on me because the author takes a very mathematical view of racing. That’s something I could sink my teeth into because I had more experience with math than performance driving. Then I got to the part where he went to a racing school at Sebring. He was more experienced than the novice racers but he was also older. All the students drove identical Panoz cars. He found that his old-fashioned straight-line braking left him 65 feet (about 0.5 seconds) behind the more modern students who were trail-braking. Then he drops this bomb.

A record time around the course in the Panoz school cars is 2 min 28 seconds. The students were doing 2:40 to 2:45. I believe I uncorked a 2:36 somewhere along the way, but my typical lap was 2:40 and the quicker guys pulled about 65 feet on me at the start-finish every lap, which I reckoned before to be worth half a second

I don’t want to know why he thinks he’s 0.5 seconds slower than a bunch of rookie racers. I want to know why his typical lap was 12 seconds off! Clearly there’s a more important lesson here than a little trail-braking. If the lap record is a 2:28, a 2:36 isn’t uncorking anything other than a bottle of shit. That said, he posted his lap times, and for that he should be commended. It puts things into perspective. He’s a guy who understands the theory of racing but has some trouble putting it into practice. That’s okay. Lots of people are in the same boat. Like me, or maybe you.

YSAR in 2019

As this is my first post of 2019, I thought I would say a few words on the future direction of YSAR. There are a lot of people who offer insight on performance driving. Most of them know their shit better than me. I’m not Ross Bentley or Peter Krause. So why tune into YSAR? I guess because you like your driving content with an eclectic mix of math, simulation, video, science, irreverence, and irrelevance. YSAR used to focus on crashes, but I think it has evolved into some kind of mental pit stop for the improving driver.

As we look forward to 2019, I’m eager to find out where this performance driving journey will take us. Frankly, I’m as much a passenger as a driver in this endeavor. Before we start, let’s agree to chuck the poseur bullshit into the corner. There’s no room for artifice where we’re going. There is room for incompetence though. Let’s find out where those 8-12 seconds went and fix that shit. Oh, and there’s also room for a metric ass-ton of swearing. This is you suck at racing, after all. The shit has, and always will be, fucking real. Or in more gentlemanly terms, I will always be honest with you. Whether it’s modeling vehicle dynamics, debunking driving myths, reviewing the latest gizmo, or recounting my latest driving adventure, I will present stuff as factually as possible. I give zero fucks about impressing professionals or companies, and won’t alter my content in an effort to impress or appease them.

Am I just going to ramble on this week or is there going to be any actual driving content? Okay, okay, let’s call bullshit on someone with more racing credentials than me.

The Euler Line

Do you subscribe to Speed Secrets Weekly? It’s a weekly newsletter delivered to your inbox. If not, you might consider it. Every Tuesday there’s new content from Ross Bentley and usually a guest writer. Professional drivers, engineers, and coaches contribute regularly. And also amateurs like me. I’ve written two articles for him in the past and just a few days ago I started a new 2-part article on why spinning is an important part of driver development. I won’t regurgitate those posts here but instead urge you to subscribe to SSW. It’s only $15 per year and makes every Tuesday just a little better.

One of the recent posts that got my attention was written by Randy Beikmann. It’s a theoretical post about the ideal driving line that compares the circular arc to an Euler spiral (pronounced “oiler”). Probably every book since Piero Taruffi’s 1958 classic, “The Technique of Motor Racing”, introduces the racing line as a circular arc. Nobody actually drives this arc. It’s used (1) to demonstrate the largest possible radius through a corner and (2) as a point of comparison to the typical late apex racing line. Here’s an awesome picture of the ideal line from that book.

One unrealistic thing about the circular arc is that one goes from straight wheels to turned wheels instantaneously. The author suggests that instead of turning the wheel suddenly, you should turn the wheel at a constant rate. Steer it in gradually, steer it out gradually. The path through the corner is not circular. It follows an arc called an Euler spiral, which is more gradual at the entrance and exit. The author goes one step further and shows through a Mathematica simulation that driving on the Euler arc is faster than a circular arc. In the diagram below, you can see the flatness of the blue line. That’s the constant speed of a circular arc. The Euler line has a lower minimum corner speed but makes up for it by getting to throttle sooner.

I greatly admire the elegance of the Euler spiral model, but it left me wondering “does anyone actually steer like this?” We can answer that pretty clearly by comparing theoretical and actual steering traces. TL;DR nobody drives the Euler line.

The black line below represents the steering angle of the Euler line: constant winding in followed by constant winding out. It’s shaped like a capital A. In reality, there are steering corrections. An idealized representation is shown by the green line, which looks like a capital M. The steering wheel is turned in a little, but then the back of the car rotates around (often from trail-braking). A steering correction (steering the opposite direction and back) puts the car back on line, and then the steering wheel is unwound towards the exit.

Here are some traces driven by the Assetto Corsa AI. Steering angle is the 3rd panel. As you can see, it doesn’t look like the letter A expected from an Euler line. The top of the peak is flattened and there’s often a spike in the middle representing the steering correction. At around 4000 feet the trace looks like the letter W, not V.

How about real drivers? Here are the “alien” steering traces I showed in part 5 of the Ghosting the Aliens series of posts. Where are the isosceles triangles? The steering wheel is rarely turned at a constant rate, and sometimes very quickly.

Here is me driving in simulation with 3 very different setups (blue understeer, red oversteer, green neutral). The middle panel is the steering angle. The understeer setup is the most similar to the Euler line, but it’s hardly symmetrical and there’s a steering correction late in the corner.

In theory, there’s no difference between theory and practice. In practice, there is.

So if nobody drives an Euler line, why is Randy Beikman wasting time writing and talking about it. It’s because it’s not a waste of time. It’s important to understand the theory behind racing. It’s even more important to understand where the practice differs from that theory. In the end, we want the theory to catch up to the practice. When that happens, we can take our speed beyond our current understanding. It takes time to model these things correctly. While less than perfect, I admire the work by Beikmann and his Euler model. Beautiful things can have flaws.

You suck at point bys

The winner of the YSAR Author Contest and RumbleStrip lap timer was Steve Danielson. I think you’ll agree with me that his post is as good as anything else on YSAR. Informative content, animated videos, in-car video, humor, check, check, check, check. Thanks Steve, you knocked it out of the park with this one.

How many times have you heard the following at a driver’s meeting: “If you see a car in your mirrors that wasn’t there before, at the next passing zone lift off the gas and give them a point by”. Seems to make sense, right? But how many times have you caught up to and then been stuck behind somebody that just wouldn’t give a point by? Is it because they are a jerk or have a big ego and can’t be passed by a lesser car?

Let’s take a look at it from a different perspective. You are at the track driving, and in one of your sessions, a Miata starts catching up to you in the corners, but you always manage to leave it in the dust once you get to the next straightaway. The battle is on! They are getting close, sometimes even quite close, but you are able to get away after each corner. As you pull in at the end of the session you are thinking “What a great session! Toward the end they sure seemed to get aggressive and really on my tail in the corners, but they still couldn’t catch me!” After the session you go and find the other driver to share stories about your “epic battle”, but as you approach you hear them talking with their buddies along the lines of “That session sucked, I was stuck behind some $%^& for half the session”. Why didn’t they seem to have the same great session that you did? What happened? Turns out, you were holding up a driver that was running faster laps than you until they got stuck behind you. You suck at point bys, and didn’t even know it.

Why does this happen so often?

Fallacy: When a lower powered car catches a more powerful car in a corner, often no point by is needed, because the power of the “faster” car balances out the faster cornering speed of the “slower” car on the next straight.

Reality: Power and handling only balance each other out if the two cars are running the same lap times. And if that is true, the two cars will likely never come within sight of each other. If a car catches up to another car on track, it is because the second car is running a faster lap time.

Here’s a simulation of a high powered car and a low powered car driving a lap with the same lap time. Even though one car’s lap is based on power and the other based on handling, they stay on opposite sides of the track and never catch up to each other.

Here’s the same simulation, but with the car positions overlaid. You can see where one car or the other pulls ahead briefly due to power vs handling, but they make it to the start/finish line at the same time, because they are running the same lap times. Sometimes at the very start of a session, cars can get bunched up similar to this, but usually after 1-2 sessions folks can figure out who is faster and get it sorted out in the first lap or two, or by gridding near the front or back.

What happens when a lower powered but faster driven car catches up to a more powerful car, and gets stuck behind it? Say a Miata is running a string of 89.3 second laps and catches up to a more powerful car, let’s call it a 6000 SUX, that is running 92.9 second laps. Due to being held up in the corners and losing all its momentum, the Miata will now be running laps even slower than the 6000 SUX. That truly does suck…

Fallacy: If a lower powered car catches me in the corners and I point it by, I will just be stuck behind it on the straightaways.

Reality: If you lift off and give a point by, you may have to ease off and not go full blast for the duration of that straight, but once you get into the next sequence of corners, you are not likely to be held up any longer and can resume your normal pace. In order for a less powerful car to be running faster laps than a more powerful car, it must be cornering much faster. And in that case, it will most likely leave you behind after the next set of corners. Let it by and maybe you can learn something by watching it.

Here’s a simulation of our Miata catching up to and getting stuck behind the 6000 SUX. After a few laps of holding up the Miata, the 6000 SUX gives the point by. After letting the Miata by, the 6000 SUX does get close on some of the straights but is not held up, and shortly after both cars are back to clear track and running at their own pace.

Fallacy: When I catch up to another car and they don’t give me a point by, it is because they are a jerk.

Reality: Sometimes true, but maybe it is an educational issue. A lot of times they really think that their extra power on the straights balances out your extra cornering speed, and so they don’t know that they need to give a point by.

I was at an event a few years ago and was in a run group that had about 10 Challengers. A couple of them were very fast, and I never saw them except when they zipped by. A couple of them I never saw at all, because we were running about the same lap times, as illustrated in the first simulation above, and a couple I would catch up to, but they would rocket away on every straight, and if they did give a point by, they didn’t lift and so I had no hope of completing the pass.

In this example it was an educational issue and not because they were a jerk. At lunch the event organizer talked with them, and it was totally resolved, with very courteous track etiquette after that.

It is a lot of fun to catch up to other cars when driving at the track, but can be frustrating to get stuck behind a slower car that won’t let you pass. Sometimes you can drop back for a few moments to build a gap, or you can roll through the pits to get some space, but it is better when it doesn’t happen. We’re all out there for the same reason, to learn and to have a good time, so when someone catches up to you, lift off the gas and give a point by. Try and keep up and you might learn something, and you just might run your fastest laps trying to catch back up. Don’t suck at point bys, and you won’t be this guy:

 

Real Heroes

Guest post and 2nd place in the 2018 YSAR Author Contest. This one comes from Jenna Korf, my brother’s wife. Why did my brother and his wife get on the podium? Is this a case of nepotism? No, there were only 4 entries. I thought it would be fun for others to share their stories but apparently not. As usual, editorial comments in red.

When my husband initially told me about this writing contest and that the winning prize is a lap timer, my first thought was “I give zero fucks about a lap timer.” It was then that I knew I had to write this. 

So, what’s it like to be married to a race car driver? A couple of words that come to mind are Annoying. And frustrating. 

Annoying because it seems like every time we get in the car, it’s a call to his twin brother, on speaker of course, so I can’t escape it. to discuss… you guessed it, tires. You’d think maybe they would want to discuss different aspects of the car – or life. But no. They have the same conversation, over and over and over. It goes something like this. 

“Did you see that test they did on the wiley tires?” “I did! Let’s test all 10 sets of crazy train tires on 10 different tracks in different weather so we can gain that .0001 second!” “Well the front tires wouldn’t make a difference because of the fire roasted tread.” “Yeah, but if you swap out the front right tire and coat it with dressing and put a hat on it you’ll get .05 seconds back that you lost when you first turned the back tire out. And then we can stay on the track for 2 seconds longer!”

Just. Wow. 

I often wonder how my husband would like to be trapped while I talk to my girlfriend about her relationship? For hours. On end. 

Oh, and if you’re lucky enough to be married to a racer who participates in the 24 hours of Lemons race, it’s not just any car that takes up their time, money and energy. It’s a Noah’s Ark car – animals hanging out of it and all. Or a Scooby doo van. Or a half and half Lamborghini / Ferrari car. 

But it’s a serious sport, you know. Deserving of respect. 

I think what I mostly don’t understand about how awesome racing is when you spent thousands of dollars (on a car that we’re sure to make our money back on when he’s ready to sell), hundreds of hours working on it, (time that he could have spent with me), all to have the engine blow after 10 minutes on the track. True Story. 

The kicker is that after that experience, instead of doing what most intelligent people would do (and my husband IS super intelligent), like sell the car, somehow the logical thing to do is to sink even MORE money into it so he can fix it, get some more use out of it and then sell it at a better price. Um… I can’t even. 

So am I missing something about the greatness of this “sport”? Maybe. But in my opinion, the spouses of the racers are the real heroes here. And who can blame me for thinking that? My husband once sent me a picture of himself at the track. He was wearing nothing but a sun hat and an adult diaper. I rest my case. 

Portrait of a real hero. All 4 feet 12 inches of her disappointment look down at your silly, wasteful hobby that you happen to suck at. Since her post was like her, short, I thought I’d get her to respond to a few famous quotes.

To finish first, you must first finish.
— Juan Manuel Fangio

I’m already finished with this. The question is, when will you be?

The winner ain’t the one with the fastest car, it’s the one who refuses to lose.
— Dale Earnhardt

So why do you spend so much fucking money on the car?

To achieve anything in this game you must be prepared to dabble in the boundary of disaster.
— Sterling Moss

What about wallowing in disaster? I mean, I’ve seen a lot of wallowing. It’s pitiful. I suggest you give it up before it gets to the wallowing stage.

The basic problem with motor racing as a profession is that it costs too much money to get good enough at it to get paid for doing it.
— Carroll Smith

And the basic problem with motor racing as a hobby is it costs too much money and you never get paid for doing it (or get good at it).

Racing is life. Everything that comes before or after is just waiting.
— Steve McQueen

Did you say something? Cause I could have sworn I just heard you say you will always be a wanker. Fucking wanker.

Lessons Earned

Guest post and 3rd place in the 2018 YSAR Author Contest. This one from my twin brother Mario. Editorial comments in red.

Lessons Learned Earned

I’ve been endurance racing for six years now, which is that middle ground where I’m no longer a noob, but I still don’t know shit. I’d like to think I’ve learned a thing or two, but if I add up the time and money spent, I think it’s fair to say the lessons have been earned, more than learned.

Alignment first – When we got our 1997 Miata it was set up with toe-out in the rear because the previous owner wanted to drift it. I found out really quick in Sonoma by spinning in T4. The instructor with me said “this doesn’t handle like a Miata.” I skipped a session, got everything aligned to zero, and it fixed everything. Another time our MR2 got sideswiped and it would crab sideways through a corner thereafter. Our teammate Ben Dawson could drive it like that, but I couldn’t get through two corners that way.

It wasn’t sideswiped. The axle broke from metal fatigue and the only replacement we could find on the day was from a previous year MR2 whose suspension geometry was slightly different. You had to saw the wheel just to keep it going straight. Mario got out of the car after one lap and said something like “I value my life too much to drive this”.

Don’t be obsessive about tire pressure – 200TW tires seem to work under a variety of tire temperatures. At a Hooked on Driving day I was at the center of a fairly volatile conversation between a Spec Miata guru and a tech from Tire Rack who completely disagreed on what my tire pressure should be. The former said to run my tires at 38-40 psi, the latter at 28 psi. The comments went from “You’ll fall off the track,” to “the tire will fall off the rim,” and back and forth.

Grassroots Motorsports recently did a 200TW tire test and tried a range of tire pressures. They found out that it didn’t matter much.

It was a bit shocking to find that the lap times were all the same. I think pressures start to matter more when you don’t have square setups. When goofing around I pump my rears up absurdly high. Also, off road so that the tires stay on the rims. 

Safety wire your oil drain bolt – I ruined half an HPDE day for everyone because the oil drain bolt came loose. If the corner workers had flagged me there would have been less cleanup, but for sure it was my fault. I now drill and wire the drain plug, and you should, too.

Get an infrared thermometer – If you’re a pro driver then you need a pyrometer to measure tire temps, but if you’re reading this blog, you can use a $20 infrared gun. It’s great for checking tire temps, seeing how hot your rotors get, checking track temperature, and various things under the hood.

MR2s are great endurance cars. Not. – Our MR2 spun every other race. No, it didn’t spin from snap oversteer like everyone wants to tell you, but it spun bearings all the time. And that requires rebuilding the bottom end. If you want to have a couple really great races and then replace the engine, the MR2 is an ideal platform. If you want longevity, look elsewhere.

Black flags matter – After too many black flags and unnecessary pit stops, we calculated the amount of time lost for a single pit stop vs different lap times. I wrote a whole blog post on this subject, but I can sum it up by saying the fastest driver with a single black flag is the slowest driver.

On some tracks where the stewards are outside the timing loop, a black flag can cost an extra lap.

Don’t trust a racing resume – We’ve had arrive-and-drives with impressive racing resumes, but they don’t mean much. One guy was slipping the clutch on purpose to keep the revs up (and bragging about that being the fast way around), and another had his hand on the shifter the whole time. He also downshitted and put our car to 9k revs, fucktard.

You need a coolshirt – We ran our first couple races without coolshirts and could manage 40-minute stints before we were a danger to ourselves and others (it was over 100 degrees and probably 114 off the pavement). One time we used dry ice to super-cool our ice, but haven’t done that since because most of the energy is locked up in the phase transfer from solid to liquid, and so it’s not worth the hassle of cooling ice further. A big block of ice is better than ice cubes.

Pit stop strategy – No battle plan survives contact with the enemy; no pit stop strategy survives the weekend. But it’s fun to plan them anyway. Also, you can make up time in the pits easier than on track. But like black flags, an unplanned stop takes more time than driving slowly.

Miata is always the answer – They handle, there’s always spare parts at the track, and they don’t break too often. They are underpowered and a bit too common, but still the answer.

Wear a diaper and a big hat – It took me a few races to get to where I could comfortably drive a two-hour stint, and when I was finally ready, my bladder wasn’t. Forty minutes into it and I was weighing the pros and cons of a pit stop vs peeing in my suit. I pitted and ruined our race strategy, but at least I didn’t soil the seat for everyone else. Now I wear a diaper (Depends) every time, and weirdly, have never had to use it.

I also wear a big hat because the sun can tire you out as much as anything. We were racing at Willow Springs one day and it was 108 degrees IIRC, and I had just finished my stint, so I was wearing nothing but a diaper and a big hat. I thought it was funny, so I texted my two sons a picture. One said “I can never un-see that,” the other said “Now I have to burn my phone.” It was so worth it.

Pit board > radios – We’ve had terrible luck with radios and headsets. We now run Boefang radios, but at the lower, and legal, 2w setting. And they still suck. Have a pit board on hand.

Bring a skateboard – Skateboards are great pit transportation, and if you have a longboard, you can carry a gas can on the front.

Don’t race on untested components – At the 24 hours of Buttonwillow, Ian put on tires we’d never used before, and the best brake pads we could find, but also hadn’t tried before (the Yaris has a dismal selection of brake pads). The tires sucked. And we ran out of brakes in the 8th hour. Of a 24-hour race. We only had one extra set of brake pads, and so the last 8 hours was pretty much downshifting and coasting with no brakes. Still placed third overall, tho!

Me culpa.

Put your most aggressive driver in last – I flew across the country for a race weekend. Our most aggressive driver went first. Nobody went next.

FWD is great – I love rear-wheel drive cars, especially in slow corners, but most of the time it doesn’t matter which wheels are driven. Some of the most fun I’ve ever had racing has been in my brother’s Yaris and Tom Pyrek’s Honda Odyssey minivan (Ninja Turtles theme). FWD is especially fast in the rain, and at the NJMP Lemons race, Tom’s rain laps were within 1% of our team’s best dry laps.

Quit racing – Ian and I keep talking about the day we sell our race cars. Then we’ll buy a couple brand new Miatas (him a Fiat) and do HPDEs and arrive-and-drives. Maybe we’ll still be saying this five years from now? I don’t know, but my wife was ready for that yesterday.

Mine too. Racing sucks most of the time.

Ghosting the aliens: part 5, fast is fast

This is the last of the Ghosting the Aliens series of posts. Not to fear, we will return for more telemetry analysis in 2019.

Slow is smooth, smooth is fast

— said no alien ever

In this post, I’m going to argue that an overemphasis on “slow is smooth” results in “slow is slow”. If you truly want to be fast, there are some techniques that require you to move quickly. From the outside of the car, everything looks smooth, however. How does interior violence become external elegance? As we did the last couple weeks, let’s load up Alex Czerny’s fast lap in iSpeed. This time, let’s add the second fastest lap of the season, Riku Alatalo’s 1:39.842. Time for a closer look at alien anatomy.

Braking

Both Alex and Riku have similar braking profiles. They hit the brake pedal hard and fast. The release is slow, however. I think I’ve talked about “hard on, soft off” nearly every post in this series. It’s that important! Next time you’re on track, try to spend a little mental energy to examine your brake release. Do you get to maximum brake pressure quickly? More importantly, do you snap off the brake pedal or ease off? Hopefully you’re running telemetry and can look at the traces when you get home.

Clutch

There is only one way aliens use the clutch: fast. Look at the traces below. The clutch pedal is in and out instantaneously. If you find that you’re easing out the clutch, it’s because you didn’t match revs. The fix is pretty simple: wait. As you approach the corner, apply the brake pedal only. Wait. Wait some more.  Step on the clutch right before the shift.

Gearbox

There really isn’t a slow vs. fast argument in using the gearbox. If you’re sprint racing, you shift as quickly as possible and don’t care about abuse. If you’re endurance racing, you shift gently to ensure longevity. What’s interesting in the trace below is that these two aliens don’t agree on the best gear choice. Alex shifts briefly into 5th before T2 and Riku shifts briefly into 3rd in T10. If you’re looking for those extra tenths on track, your gear choice is probably the last thing to optimize.

Throttle

In a low powered car like a Miata, the throttle can often be used as an on/off switch. Note how many of the traces look rectangular. However, this is not true in the middle of the corner where the drivers are balancing weight to optimize grip. It would also not be true on a wet track.

Steering

The thing that separates aliens from the rest of the pack is that they can drive on the ragged edge while under complete control. The initial turn in to a corner is pretty gentle. At this time, their foot is still on the brake. The combination of steering and braking causes the back to lose traction and start rotating. This is intentional oversteer whose role is to point the car towards the exit. The car is now exhibiting excess yaw, and unless something is done about this, the car will spin. That something is a steering correction, and it is very, very quick. In the image below, I’ve put red dots where the steering wheel is moved with great speed. After the correction, the steering becomes slow again (unless another correction is required).

Aliens make steering corrections all the time. If you overlay multiple laps from the same driver, you’ll find that not all corrections are in the exact same place or have the same magnitude. The ragged edge isn’t always repeatable.

Let’s take a look at a couple videos featuring fast and slow corrections. The first video features me driving my brother’s Miata. If the video doesn’t queue up to the right spot, go to 1:30. Or just keep watching. I make steering corrections in a lot of corners.

Here’s what happens when you don’t make fast corrections…

Slow vs. Fast

So let’s review which parts of driving are slow and which parts are fast.

  • Brakes on is fast (assuming you’re traveling in a straight line)
  • Brakes off is slow
  • Clutch in is fast
  • Clutch out is fast if you’re rev-matching
  • Clutch out is slow if you’re not rev-matching
  • Throttle off is fast (usually, but not mid-corner)
  • Throttle on is fast after mid-corner balancing
  • Steering in is initially slow
  • Steering correction is fast
  • Steering out is slow

Final Thoughts

If you want to be a faster driver, telemetry analysis is a really useful tool. While comparing your laps to each other is helpful, the most gains occur when you compare your laps to someone faster. The cheapest way to go down this path is with a simulation rig. The telemetry is already built into the software and you’re not going to do any permanent damage along your bumpy performance driving education journey.

Ghosting the Aliens: part 4, advanced techniques

If you’re joining this post in the middle of the series, go back a few weeks to the start and read those. There’s software and data to download.

When thinking of advanced driving techniques, two of the most common topics are rev matching and left-foot braking.

Rev Matching

The way iRacing models a manual transmission is somewhat of a joke. You can shift the car into gear seconds ahead of the shift and then quickly bounce the clutch to change gears. If you look at clutch traces, you’ll see that most upshifts are incredibly quick because of this. You can also choose to have iRacing blip the throttle for you on downshifts. Doing so gives a slight penalty to your lap times because there is a pause before the throttle is fully activated. Some drivers don’t cheat on downshifts and do their own rev matching. Let’s load up Andrew Barron’s 1:42.279 lap to see what that looks like.

In the figure above, I’ve got the brake pressure selected rather than the clutch. But what you see is incredibly ragged. If you cycle between clutch, brake, and throttle, you’ll find that his feet are pretty busy in this section. The reason that his brake trace has valleys in it is because he’s also using the clutch to slow himself down. Why? Partly because he stepped on the clutch too soon. If you do that, the revs start to fall and you’ll have to spin up the transmission again to match speeds. Gradually letting out the clutch is a sign that you didn’t match revs at all. Andrew’s lap time is actually pretty good compared to others we’ve looked at. That’s because he’s been a member of iRacing for 7 years. Unfortunately, he’s perfected a suboptimal way of driving.

LFB

There’s an old saying “in a spin, two feet in”. People who try to recover from spinning often end up crossing the track several times, taking out multiple nearby cars. The two feet in question are on the brake and the clutch. The clutch application is so you don’t stall the car when it comes to rest. This reminds me of my very first track day where I spun and stalled… Hey, we all start from somewhere, and I started at good old rock bottom.

But wait, there’s another kind of driving with two feet in. It’s called left-foot braking, which is often abbreviated LFB. It’s easy to determine if a driver brakes left-footed because the brake and throttle traces overlap for extended periods (not just when blip shifting). Most Formula 1 drivers brake with their left foot. Also lots of ass-idiots on US freeways. LFB is an advanced skill when done properly and a source of amusement when not.

Let’s load up Alex Czerny’s 1:39.681 into Lap 1 of iSpeedLapAnalyzer just like we did for the last few weeks and then add Alberto Moraes’ 1:47.265 into Lap 2.

The first thing you will notice is that Alberto’s speed trace shows really gradual deceleration in turn 1. This is highlighted in the image above. If you don’t look at the braking graph, you’ll assume it’s because he’s braking too softly, much like Bastian last week. But upon closer examination (click the brake tab) you’ll find that his initial brake pressure is actually higher than Alex. But he’s also got the throttle pedal on the floor at the same time! He eventually releases some left foot pressure but it’s synchronized with the right foot. Both feet in, both feet out. If you look across the whole lap, you’ll find that his foot is on the throttle to some degree pretty much all the time. This must be a carry-over from driving a single-speed go-kart where he’s trying to keep the revs in the power band. It has no place here. Common sources of track driving errors are skills learned elsewhere. Possibly the most insidious are street driving habits. But that’s a topic for another day.

More LFB

Now load up Joshua Homan’s 1:42.730. This is a pretty fast lap compared to the others we’ve been investigating.

If you look at the brake trace, you can see that Joshua has good technique. He hits the pedal hard and then modulates it as he steers into the corner. Switch from brake to throttle view in the highlighted region and you’ll see that he stabs the throttle a lot while braking. Not just here, but every corner. He’s late on throttle because he’s braking too late and trying to make up for it mid-corner.

As an aside, if you look at the throttle trace you’ll see that there are huge regular dips at the shift points. That’s because he’s using an automatic transmission. This slows the car a couple tenths over the entirety of the lap. It’s not a big deal until you’re trying to chase aliens.

Opinions

I don’t feel that strongly about rev matching. If you shift really late in a corner, it’s not really necessary. That said, I almost always rev match. And while I’m against using the clutch as a brake, there is one corner on one track where I do it to help rotate the car. In any case, if you’re going to rev match, learn to do it correctly. If you’re constantly feeding out the clutch gently, you’re driving poorly.

I don’t practice LFB ever. I do see the advantages though. Some of the fastest drivers set up their cars with extra rear brake bias. While a normal driver might find this hazardous, those who practice it can use the brake and throttle against each other to dynamically change the balance with great precision. Brake bias is something we normally set up in the paddock. If we’re lucky, we might have an adjustable bias control in the cockpit which we can change if it starts to rain. Advanced LFB-ers can change it mid-corner as they modulate brake and throttle. That’s pretty awesome. Having both feet on the pedals means there’s no delay between getting off the brake and on throttle. If you’re searching for every tenth of a second, there’s a good reason to learn to LFB. If you’re an endurance driver who cares a lot about wear on the car, there’s not much to gain.