Big Lies #6: aero doesn’t matter

This is post #6 in a series of articles about some of the biggest lies in high performance driving. In this post, I’m going to address one of my least favorite topics: aerodynamics.

Why I don’t talk about aero

If you are a long time reader of my blog, you know that my posts are mostly about safety, driving technique, sim racing, and data analysis. I sometimes talk about tires, rarely talk about brakes or suspension, and never talk about engine or aero. Why is that? Three reasons.

  1. I value the driver first, the interaction of the driver with the machine second, and the machine itself last. However, I think most driving enthusiasts have the opposite priorities. How many people spend $2k improving their cars? Lots. How many spend $2K on coaching or sim racing? Not many. I’m generally offended by car enthusiasts for that reason.
  2. This may be silly, but I don’t like the look of proper aero. I prefer the classic lines of the 1960s and such when aero was completely misunderstood.
  3. Honestly, the most important reason for not talking about aero is that I don’t know much about it. It’s difficult to measure without the right equipment. To become knowledgeable, I’d have to do a lot of reading. I am similarly willfully ignorant of engines.

Aero matters at all speeds

Let’s ignore my biases for the time being and actually talk about improving the vehicle. Specifically, let’s talk about aerodynamics. Put your hand outside your car window at speed and you can get a profound appreciation for how the shape of your hand affects its disposition. Some shapes cause lots of drag. Others produce lift or downforce. As you drive around a track, the path the air takes around your vehicle similarly affects its handling and performance.

If you want to make your car faster, the best investment you can make is grip. Grip determines your speed out of a corner, your initial speed down the straight, and how late you can brake. A well sorted aero package makes you faster because it increases grip. The faster you go, the more important aero is, but even at autocross speeds it can be the difference between winning and losing. If you want to see some hard numbers, I suggest you check out my brother’s blog, Occam’s Racer, which is a site that focuses on Miata aerodynamics. He has done the right experiments with the right equipment. Aerodynamics isn’t just a few tenths of a second, but whole seconds. There are several ways to buy whole seconds of speed like dropping in a more powerful engine or upgrading tires. A basic aero package isn’t very expensive and is a one time cost.

Components

Aero modifications fall into 3 categories

  1. Front
  2. Rear
  3. Underbody

One of the best things you can do to improve your aero is to install an air dam and splitter. Not only does this increase  downforce, it also reduces drag. So there’s really no reason not to have one.

The most common modification people make is to add a spoiler or wing. Both provide similar benefits. Most car shapes produce lift, and the faster the vehicle goes, the more lift is generated. Spoilers can negate this lift and wings can do one better and provide downforce. The combination of a splitter and wing is highly effective.

The underbody of a car is aerodynamically under-appreciated. If you’re going all-in, a flat bottom, side skirts, and diffuser should be part of your plan. Again, because they provide more grip. But stay away from vortex generators, which do nothing.

Results

Here are a few important results from Mario’s real world testing at Watkins Glen with thousands of dollars of sensors decorating his Miata.

  • Adding a 4″ splitter to an airdam reduces drag slightly, (.01 Cd) and adds a lot of downforce (.38 Cl).
  • If you race with an open top and a wing, it’s faster than an open top without a wing. However, an OEM hard top helps the wing generate 250% more downforce than an open top.
  • My fastback measured 17% less drag than an OEM hardtop. When used with a wing, the fastback generated 130% more rear downforce. In other words, the 60″ wing behaved as a 78″ wing, but without any more drag.
  • Don’t use vortex generators, particularly if you use a wing.
  • A cheap dual-element wing created a lot of drag, but also created a decent amount of downforce. Using one is faster than not using one.
  • The 9 Lives Racing single-element wing made less drag and more downforce than the cheap dual wing. By a lot.

Is aero worth the costs?

If your goal is to increase the speed at which you can lap a track, then aero is a worthwhile investment. It will make your car faster if installed properly. But aero isn’t free. It comes with costs:

  • Money – Modifying your car costs money, and good aero products cost more than cheap ones. An aluminum eBay wing with 2″ uprights doesn’t have the same value as a fiberglass wing with swan neck supports.
  • Weight – All aero adds weight to your car, and sometimes that weight is high up where you don’t want it.
  • Drag – Aero may increase or decrease drag depending on the component, but if you’re maximizing downforce you will increase drag. The benefits of downforce almost always outweigh drag.
  • Time – Aero adds an additional layer of tuning, which means addition time spent testing and tuning.
  • Parts – Aero adds parts to your car and parts have a way of breaking.

If I was building up a new car, would I add aero to it? That depends on what I was using it for. For daily driving with the occasional track or coaching day, probably not. Driving around with a splitter would be a nuisance. However, if I was building a car for competition, then yes, of course. Aero is a relatively inexpensive way to make a car go faster.

Wings on FWD cars?

Do wings make sense on FWD cars? Oddly, it turns out that they make a lot of sense. Maybe even more sense than RWD cars. FWD cars should be set up to turn via lift throttle oversteer. Having an unstable rear end makes FWD cars easier to drive in slow corners. However, an unstable rear end in a high speed corner is nerve-wracking and dangerous. So slap a wing on there. At low speeds it won’t affect handling much, but at high speeds it will pin the rear of the car down. I’ve experienced this firsthand in my Yaris. To my shock, even a cheap eBay wing makes a difference in high speed corners. The next developments for the Yaris will be a splitter and a proper wing.

Big Lies #5: the string analogy

This is post #5 in a series of articles about some of the biggest lies in high performance driving. In this post, I’m going to address one of the dumber teaching analogies.

The string analogy

Imagine a string connecting the bottom of your steering wheel to the throttle pedal. When you’re at full throttle with the wheel straight, the string is taught. If you turn the wheel, it will pull on the string, causing the throttle pedal to rise. In a very coarse-grained linear model, you have inputs something like this.

  • 100% throttle, 0% steering
  • 75% throttle, 25% steering
  • 50% throttle, 50% steering
  • 25% throttle, 75% steering
  • 0% throttle, 100% steering

So what’s the point of this analogy? I think the lesson is that drivers need to find a balance between throttle and steering. And that’s a good point, but it’s an over-simplification that ultimately misdirects attention that would be better spent elsewhere.

Alternatively

The reason people suck at racing isn’t because of the corner exit, it’s because of the corner entry. Instead of imagining the string being connected to the throttle pedal, what if we attached it to the brake pedal? As you turn into the corner, you simultaneously release the brake pedal. That’s a useful thought because one of the biggest mistakes intermediate drivers make is snapping off the brake pedal. Easing off the brake will keep the car from rocking, which will improve grip. Good. Having a mixture of steering and brake will help the car rotate. More good. But ultimately, this analogy is also flawed.

Timing

The problem with the string analogies is that they over-simplify driving mechanics. As Paul Gerrard says in Optimum Drive, competence lies in the subtleties, not generalities. You should start to release the brakes slightly before turning, not at the same time. And as the back end loses some grip and rotates, you may not need to increase steering at all. In fact, you may have to make a steering correction in the opposite direction to prevent spinning. You may also find a mid-corner stab helps if you entered just a little too slow or used up too much grip. On the way out of the corner, you should open the steering wheel a little before adding power, not at the same time. And in a momentum car, you can actually mash the throttle much of the time.

Mind and Body

A studious person might try to break down all of the little steps and memorize each stage. While that’s useful from a pedagogical perspective, it fails in practice. Knowing in your brain doesn’t equate to knowing in your body. Books don’t improve muscle memory. But practice does. However, practice refines your current technique whether it’s correct or not. So you also have to use your brain to figure out if your muscle memory is going down the optimal path or not.

How do you use your brain to figure out if you’re practicing correctly? Data. Examine the data of faster drivers and compare them to your own.

What if you don’t know how to analyze data? Get help in the form of a coach.

Where do you get data of racers driving the exact same car under the exact same conditions? Simulation of course.

How do you train your muscle memory? You can do it with a decent sim rig, which can be built for $1000-3000 depending on how you do it. Oh yeah, and a few hundred hours of deliberate practice with some coaching sprinkled in.

Big Lies #4: they’re just driving harder

This is post #4 in a series of articles about some of the biggest lies in high performance driving. In this post, I’m going to address one of the favorite excuses of the slower driver: “they’re just driving harder”.

Just

What does just mean in this context? That driving harder is a simple switch that can be turned on and off at will. It’s like saying “I could drive faster if I wanted, but I choose not to”. If you’re on a race track with the intent of driving fast, what would motivate someone to drive slower? Actually, there are legitimate reasons for driving at 7 tenths rather than 9 or 10.

  • Safety – As you drive closer and closer to the limit, danger increases. And by limit, I mean both the limit of the driver and the car. But it’s more about the limit of the driver. A driver who gets in over his head may wreck his car, someone else’s car, parts of the track, etc. All of these can add up to expensive expenses. Knowing your limit and the limit of your car will help you identify danger, and driving under that limit will keep more money in your pocket.
  • Consumables – Driving faster means using up more obvious consumables like tires, fuel, and brake pads. But all components on cars are wear items to some degree, and all get used up more quickly the faster one laps a track. In an endurance race, saving fuel, tire, and pad can mean the difference between winning and losing, or even finishing. At the Buttonwillow 24, we brought 2 sets of brake pads and the first set lasted only 8 hours. Driving the next 16 hours on one set of pads meant we had to completely change our driving style to save the pads. We ended up placing 3rd overall with less than 1 mm of pad.

Harder

The real problem with the phrase “they’re just driving harder” is that driving harder isn’t what makes one person faster than another. Speed comes from acuteness of perception, quickness of action, and precision of inputs. Fast drivers understand the subtleties of driving better than slow drivers. It’s been a while since I made a tennis analogy, but I think tennis will put this into perspective.

They’re beating me because they’re just hitting harder

If you have ever played tennis in your life, you know that hitting the ball harder isn’t going to win many matches. At nearly every level of play, the placement of the ball (in the court) is much more important than its speed. At higher levels, ball speed can become a weapon, but it takes a lot of skill to hit a ball hard and make sure it stays inside the lines. And so it is with driving. Driving faster requires skill earned from many hours of practice. It’s not a switch to turn on and off on a whim.

Just Harder

There is no just harder. Anyone using this phrase is protecting their ego with a misunderstanding of high performance driving. It’s like a double ended sword: they’re cutting themselves as they say it.

If you really want to show people how conscientiously you drive, prove it. Let your actions speak for themselves. Do one burner lap that shows what you’re capable of and then back off the rest of the day.

A walk on the mild side

If you’re one of those people who makes a conscious decision to optimize safety and wear, I applaud you. Not only that, but I’d be happy to have you race on my team. I don’t care about winning. So I don’t care about your lap time. I do care about maintenance and making sure everyone gets to drive. So drive under your limit, save the car, and don’t be a hazard. But you can probably find a space for a burner lap in there somewhere.

Big Lies #3: don’t coast

This is post #3 in a series of articles about some of the biggest lies in high performance driving. In this post, I’m going to address the myth that you should never coast on a race track. Another way of saying this is “you should always be on throttle or brake”.

Crabbing and coasting

There are two common behaviors you see in drivers who are early in their development: crabbing and coasting.

Crabbing is moving sideways on the way into a corner (like a crab). The driver sets up on the outside of the track, like they were told to by their coach (except me, see last article). But instead of turning in from the outside of the track, they start creeping in toward the middle of the track as they approach the braking zone. This decreases the radius of the corner for no good reasons. There are good reasons to set up mid-track, such as defending position, or driving a rain line, but crabbing is unintentionally throwing away speed or grip.

Lots of novices and low intermediates coast into brake zones. Instead of holding the throttle open all the way to the braking point, they let off the throttle and then coast a little before applying their brakes. Coasting a little before braking is a way to save tires and brakes when endurance racing. So it can be appropriate under specific circumstances. But during an HPDE session, there’s really no point.

Both crabbing and coasting are caused by a lack of confidence, or fear if you like. Both should go away in time as the driver gets used to the track and the car. That said, I’ve seen coaches who coast into brake zones (see the Cliff’s Notes post).

Coasting as an exercise

Two posts ago, I showed a speed trace of my brother doing a 3rd gear no brakes exercise. That’s a really great drill for several reasons.

  • You appreciate how much the car slows down from wind resistance. At 100 mph, taking your foot of the throttle makes a noticeable difference.
  • If you’re not allowed to use the brakes, you’ll naturally start to increase your entry speed. This is a good thing!
  • The more you do the drill, the better you will get at sensing your speed.
  • As you increase your entry speed, you’ll start to realize how much speed you scrub off by turning. This is especially true in slow corners because 3rd gear will be too tall and you’ll appreciate every mph lost.

As a training tool, intentional coasting is a great drill.

Always throttle or brake?

The problem with telling people they should always be on throttle or brake is that the phrase has no nuance. How much throttle? How much brake? Without knowing, I think drivers assume that means 100%. Why do I think this? Because most intermediate level drivers I coach alternately mash one pedal and then the other. But maximum speed requires maximum grip, and to attain maximum grip, you have to balance the vehicle. That happens at partial throttle and partial brake. And the utmost balancing happens between the two: i.e. coasting. In longer corners, there may be extended periods of partial pedal and in U-shaped corners where the 2 bends are are at an inconvenient distance, there may even be periods of coasting.

Being witty

With each one of these posts I’m trying to come up with a witty counter-phrase. The phases “never coast” and “always throttle or brake” just aren’t that catchy. Here’s my effort.

Coasting is like asymmetry: ugly when accidental, elegant when intended.

Big Lies #2: use the whole track

This is post #2 in a series of articles about some of the biggest lies in high performance driving. In this post, I’m going to address one of those things HPDE coaches say with a chuckle: “use the whole track, you paid for it”.

The whole track

What exactly do people/coaches mean when they say “use the whole track”? Certainly they don’t mean that you should zig-zag back and forth to make sure you tread all of it, but that’s the image in my mind when I hear it. Since I never say it, I’m going to suppose they mean to take an outside-inside-outside path through a corner. You know, set up on the outside, turn in and touch the apex, track out to the exit. That kind of path maximizes the radius through the corner and therefore maximizes your speed. That should minimize your lap times too, right? Not always.

Imagine you’re all alone on a 16 lane highway (8 each side) and you want to make a U-turn. Given that nobody else is around and you can take any path to make that turn, are you really going to set up on the outside, cross 8 lanes to hit the apex, and then cross another 8 lanes to track all the way to the exit? Legality aside, it’s actually not faster because you traverse way too much track. The racing line through a corner depends on the acceleration of the vehicle, the grip of the tires, the geometry of the corner, and the width of the road. When acceleration approaches grip, it’s better to drive the shortest path even in a 90 degree corner. At this point you should be saying “show me the data”. And I will, but in another post. For now, let me point out that in a 360 degree corner (a skid pad) the smallest radius is always the fastest way around. That’s because velocity increases with the square root of the corner radius but the circumference increases linearly.

Explore the space

I think “use the whole track” is actually a very advanced lesson, and not something you teach novices. In fact, I don’t want novices to use the whole track. I would prefer that they leave quite a bit of margin for error, especially on the exit. So I never say “use the whole track”. If you were my student, I would tell you to “explore the space“. By space I mean both the physical dimensions of the track and the limits of grip, but more grip than space. Feel what the car is telling you. Listen with both your hands and ears. Once you have the confidence to control a sliding car, then you can worry about minimizing your lap time by maximizing your speed through a corner. Until you can balance a car on the edge of traction, I don’t want you going anywhere near the edges. So drive harder closer to the middle of the track and get a feel for a car being driven aggressively. If you mess up, there’s plenty of space to recover.

Going faster

So let’s say you have decent car control and you want to go faster. Now you’re ready for the real lesson in using the whole track. You need to use all of the grip through all of the corner. The line isn’t an arc through a corner. It’s also got dimensions of grip and yaw along its length. Maximum grip is at a slight slip angle. Meaning you have to be slightly sliding through the entire corner. If you’re not sliding on the way into the corner, you entered too slowly. If you’re not sliding on the way out of the corner, you were late to throttle. If you’re not making subtle steering corrections, you aren’t getting enough oversteer. If you’re making big steering corrections, your technique lacks precision. If you find yourself spinning, you didn’t open up the steering wheel before adding throttle. If you find yourself running out of track at the exit, you need a later apex or more rotation. If your tires screech and then go quiet, you used too much grip at once. This is a lot to digest. Ultimately, it’s not about the track, but rather your ability to maximize the grip of the car along its entire path through the corner. In most corners, that will see you taking an outside-inside-outside path, but the exact geometry of the car on that path must also take into account the angle of the car at all points along the path: it’s not exactly parallel to the path at all times. “Use the whole track” is a heck of a lot more complex than it first appears and sends the wrong message to the student. Here’s my alternative.

Use the whole car, you paid for it

Big Lies #1: in slow, out fast

This is post #1 in a series of articles about some of the biggest lies in high performance driving. Where to start? How about the one you’ve heard 100 times: in slow, out fast.

So what’s the big lie exactly? That “in slow, out fast” is the proper way to drive a corner. Of course you have to slow down before a corner, but exactly how slow is slow? Given the way most HPDE drivers navigate a track, slow is way too fucking slow. The problem with the phrase is that it makes one think that mashing the brake and throttle is a fast way around a track.

As driving coaches, we say “in slow, out fast” for our own personal safety, not because we want the student to be fast. I don’t get paid enough to risk my life for a day of someone else’s thrills. You think I want to get into a 500 hp car with a novice behind the wheel? No, no I don’t. So me and every other coach says “in slow, out fast” and pray that we survive the day.

Hitchen’s Razor

I made this infographic/meme as part of my Pandemic Memes. On here you’ll find Hitchen’s Razor.

Next time someone says something provocative, ask them to show you the data. For example, let’s say you’re reading a blog about high performance driving and the author says “in slow, out fast is a big fat lie”. Ask the author to show you the data. Some statements may be made by experts with decades of experience. Other statements aren’t meant to inform you, but to con or troll you. Ask to see the data. Here, I’ll take the lead. “Hey Ian, if you’re going to say in slow, out fast is a big lie, why don’t you show some data?”

Data

In the following graph, you will see two speed traces. On the Y-axis is the speed of the vehicle. On the X-axis is the distance the vehicle has traveled. The graph is synchronized on distance so each point along the X-axis is the same part of the track. What do you notice here?

  • The driver on the blue line is going in slow and out fast
  • The driver on the red line appears to be afraid to brake
  • The minimum corner speeds of the red line are a little higher than the blue line
  • The maximum straight speeds of the blue line are much higher than the red line

So which driver is lapping faster? It turns out that they are only 0.183 seconds apart over a ~1.5 minute lap time. The driver on the red line (my twin brother Mario) was doing a 3rd-gear-no-brakes drill. Yes, that’s right, he wasn’t using his brakes at all. And yet he’s doing the same lap time as the driver furiously mashing pedals on the blue line. Looking at the graph, would you be able to predict this? Not unless you have some experience reading speed traces. The high speed differences look like a big deal. But it turns out that going slow for any length of time will really kill your lap time.

In fast, out slow

You know why nobody ever says “in fast, out slow”? Because it’s fucking terrible advice. It’s dangerous and slow. So by contrast, “in slow, out fast” must be great advice, right? Despite being catchy, and having some nicely contrasting words, no, it isn’t good advice if you want to improve as a driver.

Cornering faster

So what would I tell a student who wanted to improve and wasn’t threatening my life? It depends on the skill and experience of the driver.

For lower intermediate drivers, I would focus on minimum corner speed. Your minimum corner speed defines pretty much your entire cornering strategy. How slow do you plan on going and where exactly is that spot of minimum speed? I call the position of minimum speed the nadir. Everything before the nadir is slowing down and tightening. Everything after the nadir is speeding up and opening. In a typical corner, the nadir is before the apex. To summarize this in one punchy statement I offer this: don’t go any slower than the slowest point in the corner.

For higher intermediate drivers, I would focus on rotating the car. If the car isn’t slipping on the way into the corner you probably went in too slow. If you never have to make steering corrections, you’re not driving hard enough. And by hard I don’t mean hitting the brake pedal hard, but quite the opposite. Oversteer is generated with a soft brake pedal. A gradual release increases oversteer. To be clear, the oversteer you’re generating is on the way into the corner, not on the way out. Here’s my phrase to remember these things: slip not, win not.

Appendix

Here’s the graph with the time delta at the bottom. Remember, always demand the data.