The most important corner

Which is the most important corner on the track? Every track has one, and it’s not always obvious. YSAR reader Eric recently shared some AiM Solo data with me that got me thinking about this. The event was last month at Oregon Raceway Park in the Lucky Dog Racing League. While I’ve never been to ORP, I have driven it in simulation (rFactor2) and it’s at the top of my bucket list due to its mixture of elevation, camber, and corner geometries.

Take a look at the track map below and try to figure out which corner is the most important one. While ORP can be driven in either direction, let’s consider the clockwise direction, which follows the black turn numbers from 1 to 16.

The common logic is that the most important corner is the one that leads onto the longest straight. By that logic, T16 and T2 appear to be pretty important. What if I told you that it’s actually T4? Why is a slow corner followed by a short straight the most important corner? After T5, the track goes uphill and is basically straight until T7. So really, what we have here is that T5 is the critical corner that precedes a long straight. T5 is also complicated by having a slightly blind entry. But regardless of the particulars about T5, there’s no way to take it optimally without throwing away the exit of T4. Which makes T4 the most important corner on the track (clockwise anyway).

One of the reasons I was eager to look at the telemetry data was because the team had Randy Pobst drive one stint. I’ve never examined the data from a pro driver, so I was eager to see what he’s doing differently than us amateurs. The difference between Randy and the team hotshoe was about 1 second, and the specifics of those differences are mostly about backing up the corner, a topic mentioned on YSAR plenty of times. When you look at lap times that are 3-5 seconds off, it’s some mix of the following:

  • Mashing brakes
  • Mashing throttle (causes understeer and a lift at the exit)
  • Coasting into brake zones
  • Crabbing into an early apex
  • Sub-optimal line through compromises (the main topic of this post)

Randy is a professional driver, and I don’t expect anyone on my team to match his lap times. I’d be over the moon if someone was within 1 second. Heck, 3-5 seconds off is fast enough on my team.

Beyond Thompson

At the last Lemons race at Thompson, I only got in 6 laps of practice. However, the AiM Solo was running then and during the race, so I got to do a little comparative analysis afterwards. In the graph below, the red line is my fastest practice lap while the blue line is the fastest race lap on Sunday. Click on the image to open it up in a larger window and then write down at least 3 things you notice that’s different about the two traces.

  1. OK, so the most obvious thing is that the drive down the main straight was very different. I had an extra 200+ lbs of passenger and gear in the car and was driving in 4th gear. There may also have been traffic.
  2. The second thing you probably noticed was the very low speed in T2. I was experimenting with the brakes seeing how good they were, so my braking point was very late and this caused me to botch the corner. No big deal, this is what practice laps are for. I had never driven the car before and I needed to experiment. I tried different lines and gears nearly every lap.
  3. The thing I want you to notice next is that all the red lines are shifted left relative to the blue lines. The braking points are earlier and the acceleration points are earlier.
  4. Because my acceleration is earlier, I tend to have higher speeds on the way to the next corner.
  5. The most important area of the track is the 9-10 combination that sets up the main straight (6000-7000 ft). I take this as a single descending radius corner rather than two corners.
  6. While the 7-8 carousel (5000-5500 ft) isn’t nearly as important, I have a very different line compared to everyone else on the team (who all take a line similar to the blue one).

We could go through each corner talking about the trade-offs of taking different lines. But the differences in the red and blue lines aren’t really about Thompson. We can summarize all the specific differences with two general strategies, which I’ll describe below.

Backing up the corner

In point #3 above, I noted that my driving style involves braking earlier and accelerating earlier. This is called “backing up the corner”. The earlier you can get the car pointed to the exit, the earlier you can get to full throttle. Getting the car rotated early is usually accomplished by trail-braking deep into the corner so that the steering and braking inputs overlap quite a bit. This has the effect of swinging the rear of the car around, and you may have to make a steering correction to prevent the car from oversteering into a spin. There are risks involved when driving with this style. That said, no matter how hard I tried, I couldn’t get the car to rotate. It was set up with a lot of understeer. While I could get on throttle early, the car was leaned over quite a bit, and the open diff caused the inside front tire to search for traction. But even without getting the rotation I wanted, you can see from the telemetry graphs that there are gains to backing up the corner.

Connecting combinations

There’s only one combination corner at Thompson: 9-10. The blue driver “sees” this as 2 corners with a small straight between them. You can see this as the hump in the speed graph. The red driver (me) sees this as one long corner. Why? It’s the most important corner of the track and my goal is to optimize the position, angle, and speed of the nadir (slowest part of the corner). So I focus all my attention on getting to the nadir with the best combination of grip and speed that I can, which means throwing away the first corner. By slowing down early and keeping the suspension quiet, I optimize grip. If I speed up too much, or turn too much, I’ll upset the car and lose grip. This costs me some time at the start of the corner, which you can see at 6100 ft. But the investment pays off as from then on I’m gaining time.


Next time you’re on track, try making a conscious effort to get your shit (braking, turning) done earlier. Stop optimizing the straight you’re on and start optimizing the straight coming up. Also try to get your connected corners more connected. Think about how the first corner affects the second. Try some different lines to see what works and what doesn’t. Make sure to bring a data acquisition device. Not only will it help you sort things out later, it also makes the downtime between track sessions a lot more interesting.

Lemons Telemetry Analysis

After a race I like to look at telemetry. It shows what each driver is doing. It’s important to also run video so you can point at a corner that is 10 mph off and say “there was a yellow flag”. As usual, my telemetry is recorded with an AiM Solo DL and I view it with Race Studio Analysis. I’ve taken a screen shot of the fast laps of each driver (actually a pair of fast laps) with my fast lap as the reference lap (black line). The screen shows three graphs (1) GPS speed (2) engine RPM (3) time delta. Ideally, I’d love to have brake pressure and steering angle, but these are generally enough to infer what’s going on inside the cockpit.

One of the first things to note is that the blue driver’s RPMs are so much lower. The blue driver shifts well before he needs to. However, this doesn’t impact his speed or lap times very much. The red driver shifts much more often and is in 2nd gear several times, also not affecting lap times very much. When in doubt, drive the higher gear.

None of these laps were completely free of traffic. The red driver lost ~4 seconds in T3W to a yellow flag, for example. You can also find GPS errors where the speed is clearly recorded incorrectly for a brief time. That’s why it’s a good idea to examine multiple laps and have the corresponding video.

The biggest issue I find in the driving is that the green and red drivers slow down too early and too much in the faster corners. They do okay in the slow corners, and their final speeds may be as good as the reference lap. In slow, out fast, does actually lead to high speeds on straights! But in slow also leads to throwing away speed, and in a momentum car with very little engine, that’s a no-no. The better mantra is: in on the limit, out on the limit. That’s easy to say, but not easy to do.

Exiting a corner on the limit is like tightrope-walking; entering a corner on the limit like jumping onto a tightrope while blindfolded. — Mark Donohue

So how does one get better at jumping on a tightrope blindfolded? Do I really need to say it? Practice. And where does one practice such a dangerous activity? Do I really need to say it? Simulation.

Holiday shopping guide

Special mid-week post! Check back in a couple days when the Ghosting the Aliens series resumes.

Black Friday, Cyber Monday, and the holiday shopping season are upon us! Sadly, so is the annoying Christmas music. Some of the deals you can find at this time of year can be really great. For example, last year I bought a new gaming computer. Even though prices always drop on computer stuff, I still can’t find a better deal than what I got last year.

In my family, we have some unusual holiday gift giving practices. Of course we buy presents for each other, but we also buy presents for ourselves. We wrap these up and put them under our tree. Well, it’s not always much of a wrapping, often just the shipping box. And truthfully, it isn’t always a tree, sometimes just a decorated table with cookies. And we don’t necessarily open them on Christmas day. We like the French-style midnight opening and we like how Hanukah spreads out the gifts over several days. So we mix it up and open presents at odd times (breakfast on Saturday, dinner on Sunday, midnight on Monday, whatever). Anyway, part of the fun of the holiday season is opening presents and sharing that joy with others. Believe it or not, the gifts you buy yourself can be some of the most fun for the others to share. “Oh, I didn’t know you wanted that, how cool!” is a lot more genuine than “thanks for the socks” or “just what I wanted” (because I gave you explicit directions on what to buy 2 weeks ago). With that in mind, let’s imagine some gifts to improve the driving of someone you care about (even yourself).

Expensive Stuff

  • Simulation Rig – While it may seem expensive, the return on this investment is huge. High performance driving is like any other athletic endeavor. To get get good, you’ll have to spend hundreds of hours practicing. There’s no cheaper or safer way to put in that time than with virtual training. You can buy a complete gaming computer for under $600 if you shop around. But make sure the video card is has a Passmark score of at least 2,500 (an nVidia 1050 is good). For the steering wheel and pedals, the best place to start is a Logitech G29 (PC + PS4) or G920 (PC + Xbox). These list for $400 but you can find them at Newegg for $200. There are lots of 1080p monitors for $100. If you want a system that can do VR, expect to pay more than twice as much. For more info, see the Simulation link above.
  • Telemetry System – There are lots of choices for telemetry systems from manufacturers such as AiM, Motec, RaceLogic, and RacePak. One of the most popular is the AiM Solo DL. This is a great lap timer and data logger that also reads OBDII data from your vehicle. Works best with 2008+ vehicles with CAN bus. On modern sports cars you get to tap into thousands of dollars of sensors for free (e.g. steering angle, individual wheel speeds, brake pressure, throttle position, RPMs, etc.).
  • HANS Device– There are several head and neck restraint devices available today. Personally, I like Necksgen because the tethers also protect you from side impacts. The Rev2 Lite model is their latest and best design. Generally, HANS devices like these require that you have a roll cage/bar and harnesses. If you don’t, you might consider a Simpson Hybrid, which also attaches to your body.


  • APEX Pro – This is a slick lap timer and data logger with an attractive LED interface that shows how hard you’re driving (it’s some mixture of G-forces and yaw I think). It sends data to your phone. You can review with the data with their phone app or download the data to your Mac/PC and view with Track Attack.
  • Aim Solo – The standard in stand-alone lap GPS timers. Rugged design. The Aim Solo 2 now has a color interface but the original unit is still great. The software looks like it was built for Windows 98, but it works well and most of the bugs have been squashed over the years.
  • Yi 360 VR – The latest thing in cameras are those with dual 360 lenses. They capture everything from a single point of reference. After shooting, you decide which camera angles you want in order to produce a typical HD video. I don’t have one of these and I don’t know which one is best, but I like Yi cameras so I’m listing theirs.


  • Rumblestrip DLT1-GPS – It’s just a delta/predictive timer with big red 7 segment LEDs, but it’s also the best thing I ever bought for my car. I feel naked without it
  • Cordless Impact Wrench – Changing wheels at the track is so much faster with an impact wrench. Buy one of the major manufacturing brands so that your batteries interchange with lots of other tools. I’ve got drills, saws, work lights, vacuums, etc. that all power from the same batteries. The tool I use most is the impact.
  • Action Camera – You can learn a lot by watching yourself drive. There are lots of cameras and they keep getting better and cheaper. While GoPro is the standard everyone knows, I’m using Yi cameras for both live streaming and SD recording. In addition to the cameras, you will need a good mounting solution. I use RAM mounts everywhere.
  • Coolshirt – On a really hot day, a coolshirt is a safety item. They are a little over $100. The big ticket item is the cooler. Fortunately you can pick these up used on eBay or Craigslist as cold therapy systems for $50. They both have the same fittings. You just have to figure out how to mount it solidly. I use a lasagna tray and ratchet strap.


  • Joes Racing Pyrometer – The best way to record tire temperatures is with a needle-type pyrometer. The one made by Joes is both inexpensive and robust. It has a convenient 90 degree handle which makes it easier to fit under the wheel well.
  • Bluetooth GPS Receiver – Your phone can be used as a lap timer, but with 1 Hz GPS updates, it’s not accurate enough for comparing telemetry data between runs or between drivers. With a 10 Hz antenna, you’ll get acceptable performance.
  • Dash Cam – Instead of using an action camera, you might consider a dash camera. If used only in your car, you don’t need one with a durable case or big battery. It’s crazy how inexpensive these have become. For insurance purposes, or just to capture the crazy shit people do, you might consider running one all the time in your street car. Some of the high end models have GPS and G-force sensors. Prices vary from $30 to $200 depending on features.
  • iRacing – If you want to learn how to race and stay out of trouble, working your way out of the rookie ranks in iRacing is a valuable experience. Price is normally $12 per month, but with holiday pricing you can subscribe for a whole year for half that. The subscription comes with some great cars and tracks but you’ll probably want to buy a few more.
  • Brake Bias Adjuster – One of the cheapest and most educational performance modifications you can make for your car is to install a prop valve. They don’t cost much but installing could be expensive if you have someone else do it.


  • rFactor 2 – There’s a lot of people who think rFactor 2 has the most realistic physics. I think it depends on the car. But definitely, the physics are very good.
  • Assetto Corsa – If you want to drive obscure cars on obscure tracks, Assetto Corsa is the best simulator because of all the community created content. It’s also great for everything else.
  • Tire Pressure Gauge – Everyone needs a high quality tire pressure gauge. The simple analog ones from Joes Racing and Longacre are excellent.
  • Wide Angle Mirror – This is a great upgrade for your street or track car. The ones that clamp on top of your standard mirror work amazingly well. If your mirror wobbles too much with the extra weight, a little sugar water will make it stick in place.
  • Gear Bag – I recently started using the Harbor Freight Rolling Tool Bag as my travel bag. It’s so nice having a rolling bag in long airports. Turns out that it fits my helmet and race gear too. The design is more robust than typical luggage and the price is hard to beat.
  • Helmet Hook – Nothing says racecar quite like having a purpose built helmet hook mounted to the roll cage. It’s a bit of a frivolity, but that might make it the perfect little gift.


Check the Library link above for a list of books I’ve reviewed. The following three are highly recommended.

  • Going Faster! Mastering the Art of Race Driving  – Basically the textbook from the Skip Barber school. Nuff said
  • Ultimate Speed Secrets – It’s one of the best book on performance driving. I’ve read it cover to cover several times. Get the kindle version so you can read it wherever you are.
  • Optimum Drive – My latest favorite driving book and the best thing you can listen to while driving to work. That’s right, it’s available as an audio book.

Power, grip, and aero in theory

Six months ago I did some simulator tests where I used Assetto Corsa to answer questions about the relative contributions of power, grip, and drag. I wanted to follow that up a little with something a bit more rigorous. So I took my driving inconsistencies out of the equation and had the AI drive the car. I did a bunch of experiments on a lazy Sunday using the original rFactor. That was fun and informative, but I’m not reporting on that today because I decided to write a program that simulates a car driving around a track. Why? Well, honestly it’s because I wanted to implement the various equations myself. Most of the math is pretty easy in isolation. Equations for acceleration, lift, drag, etc. aren’t too complicated. Putting them together sometimes is though. For example, as you increase speed, you increase drag. So acceleration gets worse the faster you go.

The Model


The track is modeled as a series of alternating straights and corners. The simplest description would look something like this.


This means a 2000 foot straight followed by a 200 foot radius corner with a 60 degree arc. You can chain together any number of straights and corners to create whatever track you like. The sections don’t actually need to connect in a closed shape. I decided to use Thunderhill as that’s one of the most popular tracks in the region. I used Google satellite images and scale bar to rough out the track. It comes out as 2.94 miles, which is pretty close to the actual length. Note that my track model doesn’t take into account elevation or camber (yet).


Under the assumption that the driving line is circular, corner speed depends only on the radius of the corner and the grip of the tires. This is made a little complicated by aero modifications that increase grip and speed by adding downforce, but only a little. Because the corner speed is constant, it’s trivial to determine how much time was spent in the corner.


Straights are somewhat complex to model because the vehicle increases speed for some time, and then brakes to arrive at the correct speed for the next corner. This calculation depends on initial speed, engine power, gearing, aerodynamic drag, frontal area, and grip of the tires. A simple way of thinking about it is that the total time is the sum of the accelerating time plus the decelerating time. The way I solve it is by binary searching the transition from throttle to brake. At some number of seconds the distance covered and the final speed will be correct: it’s just a matter of making refined guesses.


Since Miata Is Always The Answer, I decided to do experiments with a virtual Miata. People sometimes say “the answer is always Miata” but that would spell out TAIAM, which doesn’t mean shit. Let’s give some parameters on the typical Miata that we will vary to see how the lap times change.

  • 2300 lbs with all fluids including the driver. We’ll strip some weight out of this to see what happens. We’ll also add a little.
  • 100 HP. My model assumes an engine of constant output. I don’t take into account the torque curve or gearing yet. It’s best to imagine “100” as a placeholder for both torque and horsepower, and the value of 100 is not a very healthy example of the breed.
  • 0.40 Coefficient of Drag. A hardtop Miata with windows down has a drag of something like 0.4. But topless it’s worse, and you could always add theme and make it terrible. For reference, a Prius is below 0.3 but it would be hard to get a Miata that low. However, a Prius has a larger frontal area.
  • 0.0 Coefficient of Lift. I abstract the various aero components into a single item rather than wing, splitter, diffuser, etc. A wing can be flat surface made from plywood with a CoL of 0.75  or something wing-shaped with a CoL of 1.0-1.6. The default value is 0.0 but a base Miata probably has some lift.
  • 0.0 sq-ft wing area. I’m not sure how to convert the various aero surfaces into wing area, but 0-12 feet in 4 foot increments seem like a reasonable range. The default value is 0.0.



It’s probably no surprise that more power reduces lap times. This is especially true if you have an anemic engine. Adding 20 HP sees lap times dropping by 3.08 sec. Another 20 HP is 2.57 sec. While there are diminishing returns, there are significant benefits to 200 HP and beyond. What’s amazing about engines is that you can realistically have them vary over a huge range. A turbo or supercharged Miata can make 300 HP. It might not make a good endurance racer at that point. However one of the most successful Lemons cars is the turbocharged Miata from Eyesore racing. In a race situation, high HP is doubly useful because it’s much easier and safer to pass under acceleration than braking or cornering.


The more corners a track has, the more grip becomes the key factor in performance. On a circular track, grip would be the only factor (assuming you have enough power to drive a given speed). Even a small change in grip can make a large difference in lap time. For example, a change from 1.00g to 1.05g drops lap time by 2.77 seconds. If you look at the telemetry of different drivers in the same car, you’ll see some people can extract more grip than others, and I think this is largely why some drivers are a couple seconds faster than others. In this model, an all season tire is about 0.90 grip. Summer tires 0.95, 200TW 1.0, Semi-slicks 1.1, Slicks 1.2. While these figures may not be correct, it’s the relative difference that’s important. If you want to win, get the grippiest tire allowed by the rules. The UTQG rating is only a rough indicator of the grip. In the crowded 200 treadwear class, I’ll bet there’s more than 0.05g of variation, especially when you consider differences in rim widths and tire pressures.


There are two components to aerodynamics, drag and lift (three if you count aesthetics). Drag has a relatively mild effect on lap times. Slipstreaming the heck out of it won’t see more than 1 second improvement. Similarly, ruining your CoD to a tune of 0.5 won’t see you slower by more than 1 second. Of course, every second counts, but this is the least useful area to tune. However, cosmetically, not much says racecar more than a wing.

Because lift affects grip, and grip is incredibly important, an aero package that increases downforce has a reasonable effect on lap time. Simply adding a wing could see your lap times dropping by 1.3 seconds (this is the Ideal 4 column below). There is some drag associated with wings, however, and on a track that is more straight than corner, a wing may do more harm than good. Note that a splitter can both decrease drag and increase downforce, so not all downforce increases drag. While you won’t see huge improvements in lap time from aero, it’s a one-time cost, unlike tires, and a well made aero package could see you dropping 1-2 seconds.


Removing 100 lbs will see lap times dropping by only about 0.6 sec. Weight reduction appears to have a relatively minor effect because it varies over such a restricted range. It’s a lot easier to improve your power:weight ratio by adding horsepower than removing pounds. So weight reduction might not seem like it’s worth doing, but it is. Out in the real world, the relationship between load and grip is sub-linear, so dropping weight is better than the model shows. There are also gains to be had in component longevity and fuel economy. The simple weight loss associated with angle grinders is relatively cheap, but when you start replacing structural parts with lightened versions it gets costly.

Some example builds

Let’s close this out with some example builds and lap times. Note that for a variety of reasons, the absolute lap times aren’t exactly as you would see at the track, but they aren’t very far off. It’s more important to think of the relative differences.

  • First day at the track – untuned engine (120 HP), all season tires (0.90g), open top (0.45 CoD, no downforce), and a coach in the right seat (2500 lbs) = 2:33.20
  • Solo – as above, but with Summer tires (0.95g) and no passenger (2300 lbs) = 2:28:91 (4.29 sec faster than above)
  • Sport build – engine is mildly tuned (130 HP), 200 TW tires (1.0g), hard top (0.40) and enough weight reduction to offset the top = 2:24.25 (4.66 sec faster than above)
  • Budget enduro – 100 lbs of weight reduction (2200), an additional 5 hp (135), DIY splitter and wing (0.35 CoD, 0.75 CoL, 8 sq-ft area) = 2:21.14 (3.11 sec faster than above)
  • TT build – as above, but using stickier, wider tires (1.05g) and professionally designed aero (CoL 1.3) = 2:17.36 (3.78 sec faster than above). Now I’m sure you’re wondering if it’s the tires or aero. It’s mostly tires (2:18.44 vs 2:20.09).
  • Eyesore – a famous Lemons car with a ghetto-charged motor that was dyno’d at 197 hp. It’s light (2200), has 200TW tires (1.0g), and theme for aero (0.45) = 2:17.29.

At some point I need to put this theory through some real life testing. I honestly can’t imagine anything more fun than going to a track day with 4 sets of tires, removable aero, and some ballast. It would be a long, hard day of work, but what a day. It costs $2200 to rent Thunderhill West for a 2-car test day. In the off-season, they sometimes cut that in half. I just need to find another car to share the session with and a crew to help out with the pit work.

Product Review: APEX Pro

TL;DR: Buggy software and difficult to use but with a simple change could replace RumbleStrip as the best delta timer.

Beautifully Designed

If you saw the video in the post last week, there was a curious device with blue and red LEDs on the dash. That’s an APEX Pro, and it’s one of the most interesting driving devices in recent history. The hardware itself is gorgeous. It’s a block of metal the size of a pack of gum with one button, one USB port, and 12 LEDs. It feels great in the hand and looks better in the car. There is a separate base that attaches to the car with an adhesive and the APEX Pro magnetically locks in place very securely. The internal battery lasts a couple hours, but you can also plug it in if you’re running endurance races, for example. The physical design is really appealing and I wouldn’t change a thing.


Phone Required, Desktop Supported

The APEX Pro requires a phone. That’s how you tell it what track you’re on. It has a huge track library but you can also define your own track. The phone software is pretty slick. It lets you export data, see who’s using the device at the moment, and let’s the team examine your laps from the inconvenience of their phones. I say inconvenient because looking at squiggly lines on a phone is tedious. The better way to review APEX Pro data is with a desktop app where you have a large monitor and a mouse. Although APEX Pro doesn’t come with its own desktop software, it imports into the Track Attack desktop app really easily, and Track Attack is pretty good.

Data Logger

As a data logger, it works well. It has high resolution GPS and a bunch of accelerometers. Other similar products include the AiM Solo and several phone-based apps like Harry’s Lap Timer, CMS Pro, Track Addict, and Track Attack. At $450, the APEX Pro is $50 more than an AiM Solo. But once you figure in a secure mount for the Solo, it’s not much different. The biggest difference is the display, which I’ll get to later. As a data logger, there’s not much difference between the two devices. But why fork over $400+ when you get the same functionality out of a $10 smartphone app? Because smartphones have lower quality sensors. If you decide to use your phone, you’ll need a very secure mount and a high resolution GPS antenna. This will set you back around $150. That’s a lot cheaper than an APEX Pro or AiM Solo and the quality will be acceptable. I prefer dedicated devices to phone apps, but I’ve also had good experiences with phones.

Apex Score

The sine qua non of the APEX Pro is its Apex Score. The brain of the device learns both you and the track while you drive it. After a couple laps it can tell you where you’re driving under the limit. The idea is that it’s like live coaching. A quick check of the LEDs tell you your current Apex Score. What exactly is Apex Score? Some combination of speed, G-forces, and yaw I suspect. Under the hood, the APEX Pro is doing some machine learning magic. Unfortunately, that magic is full of bugs. You can observe these bugs really easily. Just load up a couple of laps and overlay them. Turn on all the sensors so you can see their raw outputs. If you’ve been driving consistently, you’ll see consistent sensor values. But the Apex Score will be all over the place. Whole sectors of the track will differ in Apex Score from one lap to the next. It makes no fucking sense.

For racers who are driving close to the limit, the Apex Score is not something you’re trying to optimize. If two drivers have the same lap time, the one with the lower Apex Score is the one doing less work. They’re driving more efficiently, which pays off the longer the race goes. So novices will be interested in maximizing their Apex Score while racers will be trying to minimize it. That’s sort of confusing.

LED Display

The LED display is really cool. You can adjust the colors and brightness. Apart from looking totally amazing, it’s completely useless. The idea is that you can check your Apex Score at any time. But the only time it’s really safe to look at it is when you’re on a straight. You simply cannot look at it mid-corner. I’m a pretty advanced driver, and I had a hard time watching the thing. A novice who is struggling with finding the limit is going to be a hazard on track if he’s also trying to monitor his progress by watching LEDs.

So what happens when you look at it on a straight? It shows 4 green and 4 red lights. Let’s talk about what the lights mean. If there are 8 red lights, it means the total grip available is 8. As your performance increases, green lights will overwrite the red lights and you might see 6 greens. There are still 2 more greens to go if you push it harder. So what does 4 green 4 red mean on a straight? That I’m not pushing hard enough? Uh, the pedal is all the way on the floor. I literally can’t go any faster yet the Apex Pro thinks I can. But if I crest a hill and the car gets light (e.g. T7 at NYST last week) then all the lights go green because somehow the change in vertical acceleration indicates I’m at the limit. Bonkers.

Let’s sum up.

  • When you can look at the Apex Score (straights), it gives the wrong answer.
  • When you want to look at the Apex Score (corners) it’s not safe to do so, and if you did, the Apex Score might be wrong anyway due to software bugs.

Ultimate Lap Timer?

Data loggers are essential for reviewing your performance after the session. While you’re in the car, the most important tool is the delta timer, which lets you perform and analyze driving experiments every corner. It works like this: “I wonder if staying in 4th will be better than downshifting to 3rd?” Check timer before corner. Drive the corner. Check timer after the corner. “Hey, I dropped 2 tenths, that was better”. Note that I didn’t try to check the timer mid-corner. That’s dangerous. My favorite delta timer is the RumbleStrip DLT1-GPS. Why? Because of the big red LEDs. You see them instantaneously even on a sunny day. It’s so much easier to see than an LCD from a phone, tablet, or AiM Solo. You might think $300 is too much for something that doesn’t even log data. But it’s the best $300 I’ve spent on racing.

My RumbleStrip is such an important part of my driving that I literally feel naked without it. If you do a lot of sim racing, you probably feel the same way about your on-screen timer. iRacing has a particularly beautiful delta bar that shows how far off you are from your best lap and if you’re gaining or losing. It’s just a red/green bar on the screen, but it’s incredibly effective. The APEX Pro could be configured similarly with its LED strip. I understand that the underlying motivation behind the APEX Pro is the Apex Score. While that may be a useful tool for coaching novices and intermediates, it’s not what advanced drivers want. Give us the option of a race mode where the LEDs display a time delta. Give us the sexiest damn lap timer on the planet. And unlike my RumbleStrip, I’d get to review the data after the session. Yeah, that would make the APEX Pro worth every penny.

Coaching 86s

Normally, I coach for Hooked on Driving. I’ve also coached for a variety of other HPDE organizations, but not often. 2 weekends ago I did my first private coaching gig. I was asked by a driver who runs in the GT86 time trial series if I would be interested in doing some private coaching for some of the drivers in the series. I thought that sounded like fun and a good learning experience on both sides, so I agreed.

How much does one charge for such a thing? That’s a very good question! In my day job, I sometimes get honoraria for giving talks or reviewing grants. Those events might run $250-$1000 per day, and usually on the low side. If a company wants my services, I’d probably charge $250 per hour. But that’s my professional side. Performance driving is a hobby. So I decided that I would charge a hobby rate: $400 for the day for a group of 4.

So what does $100 get you? 2 sessions of me in the right seat, some chatting before and after each track session, and a group online telemetry analysis review a few days later (I brought my Aim Solo DL with me each session). Would I do this again? Sure, see my prices in the For Hire link at the top. You can also rent a car from me.

So let’s take a look at what one of the GT86 drivers learned. I’m particularly proud of what this driver was able to accomplish in one day.

The blue traces are a couple typical laps from his first session. The red traces are from his second session. I was in the car both times. Between those, he had one or two stints where he was working alone. The track is Thunderhill West. For some reason, Aim Solo thinks the start/finish line is on the straight between T2 and T3, so that’s where the left hand side of the graph begins.

The first thing to notice is that the red line is higher everywhere in the speed graph. He’s faster everywhere. Well except for 5900-6600 feet. We’ll get to that later. Let’s discuss the turns starting from the beginning (or rather T3).

  • T3 (500 ft) – There are 3 big changes here. The most obvious one is that his minimum corner speed is higher. Over the course of the day, he learned that he didn’t have to brake so much and therefore carry more speed through the entry. He also gained confidence in using the brake pedal to set speed rather than just scrub speed. This is why the shape of the curve is more U-shaped than V-shaped. He’s blending cornering and deceleration. Finally, the upward slope of the red line is higher, meaning he’s getting the throttle down more fully albeit slightly later.
  • T4 (1300 ft) – He brakes and accelerates at pretty much the same place, but he’s going much faster. This is mostly an improvement in confidence. An improvement in technique would also show him backing up the corner. Something to learn for next time.
  • T5 (1800 ft) –  The downward slope of the blue line shows that he used to brake for this corner. But now he just lifts off throttle a little.
  • T6 (2500-3200ft) – The red line starts to decelerate gently and then aggressively. He’s going very fast here and is a little worried about the upcoming corner. So unconsciously, he’s starting to lift before applying the brake. He could easily gain time simply by keeping his foot at 100% throttle. It’s fine with me that he doesn’t. If your self-preservation instincts kick in at the highest speed part of the track, I’m totally okay with it. The more important and impressive thing is that his minimum corner speed is 15 mph higher. Amazing!
  • T7 (4000 ft) – We didn’t really work on low speed corners, and you can see that there isn’t much difference in time from 4000-4500 ft.
  • T8 (4700 ft) – Confidence gets him accelerating over T8 rather than decelerating.
  • T9-T10 (5200-5900 ft) – Although we didn’t work on low speed corners, you can see that his minimum corner speed is higher. Not only that, but it’s happening later. He’s clearly trail-braking to make that happen. Now all he needs to do is move all that deceleration and rotation earlier in the corner. Sadly, it’s much easier to say than do, and he’ll be working on this skill for a long time.
  • T1 (6700-7400 ft) – The blue trace is actually higher than the red trace. Yes, he could go faster, but our attention was on how to drive T1 faster, not how to drag race down the main straight. Honestly, I would prefer if students never used 4th gear. Look what he does here. It’s smashing. He previously applied brakes, then accelerated, then braked again. The red trace shows him turning this complex of turns into a single turn.
  • T2 (8000 ft) – On the way into the carousel, he’s going so much faster that he bleeds a bit too much speed on the entry. Oh well, it’s an overall gain as shown by the time graph. Again, something to work on next time.

Wow, right? He gained 8-10 seconds over the course of the day. Partly it was increasing confidence, but there were changes in technique too. They go hand in hand. You can’t really trail-brake until you gain confidence. And once you gain confidence, it improves your trail-braking.

24 hour race prep: part 1

In just 4 weeks I’ll be in my first full 24 hour race. As car owner and team captain, there’s quite a bit to do to get ready. The next posts will describe all the prep going into the race. The car is my cute little B-Spec Yaris. There’s a lot of new stuff planned for this race including:

  • Radios – We often race without radios, but this time everyone will have them wired into their helmets.
  • Telemetry – I usually run a RumbleStrip and AiM Solo DL. This time I’ll be broadcasting telemetry from the car to the pit. The system also allows sending text messages from pit to driver, which may be useful if the radio system goes down.
  • Lights – The Yaris has stock headlights, but it’s not enough for a twisty race track with no lighting. In addition to extra headlights, it needs lighted numbers.
  • Camera – I hate changing cameras or cards and doing that at night will be doubly painful. So I’m building a set-n-forget camera that will run for 24 hours using components that cost under $100.
  • Transportation & Accommodation – The team needs an HQ to monitor the race and sleep when possible.

So last item first. The team will be staying in a rental RV. I went to and found that there are tons of RVs for rent near Buttonwillow. The owner lives maybe 15 miles away from the track. He’s going to drop it off on Friday and pick it up on Sunday. The all-inclusive price is just under $400, which is a bargain for the whole team. The RV will serve as team HQ during the race. It sleeps about 6 people, so there should be plenty of space to hang out, eat, or nap as necessary.

If that wasn’t enough, an RV that I had admired a few times at previous Lemons races became available when the owner decided to upgrade. The “Van Cave” as it was called, is kind of old (1991) and small (1-3 people) but well sorted. And it has both racing stripes and flames! How could I say no? So now I’ve got my own RV. It’s got a big 7.5L engine, so it doubles as the tow vehicle. I can’t wait to have all sorts of adventures in this thing, racing and otherwise.

Budget Racing Builds

Do you want to build a car for endurance series like the 24 Hours of Lemons, American Endurance Racing, ChumpCar World Series, Lucky Dog Racing League, or World Racing League? Here are my thoughts on that topic.

Cheap, fast, reliable: pick two

This post is about budget racing, so cheap is non-negotiable. Also, in my opinion, the whole point of racing is the driving. That means being on track, not running to the junk yard to find obscure parts. That means reliable is non-negotiable. The good news is there are lots of cheap and reliable cars out there.

BMW or Mazda?

When it comes to budget endurance racing, two brands stand out: BMW and Mazda. Popularity is a good thing. It means that maintenance, tuning, and repair expertise is near at hand and that spare part you need is probably already in the paddock. Mazda Miatas are the most popular track cars now, and have been for some time. They are robust and so light on consumables (fuel, tires, brake pads) that they are very cheap to run. In addition, they have the highest corner speed, which makes them incredibly fun to drive. Before the Miata was the de facto club racer, there was the RX-7, which is also a good choice.

BMW 3-series are rugged and handle extremely well. The BMW 325 in the e30 or e36 platform is a fantastic track car. Each one is almost as popular as the Miata, and e46s are also becoming very popular. Although less common, the 5-series cars also make great endurance racecars. The 2.5 liter inline six is plenty of motor. The 1.8 is very durable and burns very little gas, but few teams are able to make it competitive.

There are lots of other cars that make good endurance racers. Volvos are the most reliable in Lemons. Simple FWD cars like Civics and Escorts do well. If the car is light, which it should be to keep consumable costs down, you don’t need much power.

Build or Buy?

When sold, racecars return about $0.25 on the dollar. An inexpensive $10,000 build is only worth about $2,500. That’s bad news if you ever want to sell a car, but great news if you want to buy one. In order to be competitive in Spec Miata, you need a 1.8 liter engine these days. That means there are lots of 1.6 liter racecars available for cheap. You can also find RX-7s that were former SCCA/NASA racecars. Expect to pay more for an e30 (Spec E30) or e36 (Spec 3) racecar because they are (a) less common (b) more expensive to build (c) BMWs.

As you peruse Craigslist, RacingJunk, racing forums, classified ads, etc., you may come across some can’t miss deals. Some of these will see you spending more money than a Mazda or BMW in the long run, even if you picked it up for free. You know that car that you coveted in your youth? It will break your heart and your bank. Racing is hard on cars. Use your head, not your heart.

Mandatory Upgrades

If you decide to build a car, there are certain things you absolutely have to upgrade or at least replace.

  1. Brake pads. Stock brakes are generally fine but OEM pads are not meant for racing. Brake pads work in defined temperature ranges. OEM pads are designed for stopping you when the pads and rotors are cold. Race pads are for when the pads and rotors are hot. At a minimum, get a ceramic pad designed for autocross. But you really want a pad that was designed for full on racing. Replace all the rubber hoses and replace the fluid with something designed for racing.
  2. Suspension. Replacing tired/worn suspension isn’t necessarily going to make you that much faster, but it will prevent you from getting into some bad situations and help you drive out of those you do get into. It’s okay to have some body roll, but you don’t want the car bottoming out or wandering around on you.
  3. Oils. Replace fluids as often as you can. Frequently changing  engine, transmission, and differential oils prolong the life of those components, which means you’ll have fewer lost days at the track. In endurance races, cars go home early all the time due to failures in these components.
  4. Tires. The simplest way to improve the performance of your car is to upgrade the tires. There are a large number of 200-ish treadwear tires on the market. Some are stickier than others and those also tend to wear out the soonest. See the end of the post for more thoughts on tires.
  5. Fueling. Another really simple way to improve your performance is to spend less time in the pits. Remove the ball valve in the fuel filler neck and figure out how to safely empty a 5 gallon tank into your car in under 30 seconds. Fuel spills can take extra time to clean up, so make your fuel filling routine as foolproof as possible.


Every racecar needs at least one camera and some kind of telemetry device. Cameras are important for training and critical to untangle fault in an incident. Don’t go racing without a camera. It should be mounted to the roll bar with the driver in the field of view. Adjust the vertical position of the camera so that it also captures the rearview mirror. There are so many choices when it comes to cameras. You can go with the usual GoPro, but even dashcams are fine. I have a Mobius ActionCamera powered by a USB cable connected to the cigarette lighter. It shoots whenever the kill switch is on. It is set up to record in 1080p and lasts about 10.5 hours with a 64GB card. I also have a Tomtom Bandit for head-mounting and other uses.

To improve your driving, some kind of telemetry device is very helpful. There are two basic flavors: (1) immediate driver feedback (2) data loggers. Some devices do one, others do both. For driver feedback, I like the RumbleStrip DLT1-GPS. It shows your current speed and lap delta (difference between this lap and last lap at this position in the track). For data-logging, I use an Aim SoloDL. While the Aim also does predictive lap timing, I like the big red LEDs on the RumbleStrip. Smartphone apps can also be very useful. They have the ability to do feedback, data logging, and even video overlay. But the quality is usually a little less. An external GPS unit can improve things I hear, but I prefer dedicated devices.


Budget endurance racing series have converged on tires with 200 treadwear ratings (and some allow 180). There are a lot of tire choices. One of my favorites is the  Falken Azenis RT615K in 195/60/14. Yes, 14″. These routinely go on sale at Discount Tire Direct, and with free shipping and no tax, you can have them shipped to your door for about $85 per tire. They have good grip and are very durable. You can get about 25 hours of racing per set. If you have a Miata you may already have the 14×6 7-spoke rims that weigh less than 11 pounds. If not, you can pick them up cheap. BMW e30s came with 14×6 bottlecaps that weigh about 14 pounds. The nice thing about these rims and tires is that they are a breeze to mount with a $40 Harbor Freight manual tire changer. Wider tires with shorter sidewalls are a pain in the ass. The problem with 14″ rims is that there isn’t much choice for tires (there are Dunlops in 185/60/14, but they are much more expensive). Also, wider tires are faster.

Once you get to 15″ wheels, there are over a dozen that have 200-ish UTQG ratings. The sticky ones, like Bridgestone RE-71R, tend to wear out quickly. Although the treadwear rating is supposed to be indicative of how long they last (and therefore inversely proportional to grip) this number is controlled by the manufacturer (and their marketing department). Some 200-ish treadwear tires are more like 100 and some are more like 300.

  • BF Goodrich Rival – they are on the quiet side
  • BF Goodrich Rival S – never tried them, but they are often equated with RE-71R
  • Bridgestone RE-71R – fastest 200
  • Bridgestone RE-11A – middle of the road
  • Champiro SX2 – no idea, but some time trial folks win on them
  • Dunlop Star Spec II – most popular?
  • Falken RT615K+ – equally most popular?
  • Federal 595 RS-RR – cheapest and surprisingly good
  • Hankook R-S4 – liked the R-S3, and this is supposed to be better
  • Kumho V720 – seen bad stuff happen to these
  • Maxxis VR-1 – more PSI-sensitive than others I hear
  • Nitto NT-05 – lots of audible feedback, cheaper than most
  • Toyo R1R – supposed to be very soft, good for rain
  • Yokohama AD08R – also supposed to be a good rain tire

Obligatory Video

In the UK they race Jaguars as if they were crap cans…

Data Analysis: Thompson

Last week I wrote about the ChumpCar race at Thompson. This week I want to take a look at the telemetry we recorded with an Aim Solo. As a reminder, this is what the track looks like.

The first thing I want to explore was the difference between my practice and the race. My fastest race lap was more than 2 seconds faster than my practice. Why was that?

The top panel is speed. The next two are G-forces. The bottom is time difference. I don’t tend to find the G-force graphs very useful.The black line is the “reference” or fast lap. The red line is the practice lap.

If you look at the speed graph, you can see that I’m pretty much faster everywhere. I’m braking deeper into the corners, and I sometimes have lower speeds in the middle of the corner (actually slightly before the apex). I knew when I was driving my fast lap that I had pushed too hard at point A and was understeering badly. This turned out to cost me about a tenth, so it wasn’t that bad. In order to get into the 1:26s, I’ll have to find more speed. So let’s look at the other drivers to see what I can learn from them.

I brake later and carry that speed much farther into the corner. By the time I’m on the gas, I’ve gained over a second on the green and red drivers. But I’m much later getting on the gas, and that advantage starts to decay. If there was a long straight following T1/T2, they would catch and pass me. However, on this track, my strategy would allow me to pass them going into T1 and block them on the way to T3. I brake later and keep more speed through T3.

Despite my more aggressive driving style, I’m no faster than the blue driver, and the red driver has mostly caught me by the time we fully exit T4. At some point I’m going to gap them by 2 seconds, but it isn’t through these slow corners. T5 has a funny data error; ignore that. I brake much, much later in T5 and carry the same exit speed. So I put some distance between myself and the red/green drivers. But the blue driver has a similar line to mine and we’re still neck-n-neck as we head toward the bowl.

In T6, you can see that I have the lowest mid-corner speed. I took a lot of different lines through here and this one wasn’t that good! By the time we are running down the straight between T6 and T7, I’m not much ahead of the red or blue drivers. What happens next is critical.

The red and green drivers brake much earlier. They have a somewhat constant rate of deceleration all the way to T8 and then pick up throttle from there. Without a throttle or brake trace it’s hard to say if they are coasting, but my bet is that after some initial braking, they are scrubbing speed by coasting. Coasting is generally not the fast way around the track, but it does have its uses. In contrast, the blue and black drivers have a roller-coaster speed trace. They brake much later on the way to T7 and speed up between T7 and T8.

The blue driver is losing nearly 2 seconds by overspeeding between T7 and T8. He ends up turning T8 into a braking zone. His speed never recovers and he ends up with the slowest speed down the main straight. This is a Miata, not an M3. The throttle is a suggestion to go faster. You have to keep as much speed as possible, especially in the fast corners.

Thinking back to last week, I was really excited about this series of corners. It’s a Type II followed shortly after by a Type I. That is, you brake way late for T7 to keep as much speed as possible. Then you throw away the exit to set up for T8 with just enough speed that you’re full throttle from just before the apex until the end of the main straight. That’s what I did, and it’s 2 seconds faster than the other drivers. That said, even if the others had taken my same line, they are unnecessarily lifting or braking to set up T9. That section is really about confidence more than technique. They’ll get faster as they get more laps.

3rd Gear Experiment

Late in the day we started losing the clutch. So Mario decided to do an entire stint without using 2nd gear. The results are pretty surprising.

The black line is his reference lap (fastest 2nd gear lap). There are two 2nd gear corners: T1 and T4. Once you hit T5, it’s 3rd and 4th all the way. So let’s look at the time and speed through T4. Amazingly, the loss is only 0.2-0.3 sec. In T1, he consciously holds more speed in 3rd gear. While he doesn’t get as much drive leaving the corner, he loses no time to shifting. The net effect is that he has lost no time by the time he hits T3. He does lose a couple tenths in T4 though. It’s a really tight corner, and 2nd gear puts the power down much better than 3rd. But it’s just a couple tenths. OK, so I’m driving in 3rd next year, at least in T1.

GPS Alignment Issues?

One of the YSAR readers, Sten, who happens to be a data analysis professional, claims that “some of the data is definitely misaligned”. I admit that I suck at telemetry  analysis, so I followed up with him. Over email he further specified that it was impossible for the black and green lines to be accurate in T1 and T3, for example. Here’s an overlay showing the 5 fastest laps from the black and green drivers. They are fairly consistent.