Endurance tire testing: part 2

Before getting to the latest post, I want to remind people that there is a YSAR author contest with the top prize being a Rumblestrip DLT1-GPS lap timer. For details, click the Contest link at the top of the page.

Last week I blogged about how my brother and I tested a few tires to find out which one was the best. What exactly does best mean? Lap time certainly matters, but also consistency. We do endurance racing, not time trials. So our ideal tire is one that gives the driver the confidence to lap consistently fast. I’ll summarize Mario’s impressions from last time.

  • RS-4 is the best tire because it feels best and records fastest laps
  • RE-71R is a good tire, but hard to drive consistently fast
  • RT615K is a good rear tire, but it lacks grip and feel on the front
  • R1R is soft and feels weird

This week, let’s take a look at telemetry traces and see if we can get a little more resolution on the differences among the tires.

RS-4 (first run)

The two laps in the graph below have nearly identical lap times (1:37.4). But they are really very different laps. Looking at the time difference in the bottom pane, you can see that one lap gets ahead of the other by about 0.25 seconds. Then it loses all that time and ends up 0.12 seconds behind. While the fastest lap recorded was 1:37.4 it could very easily have been a high 1:36.

R1R

Here are 3 laps on the R1Rs in the same 0.2 second span (1:38.3 – 1:38.5). Again, while that sounds pretty consistent, it isn’t. Mario drives the first and second halves of the course very differently. The first half of Thunderhill West has more compromises and high speed corners. The second half features several hairpins. He drives the hairpins very consistently, but not the high speed corners. Why? Maybe he has better braking markers in the hairpins? In any case, when trying to figure out which tire is best, we have to take into account each corner, not the lap time.

RE71R

The 3 laps graphed are all 1:38.1X, so amazingly close together. I haven’t plotted the fastest lap here. Overall, the laps look more consistent than the R1R laps. Is that because the driver is getting more accustomed to the track or because the tires give better feedback?

RS4 (second run)

These 3 runs are within 0.1 seconds of each other. The fastest lap was not plotted. Overall, consistency is much better.

All runs combined

Overlaying all the runs, you can see just how much variation there is in first half of the track. Mario felt much more confident on RS4s, and this translates into braking much later. This produces a transient time gain that is partially lost by braking a little too deep. These are bumps in the time graph at the bottom relative to the fastest blue lap. The corner where RS4s appear to help the most is T6 through T7. Here, the blue lines pull away from the others (see bottom time lost). Once in the hairpins, RE71Rs appear to be just as good as RS4s despite having narrow tread and wheel widths.

Conclusions

So what did we learn? For one thing, laps that look the same from the perspective of a stop watch can be really different in detail. There’s too much variability in the first half of the lap to say much about the relative grip of the tires. We can say, however, that the feel of the tire matters very much to the driver. In the second half of the track, where comparisons are more robust, RE71Rs may be slightly better than RS4s. Despite having only one session on RE71Rs, he drove them at least as well as the RS4s.

Let’s finish this off with a few bullet points

  • Because feel is such an important characteristic, you really should try a few tires rather than settling on what is cheap or convenient.
  • It’s probably easier to fit tires to the driver rather than asking your driver to change their style to fit the tire.
  • Don’t rely on a stopwatch to tell you which tire is best.
  • Doing tire tests on a 5-run HPDE day with a driver who hasn’t driven the track in over a year isn’t going to get the most consistent data.
  • It was a great day of driving and data mining, and I can wholeheartedly recommend taking tires and timers to the race track.
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Endurance tire testing: part 1

Before getting to the post this week, I want to turn your attention to the 2018 YSAR Author Contest. Also linked in the menu above. Write an article for YSAR and you might win a great prize.

I had an MRI recently that shows I have a herniated disc. So my back problems are pretty fucking real as well as being debilitatingly painful. As such, I can’t do any performance driving for a while. Good thing I have a twin brother who can step in and drive for me. In this case, it was a tire test day at Thunderhill West (follow link for instructional video). The car was my Yaris in mostly B-Spec trim but I recently upgraded the calipers to increase the brake pad choices. The Yaris has such a huge cargo area that we were able to fit several tool kits, 2 people, and 6 tires inside even with a full cage. I also have a custom tire rack that fits on a mini hitch that increases its capacity to another 4 should the need arise.

Here is a brief list of the tires we were testing. A more thorough description is given below.

  • Falken RT615K+ 205/50/15
  • Bridgestone RE71R 205/50/15
  • Hankook RS4 225/45/15
  • Toyo R1R 225/45/15

Five 20-minute sessions isn’t an ideal way to test tires. There aren’t that many runs, the runs are a bit longer than necessary, and there isn’t enough time to make a tire change in the middle of a run with a pit crew composed of exactly one gimpy 51-year old (me). So how do we figure out which is the best tire when the test conditions are so volatile? We have 3 methods.

  1. Lap times
  2. Feel of the car from the driver’s perspective
  3. Telemetry analysis

In part 1 of this post we’ll look at lap times and how the tires feel from the perspective of the driver. Next week I’ll present the details and show why telemetry is so important. Now let’s hear from Mario, whose contributions are in blue text.

I tried to stick with a pace that I would do in an endurance race, and not to find faster lines or experiment with driving style too much. The point was to go for consistent laps, and measure all the tires on a level playing field. Naturally the air and track temperature changed throughout the day, and as this was a HPDE session, I had to throw away some good laps to manage traffic. Also, I don’t know the track that well, and so my driving was certainly going to improve throughout the day.

Let’s talk about the tires in the order they were run.

Falken RT615K+ 205/50/15 15×7

Fast 1:40.9, Median 1:41.6

Our team has used a lot of different performance tires over the years (Bridgestone RE11A, RE71R; Dunlop Z1, Z2; Falken RT615, RT615K, RT615K+; Federal 595 RSRR; Hankook RS3, RS4; Hoosier SM7; Toyo RR, RA1; Nitto NT01, NT05, Yokohama S.Drive). Historically, some version of Falken RT615K has been our go-to tire. The reason for this is that it strikes a nice balance in expense, life, and grip. It’s not the fastest tire, but it is one of the more durable in the 200TW category. Given that we’re more cheap than fast, we like Falkens. We almost always mount these on 15×7 rims even though 15×8 (or even 15×9) are supposed to be faster. Why? No good reason. Possibly because Spec Miata uses a 15×7.

I’ve heard that the RT615K+ is made in the same plant as the Dunlop Z3 Star Spec. The difference is the tread pattern. Falkens are typically $10 cheaper per tire. If they truly are the same thing, the choice comes down to camber wear. Dunlops have a symmetrical tread pattern, which means you can flip the tires on the rims, which may extend tread life quite a bit. If you read reviews on the RT615K+, people say they get greasy if you run them hard. That’s not a bad thing if you ask me. If you’re driving the limit, any tire will get greasy.

The tires we had for the test day were mounted on 15×7 Kosei K1 rims. They had seen quite a bit of track action, but only as rear tires on the Yaris. That means they were hardly worn at all. For the rears, we had a set of old RE71Rs (see below). Let’s hear what Mario has to say about the RT615K+..

I’ve driven the Falken Azenis 615K probably more often than any other tire, and they are the gold standard which I measure everything against. I hadn’t tried the 615K+ yet, so I was happy to go out on the Azenis first and see what all the plus was about.

My experience with them is that they warm up quickly, and usually the fastest lap is the second lap, but then they get a bit greasy when hot. Traction drops off a bit then, but stays at that level forever. And so they felt the same as always, with good audible feedback and a generous traction limit that doesn’t suddenly go away.

However, after trying the other tires, the gold standard is now the old standard. By comparison, the turn in was vague, and they simply don’t have as much stick. Perhaps on a 8” rim they would have worked better, but I doubt an inch of rim width was going to be the night-and-day difference I’d experience with the other tires. Later in the day we’d put these on the rear, and for that, they are my tire of choice.

Hankook RS4 225/45/15 15×8 (first run)

Fast 1:37.4, Median 1:38.4

The RSR has become one of the most popular endurance racing tires. One reason is that much of the competition has reengineered their tires for the larger autocross market where grip is more important than longevity. RS4s are a more traditional 200 TW tire that last a long time.

The tires used in the test were mounted on 15×8 TR C1 rims. The tires had been used in a previous Lemons race and had about half of their tread remaining. The rear tires were the same as the test above (old RE71R).

The second time I turned the wheel I knew I was on a totally different tire. I was initially a little bit nervous because the steering was so different than the Azenis, but the tires warmed up quickly, and I to them: super accurate turn in, great feedback, and you can hear them working. I put down a few consistent laps and was surprised to see they were over 3 seconds faster than the Azenis!

That’s pretty astounding considering these were back-to-back sessions an hour apart. The track and weather conditions were probably as similar as they were going to be, and I don’t think my driving line or technique changed much from the previous session.

The RS4s seemed to take a bit longer to come in than RT615K+, and were fastest on the 4th or 5th lap. After that they seemed to fall off about a quarter second.

Toyo R1R 225/45/15 15×9

Fast 1:38.3, Median 1:39.3

Originally a 140 TW tire, Toyo later rebranded the R1R as a 200 (probably to get more sales). Magazine tire reviews consistently report that the R1R is a pretty soft tire that wears quickly. It’s supposedly really good in the rain. It has one of the more interesting tread patterns. The brand new tires in the test were mounted on 15×9 Konig Dekagrams. Rear tires were as above.

I thought these were going to be the fastest, because they were the only ones on 9” rims, and they are basically rebadged 140 TW tires. But I just didn’t have much confidence under braking. They didn’t have as much audible feedback, and even through the wheel and pedals I never knew what they were doing. Any corner which required some initial braking cost me time, and while I thought these were the fastest tires around T2 (I could floor it all the way around), it was simply because I didn’t have the confidence to go through T1 faster. The run up to T7 requires the longest and hardest braking, and I felt like I was going to flat-spot them every time.

When we pulled the tires off, they looked totally different. The way the rubber was melting off the tire made them look like they were much softer than the other tires. I’d worry about the longevity of these in an endurance race. However, they were also brand new tires with full tread, and probably got the hottest because of that. I hear that R1Rs are good rain tires, and that’s probably where these will be used now.

Bridgestone RE71R 205/50/15 15×7

Fast 1:37.1, Median 1:38.2

The RE71R is well known as a cheater tire because it’s more like a 100TW than a 200TW in grip and longevity. I’ve heard some stories of them lasting only a few hours. My experience is that they are actually more durable than other tires on my Yaris. Despite its low power, my Yaris has caused blistering and chunking on most of the tires it has seen. It’s pretty frustrating to see a tire with very little wear except the shoulder has been completely chewed away. RE71Rs don’t do that because they can handle the heat.

We had planned to use these on 8” rims, but due to some fitment problems, we had to use the ones that we’d been using as rear tires, which were on 7” rims. That meant we had to move the Azenis to the rear, and so this wouldn’t be an apples-to-apples comparison with the other rubber.

But that turned out to be not such a bad thing, as the RE71R front and RT615K+ rear made a balanced combination with neutral handling. I was able to rotate the car much easier and play with balance more effectively.

As such, the RE71Rs set down the fastest time of the day (so far), but I didn’t feel they were as consistent. I felt like the one fast lap was an outlier, and that I couldn’t drive them that way lap after lap. These were also the oldest tires, and I’m not sure the effect of that.

Hankook RS4 225/45/15 15×8 (second run)

Fast 1:36.7, Median 1:37.3

We went back to RS4 front leaving the 615K+ on the rear, and again the handling was very neutral, similar to the RE71Rs. Taking some traction away from the rear definitely helps me.

Compared to the RE71R, the RS4s instilled more confidence, and this might be down to simply the sounds they make. A better driver might go fastest on the RE71R (or maybe even the R1Rs), but I felt better on the RS4s. And they were more fun.

So much so that on the last two laps I decided to screw consistency and up my pace. I immediately dropped half a second and did a 1:36.4. On my second flying lap I looked at the RumbleStrip and saw I had another .3 seconds in hand and thought I had a sub 36 lap in there… But they threw the checker on me in T8, and so I didn’t get a chance to find out.

Conclusions Part 1

Although we had come to the track to determine which tire was fastest, one of the most important lessons we learned was how much feedback is important to the driver. A simple tire swap can make a huge difference in the way a car feels and consequently what performance a driver can extract from a car.

Mario drove the RS4s faster and more consistently than any of the other tires. He also felt more confident with RT615Ks on the rear rather than the stickier RE71Rs. Moving forward, we’re now considering new combinations of tires. Perhaps 245 width RS4s in the front? Maybe something in 195 width for the rears? More tests will follow, but not until my back heals or my brother visits again.

Next week we’ll take a higher resolution look at the data using telemetry and see why you should always run telemetry.

It’s raining lies: part 3

Are we finally going to end the “It’s raining lies” series? Yes, yes we are.

Screamer vs. Big Bang

Before we begin, let’s take a brief tour through a seemingly unrelated topic in the motorcycle world: big bang vs. screamer engines. A big bang engine is one where all the pistons fire at the same time (or very close together). A screamer engine spaces out the ignition pulses as much as possible. From an engineering standpoint, it shouldn’t matter much, but the screamer is a little more powerful because it vibrates less. However, from the rider’s perspective, the firing order makes a big difference. Bikes with screamer engines tend to send their riders off the high side. How the heck does piston firing order affect the rider?

In a big bang configuration, the tire gets a big kick in the ass every 720 degrees of rotation. But it also gets a long rest period before the next kick. In a screamer, the tire is getting kicked every 180 degrees (assuming a 4 cylinder motor). Apparently the downtime in the big bang configuration gives the rider more time to sense the level of grip and adjust accordingly. In a word, the big bang gives compliance.

Softer Suspension

Before getting to the objective stuff, let’s be subjective and talk about how driving in the rain makes us feel.

  • How does a car feel on a wet track? Unpredictable.
  • What are we afraid of? Crashing the car.
  • How does that make you drive? With a large margin for error.

It’s fine if you don’t want to admit it, but I will. Racing in the rain scares me a little. The tires don’t make the same sound. The steering wheel doesn’t have the same tug. The throttle pedal feels like an on/off switch. When things go wrong, it seems they go wrong suddenly and without warning. That said, I actually really like driving in the rain. The extra stress makes it extra fun.

The reason why we soften the suspension in the rain is to slow down weight transfer. A car with a stiff suspension is sort of like a bike with screamer engine. It is theoretically the faster configuration. Stiff suspension leads to less weight transfer which leads to more grip. Lap times should be lower with stiffer suspensions. This is true regardless of the wetness of the track. However, there is also the human element to consider. The weight transfer in a car with stiff suspension is much more abrupt than a car with soft suspension. A human driver needs time to make adjustments to grip, and a suspension that is too stiff does not give the driver enough time to sense and react to changes in traction. So what are the physics underlying this phenomenon?

Basics of Friction

The coefficient of friction (CoF, or µ), is a ratio of the downward force of gravity divided by the frictional force. In the old days it was thought that you couldn’t get more than 1G of frictional force, and that the CoF was limited to 1.0 (this was due to blindly following Coulomb’s Law, which doesn’t really apply to viscoelastic compounds like rubber). Racing tires can generate over 1.0G, and much more with downforce.

Tire grip comes from the interaction of the rubber with the road. These interactions occur at a variety of scales from invisible molecules to stuff the size of tires themselves.

There are two separate properties that account for tire friction: adhesion and hysteresis.

  • Adhesion – Microscopic contacts between the tire and surface. This is also called mechanical keying.
  • Hysteresis – Macroscopic contacts that deform the rubber. The energy used to deform the rubber creates grip.

Adhesion and hysteresis sometimes compete with each other. As a tire gets hotter, it increases its adhesive properties but loses hysteresis. Adhesion likes a smooth surface while hysteresis likes a rough surface. The optimal operating temperature of a tire is therefore a complex function that depends on the properties of the rubber and both the microscopic and macroscopic texture of the surface.

To simplify matters, one usually talks about the optimal friction and relates this as the CoF. The CoF of a steel plate doesn’t change, so it’s a convenient simplification to think of the CoF as a single value. But the CoF of rubber actually changes and therefore can take a variety of values depending on the situation.

Load is sub-linear

It is well known that friction increases with load. But the grip of tires with respect to load is sub-linear. That is, if you increase the load on a tire by 2-fold, it gives less than 2-fold more grip. As a result, all things being equal, a lighter car will have higher corner speeds than a heavier car. One reason for this may be that there are physical limits to hysteresis. Colloquially, once a tire has been sufficiently mashed into a surface, it can’t be mashed any further.

Optimal slip

Whenever a tire is asked to do anything other than roll freely, it will have some slip. We’re not talking about slip angle here. Imagine braking instead. There is a continuum from freely rolling to fully locked. At 0% slip, the tire has a CoF of nearly zero (there is some rolling resistance). At 100% slip the tire is locked into some amount of grip, but that grip isn’t optimal. The peak friction occurs at a relatively mild amount of slip.

Speed affects grip

A tire that is moving across a surface a high speed cannot press into the surface as well as it can at low speed. This means that tires have less grip at higher speeds.

The optimal slip ratio also changes with speed. The faster you go, the lower the optimal slip ratio. We often think of the CoF as a fixed value, but it isn’t. Given that you have less grip and a lower optimal slip ratio, it’s not just self-preservation that should make you drive more reservedly at high speed.

Water affects grip

Water affects grip by getting between the tire and both the microtexture and macrotexture. It can therefore reduce adhesion and hysteresis. Grooves or other kinds of texture in both tire and surface can help evacuate water.

The amount of water on the surface is really critical. If the water film is thin, slick tires grip better than grooved tires. But if there is too much water to be evacuated by the macrotexture, the grip of a slick tire becomes terrible.

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Hydroplaning

Under certain conditions, a tire may hydroplane. In the figure below, the dashed line represents a constant CoF while the solid line represents a variable CoF. The actual stopping distances are given in the inset, which match the variable CoF. The take-home message here is that the grip of wet tires depends on speed. Presumably that’s because of hydroplaning.

Summary

Water interferes with microtexture and macrotexture. It can also cause hydroplaning. As a result, the coefficient of friction of a wet tire is anything but constant. A dry tire is easy to drive because it has a very broad band of traction in which the CoF doesn’t change much. You can over-drive the hell out of it and it will still perform okay. This is not true of a wet tire, whose CoF depends on the amount of water, the grooves in the tire, and the speed of the tire. Push a wet tire too far and suddenly, you’re spinning.

The reason why one softens the suspension in the rain is because the coefficient of friction of a wet tire is variable and volatile. By slowing down weight transfer, we give the driver time to adapt to an unpredictable CoF.

Let’s finish off this series of posts with a few key points about driving in the rain.

  • The reason why traction loss feels sudden in the rain is because it actually is. So be careful out there.
  • You may not notice much difference in braking in wet vs. dry but it is substantial.
  • Be extra careful at higher speeds where hysteresis and hydroplaning effects seek to rob you of traction.
  • When applying throttle, make sure you do so gradually because once a tire starts spinning, the loss of traction is catastrophic.
  • Grip in corners is pretty good as long as you don’t upset the traction with too much throttle, too much brake, or jerky inputs.
  • The more water there is, the bigger the tire grooves need to be. If you don’t have grooved tires, pump them up so they have a crowned profile. If you do have grooves, decrease tire pressure.

It’s raining lies: part 2

Where Were We Anyway?

If you recall, three weeks ago I did the following:

  • Called Ross Bentley a liar
  • Committed career suicide (see above)
  • Claimed that wet tires have 9/10 braking grip, 3/4 cornering grip, and 1/4 accelerating grip
  • Showed telemetry traces that support said claims
  • Calculated the G-forces in a Car and Driver tire test and found that braking loses much more grip than cornering
  • Lied that I would resolve the mystery the following week

In my defense, the series is called “it’s raining lies”. So let’s get back to our watery tale and see how this story resolves.

The Braking Mystery

Why do I feel like the car brakes equally well in the wet and dry when the data shows dry grip is so much better? I believe this is pretty simple. When the track is dry, we aren’t braking as hard as we could. Thinking back a couple weeks, let’s be Paul Gerrard and see if we can get to the root cause. It’s certainly not physics holding us back. Do we fear excessive Gs? Not exactly, what we fear is flat-spotting a tire. Our team races on a small budget and tires are the largest expense. Flat-spotting a tire is a huge no-no. Everyone on the team is acutely aware of that. Because we are afraid of destroying tires, we don’t brake as hard as we could.

If the car had ABS, we would probably brake harder in general because ABS prevents flat-spotting. Braking is so much easier with ABS: just mash the pedal and let the computer take over. Surely the Car and Driver tests were done with an ABS-equipped car. It makes the testing procedure much more repeatable if you minimize the human element. And why not use ABS? ABS systems probably brake better than you do. Nannies in cars are getting better and better. For most drivers, having various nannies on is faster and safer than driving fully analog.

Have you ever noticed that WWII fighter planes have wings that slope up and modern fighter jets have wings that are straight out or even slope down?

A dihedral wing, one where the wing tips are higher than roots, is inherently stable. But an anhedral wing is not. Build a paper airplane with an anhedral wing and it will flip over and fly as a dihedral. It’s very difficult to fly a plane with an anhedral wing angle. Human pilots can’t do it. There isn’t enough compliance. They need a fly by wire system that makes hundreds of tiny adjustments per second to keep the plane flying level. So why have anhedral wings? Because the inherent instability makes the plane want to turn, making it more agile. Could cars be tuned the same way, so twitchy that no human could drive one without nannies? Surely. The evolution of performance driving will someday see computers outperforming humans at every level of the sport. When that happens we’ll become even better drivers as we learn from computers whose AI can explore the parameter space more deeply than we can.

Let’s return from my crystal ball and recap: we under-brake in the dry because we are afraid of flat-spotting our tires. I’m happy to make this compromise for 3 reasons.

  1. A flat-spotted tire is a waste of money
  2. A tire that fails on track could cause a crash
  3. Time spent fixing things in the pits is time not lapping

Brake Bias

When tuning a car for driving in the rain, one parameter that is often changed is the brake bias. Since there is less overall weight transfer on a wet track, there’s less weight on the front wheels. With more weight on the rears, more braking is possible out back. In my old E30, I installed a manually operated prop valve. To adjust the bias, you lift the hood and twist a dial. Real race cars put the bias adjuster in the cockpit so the driver can make changes mid-race. Until you’ve tried an adjustable prop valve, you probably haven’t experienced how much it changes the handling of your car on corner entries. If you don’t trail-brake, you won’t notice much at all, but if you do, it’s basically an oversteer tuning dial. Want more oversteer? Add more rear brake. It’s really that simple. If you don’t have a prop valve, you can still tune your brake bias with different pad compounds, but the resolution is much lower.

The main problem with adjustable bias is forgetting to dial it back when the track dries. This can lead to disaster. The rears will lock up first, causing the back of the car to wander when braking in a straight line. This can even happen on a wet track if the brakes are horribly out of proportion. Early ABS systems were kind of crappy and just kept the rears from locking up. If you’ve got such a system and the ABS computer is defeated or the fuse is blown, the bias is dangerously out of whack. Watch below as the fast POV is destroyed by a slow BMW that loses control while braking in a straight line.

How did the BMW team not realize their brakes were so horrible? Probably because they usually brake very gently. The rain moved the lock-up G-force threshold lower and the driver found himself in unfamiliar territory. How do you mitigate this? That’s a very good question. On the one hand, you can tune the brakes appropriately with a prop valve, pad compounds, or ABS. That fixes the problem with the car. But there’s another problem, which is how to fix the driver. Should the car be good enough that the driver doesn’t matter? Or is it the responsibility of a driver to work around problems with the vehicle. Probably a little of both don’t you think?

So how do you get practice driving a car with horrible brake bias? How do you get experience with locked up rear tires? If you want to train yourself for disasters, you have to put yourself in disastrous situations… without wrecking other peoples’ property, your car, or your body. The answer, which you can guess if follow this blog, is simulation. Not every car has adjustable bias even in a sim. Find one that does and then experiment with brake bias. Once you experience how useful and fun it is to tune your corner entry oversteer, you may want to install a prop valve in your race car. It takes all of 30 minutes and costs less than $100.

There’s still more to come in the “it’s raining lies” series. We still haven’t discussed why you soften the suspension in the rain. Check back next week for the resolution (or possibly more lies).

Pineview Run, Optimum Drive, and S.Drives

Emergency. We interrupt our series in progress for an important and timely message on performance driving. This guest post comes from my twin brother Mario. Incidentally, if you have content you want to contribute to YSAR, I’d love to post it.

This last Sunday, Pineview Run held its first annual Pineview Challenge Cup, a time trial “race” of sorts. After an initial practice and qualifying session, you got three runs. Each run consisted of a warm up lap, and three timed laps. Trophies and $500 membership vouchers awarded for fastest times and most consistent laps.

For sure my 1.6 Miata on 195 S.Drives were not in contention for fastest laps. Here’s me lining up behind a McLaren 570. There were other fast cars: a Viper, Lotus Exige, M3, 911, etc., and all of them were on wider and stickier tires.

You’ll notice the RumbleStrip lap timer in the photo. Both of us absolutely love this thing. It’s the single best car thing I’ve ever purchased.

So I wasn’t going to be fastest, but I thought I had a shot at putting in the most consistent laps. Until a funny thing happened: I started driving better and better. I’ve been listening to the audio book Optimum Drive, and through some coincidence I had a moment of what the author calls driving greatness. Or what others have called being “in the zone”. In my terms, I started driving the Miata like a go-kart.

And that’s a good thing because I’m decent in a go-kart. Maybe it’s the lower speeds or simpler interface, but I can “zero steer” a kart and eke out more performance than most. In fact, after trouncing too many friends, Ian had a standing offer to pay for anyone’s track time if they beat me. He didn’t lose any money, but I also never translated that kart skill to car driving.

At least not until the Pineview Challenge Cup. Something clicked and I kept getting faster and faster. I enjoyed this so much that I stopped trying to put in consistent laps, and just explored the space, going faster, with less effort, lap after lap.

The less effort part was interesting. On corner entry I’d let off the throttle to shift the weight forward, turn the wheel slightly to tip the nose in, scrub off speed with the sides of my tires, and let the chassis come around on its own. Then I’d get on the gas and spin the rears to finish turning the back around. In all, I did very little steering with the wheel, and most of it with weight balance and throttle control. Some of you reading this might be good at that already, but I’d only done that in karts.

In three short sessions I knocked almost 3 seconds off my time, which is pretty incredible. To put this in perspective, the first time Ian and I went to Pineview, my best time was a 1:27 flat and Ian did a 26.5. I only did 5 laps total that day, but I thought I was doing OK. However, this time I put down an early 24.5, and in the last session I saw a 23.0 in disbelief. But my final lap was a 1:21.7! The kart nirvana I’d experienced finally made its way into my driving game. Man that was fun.

Now I’ve gone on talking about go-karts and Pineview at the same time, and I’ll never do that again. Anyone who says Pineview Run is a big go-kart track is just plain wrong. I’ve been on big go-kart tracks, like Dixon, Wenatchee, Stockton, etc, and Pineview simply isn’t one. There’s a lot of elevation and I think anything but a shifter kart would chuff annoyingly up the hills.  

Neither is Pineview a short race track. I raced Thompson last year, and did a HPDE at Waterford Hills this year, and while they have similar lap times to Pineview Run, they are meant for racing, with long straights and not many compromise corners. Comparatively, those tracks are tame. Boring, even.

Pineview Run run is a workout. It’s a rollercoaster. It’s a training and skills track. A test track. Pineview Run is also a great equalizer. The top cars on this day were a very modified BRZ and a M3, both driven extremely well. But there were a lot of fast cars, all of them so different, it really came down to the driver.

Well, ahem, unless you’re in a stock-ish Miata on 195 Yokohama S.Drives. At 300 treadwear and 10/32″ tread, they aren’t designed for the track. However, they are perfectly matched to my Miata’s 106 whp, and while I would have gone faster on stickier rubber, I wouldn’t have had as much fun. I ordered the S.Drives online at Walmart, and with free shipping and mounting, I was out the door for $200 for all four tires. Hard to beat that on a smiles-per-dollar ratio.

One final word about Pineview Run that Ian didn’t mention in his initial review, which is that it’s not just a car track. Pineview Run is also a shooting, hunting, ATV, snowmobile, horseback riding, and family-oriented outdoor country club. I’d never heard of a country club without a golf course or tennis court, but there you have it. And while I’m not into horses (yet), the rest of it was designed for people exactly like me. It’s an hour drive away on scenic back roads. Of course I joined.

We now return you to our previously scheduled programming (check back next week where we pick up the “It’s raining lies” series).

Book Review: Optimum Drive

Emergency, we interrupt the “It’s raining lies” series for an important service announcement. I just read a really great book.

Amazon had suggested this book to me several times. I was initially turned off by the cover, which looks like it came from a Tron movie poster. The title, : “Optimum Drive: The Road Map to Driving Greatness”, sounds a bit too much like an advertisement. Looking beyond the cover, we get to these summary sentences.

  • Optimum Drive is the complete step-by-step guide to maximizing human performance in any endeavor you choose to conquer
  • Optimum Drive is a motivational book that uses top level race car driving as a metaphor for peak performance.

Is this or is this not a book on driving? If it’s a book on driving, I’m interested. Self-help? Not so much. That said, “The Inner Game of Tennis”, by Timmothy Gallwey, has become a must-read in performance psychology. On the surface, it sounds like Optimum is trying to be the auto racing equivalent. The Inner Game is fantastic book, but I don’t recall there was that much Tennis. It’s not going to teach how to hit a topspin second serve, for example, which is the most crucial stroke in the game.

So let’s turn a few pages to see what’s inside Optimum Drive. I love audiobooks. I listen to them while working out, doing chores around the house, working on the racecars, and commuting. I even had this crazy idea of doing a Lemons theme with the Yaris (it has a complete sound system) where racers listen to an audiobook while driving and then give a quick synopsis while the next driver was getting in. Anyway, I didn’t actually turn any pages of Optimum Drive, but rather listened to it. As audiobooks go, it’s not very long: 3.5 hours. At first I didn’t love the narrator, but he grew on me and by the end I thought he was a great match for the content.

So is Optimum Drive another Inner Game? Yes and no. Yes, it is another performance psychology book that talks about flow psychology. That’s the modern term for getting in the zone. But overlap isn’t necessarily a bad thing. Even if the content was largely the same, it’s often very useful to have domain-specific books because the examples are more relevant. I see this all the time when teaching Biology students how to program. It’s much harder to learn fundamental principles of computer science when the exercises are things you don’t care about. But let’s be clear here, Optimum Drive is more than just a flow psychology book, it’s a damn good driving book. It teaches you the topspin second serve of driving. Will it transcend autosport and become as important as The Inner Game? I suppose it could, but tennis is more approachable. Anyone can pick up a tennis racquet but not everyone gets to drive a racecar. Should you get it? Absolutely. Here’s the brief 5-star review I wrote on Amazon.

I have a pretty large library of racing books. I’ve even written one of my own called “You Suck at Racing: a crash course for the novice driver”. I’d be flattered if you picked up my book but this book is better than mine. Read it, unlearn your bad habits and start from the root cause. This applies to all things, but very much so to driving where there’s so much misinformation and years of coping mechanisms.

Let’s look at one very specific example of the author’s way of thinking. Suppose you’re coaching a driver who is looking no farther down the track than the hood of his car. Saying “eyes up” or “look farther down the track” doesn’t really help the driver. The problem isn’t where his vision is. It’s that he is so concerned with what the car is doing this instant that he can’t plan for the future. The root cause is that he doesn’t have the car control skills to let his subconscious drive. The fix in this specific case is to slow down so the driver has more time. In order to solve problems, you need to get to the root of the problem. If you don’t, you’ll just lay some coping mechanisms on top that will prevent you from actually improving. And then later when you want to get better, you’ll have to break down these walls, which is a waste of time and will see you getting worse before getting better.

There are similarities between Paul Gerrard’s Optimum Drive and Carroll Smiths Drive to Win. They both have a bluntly honest writing style. However Gerrard would never say “other sports beckon”. He feels like anyone can attain greatness. Personally, I don’t need to be great and I have no aspirations of racing professionally. As a hobby racer, I don’t need to be an A+ driver. I tell my son that the best grade to get is A-. Above that you have diminishing returns that prevent you from learning more stuff. Why get an A+ in one class when with the same effort you can get an A- in two? Anyway, the parts of Optimum Drive that are out of my direct interests were still really fun to listen to. It’s great hearing what it’s like in the pro ranks even though I’ll never be there.

So what is the topspin second serve of driving? He calls it zerosteer. The driver who turns less wins. How can you get around a racetrack using less steering than the other guy? By driving with the correct amount of yaw. You can’t ask your front tires to do all the work because racing really comes down to tire management. Yes, you can progress up the tennis ladder hitting flat serves. But if your second serve is a patty cake, it puts a lot of stress on your return game. So you focus on your ground strokes because you like them more and they win you more games. That’s basically where B level tennis ends. Once in the A group, you have to win your serve and pressure your opponent’s.

Fucking tennis digressions… back to driving. Until you have the confidence to let your muscle memory drive a sliding car, you will enter corners too slow and with too little yaw. The entry determines everything about a corner. Unfortunately, most drivers have coping mechanisms between themselves and driving with enough yaw. Getting the car to step out a little isn’t something you do with the throttle. That’s too late. It has to be under braking. Zerosteer starts with trail-braking. I’ve talked a lot about trail-braking on this blog. I believe it’s the single most important skill in racing. It’s so nice to have that opinion validated.

Gerrard also talks about how to set up a car. Every tuning adjustment is a compromise. Making a car faster in one corner may make it slower in another. The job of the driver is to enjoy the corners where the car is set up perfectly and to earn his paycheck where it’s not. The setup used for qualifying is not the same as racing. In qualifying and time trials you are looking for the fastest single lap. But racing requires the driver to make constant changes throughout the race, and it’s the average lap time that matters more than the best. The word he uses to describe this is compliance. A setup that makes a car mathematically ideal may not work in practice because there is too little compliance for the human operator to work with. The struggle between engineers and drivers is finding the proper compliance.

If I have one criticism of Optimum Drive it’s that Gerrard only briefly talks about the importance of simulation training. At the very end he mentions that the top drivers spend more time in simulation than in real cars. Skid pads are his favorite tool for beginners. I also love them. But a sim rig is a lot more convenient, and in my experience it’s 90% as good as the real thing. If you have a chance to get on a skid pad, do it! Whatever your training plan is, you have to put in the hours. This is what he calls process. One reason I don’t like autocross is that there isn’t enough time spent driving. It can be a great reward for training, but it’s not training unless you can do it for hours upon hours. Musicians practice scales endlessly. Why should driving be any different? What you do on the street has almost zero overlap with what you do on track, so street hours don’t count. There are no shortcuts in the process. You have to put in the hours. Sometimes it may feel like Hell. You know what the trick is when going through Hell? Don’t stop, keep going.

After posting this, the author contacted me and told me that the ‘Tron’ car on the cover was his actual car, which took 2nd place at Pike’s Peak in the unlimited class. It’s unfortunately illegal to run anywhere else. I find it both humorous and humbling that I have written a review of his book and that he has talked to me about his car. More on the car: 7000 lbs of downforce at 12,000 ft, 5G cornering and braking, and 1.8G accelerating in 4th gear. The reason it looks like a spaceship is because it actually is one.

It’s raining lies: part 1

This week I attended a Ross Bentley webinar titled “The Art and Science of Racing in the Rain”. He runs webinars several times per year with a cost somewhere in the $50-100 range. Is it worth it? Yes, I think it is. If you’re serious about racing and improving your lap times, $59 is one of the cheaper expenditures you’ll have. Looking back, I’ve attended a bunch of his webinars: Speed Secrets, Tires, Drive Faster, Reading Your Car, Chalk Talk, and now Rain. That may be all of them. I’ll be the first to admit it, I’m a huge Ross Bentley admirer. But I’m also here to tell you he lies. OK, so that’s maybe too strong a statement. It would be more accurate to say his theory is sometimes incorrect. But this is YSAR and we write provocative shit here, so yeah, Ross Bentley is a goddamn liar.

Before some other Ross Bentley fanboi punches me in the face, let me explain (yes, I said other and I’m a little worried about hitting myself in the face as I write this). I don’t dispute Ross’ advice on driving in the rain. I’m going to do exactly what he says. What exactly did he say? Well, you have attend the webinar for that. I’m not about to pirate his content. But I will reference the parts that need critique.

In the rain, soften the suspension to decrease weight transfer.

— Ross Bentley

Softening the suspension does not decrease weight transfer. The more the vehicle pitches to the side, the more weight is transferred because the center of gravity moves more. One of the attendees wrote the equation for that in the chat box and it stopped all chat for a while. Nobody wrote “Ross, you’re full of shit” because we all respect Ross too much. But let’s be clear, softer means more weight transfer, not less. It is true that in the rain there is less weight transfer compared to dry, but that’s because the corner speeds are lower, not because the suspension is softer. So why, I ask you, should one ever soften the suspension? You’ll have to wait for that answer…

In the rain, lateral grip is affected more than longitudinal grip.

— Ross Bentley

This is not my experience. I find that braking works nearly as well in the wet as the dry. I use pretty much the same braking markers. Now it’s true that my straight speed is slightly lower in the rain, and pick up a later apex, but the grip is still darn good. Don’t take my word for it, or anyone’s word for it. Look at the data. In the image below, the blue line is dry and the black line is wet. The downward slope of the lines in the braking zones are nearly identical. The longitudinal G-forces in the 2nd panel show that peak Gs are similar, as you would expect.

Have you ever stepped on the throttle a little too eagerly in the rain? The car spins around without giving any warning. The grip under braking and accelerating are totally different in the rain. Note that this is from my experience driving high performance street tires not F1 racing tires. Since I’ll bet that you’re racing on tires sort of like mine, I think the difference between braking and accelerating grip is a very important distinction. My experience with corner grip is that it’s not as bad as you might think. The graph above backs that up. If I was going to put some subjective numbers on comparative grip levels in wet vs dry, I’d say braking has 9/10 grip, cornering is 3/4, and accelerating is 1/4. Although Ross didn’t put such numbers on these, he ranks them as braking > accelerating > cornering. So who is right? Turns out we’re both wrong.

Back in 2012, Car and Driver did a really nice comparison of 9 performance tires. For example, on the Bridgestone tire, the skid pad grip was 0.89G in the dry and 0.83G in the wet. That doesn’t sound like a very large change in grip level. They also reported 50-0 mph braking distance as 80 feet dry and 101 feet wet. Putting those distances in terms of Gs, that’s 1.04G dry and 0.83 wet. There are actually two lies we need to debunk here. The first one is that cornering grip is more adversely affected than braking. It isn’t. In terms of Gs, 0.06 is smaller than 0.21 by a metric shitload. To put this in terms that you might appreciate more, you can go 75.7 mph around a 200 ft radius circle at 0.89G. At 0.95G (plus 0.06) you get 78.2 mph. Racers would throw loved ones under a us for a 2.5 mph corner speed advantage. At 1.2G (plus 0.21) speed is 87.9 mph. I don’t think I have the macabre imagination required to describe what a racer would do to get a 12 mph advantage.

WHAT THE FUCK IS GOING ON HERE? This doesn’t mesh at all with my driving experience, the data above, or Ross’ instruction. Corner grip is less affected than braking? It’s true. It’s right there in the numbers. So why do we feel like it is less? And why do the telemetry traces tell a different story? Sorry, but you’ll have to check back next week for those answers.

What’s the other lie? It concerns the friction circle. The way the friction circle is explained, your tires have a certain amount of grip and you can divvy that up between lateral and longitudinal axes. So you could go 50/50 or 90/10 or 100/0. But it’s not symmetric, and therefore not a circle. Tires actually have more grip under braking than cornering. In the example above, 1.04G braking and 0.89 cornering. Circle shmircle. What’s one more drop in a bucket of lies?

Check back if you want to see how this mystery resolves…