Telemetry: trail-braking

I’m relatively new to telemetry analysis, but I thought I’d share some of my experiences. The product I use is an Aim SoloDL. The companion software is called Race Studio Analysis. I don’t really like the software, but it’s better than several competing products. Rather than show you traces from my real racecar, I thought it might be more useful to use a simulator. That way you can call me names after you beat my lap times.

The simulator we’ll use for this is Assetto Corsa. Earlier this year, I posted on the state of the art in racing sims, and if you want to see a comparison of what’s out there, check that out. AC is one of the better sims, and possibly the best place to start. I’m using the Brands Hatch Indy track and the NA Miata. Just to get lap times out of the way, I usually lap in the 1:03-1:04 range. I’m sure someone who is more familiar with AC and Brands can take a couple seconds off that.

The point of this post today is to look at what trail-braking looks like from a squiggly line perspective. Trail-braking is a term that gets thrown around as an advanced cornering technique. It’s actually pretty simple: gradually release the brakes as you turn into a corner. This is in contrast to the more basic technique of separating pedal input from steering input. The reason it’s an advanced technique is that the rear of the car gets light under braking. So if you turn with the brakes on, the rear can rotate around and cause a spin. So why do it? I think most people will tell you that it’s because it saves a few tenths here and there. But the reason I do it is because I like getting tactile feedback from the steering wheel under braking. It helps me judge my corner entry speed.

So let’s say you just ran a few laps in Assetto Corsa. How do you get this into Race Studio Analysis? It turns out to be super simple. You’ll find the telemetry file in your Documents folder (open the Assetto Corsa folder there and then the aim folder inside that – there’s only one file ever in there). Race Studio Analysis can import this file. I don’t have enough time in this blog post to show you how to configure RSA, so let’s skip to the view of squiggly lines. I want to draw your attention to the parts marked A, B, and C.

The point marked A is Turn 1, which is a tricky downhill right-hander. The top row is speed, and you can see that the blue line has much more speed through corner, but the black line later catches up. That difference turned out to be 0.5 sec (bottom row). Look at the 3rd row (brake pressure). Do you see how the black line is on then off whereas the blue line tapers off? That little bit of braking while turning (4th row) is the sign of trail-braking. The 0.5 sec difference is more than usual, and had I carried more speed on the black line, the difference would have been half that.

Point B is more interesting, and you should look for it in the video below at about 1:53. The car is mostly straight as it goes through the apex. Do you see the dip in the steering angle of the blue line? With more weight on the front tires, you can turn more. What’s really important is the recovery after that. The car is steered in more aggressively while braking, and then counter-steered as the throttle is applied. The car on the black line can’t rotate as fast and can’t get to throttle as quickly. The result is about 0.4 sec. Point C is similar to B in that the car is at full throttle sooner because the car gets rotated earlier.

The cumulative effect of trail-braking a few corners turned out to be about 1.4 seconds. That’s probably a little bit of an exaggeration because I don’t normally separate my inputs, so it felt a little odd to me. But certainly there’s 0.5 seconds in the technique even on a very short track. More importantly, I think trail-braking makes you feel more connected to the car, and for me, that’s where the enjoyment is.

On Radios…

In my experience, radio communication can be a real pain. The pain comes from three principle sources: (1) the radios themselves (2) the wiring harness (3) noise at the track. I don’t claim to be an expert in solving radio problems, but I can hopefully provide some useful information.

The first question to ask yourself is if you really need radio communication. I’ve run plenty of events without radios, so my answer would be no. If you know you don’t have radios, you make plans to communicate from track to driver (usually with signs) and driver to track (with some kind of hand signal). The pit has to be a lot more attentive without radios. As soon as you put a radio in the car, everyone is a bit more relaxed. But that’s not always a good thing. If the radio goes out, it can mean you’re even less prepared than you would have been if you never plugged them in. So even if you run radios, you have to have a backup plan. That said, you probably won’t and when that comes back to bite you, there’s a preemptive “I told you so” that will fall from the recesses of your memory.

So once you decide to get radios, which one should you get? There’s more than one competing technology. Some teams are using phone apps to do voice messaging, but that requires the track to have decent cell coverage, which isn’t always a given. Radios will still work though. Among radios, a critical choice is which radio frequency you want to use. Each has its advantages and disadvantages. CB radios have respectable range on a flat highway despite their low power, but the lack of channels and really long antennas makes them impractical on a race track.

Enter the grown-up walkie-talkie. These operate on the FRS, GMRS, or MURS bands (and possibly more depending on the radio). Let’s review the various bands you’re legally allowed to use (in the USA).

FRS: The Family Radio Service band is composed of 22 channels in the 462 and 467 MHz range. This is designed for backpackers and similar activities. Depending on the channel, you’re allowed to transmit at 0.5 to 1.0 watts without a license. While it seems like 22 channels isn’t a lot, you can also include a privacy tone that squelches anything else that doesn’t include the privacy tone. It’s not true privacy. It’s not encrypting your message. It’s more like a filter that removes everyone else and lets you listen to just who you want to listen to. There are dozens of privacy tones, so it’s highly unlikely you will overlap with users outside your group.

GMRS: The General Mobile Radio Service band is composed of 15 bands in the 462 MHz spectrum. The channels completely overlap FRS channels 1-7 and 15-22. GMRS radios are allowed to transmit at 5W, but you need a license for that. The current cost is $90 for 5 years, but there are recommendations for removing the licensing fee altogether.

MURS: The Multi-Use Radio Service band has a longer wavelength (151 MHz) than the FRS/GMRS. MURS limits you to 2W for transmission. There are only 5 MURS channels, but the dozens of privacy codes means it’s unlikely you will collide with another user. There is no license required for MURS operation.

Baofeng UV-5R

One of the most popular grown-up walkie-talkies is the Baofeng UV-5R. These are about $25 and can operate on the FRS, GMRS, and MURS frequencies. They can also operate (legally or illegally) on many other frequencies. Want to become a HAM radio operator? You can do that with a UV-5R.

Out of the box, the UV-5R is not set up for frequencies you want to use. You can manually tune them, but it’s much more convenient for users to page through the channels with frequencies and privacy codes already set. To do that, you have to program the radio. That sounds like a daunting task, but it’s really just filling out a spreadsheet. There are lots of programming resources out there already. Here’s a good one. You’ll need a serial cable for the radio-to-computer connection and the CHIRP software (Mac, Windows, Linux friendly). Make sure that the serial cable comes from Baofeng and not some cheap knock-off.

I set up my radios with 5 MURS and 5 GMRS bands, each with its own privacy code. The MURS bands are set to 2W and the GMRS are 5W because that’s what the law says. But like everything else in racing, someones always breaking the rules.

Wiring

I’ve had more problems with wiring than radios. Rather than buying the wrong stuff, I recommend having Troy Hogan at Nerdie Racing set you up. It’s better to pay for expert customer service than to buy the wrong thing several times.

Noise

Noise on pit lane can be pretty loud, and can easily interfere with voice communication. You’ll probably want a headset with around-the-ear insulation. I don’t have a product recommendation here, and if you do, please leave a comment.

Product Review: Thrustmaster TS-PC Racer

I recently upgraded my steering wheel from a Logitech Driving Force GT to a Thrustmaster TS-PC Racer. The DFGT was sold as a wheel + pedals package for about $150 while the TS-PC Racer wheel is $500 by itself. So the question I’m sure you’re asking is if the difference is worth $350. Yes, but no. Read on for what the means.

There are basically 4 kinds of force-feedback (FFB) steering wheels on the market today.

  1. Low-end crap that costs less than $150. Stay away.
  2. Logitech. The current versions are the G29 and G920, which replaced the G27, G25, and DFGT. These use helical gears and costs about $300 including pedals. These are robust wheels and finding a used one cheap is a great place to start.
  3. Thrustmaster & Fanatec make belt-driven wheels. They are quieter and more powerful. They also feature removable wheels, so you can switch from GT to Formula style. Prices are $300-600.
  4. Direct-drive wheels. These are not mass-market items and have a price tag to match ($1500-3000).

Logitech has been making very good wheels since the G25. Anything older than the G25 isn’t worth using. Whether you’re talking about the G25, DFGT, G27, G29, or 920, they are all very similar. The FFB is good and the wheels last a long time. I was very happy with the G25 and DFGT I had, but I wanted to try a better wheel, which means a belt-driven Thrustmaster or Fanatec. While I love sim racing, and find it a valuable learning tool, I can’t justify $1500+ for a direct drive wheel. Heck, I’m having a hard time justifying a $500 wheel. So what does $500 get you?

One way to compare wheels is by the torque of their motors. Logitech wheels are around 2.5 nM. The Fanatec CSW has about twice that: 4.8 nM. The TS-PC Racer is about 6 nM. Direct drive can be 10-15 nM. More torque means a greater dynamic range for FFB effects, which translates to a more realistic feel. It also means you can run a larger, heavier, and more authentic wheel.

The TS-PC Racer is a Formula style wheel but my real cars have circular wheels. Does that matter? If you leave your hands at 9-n-3 where they’re supposed to be, it doesn’t matter what shape the wheel is. That is unless you’re drifting or rallying where you sometimes need to rotate the wheel more than 270°. I do a little DiRT driving, so I may want to pick up a circular wheel at some point. Changing wheels on Thrustmaster products takes about 1 minute, so it’s no big deal. But it does add another $150 to the cost…

One of the immediate differences between the TS-PC Racer and the DFGT it replaced was the sound. The DFGT was much louder. And the G25 before that was louder still. Does the external sound make a difference when you’re wearing headphones? No. But reduced noise may make other people in the house less irritated.

While driving, I noticed some important differences. The TS-PC Racer transmits more subtleties in the track surface. Every bump is more bumpy. The wheel is noticeably faster too, which makes oversteer recovery more natural. But are those things worth $350 or whatever? That depends on how much spare cash you have lying around. I learned a heck of a lot about driving using Logitech wheels and have no problem recommending them to anyone as a first wheel. They also come with pedals, so the price is a real bargain. The TS-PC Racer is a better wheel though, and now that I’ve used one, it would be hard to go back. I bettered several of my best segment times within the first hour of switching wheels. While lap times are not the reason I am sim racing (I do it for training rather than competition), if that’s something you care about, higher end wheels may drop your lap times.

Since YSAR usually has a video, I’ll drop a short highlight from last weekend at WGI. At the start of the clip below, I’m sliding through the inner loop on brakes. This is one of those cases where simulation training really helped out. If I brake too late, as happened here, I can keep the steering alive by modulating brake pressure while threshold braking. I’ve done it so many times in simulation, that it’s second nature on the track. Not long ago, I would have locked up the brakes, flat-spotted the tires, and understeered someplace I didn’t want to be.

Bucket List: WGI

I just came back from an endurance race at Watkins Glen International, which represents one of my bucket list tracks. Why is WGI a bucket-lister? Partly because of its historical significance, partly because I grew up about 25 miles away, and partly because I’ve spent quite a bit of time there in the virtual world in iRacing. So what else is on my bucket list? Hmm, let’s rephrase that as “what are my 10 favorite tracks?” and we’ll see how many remain on the bucket list.

  1. Thunderhill. I feel blessed that this gem is just 80 miles away. Thunderhill is really two completely different tracks that can be glued together to make a 5 mile track. The original East side has great flow, especially from T1-T6. The West side is highly technical with lots of compromises and off-camber turns. I think of the West track as my home track, and I would drive it above any other track.
  2. Brands Hatch. Whenever I try out a new car or track on a simulator, I always load up Brands Hatch Indy first. It has a a great mixture of challenging corners in a compact layout. This is #1 on the bucket list.
  3. Mid-Ohio. The rollercoaster ride from 4 to start-finish is the perfect mixture of corners and elevation changes. Recently, a couple endurance racing organizations have started to race there, so I hope I’ll be able to check off #2 on the bucket list soon.
  4. Sonoma Raceway. I’m new enough to car racing that I don’t feel allegiance to the Sears Point name, but I know many people who feel otherwise. This track is only 50 miles from my house and I get goosebumps every time I approach it on Route 37. The climb from T1 to T3a is my favorite stretch of 4 corners anywhere.
  5. Mosport. What an amazing mixture of technical and gut-wrenching corners. It just flows through the hills like chocolate on ice cream (ok, so I don’t like either one of those things, but most people do, so I make that analogy for your benefit). It’s close enough to my brother’s home that I hope to get there soon. That’s #3 on the bucket list.
  6. Barber Motorsports Park. There is no part of this track that isn’t fun. You get just enough time to catch your breath before another combination of corners has you grinning and sweating again. Bucket list #4.
  7. Road Atlanta. This place has a lot of history and some amazing corners. I love everything before the back straight and everything after it. Bucket list #5.
  8. Virginia International Raceway. I can’t decide what configuration I would want to run first. The North side has Hog Pen but the South side has a great run through the interior. I’m not a fan of long straights, so the main track has less appeal, but of course I want to drive that too! Bucket list #6.
  9. Laguna Seca. Even though it’s just 2.5 hours from my house, I rarely drive this track because Sonoma and Thunderhill are closer and more fun. Although the Corkscrew is the most famous part of this track, it’s not as challenging as what comes after. The weather in Monterey is beautiful most of the time, and a great place to visit even if you’re not racing.
  10. Watkins Glen International. Located in a quaint and hilly part of upstate NY, Watkins Glen is steeped in history from the original races through the village streets to the annual NASCAR race. In a slow car, like a Miata, the corners are unfortunately isolated from each other. Driving fast requires optimizing each corner, of course, but messing up one corner doesn’t really impact how you drive the next one. My favorite part is the run through the Inner and Outer Loops. I also like the exits of T8 and T10 because it’s exciting sliding up to the walls.

So let me tell you about my WGI experience! My twin brother Mario had recently purchased a showroom stock Spec Miata. These aren’t as fast as a typical SM, and this particular one did not have a race motor (or a motor in tune as we found out). Its first race was about 1 month prior and it suffered an accident that required the frame to be straightened. He got it back from the shop just days before our race. So when we got to the track, there were several things that needed fixing (e.g. water leak at the heater core) in addition to the usual maintenance. We had a busy day getting the car ready, and each driver got only a couple laps on the practice day.

On race day 1, we were still running behind schedule and arrived to the grid stylishly late (after the pack had taken off). Mario drove first followed by Jim, then Derek, then me. Mario noted that the car was running a lot slower than it had last race. He used to pick up 5th gear right out of the esses, but it didn’t go fast enough to get into 5th now. My guess is the timing got knocked out of whack in the accident. We decided the car was running well enough so we left the investigation and fix for later.

During my stint, I was concerned about fuel usage, so I found another car driving a similar pace and drafted it whenever I could. Even so, as the race was getting closer to the checkered flag, I was worried about running out of fuel because the needle was hovering around E and would go below sometimes. I decided I had better pit because I didn’t want to get towed in. Each time the trucks go out, it costs the renters a lot of money. I wasn’t going to do that to ChumpCar, so I pitted with about 5 minutes to go. Given the 5 min refueling rule, there was no point going back on track. It was a good day and everyone got to drive. We ended up 51 out of 102 cars (6 cars never made it to grid). Seeing as two of our drivers haven’t been on track in about 2 years and we had a car out of tune, that’s quite good.

On race day 2, we inverted the driving order. I decided I wanted to get some entertaining video with my new TomTom Bandit camera, and purposefully started at the back so I could record some passes. Towards the end of my session, I ran some pretty consistent laps.

2:30.942
2:30.988
2:30.636
2:30.737
2:30.952
2:30.784
2:29.755
2:29.926

My stint ended when I got punted by one of the very fast cars in the Exhibition Class. Why someone who can pass me on any straight decided to try to go inside of me when I was going inside of another car is beyond me. I pitted at the end of the lap to check for damage. Thankfully the damage was minimal. And while I was a little miffed at both the other driver for driving beyond his ability and at the organization for not throwing a black flag, they were small annoyances in what was otherwise one of the best weekends ever. It’s hard to get too upset when you’re sharing an amazing track with lifelong friends. We ended the day 42 out of 92 (16 registered cars did not grid).

Video or it didn’t happen…

View from penalty box

This weekend I was recording penalties at the 24 Hours of LeMons race at Thunderhill. Some highlights and observations follow…

  • A car spun off track and caught the grass on fire. Yes, California was very wet for a while, but it’s now desert-dry with lots of grass. Why did the grass catch on fire? Because the driver had left the hand brake on and the heat was enough to ignite the grass. The driver didn’t report to the penalty box afterward and it took multiple flaggings to get him to report.
  • A Ford Taurus SHO was a frequent visitor to the penalty box. The car was full of new drivers. No, not new racers, but new drivers. A high school teacher thought it was a good idea to bring his students. The race was in May. One of the drivers was licensed in April, and another in March. None have them had ever been on a race track before. I asked why he didn’t do the test day to maybe familiarize the drivers with the 5 mile, 26 turn course. Apparently it wasn’t in the budget.
  • One of the teams decided they would do donuts on the skid pad at midnight with a child sitting on the lap of the driving dad. They were kicked out.
  • At least 1/3 of all incidents were drivers running off course at turn 9C. This is the connector between the East and West courses. It’s a blind switchback at the top of a hill.
  • Teams that got black-flagged were usually flagged more than once. About 1/3 of the teams were completely clean.
  • Incidents are most frequent at the start and end of the day.
  • First, second, and third place were decided by who had the most penalty laps. If any of the teams had had 1 less black flag, they would have walked away with an easy win. As it turned out, it was a real nail-biter with the outcome not decided until the final lap. The race leader with a 75 second lead got a black flag and came in to the penalty box, handing the race over to the next car… which proceeded to get a penalty 30 seconds later… which they ignored. Well, you can’t win a race with a pending black flag, so they threw the checker (rightly so) on the car with 1 fewer laps.

Oversteer overanalyzed: tuning

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

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

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

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

 

 

Oversteer overanalyzed: hands & feet

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

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

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

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