Blog

Pineview’s Future and Black Friday Sale

The other day I was invited up to Pineview Run for a presentation of the club’s three-year plan, and to provide feedback. I’m honored to be included in such things, and I’ll do whatever I can to help secure the future of this club. The future looks bright!

One of the things track enthusiasts will be excited about is Phase 2 of the track, which adds more real estate. It’s much faster, with large radius corners and straights that should get the horsepower cars over 100 mph.

A racing-line (smoothed) version of the track in OptimumLap.

The details aren’t final yet, but my brother Ian made a version of the track in OptimumLap based on initial sketches, and so we’re already running simulations on lap times and top speed. On the existing track, I run around a 1:20 on Yokohama S.Drives (don’t judge!), and on the longer track I’d be looking at a 1:41. Top speed on my 110 hp Miata goes from 67 mph to 87 mph in the simulation. So, yeah, your Corvette, M3, 911 or whatever will do the ton.

I don’t know when Phase 2 will be started, but one of the concerns is surely safety. I brought this up in the meeting, and Todd, shared some statistics. Since opening the track in the fall of 2017, nearly 1500 drivers have completed 50,000 laps, with a perfect safety record. That’s zero injuries and everyone has driven their car home (barring any mechanical failures). Safety will remain a primary concern going forward, especially with the track extension in mind.

Black Friday sale (updated 12/4/2020)

Last year I bought a six-pack of track passes on Black Friday so I could give friends a discounted rate when they come to the track with me. At $150 each, I thought they were a good deal. This year Pineview has an even better deal in the annual pass.

For $149 per month, you get unlimited track time. No, you can’t join for just one month, this is based on a yearly subscription. If that’s too steep for you, there are two other options. For $79 per month, you get unlimited weekend track time. That works out to less $1000, and that’s a lot of weekend track time.

I told my brother about this, and he said that he’d be more interested in a weekday version of the same package. I guess that might appeal to people who have other things to do on the weekend, but have weekdays free. Or maybe they want to “work from home” at the clubhouse, and do track sessions in between meetings and whatnot. Todd added this package, as well.

This is a Black Friday sale, and Todd may not offer this deal every year, so if you’re weighing this vs a gym membership, do some pushups and sit-ups or something. I want to see you at the track.

NEWS FLASH – I hadn’t noticed this before, and maybe Todd added it for Cyber Monday, but the Pineview Challenge Cup is on sale for $140 plus tax. That’s 12 races for $12.60 each. This is the member price, but people who buy the annual pass also get the member price. You will need a transponder, and there are limited number available at Pineview, so I’d add that to your cart if you need one.

Pineview Challenge Cup

Last year’s Pineview Cup Challenge was a scheduling challenge for many, and the feedback was that some people could only do this on the weekend. This year the Pineview Challenge Cup will have twelve events, on Thursday nights and Saturday mornings.

5/2/2020
5/28/2020
6/6/2020
6/11/2020
6/25/2020
7/4/2020
7/23/2020
8/1/2020
8/6/2020
8/20/2020
9/5/2020
9/26/2020 – Challenge Cup final

Like last year, you’ll only need to come to some of the events to be included in the final race, and so this should work out for a lot of people’s schedules. The rules for next year aren’t finalized, and I’ve been working with Josh and Todd on some ideas. I’d like to get a rules steering committee together soon, and come up with a simple classing system that is fair to all. This is obviously going to be a challenge, since every racing series does it differently, and most of them are anything but simple. Stay tuned.

What Miatas Can Learn from a Porsche 914

A Miata and a Porsche 914 are somewhat similar in size and shape, and there’s some interesting studies and CFD data on the 914 that could help fill some knowledge gaps that exist in the Miataverse.

Image result for porsche 914
Not a Miata. But not that far.

They have similar frontal areas, but the 914 has a better coefficient of drag (.363 vs .38). I suspect this is partly the front end, which covers the tires completely from airflow. The 914 canopy might be better as well, since a vertical rear window is better than one that slopes back at 25-35 degrees, which is the worst possible angle, and about what a Miata hard top has. But in many ways, these cars are not so different, so let’s take a look at the 914 in more detail.

Published drag data

I’ve been digging around and found a few pieces of interesting data on a Porsche 914. In the May 1978 Porsche Panorama magazine, there are drag figures for a Porsche 914 in various configurations.

ConfigurationCdChange from stock
Windows closed.3630
Headlights up.380-.17
Windows open.381-.18
No roof.389.-26
No roof, windows open.447-.84
No roof, windows open, headlights up.464-1.01
  • One of the things I didn’t test at Watkins Glen was the effect of pop-up headlights (because I removed them from the race car). Miatas have slightly larger headlights, but at least this is a ballpark figure I can use for simulations in the future.
  • I also wasn’t able to test the difference between windows open and closed. Again, because race car. However, the windows open drag figure published here is very good compared to a Miata. I think it’s the Miata’s wider rear canopy that’s the culprit. The 914 canopy doesn’t stick out into airflow the way the Miata does, and it’s probably a significant drag factor when the windows are open. The 914 also has turn signals mounted on fender bulges, which redirects airflow along the car. But more on that later.

Scientific experiments on a 914

Chris Cassidy works at UCSD, in the Aerospace and Mechanical Engineering department. He also raced a Porsche 914 in autocross, and sponsored a project where his students used his car to do aerodynamic experiments to reduce drag, which would make his car faster in autocross. Much of this blog focuses on his work, thank you Chris and students!

Chris had several groups of students over a few years, each group doing a slightly different project, from preparing a scale model, to validating the model, and then doing computer analysis. His second group of students did the CFD vs water tank experiments, summarized in the table below.

FloWorks is CFD. LDV is a scale model in a water tunnel.

From the scale model and flow visualizations, they concluded that the CFD model was accurate enough. And from this, they could test a few different configurations, and see how drag affects HP at 50 mph.

Horsepower gains, via reduction in drag.

Now I’m grateful to Chris for allowing me to use his data, but I think the primary supposition is wrong, which is that drag reduction equals speed in autocross. The students concluded that the standard car with no airdam or spoiler would be the fastest, because it had a 2.1 horsepower advantage due to drag reduction.

However, I’ve done plenty of computer simulations, and I can tell you that at low speed, drag reduction isn’t that important, certainly nowhere near as important as creating downforce. If Chris wanted to go faster, he should have had his students work primarily on downforce. But let’s not skip ahead, let’s check out what they did.

CFD studies on a 914

Chris’s third group of students put 40 different configurations into CFD analysis, totaling over 400 hours of computer simulations. You can check out his website for all the results, but I’ll hit some of the higher points and relate this to a Miata.

First, take a look at the following image. The body styles are listed in order by the amount of HP gained in each configuration, which roughly (but not exactly) corresponds to the least drag. Not surprisingly, the most streamlined version, #15, gains the most HP. Being wing shaped, it also has the most lift. In the downforce column, the lower the number the better (a positive number is lift, negative number is downforce). The last two configurations are missing from this image, but are on the poster. All of this makes me wonder which one would be fastest on a race track….

Before I get to finding out that burning question, I’ll need to figure out the coefficients of drag and lift from Newtons.

Figuring out drag and lift

OptimumLap uses coefficient of drag and lift, and Chris’s students used drag force and downforce in Newtons. How am I going to convert this? I wish I paid more attention in math class, but here’s a formula I can almost get my head around. Solving for coefficient of drag Cd, Fd is drag force, p is the density of fluid, V is velocity, and A is surface area.

Cd = (2*Fd)/p*V^2*A)

For each configuration, the velocity is the same (50 mph), as are the fluid density (air) and frontal area. (17.8 sq ft). So it looks like the Cd is directly based on the drag force. This means I can set up a simple ratio, and get the relative Cd.

Likewise, I need to convert downforce in Newtons to a Cl value. I’m sure there’s a formula for this, but if I call the stock body .30 lift (a reasonable guess), I can figure out the lift of other body styles by a straight ratio using the downforce value.

OptimumLap simulations

Let’s see which of these is fastest on an autocross track using a 914 with stock weight and power (94 whp) and tires at 1.1g grip. I’ll also throw in Watkins Glen to see if anything different happens at high speed. Some of the configurations in the big image above make no sense (like the car resting on the ground), and so I’ll use only some of them. I’ve reordered these from mild to wild:

ConfigurationCdClAutocrossWGI
#33 – Stock.3630.3065.08150.17
#5 – Rear spoiler.385-0.3764.44148.30
#4 – Front spoiler .413-0.0564.77149.77
#29 – Slotted pillar.3200.3065.06149.34
#23 – Big wing.405-0.2364.59149.20
#34 – Racing open.3030.5365.28150.10
#22 – No glass.429-.4864.36148.86
#10 – Slant back.3190.7365.48151.30
#14 – Scoop front, slant back.2990.4365.18149.57
#15 – Full streamliner.2701.1065.82152.42

The students theorized that the stock configuration, with the least drag, would be fastest, but it doesn’t come out that way in OptimumLap. Configuration #22, which had the most drag, won on the autocross course. It also placed second at Watkins Glen, but got beat by the spoiler, Configuration #5, which has less drag.

A conclusion you can draw from this is that at low speed, ignore drag and go after as much downforce as possible. At a high-speed venue, go after the best L/D ratio. Most tracks are somewhere in between these two, and in this case, I would maximize downforce as long as it doesn’t require an extra stop in an endurance race.

There are some strange discrepancies in the data, like why is an airdam and a spoiler worse than just a spoiler? And why didn’t the wing perform very well? I don’t have the answers, and this is just CFD, so we have to take all of this with crack-rock sized grain of salt.

What can we apply to a Miata?

Well that was fun to see what happens to a modified 914, but what can we apply to a Miata?

Spoiler alert

The CFD study here shows that a spoiler is very effective on a 914. I’ve written about Miata spoilers before, and mine works really well. There’s really no downside.

Directing airflow below the window

Although the 914 front end directs air under the car just as a Miata does, it covers the front wheels nicely. But that’s not the part of the front end that’s the most interesting, take a look at the turn signal bulges. They look like a styling feature, but in fact they work to pull air down the side of the car, and away from the windows. These days you see this done with canards, but the 914 does this with a very simple forward bulge for mounting turn signals.

Image result for porsche 914 drag coefficient
The airflow denoted by the green line may help keep air out of the cockpit when you open the windows. It would be nice to induce that on a Miata.

Most of us race with open windows, and keeping air out of the cockpit will reduce both drag and lift. For top-up-windows-down driving, it should also mean less buffeting inside the car. I may have to build some of theses bulge-thingies and yarn test it, this could be a great way to reduce the amount of air going into the open window.

Streamlines show many interesting details, including the downwash along the door.

Roof spoiler

I’ve always wondered if the Miata roof spoilers were anything more than cosmetic.

Image result for miata roof spoiler
Cosmetic or performance?

If you look at configuration #24, they added a small roof extension to the 914. It reduced lift but increased drag, both by a tiny bit. Performance-wise, it was a wash. Maybe I spent too many years in California, but I like the way they look, and I certainly wouldn’t fault anyone for using one.

Miscellaneous drag reduction

In the CFD study there were a number of small things that reduced drag. If you did all of them, it could prove beneficial for endurance racing.

  • Removing the 914’s mirrors (configuration #19) reduced drag quite a bit. If I use the RSR calculator to calculate the power used at 50 mph, then the mirrors contribute about .035 to drag, which is a lot. Note that 914 mirrors don’t have the rounded aerodynamic shape that Miata’s have, and so it’s not apples to apples. (For more on mirror aerodynamics, you have to check out this lesson in Flow Illustrator.) A more accurate figure is probably half, or around .018.
  • Covering the rear wheels with flush covers (configuration #35) reduced drag by .02. If you use the HP Wizard tool, you get a similar value (.022). This is something I’ve been meaning to do to my brother’s Yaris, because the rear wheels don’t do much except keep the trunk off the ground. We can run skinny wheels with less offset, and get them flush underneath a side cover. However, I don’t know if it’s as practical to do rear wheel covers on a Miata, since the wheels are wider than the bodywork. Rear wheel covers that aren’t flush with the body would be configuration #17, and you can see that did nothing for drag reduction.
  • Slotting the pillar (#29) reduced drag by .043, which is a very significant amount. This directs air into the vacant area behind the rear window. We don’t see this much on street cars, I guess because they are ugly. But slots like this or guide vanes could be useful when you have an abrupt back end and turbulent wake. On a Miata, I’d figure out how to do this with air rushing past the window, and duct that internally to fill in the wake behind the hardtop, or behind the bumper.

I Don’t Want a 1.8 Swap

Just say no to 1.8 swaps

The other day I was chatting with a guy about his bitchin Miata with ITBs. He put them on his BP engine and got a lot of power and cool sounds. Forced induction would probably have been cheaper, but I totally understand wanting NA power and better throttle response. I also understand doing things just to be different, and thought I found someone who was a kindred spirit. So I asked him about putting ITBs on a 1.6, and what kind of power did he think I’d get from that? He said the 1.6 head doesn’t flow enough, and I should be swapping in a 1.8 anyway.

I’m so fucking sick of that. Everyone says don’t tune a 1.6, swap in a 1.8. But I don’t want a 1.8! I already have a 1.8 in my race car, and I don’t want one in my dual-duty street car. It won’t make sense to most people, but I’d rather have a 1.6 making 125 hp than a 1.8 making 140 or whatever. Here’s why.

NASA TT6

949 Racing built a Miata for NASA ST/TT race series. The NASA classing is based on power-to-weight ratio, and Miatas typically fall into the TT6/ST6 class, which is 18-20 lbs/hp depending on how you configure it. 949 chose the NB body because the rules give a slight bump in power for using base-trim model bodywork (BTM), and the NB has better aero, than a NA. This calculates out to a car that weighs around 2460 lbs and puts out about 138 hp. These are easy numbers to get from a BP 1.8 Miata engine with tuning. However, they swapped a 1.6 engine into the NB chassis. Huh?

Emilio says “We don’t tune 1.6s, we swap in 1.8s,” but there he went and made himself a liar. In this case, it made a lot of sense. The 1.6 engine is lighter and shorter, and this gives the car a better front/rear weight balance. In theory it should have worked better, but they later abandoned the 1.6 engine project because it was going to be too expensive to hit the horsepower number. But theoretically, a 1.6 should be better than a 1.8 if making the same power.

And so I’ve been thinking about competing in NASA TT6 as well, but I’m not going to build an engine that has 138 hp. First, that’s an expensive build, but more importantly, I want to use aero, and that means the car isn’t allowed the same power to weight ratio. If I use all the aero allowed (airdam, roof, wing), then the engine can make a maximum of 125 hp. I’m guessing my 1.6 has 110-112 as it sits, and so I can probably hit 125 without breaking the bank.

Also, I have a low milage engine. My dad bought the car when he was 69 and never drove it hard, and so the engine has had a low-stress life. Tuning this engine makes more sense to me than swapping in something of unknown origin.

Taking scalps

One of the joys of driving a momentum car is embarrassing more powerful, expensive cars. Hunting down BMWs, Corvettes, Mustangs, and Porches, and passing them (or harassing them into giving you a point-by), is great fun. For lack of a better phrase, I’ll call this “taking scalps”.

You don’t earn a scalp for passing slower cars, only faster ones. But when you’re in a Miata, pretty much every other car on track is a scalp for the taking. If you’re driving a 1.6 Miata, then 1.8 and later Miatas are scalps, as well!

Accentuating the 1.6-ness

I want to build the ultimate expression of a NA 1.6 Miata. The early 1.6s differ slightly from other Miatas in several ways, and my goal is to exaggerate all of these differences.

  • Higher redline – The 1.6 revved to 7200 rpm, which was later reduced to 7000 in the 1.8. I have a Megasquirt PNP2 and programmed my redline to 7500 rpm. I won’t go higher than that without modifications.
  • Higher compression ratio – The 1.6 had a 9.3:1 ratio, compared to the 1.8 NAs which were 9.0:1. I got a spare head and decked it, which should bring the compression up to around 10.3:1, which is close to what the later 1.8 BP engines have.
  • Lighter clutch and flywheel – The 1.6 has a smaller clutch and flywheel, which means less rotating mass and a revvier engine (at least without load). I bought the lightest aftermarket clutch and flywheel I could find.
  • Shorter final drive – The NA6 4.3:1 diff ratio is shorter than the 4.1 ratio used in the later 5-speed 1.8s. My original plan was to exaggerate this difference further by using a ring and pinion from a 4.78:1, but I’m fairly certain this will annoy the shit out of me on the street. For my county club track, a 4.1 makes a bit more sense (fewer shifts), so I’m on the fence for which way to go here.
  • Hotter cams – The 1.6 has a slightly more aggressive cam profile than the 1.8s. I went one louder and bought Kelford 264 B-grinds with 9mm lift. It will be interesting to see how much power these add.
  • Smaller brakes – The early cars came with smaller disc brakes. On a street-oriented car that does the occasional time trial, I don’t see the need for larger brakes (and more rotating mass), so I’m leaving them stock. I’ll duct the rotors, but that’s it.
  • Smaller wheels – The NA6 always came with 14” hoops, and it wasn’t until 1995 that 15” was an option. If I’m being serious about performance, then 15s are a better choice. They are available in wider widths and have better rubber selection. But if this is an exercise in nostalgia and 1.6-ness, then 14×7 RPF1s are obviously that way to go.
  • Less power – Do you ever floor the accelerator, and then pat the center console or the steering wheel, urging your Miata to giddy-up? The 1.6s have less power and torque, and it leaves you always wanting more. Somehow that’s part of the charm. A naturally aspirated 1.6 is never going to overwhelm anyone with power, so this is a goal that’s impossible not to achieve.
  • Less weight – Miatas got heavier through the years, and to keep with the theme I’ll reduce weight where I can. There’s no secret recipe, just concentrate on the ounces, and the pounds will take care of themselves.
  • Simpler – The earliest Miatas were the simplest, with fewer electronics and conveniences. Mine has a manual steering rack, manual mirrors and windows, no ABS, and came with only a single airbag (now gone because I replaced the steering wheel). Anything I do to further modify this car will stay in the same theme of keeping things simple, pure, and analog.

People say that the later Miatas are better cars, but the earlier ones are better Miatas. When you add up all the differences between the 1.6 and 1.8, you get a car that has a slightly different character. Those differences are what I’m accentuating. For sure I could make a better car, but I’m building a better Miata.

And that’s why I’m not swapping in a BP 1.8, using forced induction, or whatever else is the cost effective and logical way to get more power. Yeah, I’m tuning a normally-aspirated 1.6, get over it. And all of y’all are scalps to me!

Occam’s Racer is Looking for a Teammate

The Occam’s Racer team could use another teammate or two. We currently have a rotating group of drivers, but most of them are essentially arrive-and-drives that live far away, or are too busy doing other things to be a regular part of the team.

Photo by TJ Keller

I need help working on the car, loading and unloading for races, and all the other things required to make a race weekend happen. Currently I do 95% of this stuff myself, and it’s a lot of work. Both of my knees are held together with metal plates, and the pain of lifting heavy objects regularly reminds me that I can’t keep doing this on my own. Often times I think to myself that I should quit racing, buy a new ND, and just do laps at the country club.

But for the time being, I’m still racing, and I need help. In exchange for your labor, you get the team rate for driving, which is a straight division of all consumables.

The ideal teammate lives near Ithaca NY, knows how to work on Miatas, has some Miata spares, and has lots of free time. But that’s being really picky, and I’d settle for someone who has mechanical aptitude and free weekends.

You should have some wheel-to-wheel racing experience. AER requires that you’ve raced in five endurance races, and I intend to keep racing with AER. But if you don’t have that much experience, I may also race in Lucky Dog Canada, Lemons, and Champcar, so there’s some chance to build up to the AER level.

My racing philosophy is primarily to have fun, and that means we get along with other teams in the paddock, and that starts by being courteous on track. I’m more impressed by drivers who have situational awareness and good decision making than outright speed. You won’t be faster than Evan, anyway.

Use the Contact form and I’ll get back to you. It’s a long winter, but there’s a lot to do.

Lemons Aero Study: Star Wars Ecotec Miata

A guy recently contacted me on Facebook to ask my opinion on aero modifications for his Miata. Cameron and his team live in the Great Lakes area and race Lemons. Their Miata has a Star Wars theme, complete with R2D2 behind the seat, with a head that spins, too. The car has an Ecotec swap. Cool build, right?

Star Wars Miata. Red Nine. Get it?

My first response was to get an airdam and splitter, but the team had already done that. They ripped it off shoveling mud, so it’s not in the pic, but the team intends to put it back on. He was wondering about also adding a wing, and how much would that help?

My reply was that a wing would certainly help. From my aero tests at Watkins Glen, I know that a car with a wing will beat a car without a wing in just about any simulation I run. However, a wing with an open top or chop top is about 2.5x less effective than one with a hard top.

Cameron wanted to know what this would do for lap times at Gingerman, his home track. Luckily that track is in OptimumLap, and Cameron provided me with some data based on a recent race, and that their theoretical best lap was 1:46.65. What would happen if they added aero?

I have Miata models in OptimumLap, but nothing with an Ecotec, so I used Cameron’s dyno sheet to make a new model.

In case you wondered what an Ecotec Miata puts out, it’s a shit ton of torque.

Next I input weight of the car, final drive ratio, and set the tire grip value to 1.15g. This is a bit higher than I use for 225 RS4s, but the point was to get data close to his best lap. I made some guesstimates at drag and lift. His car has a partial roof, so I’ll use my Chop Top data and fudge it slightly because he’s using a stock front end, and not an airdam. Call it .5 drag and .34 lift.

Based on all this data, the simulation shows a 1:47.10, which is reasonably close to what Cameron said was their theoretical best lap, and was in fact their actual fastest lap in the race. So let’s see what happens when I add the airdam, splitter, and wing that Cameron asked about. At this point I can use the data I have (I tested almost exactly the same setup), and Cd is .45 and Cl is -.53.

StandardAirdam, splitter, wing
1:47.101:44.72.

So that’s 2.38 seconds faster using aero. Pretty substantial considering the wing isn’t going to work very efficiently with that janky top.

My advice was to extend the roofline and support it at the rear with the wing uprights. (While still allowing R2’s head to spin.) I sent him a crude drawing that looks like this: the red is the extended roofline, the blue is the wing and uprights.

Extend the roofline and support it with the wing uprights.

The roof extension would provide clean air to the underside of the wing, which is what a wing wants. The roof mod might look silly, but this is Lemons where silly is de rigueur. With this modification he might arrive at values of something like Cd .45 and Cl 1.0. This would theoretically drop lap times by a full second.

StandardAirdam, splitter, wingExtended roof
1:47.101:44.721:43.63

OptimumLap assumes a perfect aero balance, but in the real world you can’t just keep adding rear aero and expect faster times. This is just a simulation, after all, but it’s good to know if the trouble and expense is worth it on a Lemons build like this. In this case, I’d say yeah.

Mid Ohio, Part 5: Driver Analysis

The race is over, but we’re still living the race weekend over and over. In this installment, let’s see how the drivers did compared to each other.

Fastest laps

Evan made a video of each driver’s fastest laps. Let’s take a look at Evan first, because he set the fastest laps of the weekend, and we’ll use him as a reference for where the rest of us can improve.

Evan’s fastest laps overlaid.

From his triple-video overlay, it looks like he’s pretty consistent. However, if you look at the Aim Solo data, his laps vary by .4 seconds above and below the reference lap. On the back straight, his top speed varies by 2.2 mph.

The bottom of the graph shows the time gained or lost compared to the reference lap, which is black in this case. On the lap denoted by the blue line, you can see he had .4 seconds in hand at around 2200′ again at 6000′ and .2 seconds at 9800′. As good as Evan was driving, it looks like he could have gone one second faster.

Team fastest laps

Fastest laps from each of us.

Evan also made a neat overlay with everyone’s fastest laps. Here are some things I see in the video.

  • T1 – Everyone except me initiates the turn sharply, my hands are slower at first, and I must continue to steer through the corner. I’m also a chicken shit in fast corners, and I lose most of my time here.
  • Keyhole – We are all very similar through this turn. If you watch other laps in our full race videos, we often take different lines, sometimes diamonding it, sometimes driving a rim shot. Oddly, it doesn’t seem to make a difference in lap time or trap speed.
  • T4 – Pat and Sonny are equal through here, but Evan trails the brakes the best and this is where he makes up most of his time. From here on, he is GONE.
  • T9 – Pat and Sonny are still dead even on the approach to the corner, but by the time they pass under the bridge, Sonny has a tenth.
  • Carousel – Sonny takes a wider entry line that seems to work really well.

Team race laps

I don’t have data on Sonny’s best qualifying lap, which he set on Friday. So let’s take a look at the best race laps over the weekend. These are not the same laps as those in the video. The chart below is color-coded thusly:

  • Evan is Green (think money) – 1:44.637
  • Sonny is Orange (think 949) – 1:45.273
  • Pat is blue (like his F150) – 145.355
  • Mario is red (like his NA6) – 1:47.579
Best laps from Sunday’s race.

I’m no expert on analyzing data traces, but this is what I see:

  • Everyone goes through T1 (1000′ mark) pretty well, except me. I decelerate too much, and this severely impacts my speed down the following straight.
  • The chicane begins at the 2000′ mark, and Evan (green) is faster and later on the brakes than everyone, and gains time here.
  • The Keyhole is at the 3000′ mark, and Pat (blue) has a higher minimum speed, but can’t get on the gas as early at the exit. In the end, we all come out of the Keyhole the same. Notice the time bar on the bottom is flat from 3000-6000′, meaning we are all going about the same speed.
  • Sonny (orange) does something interesting in T4. He doesn’t gain time, but it might be a move that’s useful in traffic. Maybe he had traffic? In any case, it didn’t affect him.
  • Evan ekes out a little bit on everyone in the esses.
  • Turn 8 is at about the 8000′ mark, and it’s not really a corner, you just pin it through there. I may have experienced traffic at this point, because there’s no reason for me to slow down, and I did.
  • Turn 9 is about about 8500 feet, and this is where Sonny is better than Pat. On every other corner they are pretty evenly matched. Meanwhile, Evan flat sails through this corner and his resulting top speed at the top of the hill is where the hash marks are. You can see the speeds in the upper left hand corner. Evan’s going 90 mph, which is 3-6 mph faster than the rest.
  • Turn 10 is at about 10000′ feet, and everyone else goes through it really well. Except me, I park it.
  • The Carrousel is like the Keyhole, we might take different lines, but everyone gets through it at about the same speed.

Lies, damn lies, and statistics

It was illuminating to look at our fastest laps, but an endurance race is won on consistency, not hero laps. Let’s crunch some numbers. Better yet, let’s get someone else to crunch the numbers. Evan’s friend did some statistical analysis of our race laps, and it’s so nerdy I have to share it.

In the following box charts, the lower the box, the faster the lap, the shorter the box, the more consistent the driver. The horizontal line in each box is the median lap time. The mean (average) lap time is called out in the inset, and the horizontal line connecting the boxes is a way to visually compare that. Very slow laps (out laps, in laps) were removed from the data set.

Let’s start with Saturday. Evan is capable of low lap times nobody else can match. Sonny is a wee bit faster than Pat. All three of them can lap through traffic without dropping into the 1:49s, which is where most of my laps are. Our standard deviations are similar, meaning we were all driving with about the same consistency, but Pat was the most consistent on Saturday.

On Sunday the track was a bit slower, but we all drove better. Evan’s average lap is about the same as the day before, but look how much more consistently he’s driving. Sonny had the fastest average lap time, and he improved his consistency a bit as well. Note that we should disregard Pat’s laps, because he only did six, and hadn’t found his groove in that stint yet; he’s over a second off his normal pace.

When I look at the Sunday data, I feel a lot better about my driving. Pat has raced at Mid-Ohio a couple times before, and this was my first time. On average, I’m only 6/10ths off Pat’s faster Saturday times. I can live with that.

Also on the plus side, my standard deviation says I’m the most consistent driver, by what looks like a decent margin. I think this is because I drive with more in reserve. Some examples of this from the weekend are that I avoid contact with other cars (Sonny), I don’t put four wheels in the grass (Pat), and I don’t hit tire walls (Evan). But let me not congratulate myself too much. As we saw in the video and Aim data, I’m driving tentatively in the fast sections.

The next chart is basically the same as before, but sorted by driver, rather than day. This chart is a good way to look at driver improvement. (Again, we should disregard Pat’s Sunday stint.)

I’m told that the ANOVA p-value is a test of the difference in the mean lap time for each driver. If the p-value is less than 0.05, then there’s a statistical difference. What all this means is that I drove significantly better each day, and they didn’t. Another way to look at it is that they were all on pace rather quickly, while I took longer to learn the track.

The following histograms give another way to view the laps. Each bar represents half a second. Evan (blue) is other-worldly. Pat (yellow) and Sonny (green) both have a rhythm centered around 107-seconds. My Saturday is poop, but I like what I’m seeing on Sunday.

On Sunday I did a lot of 108-second laps, and all of my laps are within a narrow 3.5-second window. If you compare my Saturday to Sunday (red), it’s like two different drivers were in the car: Doctor Jekyll and Mister Consistency.

Racing incidents matter

Endurance racing isn’t just setting lap times, it’s staying out of trouble. Our average pit stop was 3 minutes and 26 seconds, but two racing incidents made them longer.

After Sonny and the BMW clashed, we lost two minutes in the pits. Most of those two minutes were because he caught us unprepared, but that’s what happens when you take an unplanned stop. We also spent some time looking over the car for damage. Those two minutes are the equivalent of adding 2.5 seconds per lap in his stint. On average lap time, this made him the slowest driver of the day on Saturday. As a side note, the impact bent the right rear wheel. That’s the wheel hub that would later break and end our weekend. We’ll never know if the impact damaged the hub and caused it to fail, but it can’t have helped.

When Evan hit the tire wall at pit entrance, it took us an extra minute and twenty seconds pulling the bodywork straight and checking over the car. If we add that time to Evan’s stint, each lap was 1.5 seconds longer. That single mistake at the very end of his stint made Evan the slowest average driver on Sunday (I’m not counting Pat’s handful of laps). Yes, this made Evan even slower than me! Racing incidents matter.

In conclusion, our two fastest drivers were also our two slowest drivers. The obvious take away here is that one should avoid contact at all costs.

Driver weight [updated 11/6/2019]

When I originally wrote this section, I compared data traces of Evan and I, and showed that 65 lbs was very significant for acceleration and resulting lap times. However, after going through the data some more, I think this was probably time of day. Evan’s first run on Sunday was cold, and the engine would have made more power. There might have also been a headwind. Whatever the case, there’s just no way 65 lbs amounted to .4 seconds on the back straight.

I then went and looked at many other runs, comparing the same driver on a full tank and then an empty tank (same stint), which is a difference of about 100 lbs. Even with that larger weight amount, it was hard to find any correlation between weight and speed on the back straight. Go figure.

OptimumLap simulation

Another way we can look at the difference weight makes is to do a simulation in OptimumLap. On the pro course (no chicane), the simulator says my car should do a 1:41.57, and I’ll add two seconds to that for the chicane, so call it 1:43.57. (Incidentally, this is the same lap time Evan would do if he dropped the one second we saw in the Aim data.) So then, what happens when I add 65 lbs?

WeightLap
125 lb driver1:43.57
190 lb driver1:43.93
– difference0.36

According to the simulator, a difference of 65 lbs is worth .36 seconds. I typically trust OptimumLap, but in back-to-back tests at Pineview Run, I’ve noticed that the time difference is in OptimumLap is about half of what I’ve logged in the real world, and I would expect about .7 seconds.

So let’s split the difference and say 65 lbs is worth .65 seconds. That makes every 100 lbs = 1 second, which is a rule of thumb I’ve heard before. It may not be accurate, but it’s easy to remember.

6/10ths of a second would be a big deal at the pro level, but not at my level. I have a lot of things to work on before I start using weight as an excuse. But Pat could argue that he’d be faster than Evan and Sonny if they weighed the same. Start your excuses Pat!

Mid Ohio, Part 4: Race 2

I was up before sunrise, waiting in the parking lot for the Summit guys to deliver my parts. It was dark when they drove in, and I was the only one in the parking lot. I greeted them with a creepy “Where’s my drugs, man?” and they chuckled and handed over the parts. I got back to the RV and woke everyone up, telling them we need to get the brakes done, and why is the radiator water all over the floor?

We checked everything in the cooling system, swapped an overflow bottle, blew out all the water we could find, etc. We started the car and pressure-tested the system. But we just couldn’t figure out how all the radiator water dumped out. We vowed to keep an eye on the temperature and check the water level in the pits each time, and just trust it.

The brakes were another issue, Summit gave us the wrong parts. I later went back to them to figure out how this happened, and apparently the Hawk product info says that these brakes work on a 1994-2005 Miata. I politely explained that this is not the case, and that 94-97 are different than 2003-2005, at least in the USA.

I’ll get my money back, but the point is we didn’t have fresh brake pads, and must use the 3.5 hour old StopTech Sports that nobody is really trusting to go the distance. For braking power and feel, both Pat and Evan liked them more than the Porterfield R4E. More StopTech converts? In any case, Sonny gaves us new team orders: coast slightly before braking zones and use less brake throughout the race. As if.

Race start

Evan. I don’t think I’ve ever seen him awake this early.

Evan has never started a race, and so we gave him his wish. He started in 32nd position. The Audi R8 in first was going slow and bunched everyone up, which made for a tight group as the green flag dropped. There was a brief heart-attack moment as one of the cars had a mechanical, but everyone avoided the incident well. See for yourself in the clip.

A good tight start… WATCH OUT!

We can set fast laps, but not in traffic, and on the 5th lap, we’d lost four places. But as the cars got spaced out, Evan got his head down and after 54 blazing laps, we were in 23rd position!

Evan passing a GT4 Clubsport ($165,000, 385 hp) around the outside.

Evan is our fastest driver, but he’s also our youngest driver, and young people do stupid shit. For some reason Evan thought a good place to make up time was on the pit exit (WTF), and so he came in too hot. He had to make a split second decision between running over the RFID gate or hitting the tire wall. He chose the wall.

Evan stuffs it into the wall.

We lost some time in the pits pulling the bodywork straight and checking the car for damage. Initially we thought there might be radiator damage because of all the water on the car, but a quick car wash is one of the benefits of hitting tires. I learned that earlier this year in a Lemons race when a teammate did the same thing (but while racing, not while pitting, for fuck’s sake).

Sonny went next and started in P30. I went through his footage and found a cool clip. In the video below, Sonny points by a faster car quite early in the Carousel, which shows what an aware and courteous driver he is. Keep watching the full lap for a surprise ending for the faster car.

Don’t let me hold you up.

Sonny banged out 50 fast laps, safe and consistent, and brought us up to 22nd position overall. This put us nine places ahead of where we were yesterday at the same time, and things were looking really good when I got in the car.

A few cars passed us in the pits, and so I was out in P27, but was feeling my oats and got us up to P21. I had some good racing in this stint, real wheel-to-wheel action that was fun and intense. I’m still replaying some of those in my head.

I had planned to run the car out of gas in my stint, but I thought I saw Pat with his helmet on, indicating that they were ready for me to come in (my radio wasn’t connected). But when I pitted, Pat didn’t have his helmet on, Sonny wasn’t prepared, and Evan was nowhere to be seen. Must have been some other team that was ready! Still we managed a decent pit stop of 3:22, and when Pat got in, we’d only lost two positions.

Six laps later, all hell broke loose. To be more specific, the right rear wheel hub broke loose.

Something broke, I’m in the sand trap….

Pat was going 83 mph through T1 when the hub flange broke. This took out the brake disc, the entire wheel, and spun Pat around 720 degrees. Luckily there’s a big sand trap there and he slid safely to a halt. That could have been a lot worse, and I really only care that Pat is safe and unhurt. Damage can be fixed, and I’ll replace the rear hubs every year now.

Post-race thoughts

Some thoughts in no particular order.

Miata hubs. Miathubs!

Everyone knows Miatas have weak hubs, and most of the time it’s the front hubs that fail. Evan examined my hubs before the race and declared they were crap. So I ordered a pair of Miatahubs at the very last minute. Justin Lee was also racing at Mid-Ohio (in the Finish First Racing Scion FRS, Class 2), and so he hand-delivered the new Miatahubs to us, and helped us install them on Friday morning.

Miatahubs aren’t cheap, but I was feeling pretty pleased with myself now that the car has a bulletproof solution for the front hubs, and they should last forever. Of course it was the rear hub that broke.

Aero vs power

Nobody had less power than we did, but we routinely out-handled and out-braked most cars in the field. A lot of that comes from a better aero package that give us more downforce and less drag. Case in point, here I am in a dead heat with a 1.6 Miata, the other slowest car on the track. I eventually pass him because my car has less drag, and I brake later.

Neck and neck with a 1.6 Miata.

The other NA/NB Miatas in the field were on RE71Rs, while we were on RS4s, and they probably had more mechanical grip than we did. But aero works better the faster you go, and that’s where we could take them.

Hankook RS4 225/45-15

The tires worked predictably throughout the weekend. At first we were on RS4s that had about 16 hours on them I’d guess? They were only about half worn, and didn’t wear appreciably the entire day. On day two we started on stickers, and we put down times that were 1/10th slower on average. The difference was down to warmer weather and has nothing to do with the tires. Anyway, Hankook RS4s are great tires, and I see no reason to use anything else for endurance racing. The fastest NA Miata team was on RE71Rs and we saw them changing tires after only 6.5 hours. No thank you.

No full-course yellows

We didn’t have a single FCY the entire weekend. Compare this to a race at Watkins Glen, where you can expect over an hour of parade laps each day. We had plenty of accidents, but the wrecking crew managed the entire event without stopping the race. They cleared the incidents quickly, and the flaggers were on their game. It was orchestrated perfectly time and again. Thank you Mid-Ohio staff.

Speed differential

I’ve heard some people complain that the speed differential in AER is extreme. The Audi R8 car was about 10 seconds faster than us, but it was easy to see coming and stay out of the way. There were other fast cars, and they did occasionally dive bomb us in to T1, T4, and T11, but you learn quickly to accept that.

So you drive your mirrors a bit more, and there’s the occasional “holy crap” moment when a car suddenly appears next to you. But most of the Class 4 and 5 cars were really well driven, respectful, and safe. The speed differential was actually a shit ton of fun. Those cars take different lines, and so you can still play with them in the tight sections, and even show them your tail from time to time.

Here’s a clip of me going though T1. I purposely don’t track all the way out so I can point by the horsepower car behind me. I stay on my line going into the chicane, he takes a different line, and we trust each other to dance the dance. It might look like a close call, but it isn’t.

Speed differential not a problem. But look at them go!