New Time Trial Rules

Last year’s Pineview Challenge Cup had a unique (and flawed) set of rules, using only tire treadwear to class cars. The “Race” class was any tire under 200 UTQG, the “Track” class was for any 200, and the “Street” class was for 300+. On the plus side, we had no rules lawyering or protests throughout the season, and it was easy to manage three classes. On the downside, the rules didn’t take into account power, weight, tire width, or the fact that there’s a great deal of variation within each tire class. In the end, the racing wasn’t always close.

We need a better set of rules for 2020, and so I took it upon myself to do some research. First, I put all of the lap times from the Pineview races into a spreadsheet, and noticed they fell into four groups. I figured that whatever rules we come up with, they should place people into four groups.

  • Under 1:14 – Just three people were in this group.
  • 1:14-1:17.2 – Fast cars and fast drivers, but only five people in this group.
  • 1:17.8-1:19.7 – Fourteen people, diverse cars and drivers, close racing.
  • 1:20.1+ Six people, some newcomers, a wider spread of times.

I then ran hundreds of simulations in OptimumLap at Pineview Run, using different cars, power/weight ratios, tire grip, and aero. I put all of them into a spreadsheet, and analyzed the data. Let’s take a look at what I did for a Miata with various power and grip values.

MiataHP  (lbs/hp)1.0g 1.1g 1.2g 1.3g 1.4g
Stock NA8 100  (24.5)82.3479.1376.3773.8871.65
Spec Miata125  (19.6)81.2577.9875.1472.6470.46
K-swap200 (12.5)79.6076.1473.2070.6468.42
Turbo, Rotrex265 (9.2)79.3975.6972.5169.7767.42

You can see that tire grip is the most important factor. For example, a Spec Miata on 1.3g tires will beat a K-swapped Miata on 1.2g tires. The lbs/hp ratio is also very important, especially as you add more grip. But on shitty 1.0g tires, power gives diminishing returns, and cars with better than a 12:1 ratio are pretty evenly matched.

Existing time trial rules

With this data on hand, I then reviewed the rules of nine time trial series to see if we could leverage them, and learn how others are doing it. Here’s a quick synopsis.

  • NASA PT/TT – The old NASA rules listed and ranked every car and trim level, and everything you might do to it. It seemed like a fair system, especially how they ranked tire compounds and width. But they abandoned it for a reason.
  • NASA ST/TT – The newer NASA TT rules are much easier, and seem very fair, based mostly on lbs/hp. My main gripes are 1) everyone needs to dyno their car on a Dynjojet. 2) Many common modifications are not allowed. Why not just make them a point value instead of making them illegal? 3) The new tire system favors race tires, not tire choice.
  • SCCA Autocross – 36 classes and a 387-page rule book?! I didn’t wade into this tome; this is the exact opposite of what I want to do.
  • SCCA Time Trials – I’ve got some issues with how cars are classed. In the “Sport” category, all Miatas from 1990-2015 are in the same class. If you know Miatas, you know how stupid that is. If you’re going to do that, you may as well put the BRZ/FRS in the same category as a 1990 Miata. Which they fucking did. I should have stopped there, but kept reading and found that in the “Tuner” category, they put E30s in with S2000s and ND2 Miatas. Ha ha ha ha. Anyway, there are five main categories with subdivisions that make 20 classes. The stock-ish categories are based on a car list, while in the modified categories, cars are classed by displacement divided by weight (as if displacement is a good indicator of power). These are new rules and maybe they need a few seasons to refine them, but the rules look unbalanced and unfinished.
  • EMRA – Kudos to them for making a 12-page rulebook! As such, it’s sparse and open to interpretation. There are ten classes based on a car list. You bump up a category based on modifications, but there’s not a lot of balance to the mods. The only thing they say about tires is that they must be DOT. There’s a world of difference in there, I guess everyone shows up on A7s?
  • Porsche – PCA has a great system of ranking their cars and various points for modifications. It looks very fair and complete. But they have only one brand of car, and they split them into different 28 classes. We can’t afford to give out that many trophies or manage that many classes. BTW, if you ever wondered about the comparative performance of different Porsches, look at the point values, it’s great data.
  • Speed SF – The classing system is calculated from a relatively simple worksheet that puts you into one of six classes based on a list of cars and modifications. The classing rules are simple, and because of that, there are going to be inequalities within the classes. Tires are easy: everyone is assumed to be on 100 TW or higher, and you take a slight penalty for using race tires. I like this system for a lot of reasons.
  • COM – Corvette Owners of Massachusetts have the best rules I’ve seen. It’s a bit like the old NASA system, and takes into account tire compound, width, and really anything you want to do to your car. This puts you into one of ten classes. The 98-page rulebook is a tad long, but they have a great spreadsheet calculator that makes classing easy.

After all that research, I’ve come to the following conclusions.

  • Creating a fair classing system is difficult, and nobody does it the same.
    • One starting point is to list and rank every car .
    • Another starting point is pounds per horsepower.
  • Tires are a very important factor.
    • Many rules evaluate each tire individually.
    • Tire width is a factor, and often relates to weight.
  • It would be easy to use another club’s rules, but impossible to manage them. Our time trials are run over 2 hours, and we simply can’t have more than 4 classes.
  • I poke fun at some of the rules above, but I applaud any effort to make racing fair and fun. Every system is full of good ideas, this is just a really difficult problem to solve.

Creating new classing rules

So with all of that knowledge, I went about creating new rules. My guiding principles were:

  1. I need to end up with only four main classes. Ideally these should correlate roughly to the lap time groupings observed in the 2019 season.
  2. The classing rules must be fair, and allow people to run what they brung. It should be easy for people racing in other series to cross over.
  3. The rule book should be short and simple.

Pounds per horsepower

I started with pounds per horsepower, because that’s easier than ranking every car in existence. For people who dyno and weigh their car, getting lbs/hp is easy, but most people won’t do that, so the rules allows using factory values.

lbs/hp = (Factory weight + driver weight) / (Factory HP * .83).

Of course people modify their cars for less weight and more power. So they must declare, on their honor, what their modified weight and power are. This is obviously a place someone can cheat. However, I would make the class worksheets public, so anyone obviously cheating would be publicly shamed, a-la Game of Thrones.

For people racing in the NASA TT series, which is based on lbs/hp, they can use their class minimums. Meaning TT6 is calculated at 18:1, TT5 at 14:1, TT3 12:1, and the faster classes at a 10:1 cap.

For other racing series that don’t use lbs/hp, I’m experimenting with some crossover rules. These would let people bring their race car on their spec tire, and fit into a class. But more on that some other time.

Tire grip factor

I used the tire point values from the old NASA series and COM, and then cross listed with recent tire tests, forums, and various web pages to come up with a hierarchical list of tires sorted by grip value.

PtsUTQGTypeExamples
2400+All seasonAny all-season 400+
3300-390Summer -olderYok S.Drive, DZ102, G-force Comp2
4240-380Summer – betterContinental ECS, Michelin PS4S, Bridgestone Potenza S001, Champiro SX2 (260), Toyo T1R, any 240+ not listed
5180-200200 EnduroAccelera 651, Champiro SX2 (200), Dunlop Z2/Z3, Falken Azenis 615K+, Federal RSR, Hankook RS4, Maxxis VR1, Nankang NS2R, Nitto NT05, Toyo R1R, Yokohama AD08R
6120-200Auto crossBridgestone RE71R, BFG Rival 1.5 S, Federal RSRR, Michelin PS Cup 2, Nexen Sur 4G, Yokohama A052, any 120-200 not listed
6100R-CompNT01, RA1, R888R, RC1
740-80R-comp softNankang AR1, Toyo RR. Pirelli Trofeo R, any 60-100 TW not listed
840RaceBFG R1, Goodyear Eagle RS, Hankook Z214 C51/C71, Hoosier R7, SM7, Kumho V710
1040*Race softBFG R1S, Goodyear Eagle RS AC, Hankook  Z214 C91, Hoosier A7, any 40 TW or less, not listed

I then assigned a point value to each tire, so that I could try out different formulas that would make lbs/hp and tire grip meaningful. I tried a few different ways to balance lbs/hp with different tire grip values, and make that correspond to real and simulated lap times, and simultaneously group people into four classes.

In the end, classing is based on a simple formula: FLOOR(Lbs/Hp/Tire). Or in plain english, the weight of the car with driver, divided by the wheel horsepower, divided by tire points, rounded down to a whole number. This usually results in a number 1 through 4. That’s your class.

Low-powered cars on hard tires may evaluate to more than 4, but they still must run in Class 4. We aren’t making a 5th class, there’s just no way to run that many groups in a two-hour session. For the same reason, there’s no Class Zero. So that makes Class 1 basically a no-limits class. Whatever car, on whatever tire, bring it.

Examples

To see how this works, let’s take a look at a Honda S2000. Weighs 2850 lbs with driver, dynoed at 200 hp = 14.3 lbs/hp. Different tires would put this car in a different class.

  • R7: 14.3 / 8 = 1.83, round down. Class 1
  • RE71R: 14.3 / 6 = 2.38, round down. Class 2 
  • ECS: 14.3 / 4 = 3.75, round down. Class 3
  • S.Drive: 14.3 / 3 = 4.76, round down. Class 4

Let’s take a look at a Spec Miata, which would be at the 20:1 lbs/hp cap.

  • Hoosier A7: 20/10 = 2.0. Class 2
  • Toyo RA1: 20/6 = 3.33, round down. Class 3
  • Dunlop Z3, 20/5 = 4.0. Class 4

Or using a car crossing over from NASA TT4, which has a 12 lbs/hp minimum.

  • Hoosier A7: 12/10 = 1.2, round down Class 1.
  • Toyo RA1: 12/6 = 2, Class 2.
  • Michelin PS4S: 12/4 = 3, Class 3.
  • BFG SC2: 12/3 = 4, Class 4.

So that’s how it works, pretty simple. But is it fair? I ran a bunch of simulations using four different cars that I have data for, and the lap times come out pretty close to how I had them grouped.

One thing I found out was that this formula works best for cars in the middle range. Cars with high lbs/hp ratios, like Miatas were going too fast on sticky tires, and so I put a cap on all cars at 20 lbs hp. If your car is slower than that, you still have to use that value. Likewise, high-power cars at the other end of the spectrum were treated unfairly by the classing formula, and so I put a 10 lbs/hp cap on that. So if your car is 6 lbs/hp, it’s classed at 10. With these mins and maxes set, the simulated laps fall very close to reality.

Caveats and final thoughts

The rules are based on real laps and simulated laps at Pineview Run; I don’t know if this system would be fair at any other track, that was never my intention.

I was trying to place people into four groups, and the rules work out for that. If I doubled the number of classes, there would be more equality between cars in the same run group. But it isn’t logistically possible to manage that many classes in a 2-hour evening session.

Here are some final thoughts, in no particular order:

  • This is the first year we’ll try these rules, and we might need a mid-season addendum. This should be pretty easy by changing tire point values, or adding a tire width factor.
  • To keep things simple, I didn’t take tire width into account. But an easy calculation is to take the average tire width, and divide by 245, and multiply that by tire points. This means that every tire under 245 width would get some advantage, and a width over 245 would get some penalty. As an example, a 195 RE71R would be evaluated the same as a 225 RS4. The average tire width could be anything, I’m speculating on 245 because it seems right. This could also go by class, so that Class 4 has a 205 width average, Class 3 has 225, Class 2 has 255, and Class 1 is 275.
  • I’m not stuck on tire point values, or integers. For example, we might find that Z3s and R1Rs should be evaluated at 5.5 points instead of 5. Or that RC1s are really a 7-point tire, not 6. We need real-world data before making any adjustments, tho.
  • I didn’t take into account modifications to suspension, brakes, aero, or really anything else you might do to a car. All of these are important, but not as significant as lbs/hp and tire grip. Not at Pineview, anyway.

We are still working on the final rule set, which includes things like points per race, and how the season points add up to who gets to put their name on the Pineview Challenge Cup. But I thought people would like to see the classing system ahead of time. The first race isn’t until Saturday May 2nd, so there’s plenty of time to break out your calculator and figure out the optimal tire for the class you want to run in. Or if you’re doing it the other way around, figure out how many pounds to remove or horsepower to add, so you can use your favorite tire.

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