NASA Time Trials Nonsense

I’ve already written about the nonsense of the SCCA time trials rules that pairs the following mismatched cars in the same group:

  • S6
    • Honda Fit
    • Scion FRS / Subaru BRZ / Toyota 86
  • S4
    • BMW 318is
    • Porsche Cayman

Let’s see what nonsense exists in the NASA time trials rules.


The NASA formula is based on weight to power ratio. For example, if your car is 3000 lbs and makes 300 hp, you are at 10:1. The cutoffs are as follows:

  • 6:1 TT1
  • 8:1 TT2
  • 10:1 TT3
  • 12:1 TT4
  • 14:1 TT5
  • 19:1 TT6

Weight is race weight, meaning the actual weight of the car on track as you drove it. I don’t know if vehicles are weighed at all regional events, but I’m pretty they will be at national events. It’s pretty simple to weigh a car, so I wouldn’t be surprised to see weigh-ins at region events too.

Power is taken over an average of RPM values. For a typical vehicle with a redline in the 6k-ish region, this means averaging 5 values spread over 2.5k RPM. Vehicles with high redlines use 7 values and low redlines use 3 values. Looking at the dyno classification forms available online, a 1.8 Miata making ~120 wheel hp comes out at about ~130 average hp. How did hp go up? They turn wheel hp into brake hp by multiplying by 1.15 (I think).

I have nothing against W:P as a classing method. Of course there are issues with any system. At high speed tracks, it’s better to have high hp to fight against wind resistance. At low speed tracks, it’s better to have low weight to mitigate grip loss with high loads. I’m not sure it’s 6 to one half-dozen to the other, but W:P classing appears to give lots of builds a decent chance of winning.


Once you have your weight and power, you adjust this with modifiers that have absolute values. For example, having suspensions with A-arms of any kind is a -0.7 penalty and having a mechanical throttle cable is a +0.2 bonus. So let’s say you have a 10:1 vehicle with A-arms and throttle cable. Your new WPR is 10 – 0.7 + 0.2 = 9.5. You are now in class TT2.

Using absolute numbers for modifiers is simple, but ultimately a bad idea. For example, the penalty for a wing is -1.0. In relative terms, this is 1/6 of the total cost at TT1 and 1/19 of the total cost at TT6. Also, aero affects low weight vehicles more than high weight vehicles.

Tire Nonsense

Classing vehicles fairly is a hard problem. While I don’t love absolute value modifiers to W:P ratios, overall, it’s simplicity makes it okay in my book. The problem with the NASA rules is they completely screwed up tires. This is how they break down the tire choices.

  • BFGoodrich g-Force Rival, Continental Extreme Contact Sport, Cooper RS3-R, Falken Azenis RT615K+, Maxxis Victra RC-1, Maxxis Victra VR-1, Michelin Pilot Sport 4S, Nankang AR-1, Nitto NT01, Toyo Proxes R1R/R888/R888R/RA-1/RR, Valino VR08GP +1.6
  • Bridgestone Potenza Re-71r, BFGoodrich g-Force Rival S 1.5, Continental Extreme Contact Force, Dunlop Direzza ZIII, Falken Azenis RT660, Federal 595 RS-RR, Goodyear Eagle FI SuperCar 3, Hankook Ventus RS4, Kumho ECSTA V730, Michelin Sport Cup 2 Connect, Nankang CR-1, Nexen Nfera SUR4G, Yokohama Advan A052 +1.0
  • Others (Hoosier) +0

Continental ECS is a 300TW Summer tire that works okay on track. Toyo RR is a 40 TW semi-slick race tire that is used as a spec tire in various race series. Somehow they are in the same class. How do all of the Toyo tires end up in the slowest class? Money. If cheating is the #1 problem with racing, sponsors are a close #2. Not only is the Toyo RR the best value at +1.6, it’s the fastest of all of the tires listed. The only way to go faster would be on Hoosiers, which results in nearly a full jump in class (at anything except TT6). Instead of making the rules fair or budget-friendly, NASA decided to let themselves be bribed. At the high end, there is only the illusion of choice. If you want to win, you will race on Toyo RRs, which also happen to be the most expensive tires here.

13 thoughts on “NASA Time Trials Nonsense

  1. I get the impression that the SCCA classing is well intentioned, but never updated. They put a car in a class that “seems right” when it’s new but then never re-class it based on what has since been added to that class.


    1. Not sure about their current time trial stuff, but the SCCA autox classes (which is really just time trial at lower speeds) are definitely updated. A lot of it is driven by member interest though (“write a letter”), so cars that nobody cares about will often languish in uncompetitive classes.

      You will always wind up with uncompetitive cars though, because it’s not practical to have enough classes to give everyone a playground.


  2. I have to believe that’s a typo. Toyo RR and other 100 TW tires should be .6 points. Conti ECS, Michelin PS4S, Valino whatever should be 1.6 points. It looks like they created a new category for lower performance tires, but put the R-comps in there as well, by mistake.


  3. I have competed in NASA TT quite a bit. My biggest complaint is actually that they use HP instead of torque. The 86 is way lower in torque than some other cars in its class, and in my view broad torque curves can really help make a car faster.

    I had not noticed the RR issue – most people who wanna win use the Hoosiers….


  4. The tire rules are new, they came out 2 or 3 weeks ago and AFAIK nobody’s actually run them yet. The NASA guys have said that they know there are tires in the wrong buckets and they expect to sort it out as the results come in. The intention was to err on the conservative side, which is why things like the RS4 and Federal are in the 1.0 bucket and not the 1.6.

    I think I agree the RR is probably in the wrong bucket though and I expect it’ll get moved to 1.0.

    Treadwear numbers are a lousy indicator of grip. “softer” does not always equal “grippier” because tires are complicated and there are a lot more dimensions of variance than just softness. Even if that weren’t the case, treadwear numbers are only loosely correlated to softness, there’s not much of a standard for how to measure it, and there’s certainly not anyone out there doing 3rd party validation of the numbers. Treadwear numbers are 80% marketing.

    Keep in mind the usage of these tires. In NorCal NASA TT the first session of the day is kind of a throwaway (track is cold, tires/brakes/drivers are cold, grid hasn’t been set yet so the cars are all mixed up and you won’t see any clean laps). The second or perhaps third (depending on how fast the temps go up) are where you’re likely to set the fastest lap, and by the 4th (and final) session it’s usually too hot to match the earlier times. You’re also not likely to get more than 2-3 clean laps in a session. So for TT you don’t need a tire that will last for a long time, a couple of good laps before it overheats is fine. A lot of the newer 200 tw autocross-oriented tires are really good at this, and I’ve been told that RT660 or RE-71R (no longer available) would be faster than an RR in this kind of scenario.

    Of course, the same tire rules are used for the Super Touring wheel to wheel classes, which have different tradeoffs.

    As for the non-tire prep rules, rather than taking power and weight as the starting point, I think it goes the other way. You start with a car and intended class, you look at what you can do in terms of suspension/etc modifications and what effect that has on the allowable power/weight ratio, decide if it’s worth it, and then retune the car and/or add ballast as necessary to get to the target number. The 0.2 bonus for cable-actuated throttle is because a DBW throttle means you can tune the car for a flat power (not torque!) curve to maximize the power available in the useful RPM range. That’s a lot harder to do with a mechanical throttle.

    Also, the “A-arm” thing is only in ST5 and ST6, not ST1-4 and I think it’s basically there to try to nerf Miatas.


  5. Also, on the topic the power classification it’s definitely not a multiplication factor applied to specs from the manufacturer. ST/TT cars have to be run on a dyno (specifically a dynojet) and the actual measured hp numbers across the RPM band are used in the calculations. Many (perhaps all?) NASA events have a dyno on-site that the officials can use to measure a car in impound to verify the numbers that the competitor submits with the car.


    1. The 1.15 is added to the wheel hp not specs from manufacturer. At least it works out that way if you look at the dyno sheets in the database.


      1. When you submit the dyno, it’s generally recommended to pad the numbers by a bit. Dynojets are pretty consistent with each other, but even so there’s a small amount of variance and you don’t want to get disqualified for being 2 hp over your submitted number. That might be what’s going on there.


      2. Yup. I know plenty of folk who submit HP as peak HP for just that reason.


  6. Also note that the spoiler/wing modifier (-1) only applies to ST6/TT6. In all other classes, a wing is free. There are other differences at the TT4 level and below, as it regards aero.


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