I’ve already written about the nonsense of the SCCA time trials rules that pairs the following mismatched cars in the same group:
- Honda Fit
- Scion FRS / Subaru BRZ / Toyota 86
- 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.
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.