# 2021 Rules Time--How about no changes? ## Recommended Posts

• National Staff Hi Folks, it's time to get the 2021 rules published soon.  With the crazy 2020 season (and/or lack thereof), I don't know that we really have any data showing that any of the ST rules should be changed.  Some of the events have once again proven the ST formulas in the various classes to provide tight competition at the top of the fields.  So, maybe we should just update the wording for '21, add the few provisional classifications approved in '20, and save money and time on new modifications needed to keep up with rules revisions!

With that said, we will entertain other ideas posted here.

##### Share on other sites Change ST formula to (horsepower + torque)/2

It simplifies calculations and covers the biggest loophole that people in the know take advantage of. A power-to-weight formula does not account for torque made below 5252 rpm. Top speed is a function of horsepower and CdA. Acceleration is dependent on available torque. It's why the joke (but true) response to "what car should I build for STx?" is always C5Z (or turbo or SC).

Simple example:

•3 people with 3 identical cars

•Each car makes a flat 200hp from 2000-8000 rpm.

•1st person uses 2000-4000 rpm powerband ; 2nd uses 4000-6000 rpm ; 3rd uses 6000-8000 rpm

Here are the equivalent torque calcs for every 1000 rpm:

RPM           HP           TQ

2000       200      525

3000       200      350

4000       200      263

5000       200      210

6000       200      175

7000       200      150

8000       200      131

•1st person running engine 2000-4000 rpm : 200 hp avg , 379 tq avg

•2nd person running engine 4000-6000 rpm : 200 hp avg , 263 tq avg

•3rd person running engine 6000-8000 rpm : 200 hp avg , 152 tq avg

Identical cars and all legal at 200hp, yet it's obvious who will and won't win off corners. You can average 600 data points. "Power-to-weight" leaves a big loophole open by ignoring torque-to-weight.

On the other hand, if it isn't fixed this one of the loopholes people need to take advantage of when building an engine for an ST class. Turbo/SC/V8 to 600lbft @ 2000rpm, 180whp at 6000 rpm redline.

Can divide by CdA for aero balance, but that's the advanced class.

##### Share on other sites And, if we're being honest, points for engine placement looked at again.  I know we took a lot of slack in the past for P-Car's getting points for rear engine placement but that's really only because certain drivers don't make up the difference then and complained.  C8's and Caymans/clubsports starting to show up and they can't technically be assessed the same as a C7 nor can a 911.  Each of the other orgs accommodate for this typically.   As it sits only AWD's are getting penalized for orientation.  That's only half the equation as mentioned above.  Time to update.

##### Share on other sites Acceleration is based on power available.  A moving object has a certain amount of kinetic energy depending on speed and mass (KE = 1/2 M * V^2).  Units for energy are J(oule) aka Watt * second.  1 horsepower = 757 Watts.  So, exert power for a set amount of time and you add kinetic energy - aka you accelerate.  If you're going to discuss torque then we need to compare transmission and differential gear ratios along with tire size so that we can understand torque's effect as a force to move an object, but if you do all that, you'll reach the same conclusion as you would if you just compared power.

There is a reason in your example #1 has an advantage over #3 but it isn't torque.

• 1
##### Share on other sites I agree strongly with ssmith.

From a mathematical standpoint, TRQ does not matter.  Power determines acceleration.
Too many people have been brainwashed by the idea that "TRQ wins races".
Mathematically, TRQ is an instantaneous value, it has no time component.  Meanwhile, 1 HP  = 750 Watts.  A Watt is 1 Joule per second.  Joule is the standard unit of energy.  Therefore, if we multiply our power by time, we can calculate how much energy we have added to our vehicle.  In this case, kinetic energy.  Velocity is proportional to kinetic energy (KE = 1/2 M * V^2).  Therefore, our change in velocity (acceleration) is directly proportional to Power * time.

ex. accelerating at 200 HP for 10 seconds adds 200*10*750 = 1.5 million Joules of energy to our car.  Starting from an initial speed of zero, in a car that weights 1000 KG,  the velocity would increase to 54 m/s = 194 km/h = 120 mph.  Note, this example ignores wind resistance and rolling resistance.
Therefore, we achieve an average acceleration of 54m/s / 10 seconds = 5.4m/s^2
Look at that, we calculated acceleration without needing to consider TRQ, RPM, or gear ratio!
Power/weight ratio is the correct way to balance a multi-car class, because it eliminates differences in available gear ratios and max RPM.

In Bil Doe's scenario above, he did not consider gear ratio.
If all 3 cars are exiting the corner at the same speed, at 2k, 4k, and 6k rpm respectively, then they must have very different gear ratios, changing the effective wheel TRQ of each vehicle.

Edited by Tansar_Motorsports
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• National Staff 12 hours ago, Tansar_Motorsports said:

I agree strongly with ssmith.

From a mathematical standpoint, TRQ does not matter.  Power determines acceleration.
Too many people have been brainwashed by the idea that "TRQ wins races".
Mathematically, TRQ is an instantaneous value, it has no time component.  Meanwhile, 1 HP  = 750 Watts.  A Watt is 1 Joule per second.  Joule is the standard unit of energy.  Therefore, if we multiply our power by time, we can calculate how much energy we have added to our vehicle.  In this case, kinetic energy.  Velocity is proportional to kinetic energy (KE = 1/2 M * V^2).  Therefore, our change in velocity (acceleration) is directly proportional to Power * time.

ex. accelerating at 200 HP for 10 seconds adds 200*10*750 = 1.5 million Joules of energy to our car.  Starting from an initial speed of zero, in a car that weights 1000 KG,  the velocity would increase to 54 m/s = 194 km/h = 120 mph.  Note, this example ignores wind resistance and rolling resistance.
Therefore, we achieve an average acceleration of 54m/s / 10 seconds = 5.4m/s^2
Look at that, we calculated acceleration without needing to consider TRQ, RPM, or gear ratio!
Power/weight ratio is the correct way to balance a multi-car class, because it eliminates differences in available gear ratios and max RPM.

In Bil Doe's scenario above, he did not consider gear ratio.
If all 3 cars are exiting the corner at the same speed, at 2k, 4k, and 6k rpm respectively, then they must have very different gear ratios, changing the effective wheel TRQ of each vehicle.

Thanks!  I started to write this one out last week, and ran out of time--hoping that someone would make the statement and bring the physics formulas out.

I think that the big thing that gets missed is gear ratio, and also that often those "high torque" vehicles just have a much wider range of usable "flat" horsepower, requiring potentially less gearshifts (which is something, but we do attempt to compensate for this with our "Avg HP" formula.)

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