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AZBMW Forums › General Forums › Track (HPDE, Autocross, 1/4 Mile and Drifting) › NASA GTS (German Touring Series) 2015 Rule Changes
NASA GTS (German Touring Series) 2015 Rule Changes
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PostPosted: Wed Dec 24, 2014 7:03 pm
Post subject: NASA GTS (German Touring Series) 2015 Rule Changes

Posted as an FYI

Finalized rules

Pulled direct from the NASA boards discussion GTS Challenge 2015 Rule Changes

"For 2015, the NASA GTS rules will include three changes, two of which are minor, and one of which I believe will be considered major. This document has been written to explain the logic and intent of these changes. Because, as you will learn, we are still working through a few details, the final written version of the rules will not be available for another week or so. However, that doesn't mean we can't share with you the details of this year's changes.

Let’s start with the easy ones:

General availability of tires

The new paragraph covering this rule reads as follows:

All tires, whether DOT-approved or not, must be commonly available to all competitors from typical national retailers (for instance, Tire Rack), or directly from their respective manufacturers. This is to be interpreted to mean that special compounds not generally available to all competitors are not permitted.

The intent here is simply to disallow individual competitors working with tire manufacturers to create one-off or very-limited-run tires not available to other competitors.

Additional sequential gearbox penalties

Last year we added a 0.2 lb/hp penalty for racing sequential gearboxes. For 2015, we have extended that penalty to include Porsche’s PDK, BMW’s DCT, Volkswagen’s DCT, and other similar gearboxes. Specifically excluded are Porsche’s Tiptronic, BMW’s SMG, and older conventional “automatic” gearboxes.

Change the method of calculating minimum race weight

This is quite possibly the biggest rule change ever made in GTS, and one we, as series directors, do not take lightly. Because of that, and because the changes we are implementing will likely touch each and every GTS racer in some way, I would like to take some time here to discuss not only the specific changes we are making, but also the reasoning behind them.

A changing playing field

When GTS was first created, the idea was to provide a series where German cars could race one another with minimal limitations on the modifications that could be made to those vehicles.

Rather than have a highly-regulated points system like the ones used to assess modifications in NASA’s PT and ST classes, and unlike the restrictive limits set in the various spec classes, GTS has always been comparatively wide open in its acceptance of performance modifications of virtually all types. It was, and remains, the ideal series for drivers who like to tinker with their cars in search of increased performance.

Other than a penalty for using full racing slicks (as opposed to DOT-approved tires), the only real performance limitation in the original GTS rules was a power-to-weight ratio used to determine each car’s minimum allowed racing weight based on its peak horsepower (and in some cases a combination of horsepower and torque).

The point of using the power-to-weight ratio was to equalize, as much as possible, acceleration between the cars in each class. Cars with more power had to carry more weight, while those with less power could run at lower weights but, at least in theory, all of them would accelerate more or less the same.

From that relatively level base, performance differences could then come from differences in driver skills, suspension setup, etc.

This very simple set of rules lasted for many years with very few changes. Since originally written, we have added additional penalties for tube-frame construction and for sequential gearboxes (which were unheard of in amateur racing when GTS was originally formed), but not for much else.

But since those early days, technologies and, in particular, engine management systems have advanced significantly, making it possible for engines to do things that were essentially unthinkable just ten years ago. It is these new capabilities that have had the biggest effect on our decision to change the minimum weight calculation.

But before I get any further into the details of the new calculation, it’s important to clear up a few misconceptions related to horsepower and torque because these, too, inform our decision.

A quick aside about horsepower and torque as they relate to racing

While there has been a great deal of talk both ways regarding torque and horsepower, the truth of the matter is that torque is a measure of force, while horsepower is a measure of the rate of application of that force.

The bottom line is that what matters for acceleration is horsepower. And, just so there are no misconceptions, 200hp at 2,000 RPM has exactly the same ability to accelerate a car as 200hp at 8,000 RPM.

Engine speed is absolutely unimportant except to the extent it has a role in the computation of horsepower because torque is multiplied by RPM as a part of the calculation that results in horsepower. Because of this multiplication by RPM, 100 lb-ft or torque at 2,000 RPM does not create nearly as much horsepower as 100 lb-ft of torque at 8,000 RPM. But once you have a given horsepower value, it will do exactly the same amount of work, regardless of engine speed. 200 horsepower is 200 horsepower, and horsepower is what matters for acceleration.

Given that, the first thing we can say for certain is that the current GTS calculation, which averages torque and horsepower when the torque is higher, is flawed. This part of the calculation unnecessarily penalizes high-torque cars because, as I have already explained, it is only the horsepower that matters in determining the ability to accelerate.

Therefore, the alternate minimum weight calculation that is used when torque is higher than horsepower should be removed from the rules.

But if the goal with setting minimum weights is to level the playing field in terms of individual cars’ ability to accelerate, we also need to consider more than just each car’s peak horsepower. Let me explain why:

The unfair (but legal) advantage

Our current rules have no restrictions on what modifications drivers may make to their engines or their related components. Because of this, and because of the sophistication of modern ECUs and electronic throttles, several companies and numerous individuals have found ways to quite legally give themselves an enormous advantage in terms of raw acceleration on the track.

Consider the graph shown below:

This is a graph of two different GTS3 cars, one (in blue) a normally-aspirated engine running unrestricted, the other (in green) an oversized engine that has been electronically throttled back to maintain a particular maximum power level. I should note that these lines represent actual values from actual GTS cars.

What is shown here is the percentage of maximum horsepower for each car across the upper 30% of that engine’s RPM range. This is roughly the part of the power band that’s used when these cars accelerate through the gears, shifting at or near redline.

Note that the green car never drops below 97% of maximum horsepower across the entire spectrum, while the blue car only briefly makes it up to that value. Keep in mind that this is a graph of relative horsepower, and that horsepower creates acceleration. If both these cars peak at 250 horsepower and compete in GTS3, both cars will be assigned the same minimum weight: 250hp x 11.0lb/hp = 2,750 lbs. But with significantly more horsepower over the usable RPM range, the green car will have an enormous advantage in actual acceleration.

To be clear, there is nothing here that is against the current GTS rules. The modifications that tuners have been able to make to create power bands like that shown here are, frankly, brilliant, and provide an absolute advantage on the track that is perfectly legal with the rules as they are written today.

But while this kind of modification is legal, it is not in the spirit of the GTS power-to-weight rules. The intent of these rules was to equate, as much as reasonably possible, the acceleration between all our various GTS cars. Which brings us to the need for a change in the method of calculation.

A new method for calculating minimum weights

The example shown above is a good illustration of the challenge facing us, but the chart is somewhat misleading as it over-emphasizes the differences between the two cars by not showing the full 100% of the horsepower range. The chart below shows the whole range:

Looked at this way, the differences between the two cars seem smaller, but there is still a clear advantage of one over the other. But is that really enough to matter? In fact, it is.

Over the full 30% of the rev range shown in this chart, the green car makes, on average, 99% of its maximum power. Ninety-nine percent. At a peak of 250 hp, that means the green car averages 247.5hp across the top 30% of its rev range. That’s a remarkable feat of tuning.

By comparison, the blue car averages just 91% of its peak power over that same range, or 227.5hp.

So, on average, the green car makes 8.8%—20 more horsepower— than the blue car all the way across the most important part of the power band while being allowed to run at the exact same minimum weight.

It seems clear from this example that what we should be considering is not the peak horsepower of each of these engines but, instead, the average area under the curve across the most-used part of the power band—that is, the part of the power band shown in the charts here.

You may be wondering why we have settled on the upper 30% of the rev range. After reviewing gearing charts for dozens of transmissions from the various manufacturers of GTS-eligible cars, we discovered that the average drop in RPM between gears as those cars accelerate from 50-150 mph fell into a range of about 25% to 40% of maximum revs. Given that, 30% seems a balanced and reasonable compromise, and it is this 30% that is shown in the graphs above and which figures into our calculations below.

To truly level the playing field, either the green car (in this example) should carry a bit more weight, the blue should be allowed to run a little lighter, or each should move a little each way.

And in essence, that’s what we are doing with the minimum weight calculations for 2015.

Although we are still finishing up the software to support these calculations, GTS will provide an online calculator that takes inputs of the usual data (GTS class, type of tire, sequential gearbox, etc), plus RPM values for every 1,000 RPM across the useful part of your car’s power band—which is usually the top 50% or so of the rev range. In addition, there will be inputs for redline RPM and horsepower, and for maximum horsepower and its corresponding RPM value.

From these values, the calculator will identify the optimum 30% of the power band, break it into 10 equal increments, pro-rate the horsepower values for each of those increments, and then average them.

Because the resulting average horsepower values will be lower than the peak horsepower numbers we use today, the ratios for each class will be adjusted accordingly. Our goal in this adjustment is to find a balanced value for each class, where roughly half of our cars will need to add weight (or reduce average power) and about half can take weight away.

As series directors and competitors ourselves, we recognize that the changes outlined above will not make everyone happy. What we hope is that all GTS competitors—even those who find themselves having to race a little harder as a result of these changes—will appreciate these changes as helping to match today’s realities to the spirit of the GTS rule set.

Thanks for your interest and participation. Good luck out there this year."

2002 SG E46 M3

Last edited by giantkeeper on Wed Dec 24, 2014 7:14 pm; edited 3 times in total
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PostPosted: Wed Dec 24, 2014 7:11 pm
Post subject: Re: NASA GTS (German Touring Series) 2015 Rule Changes

2015 NASA GTS Weight Calculator

2002 SG E46 M3
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