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      03-09-2014, 02:18 PM   #1
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Roll Racing: Does a fraction of a second head start matter in the end?

Everybody has their preference for the type of racing they like. For whatever reason, people like racing to show how fast their car is against another. Some like 1/4 Mile drag races, others 60-130 MPH vBox results, and others roll racing.

Recently I saw a guy say he didn't like 60-130's because there were too many variables -- and roll racing is the only true and accurate way to test one car against another. "Say, what? I thought?" I understand not liking 1/4 mile drag races because the results are dominated by driver skill and not car performance. Similarly, a roll race may be fun, but if the results are close you can't ever really tell which car is actually quicker. I thought a roll race can't ever be accurate because it's impossible for two people to start at exactly the same speed or same exact time. Somebody will always start a fraction of a second before the other. But I just didn't know how much difference that fraction of a head start would influence the results.

So I thought: what's there not to like about 60-130's? There's a set of rules that apply to everybody equally. The results are measured with a vBox GPS device that is accurate to a few hundredths of a mile-per-hour. On a car like a BMW M3 with DCT, even the shift speed is taken out of the list of variables. So assuming you have two similar cars with equal tires, suspensions, but different drivers and motor mods, then I don't quite understand what's not to like about a 60-130. But it got me thinking about roll racing again.

A couple of years ago I wrote a program that can reanimate a race between two cars based on nothing but their vBox files. I called that program "vBox Racer" and you can find some of the videos on youtube that show how it works. I wondered what would happen if I could simulate a roll race between two identical cars where I changed nothing but the delay to start the race. I wondered how that fraction of a second delay from one driver hitting the gas to the other would affect the results. It seemed that vBox Racer would be perfect to help answer that question.

To find two identical cars would be easy: I'll literally use the same vBox file for both races by making a second copy of the file, and I'll insert a fraction of a second delay in the second file. Then I would use vBox Racer program to reanimate the race and see what happens. The goal isn't to prove or disprove what somebody says, but more to educate myself and anybody else who wants to learn along with me.

The video below contains three reanimated races:
1) 1/2 second head start (0.50 second head start)
2) 1/3 second head start (0.30 second head start)
3) 1/10 second head start (0.10 second head start)

To help illustrate how much or how little time we're talking about, the video contains a demonstration of a split second white screen in 1/2, 1/3, and 1/10th second intervals then shows the results of a race using that same head start. In a real roll race, any of of these fractions of a second are possible. I'd say most roll races one driver punches the gas between 1/10 to 1/3 second earlier than the other.

Here's the video. Watch and decide for yourself. (Recommended to watch in full screen mode.)



About vBox Racer

vBox Racer is a program that will reanimate a race based on the contents of two vBox files. Everything you see is rendered perfectly to scale. The cars, road, distance between cars, and even the lines passing on the road are all rendered to exact speed and scale.

The distances you see between cars (car lengths) are the actual distances that would exist based on the contents of these vBox files.

Last edited by regular guy; 03-09-2014 at 02:24 PM.
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      03-09-2014, 02:32 PM   #2
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i would think the exact draw of 1/4 mile and road course for that matter is that its about driver skill. like the appeal of playing poker vs slot machines. if you cant be good or bad at it wheres the fun!
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      03-09-2014, 06:45 PM   #3
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I wonder, what skill is involved in going fast in a straightline...
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      03-09-2014, 11:38 PM   #4
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Quote:
Originally Posted by OC3 View Post
I wonder, what skill is involved in going fast in a straightline...
Dude.

Not everyone has right foot talent you know.
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      03-10-2014, 01:05 AM   #5
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Haven't you posted this before?
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      03-10-2014, 04:47 AM   #6
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Nice video.

I agree with your conclusions. I did a similar simulation model programmed in Turbo Pascal in the early nineties and came to the exact same conclusion as you .
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      03-10-2014, 05:10 AM   #7
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If you haven't got a PC handy a "back of a cigarette packet" calculation will give you an indication of what the distance difference would be.
50mph to 180 mph with a .5 sec jump
(180-50) x 44/30 x 0.5 = 95 ft
at .1
(180-50) x 44/30 x 0.1 = 19 ft

30 mph = 44 ft/sec.

I've always though that a rolling start from tickover in 1st would give a fairer result as it factors in traction and tractability.
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      03-10-2014, 09:14 AM   #8
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Quote:
Originally Posted by tinman831 View Post
Haven't you posted this before?
Nope. I just ran this simulation two nights ago for the first time.

Quote:
Originally Posted by CanAutM3 View Post
Nice video.

I agree with your conclusions. I did a similar simulation model programmed in Turbo Pascal in the early nineties and came to the exact same conclusion as you .
Turbo Pascal brings back memories. I remember version-1 when Borland was in Scott's Valley.

Quote:
Originally Posted by SenorFunkyPants View Post
If you haven't got a PC handy a "back of a cigarette packet" calculation will give you an indication of what the distance difference would be.
50mph to 180 mph with a .5 sec jump
(180-50) x 44/30 x 0.5 = 95 ft
at .1
(180-50) x 44/30 x 0.1 = 19 ft

30 mph = 44 ft/sec.

I've always though that a rolling start from tickover in 1st would give a fairer result as it factors in traction and tractability.
Not sure I follow the significance of 44 ft/sec (44/30) in the equation.

The airport roll races out here usually start at 40 or 50 MPH.
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      03-10-2014, 09:59 AM   #9
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Quote:
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Not sure I follow the significance of 44 ft/sec (44/30) in the equation.
Never mind, I figured it out. It's just mph to fps conversion. You could have chosen any number there like 1 or 180 mph / fps and come up with the same ratio.

Hey, but on the bright side, it's good to know vBox Racer -- which has to use integral calculus to calculate distance -- came up with the same values.
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      03-10-2014, 12:30 PM   #10
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Quote:
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Turbo Pascal brings back memories. I remember version-1 when Borland was in Scott's Valley.
I guess we are showing our age here
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      03-10-2014, 12:50 PM   #11
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Quote:
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Quote:
Originally Posted by OC3 View Post
I wonder, what skill is involved in going fast in a straightline...
Dude.

Not everyone has right foot talent you know.
True. I find that out when I lift and end up fawked in the turn. Especially in the GT3.
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      03-13-2014, 12:03 AM   #12
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Quote:
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True. I find that out when I lift and end up fawked in the turn. Especially in the GT3.
TTO. Trailing throttle oversteer. Sometimes it can help. Sometimes it can hurt.
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