Speed on GPRM

[AlabamaDan]

I'm using Grand Prix Race Manager v.11 and a Best Track. I measured 37 feet and some odd inches between start pin and finish eye.

Most of our cars had a speed (mph) around 200 plus or minus. For example a time of 3.1301 came in at 201.5mph. Is this accurate?

I assume this has to do with the settings where I input the track length and scale. Is that right? Should the scale be 1:25?

Alot of people in the crowd watch this instead of the times and I wanted to make sure it is relatively correct. Also, how do you explain it? I think I said if everything was scaled up to a real size this is how fast they would be going.

[drathbun]

Also, how do you explain it? I think I said if everything was scaled up to a real size this is how fast they would be going.

I did the math this way:

A Pinewood Derby car is typically 7" long. My old Nissan Maxima was about 16' long. We have a 32' track with some distance reduced for the starting and ending gates so I guestimated it at 29'. A fast car gets down our track in 2.3 seconds. If I calculate the time it takes to go 29' in 2.3 seconds it's about 8.6 miles per hour. Next, divide 7" into 16' and that gets my scale factor, meaning how fast the car would be going if it were larger. Multiply that by 8.6 miles per hour and I got 235 miles per hour after scaling up.

So when folks ask me if the 200+ miles per hour times displayed on the overhead are realistic, I tell them yes. If they want more detail, I give them the math posted above.

[gpraceman]

It is funny how people remember the scale speed better than the actual times.

I explain scale speed with way: If you shrunk yourself down to the size of a driver for your car, it is the speed that you would seem to be going.

In the end, of course, only the times matter. Scale speed is just a calculation based on the track length (start to finish), car scale and the finish time.

[idpwdnut]

There is know doubt that the audience likes the speed read out much more. They can relate with MPH muct easier than they can with hundredths or thousandths of a second. Besides that kids (grown ups too) just think 200 MPH + is awesome.

When I talk to a crowd about it, I explain that the PWD car is a 1/25 scale of a full size car. The length of the track from the starting pin to the sensors is X feet. The race program takes the feet travelled, size of the car, time travel and through the miracle of modern math, we get the speed of the car. It usually gets a good chuckle. I then explain that official finish order is determined by the actual elapsed time from the timer. This is good for when two cars finish at 201.4 mph, I just point out that x/thousandths of a second that actually seperated the two close cars.

The time makes it technical, the speed makes it fun.