Why pinewood derby cars run fast
There are lots of wild rumors about what makes fast (and slow) pinewood derby cars.
We have this fancy electronic track which allows us to take cars, run them
enough to determine what their typical time is, and then modify them and
see what the modification does to the run time. So I feel qualified to add
to these wild rumors.
Note that the track that our pack uses is one of constant slope.
There were reasons for this, mostly due to lack of information.
In any case, if you are running races on other track designs,
then the following items may affect you to a different degree.
I do feel it would be interesting to actually do a controlled
experiment a several sample cars to measure these things in
detail. If you have a situation where you have repeatable
electronic timing and the time and place to run such
experiments, I would encourage you to do so and let me find
out what you find. Run each configuration several times and
average the results. Note that cars do change, especially if
they get bumped together.
- Airdynamics/air resistance.
It doesn't matter.
One of races included a car (made by a dad) which was simply the block
of pine with the wheels carefully put in place. The only decoration was
that the box that the car kit was packed in was glued to the block.
It gave a very good performance. Now we did modify some cars with
a slot to put in a playing card to add lots of air resistance. The
air resistance is measureable, but over the normal front area of a car,
it doesn't matter.
- Weight.
It doesn't matter.
Yes the heavier cars turn in better times then lighter cars, and varying
the amount of weight on a test car is measurable. But it doesn't matter.
- Position of the weight.
It doesn't matter at all.
I could find no significant measurable variation here.
- Wheels.
This is what matters.
Remove all burrs from the nails and wheels supplied.
Be creative in the use of files, sandpaper, graphite, and visual inspection.
Our last race had cars which had typically run twelve races over the night.
The cars turned in times of:
- 1st place; 3.988 seconds
- 2nd place: 4.035 seconds
- 3rd place: 4.045 seconds.
So these races are won on very small margins. Paying attention to details
will matter. Note that between 1st and 3rd place is 57 milliseconds. That
is approximately 1/20 of a second. When you go to the movies they only put
24 pictures per second on the screen and you see it as continuous motion.
Not everybody agrees with my opinions.
Some of this may be due to the nature of our track which is a
constant slope track.
Anyway, for other views, please see the pages on the WebRing
as well as the comments below:
Last modified 27 May 2006
Questions or comments can be sent to
Dave Regan.