Winning Pinewood Derbies - Weight

Many times I have seen fathers and sons bring their cars to the weigh in and then take the car and add more weight trying to bring it up to the maximum weight allowed.  I would actually see them come back several time just trying to get the weight just right.  So I decided to see what the amount of weight would do to times.

The test car is a pinecar that I cut flat.  I then was able to stack weight on top of it to test the effect of different amounts of weight.  Also have a flat car meant I could move the weight along the car to test the effect of the center of gravity.

I took the test car and ran several trials with different weights keeping the center of gravity in the middle of the car.  As expected the car gets faster as the more weight as added.  Also, as you get closer to the normal weight limit of 5 oz the rate of change in time decreases. Actually the heaviest weight trial of 4.96 oz is slower than the previous weight trial at 4.62 oz.  However, the difference is within a standard deviation so statistically there is no difference. 

My recommendation is, if you get the weight of the car somewhere between 4.5-5 oz then you are fine.  No need to try and get it to be exactly 5 oz.


Weight     Trial (sec)        
gms oz 1 2 3 4 5 Avg STD
47.3 1.67 2.609 2.64 2.637 2.597 2.595 2.616 0.022
85.2 3.01 2.462 2.441 2.499 2.497 2.471 2.474 0.024
111.9 3.95 2.431 2.429 2.427 2.423 2.407 2.423 0.010
130.9 4.62 2.378 2.367 2.389 2.361 2.38 2.375 0.011
140.7 4.96 2.386 2.384 2.371 2.38 2.366 2.377 0.009

Chart of the data with a polynomial fit.


Relax and enjoy the race!