Pinewood Freak

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Maximizing weight

March 24th, 2010 · 14 Comments

Mike from Phoenix wrote in with an observation on how scales work, and how to use this to your advantage.

I noticed at my son’s pinewood derby this morning that his car weighed in at 5.1 ounces (the scale they used read out to one decimal place). I was a bit surprised and did a little bit of sanding – surely not enough to even come close to one tenth of an ounce, I thought. Out of curiousity, I weighed again – this time it came in at 5.0 That got me to wondering if the scale actually rounded to the nearest decimal place. Perhaps he really came in at first at just a hair over 5.05 … then my sanding perhaps got him just a hair under 5.05 ounces and then the scale at that point rounded down to 5.0 ….so, it occurred to me that if my theory is right then it’s sort of a way to add an extra 1/20th of an ounce to one’s car and still be “legal” (and thus maximize the potential energy)

Great thought, Mike. Only quibble I have is that I’d love to see your son doing the sanding and getting the car ready on race day. It is his car, after all.

Comments

14 comments so far ↓

  • David E. // Jan 27, 2011 at 11:03 am

    I taught my kids a technique that seems to utilize your philosophy on weight “gain”. I drill small pilot holes in the back of the car so they can “tweak” the weight at the scales. We have a variety of different screws that allows them to remove / add screws to get the weight as close to the round up number as possible. It also allows them to compensate for weight changes from humidity and scale calibration issues at district.

  • Aaron Logan // Feb 14, 2011 at 5:59 pm

    In reference to Mike’s thoughts on the rounding of digital scales: Although I never got around to testing it myself, I was taught by a very wise physics teacher that digital readouts always round down. Mike’s son’s car would read 5.1 ounces if the weight was anywhere between 5.10 ounces and 5.199999(…) ounces. A digital readout simply doesn’t report the next highest number until it actually reaches that number. So unless I was taught incorrectly, your son’s car could actually weigh 5.099 ounces and still read 5.0 ounces on the scale you were using.

  • chewbiewan // Apr 14, 2011 at 12:31 pm

    I see no problem accidentally being over and still having a reading at 5 ounces, but purposely being overweight and passing inspection is unethical and is cheating. Follow the rules. Is it 5 ounces or not? Are you also going to use illegal axles that can’t be distinguished? What else? Get your speed properly.

  • RLP // Apr 16, 2011 at 1:15 pm

    A Scout should be honest and such a suggested method of going over the weight limit is not legal, moral, or praiseworthy.

  • mr. e // Jan 3, 2012 at 12:29 pm

    a scout is trustworthy.

  • David // Jan 6, 2012 at 11:31 am

    If the district has a scale that only reports to the tenth of an ounce then it is what it is. No one can distinguish the difference at the weigh in of 5.000 ounce versus 5.099 if that is the case. If you have a scale at home that is more precise you will actually be at a disadvantage to others. It is not unethical for you then to play to the scale your district/pack is using as no one is at a disadvantage and everyone is weighing on the same scale.

  • Gonzo // Jan 19, 2012 at 5:02 pm

    I pre weigh my cars very close to 5.0 oz with my wife’s food scale (BTW they are a great gift and they are very convienient come Derby Season… ). I leave one 1/4 hole in the bottom of the car with nothing in it. At the meet I will mix Elmers and saw dust into a light weight putty and drop it into the upside downcar until it comes up to weight. you can remove it as necessary too (until it dries). You can help the other kids come up to weight with this tip as well, then everyone can have agood time.

    Hot glue works well for this as well and will also allow you to attach pennies and pewter weights.

  • PWDdad // Feb 1, 2012 at 5:28 pm

    Our district’s rules include the following:

    “Official weight will be determined by the official race scale on race day. The weight decision is final regardless of the car’s weight on other scales.”

    Their scales read to the nearest tenth. If it reads 5.0 on their scales, it passes. It doesn’t matter if it weighs 5.09 on your scale. It is according to the rules, the same rules everyone in the group uses, therefore it is fair.
    We use lead tape from a golf pro shop. We cut nearly square pieces and stick them on near the rear of the car. Each piece is almost 0.01 oz. With about 10 or 12 on the car, if it reads 5.1 just remove them one at a time until it reads 5.0 and then you pass.

  • Bill Klingler // Feb 12, 2012 at 4:11 am

    I recommend you buy a scale from Hodges Hobby House that reads in grams. You want 141.75 grams which the scale will read. Your son will have fun with the scale getting his car to this weight and lots of fun while building his car. The scale can be calibrated for accuracy. Also buy Wutty from Hodges Hobby House (tungsten putty) which is the handiest thing ever developed . I do not work for Hodges Hobby House but I started with Hugh Hodges in 1985 and now deal with Jerry since Hugh retired. I also deal with Randy Davis of Maximum Velocity. These two shops have great products and a wealth of correct information. Please teach your son WHY the two of you are doing something, not just that you are doing it. Thank you.

  • Bill Klingler // Feb 13, 2012 at 2:09 am

    I’d like to leave another comment if I may. This is directed to PWDdad. As we all know, the Pinewood Derby is a very valuable lesson in the Laws of Physics. We use Physics for our fuel and Gravity for our engine. It’s not cutting a piece of wood, pounding some nails in it, throw some weight on it someplace and go to the race. There is a very specific place the car should balance and a very specific place the weight should be placed. When building the car with your son he should be told why you are doing what you are doing and make a visual with him so he can understand it. When someone asks him why his car is so fast after he takes 1st place the scout can look him in the eye and say, “Because of the Cycloid of Constant Time” and then walk away. Yes, after they attend my Clinic, that’s what they will say to you. I do wish you Good Luck in your race but Luck usually has nothing to do with winning. Have Fun and enjoy the time with your scout. They grow up very fast.

  • Galen // Feb 2, 2013 at 5:03 pm

    Honesty is the best policy. Also we, my son and I, feel that people shouldn’t be allowed to use “store bought” cars. Build them! We build ours and last year he won 1st in our pack and 2nd at district!

  • Bill Klingler // Feb 8, 2013 at 5:42 am

    Congratulations on the win.
    The BSA has teamed up with the Revell Toy Company and Pre-cut kits are made in China & Officially Licensed by the BSA. Perhaps this was done to help folks who struggle to build a car. Check your rules and make sure a Pre-cut kit is legal. I see no difference in having Revell cut out the car or your local lumber company. Don’t use the Chinese wheels. They are .2 gram heavier than the U.S made wheel and not as good a quality. However, the Chinese axles are excellent.

  • dan // Feb 8, 2015 at 8:26 am

    I could be wrong, but I don’t see any moral or ethical problem with maximizing the weight based on knowing how the “official” scale reads and we follow our pack’s rules to the letter even though our inspection is lax to say the least.

  • Mike J // Feb 4, 2017 at 10:50 am

    Every scout goes by the same scale and thus all have the same opportunity to go to the max weight as the scale allows. Everyone can bring in weight and continue adding until it tips the scale or (as recommended) bring it in heavy and sand or drill or whatever it takes to get down to weight. No dishonesty there. If the idea was to be sticklers, the cars would be weighed in grams or even grains.

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