Pinewood Derby Car Weight

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kstevens67
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Pinewood Derby Car Weight

Post by kstevens67 » Wed Jan 14, 2015 12:43 pm

Hi all,

I am absolutely horrible at building anything and have had two nightmare races so far with my son. I want him to do well in his race, but I also want him to finish the race as the last two years he didn't (my fault). I am hoping that the third year is the charm as they say. We have his car built and it currently is weighing in at 4.9 ounces (on our scale). I am terrified that the scale they use may be .2 ounces off throwing us into the over weight category. I am considering removing .1 ounce of weights so the car weighs at 4.8 ounces giving us some leeway. I'm not going to be able to get to the weights after the wheels are put on (I know, I'm not good at this). I have heard that cars that weigh 5 ounces are going to win. Is there really much difference between 4.8 and 5 ounces?

I obviously want him to win, but I will be devastated if he cannot race at all due to my stupidity think that 4.9 ounces is good. I'm not so sure I trust other scales.



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gpraceman
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Re: Pinewood Derby Car Weight

Post by gpraceman » Wed Jan 14, 2015 12:56 pm

What type of scale do you have? If it is a digital scale, I could see having a 0.1 ounce difference to the check-in scale, but likely not a 0.2 ounce difference.


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kstevens67
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Re: Pinewood Derby Car Weight

Post by kstevens67 » Wed Jan 14, 2015 1:06 pm

We have a digital scale. If I remember, they use a digital at the race also.



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Vitamin K
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Re: Pinewood Derby Car Weight

Post by Vitamin K » Wed Jan 14, 2015 1:19 pm

Two options:

1) Go at 5oz, and if you're overweight at the weigh-in, take off a little weight. You can bring a cordless drill and drill a little wood out of the bottom, for example. Doesn't take much to lose 0.1 ounces.

2) Go in underweight and bring some "trim" weight to the weigh-in. If you come in underweight, add a little lead tape or tungsten putty.

Almost all Derby weigh-ins will let you adjust before committing the final weight.

For what it is worth, .01oz is probably not going to make a difference in performance. Ask Scrollsawer about the 4.5oz hotdog. :)



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Stan Pope
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Re: Pinewood Derby Car Weight

Post by Stan Pope » Wed Jan 14, 2015 1:49 pm

How have you weighed your car? Many visit the local post office to do so. Be aware that some (maybe all) such scales that weigh to 0.1 ounce trip to 5.0 ounces if the actual weight is a hair over 4.9 ounces. If you weigh in at 4.9 ounces on such a scale, then you are between 4.8 and 4.9 ounces already.

Weight is important, but is not the "be all and end all". Get close.

More important, polish the axles and get the alignment true. There are several ways to handle alignment ... drilling true holes and using ultra-straight axles and twisting slightly bent axles. Since you are probably already committed to where and how the axles attach to the car, you may be left with using slightly bent axles. If you don't find info you need by searching Derby Talk, check pages at Measuring the Bend Angle of Bent Axles and Aligning Rear Axles, New 2013. Look about in Derby Talk regarding how to treat the dominant front wheel so that it follows the rail and helps keep the rears off the rail.


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Scrollsawer
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Re: Pinewood Derby Car Weight

Post by Scrollsawer » Wed Jan 14, 2015 2:56 pm

If it were me, I'd prefer to come in under weight to 'weigh-in', and add weight to the degree possible.

I don't know much about your 'build details', so hard to offer specifric advice. Here's the stuff to consider:

Is your current weight in/on the car easily removeable and easily 'put-back-on-able'? (i invented a new word!)

Come to 'weigh-in' at 4.85 ounces as measured by your digital scale. Bring a variety of weighting options (coins, fishing weights, etc.) or other incremental weights that you have easy access to. and some Crazy Glue to help stick it all on the car. Use small amounts of weight without glue on the official Derby scales, and when you're at 4.98 - 4.99, call it a day, and then glue the weight on with crazy glue AFTER you've come to a weighting agreement with the race inspectors.

As insurance, bring a drill with a 1/4" drill bit to the weigh-in, and if things go wrong on the high side after the final weigh-in, then (and only then) should you consider drilling into the car to remove weight. It's an option of last resort on a car that you both have worked so hard on.

There are a LOT of folks here on DT that would be very happy to give you 'tuning tips and advice' that could assist you and your son (that would be applicable at this stage of your build). Perhaps you can elaborate on the car's design, weighting, etc., and even upload a pic. or two to the site for us to see it, and make some recommendations?

Scrollsawer


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Re: Pinewood Derby Car Weight

Post by ngyoung » Wed Jan 14, 2015 3:21 pm

Does yours have a toggle for grams? 141.748 grams is 5oz. So if you are at 140 you're probably fine. Depending on the scale used you could also conceivably go as high as 5.04oz before being deemed over weight. You should also have some portion of your weight that you can easily remove or add to. An easy option is getting tungsten putty. You could also bring pennies or washers to tape into a pocket. We used some aluminum tape that is very sticky and had an empty void to add weight. Just have your scout weight it on the official scale and add weights until it just tips over 5oz and back some off. Leave to install it quick and come back.

In the grand scheme of things for speed there are plenty of 4.9oz cars that beat 5.0oz cars. If you spent some work de-burring the axles and polishing them your kid will be in the mix. That is pretty much the biggest gain in speed you can do, other then making sure the weight is in the rear and not the front. Do your rules allow for only 3 wheels touching and axle canting? Have you looked into setting up the car for rail running?



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