Weighted Wheels

General topics of interest to racers and race coordinators alike.
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Titonka
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Weighted Wheels

Post by Titonka » Sun Nov 19, 2017 4:45 pm

Recently wondering about the physics of weighted wheels. I found these online and was thinking of using them for a slender/think PWD build. My original idea was to superglue these in the rear wheels. They fit exactly within the wheels and it seems to me that they are both great for using that space up on a thin car and reduce inner wheel turbulence. My worry is that they might work against us as they would take a little longer to get rolling, however the weighted motion may kick in on the flat of the track...kind a like a flywheel. There is where my question lies....I know there are weights that work in the same way but attach to the body instead. They also have a portion removed from them so the officials can see the words on the inner wheel. Our local rules do not require that however, so we might get lucky on that.

Just looking for feedback.
Thanks,
Dan

https://www.ebay.com/itm/2-pc-extsw-1-4 ... 4902.l9144



Speedster
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Re: Weighted Wheels

Post by Speedster » Sun Nov 19, 2017 5:32 pm

You want the lightest wheels you can use legally. Scout racing doesn't use a long enough track for a heavy wheel to be an advantage.



Titonka
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Re: Weighted Wheels

Post by Titonka » Sun Nov 19, 2017 7:49 pm

Makes sense...I'm a cyclist so I thought more about it from that point of view. For speed you do want light wheels. It would probably take more energy from the start to get them rolling. With a short track, it might not result in an advantage. It is one theory I might want to test a little bit more. Toying with the idea of drilling in a couple of holes to mount them directly to the body instead. Drawback on that would be accuracy so they don't rub the inner wheel. I'm not sure I can pull that off.



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Vitamin K
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Re: Weighted Wheels

Post by Vitamin K » Sun Nov 19, 2017 10:38 pm

"Wheel Weights" made for Pinewood Derby don't attach to the wheels. They attach to the side of the body and take up the space in the void of the wheel, without actually touching any of the moving surfaces. Thus you get the advantageous weight location, and the aero advantage from blocking air inside the wheel voids.

You can also purchase "fender washers" from Home Depot or similar and glue these to the side of the car for a similar effect (though obviously not as heavy as tungsten would be.)



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MaxV
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Re: Weighted Wheels

Post by MaxV » Mon Nov 20, 2017 7:42 am

Below is a link to a test I did on wheel weighting - the bottom line is you want light wheels (as was said above). Vitamin K is correct that pinewood derby "wheel weights" do not touch the wheels.
http://www.maximum-velocity.com/pinewoo ... imes-v7i3/



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Re: Weighted Wheels

Post by Speedster » Mon Nov 20, 2017 10:14 am

Welcome to Derbytalk.
Titonka, are you racing in the Cub Scouts? Most Cub Scout racing has fairly restrictive rules, especially when it comes to the wheels. I understand what you had in mind from the ebay item you referred us to. If you're just having fun playing with different things, go for it. If you are new to the Pinewood Derby allow me to refer you to a few things. A book titled "Build a Winning Pinewood Derby car" by Troy Thorne. A You Tube video titled "Easy Pinewood Derby Car Wins Using Science" and of course, Derbytalk along with its Search function. If your goal is trying to go Fast, a lot of Derbytalk folks are on your side.
Let us hear from you and ask a Lot of Questions. I'm still learning and I LOVE SPEED.



Titonka
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Re: Weighted Wheels

Post by Titonka » Thu Jan 04, 2018 9:23 am

Speedster....you bet, we like to try new things while still following the rules. We've had a fellow scout leader in the past put and hour into "his" car right before the race and take first place several years in a row. It's nothing but a flat racer. I'm not sure how much the scout is getting out of that but the chance to brag. I an my sons are not about that. We look at the physics of things (as much as my kids can handle). We just did a test this weekend on weighted wheels and I was surprised. We angled a piece of plywood at the same angle as a track. We then "raced a weighted wheel against a standard wheel...by far, the weighted one rolled quicker/faster, every time. Now, the science of this tells me that once on the flat portion of the track, the weighted one will then act like a flywheel continuing to pick up speed...if it doesn't pick up more speed, it should take longer to slow down, using the momentum it built on the downhill. I've checked with our rules and we're good to try this. Testing this afternoon!



Titonka
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Re: Weighted Wheels

Post by Titonka » Thu Jan 04, 2018 3:20 pm

Nope...weighted wheels seem to be a bad idea. The track test was worth trying but I couldn't dial it in enough to make a significant increase in speed.



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Re: Weighted Wheels

Post by Speedster » Fri Jan 05, 2018 6:18 am

If by a Flat racer you mean the car resembled a Hershey bar, then the scout might well have gotten a tremendous amount of knowledge out of the build. The scout and his adult helper might well have been on Derbytalk 3 times a day.. The scout might well know all the Physics of the Pinewood Derby and now has to do all the other activities better then anyone else. If he keeps winning then he deserves to win because he's starting out with the best design there is to build a winning car. What do scouts like to do the most? Paint the car. The scout probably did that. There's a lot of work a scout can do when building a winning car - bore prep, axle prep, Center of Gravity, tuning, tuning, tuning. I stress Speed in all my seminars, Once everyone has the knowledge on how to build a Fast car they can then do whatever they want.



Titonka
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Re: Weighted Wheels

Post by Titonka » Fri Jan 05, 2018 9:10 am

Yeah, I'm sure he learned something but really, though they are fast cars, in my book, the learning should come from the tools introduced to the scout each year, not just repetitive "same car as last year". They "skin" the cars with candy bar wrappers is all - no painting. I think it takes all the fun out of it. I know them well, his son isn't all that into PWD. The worst part from last year and the year before is the "rubbing it in" to my kids. It wasn't very scout-like.



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