Do the "wafer" cars always win?

[Vitamin K]

So...as somebody who appreciates both the performance and aesthetic aspect of the Pinewood Derby, I am rubbing my chin at a trend that I seem to notice: Almost all of the "champion" cars (the ones that win at district and above) seem to be the 'wafer' design...that is, barely more than a slightly shaped board with hardly any sort of vertical contour to it.

You know what I'm talking about:



Anyhow...here's my questions:

1) Is this just my observation, and do other designs win in races that I just haven't watched?

2) Is it possible to get a really fast car without cutting the wood down to next to nothing?

3) Is it a really a faster design, or is it just the design that the racers who make the fastest cars tend to prefer? (E.g. is it causation or correlation?)

4) If it /is/ indeed a faster design...why is it faster? Is wind resistance really a factor between, say, a wafer and a wedge? Or does the ultrathin chassis provide some sort of flex that minimizes vibration or something?

I ask, because when I help my son make his next car, I want him to be able to create the design that he wants (in terms of looks), but since I know that he wants to win as well, I want to help him choose a fast design as well.

[FatSebastian]

I expect your questions will generate lots of interesting discussion. To start...

4) If it /is/ indeed a faster design...why is it faster? Is wind resistance really a factor between, say, a wafer and a wedge?

Yes, it is a factor, but not an overwhelming one. That is, a thick car could beat a thin one if the thin one has poor alignment, improper lubrication or inadequate weight placement. The thinner the car, the more control over how the weight can be distributed horizontally (there's less wood weight that needs to be countered). A thin car, by design, also forces the weight to reside vertically lower (close to the axle line), which seems just about optimal.

[Ickabod]

I can only speak for myself, but I think most of the time, you see these thin cars it is because they try and remove as much wood (weight) as they can so they can concentrate the weight (lead/tungsten) around the rear axle to try and maximize potential energy of the car (raise the weight to the highest point).

Ick

[FatSebastian]

I want him to be able to create the design that he wants (in terms of looks), but since I know that he wants to win as well, I want to help him choose a fast design as well.

In this case, I recommend that you build the design that he wants to build. At the level of Cub-Scout racing, shape is probably one of the least-influential performance factors, as long as it is relatively streamlined (no flags, sails, etc.). Weight placement and alignment are much more important.

[sporty]

Honestly.

You can do a 3/8th's r a 4/8th thick car with some following of the wood from the other side, but this is still a thin car, compared to a full body type car.

I attempted pretty hard to do a full size car ad making it pretty darn thin, be removing all the wood inside of the car body shape. and it still was not as fast and a thin car.

Simply put, hard to have less weight of the wood and still be very fast. Balsa wood comes to mind, but many if not all pack rules do not allow it. and the axle wholes done in balsa, a few ruff stop sections and its demolished for alignment, ect.

So, the answer is, if you want to go for looks, you are going to give up speed. if you want to do both, you are going to give up speed, but maybe not enough where you might have a chance for a 2nd r 3rd place.

But it comes down to what you're child really wants more, a cool look and design or speed. hard to have both.

and lets face it, it sounds like you need to make a choice and be okay with it.

Sporty

[Vitamin K]

Honestly.
So, the answer is, if you want to go for looks, you are going to give up speed. if you want to do both, you are going to give up speed, but maybe not enough where you might have a chance for a 2nd r 3rd place.

See, this is exactly what I don't want to be true (even if it is)

I imagine I'll have to let my son decide what he wants to put the emphasis on. That said, after I helped him make his first car (which won his Pack, lost at Districts), I discovered that there was a lot to be learned about alignment and wheel tuning. I don't think I could ever be happy with a car that was a 1/4" thick board-on-wheels. Just hard to give that shape any kind of character, you know?

[sporty]

Honestly.
So, the answer is, if you want to go for looks, you are going to give up speed. if you want to do both, you are going to give up speed, but maybe not enough where you might have a chance for a 2nd r 3rd place.

See, this is exactly what I don't want to be true (even if it is)

I imagine I'll have to let my son decide what he wants to put the emphasis on. That said, after I helped him make his first car (which won his Pack, lost at Districts), I discovered that there was a lot to be learned about alignment and wheel tuning. I don't think I could ever be happy with a car that was a 1/4" thick board-on-wheels. Just hard to give that shape any kind of character, you know?

There is still allot to learn and do, when it comes to wheels, wheel prep, alignment, rail riding, ect. weight placement. im sure you can do a fuller size one, hollowed out and be compititive, but depending on your pack, ect. I have not seen anything but thin cars in the wins for several years now.

[Scrollsawer]

I have only been building cars with my boys for 3 years (they are Bears), but I can tell you this. In order to be "typically" competitive in an average Pack, you need to be flirting with 3.05 or lower speeds. We have yet to go sub-three seconds, but we have won our rank all the three years, and we won 1st in Pack this year at 3.027 seconds.

I agree that axle and wheel prep and alignment are crucial, but if you also don't have the maximum amount of gravity on your side, it is going to be hard to overcome. I am a big believer in Newtonian physics, and for me, that means we try to put 3.75 ounces of weight packed around the rear axles. Anything less, and we are at a competitive disadvantage right out of the starting gate.

The only way I have been able to get this much ballast weight in a car is by getting the 'wood-only' weight of the car down to 10 - 13 grams. Needless to say, 10 grams of wood ain't very much wood. This is what Sporty is referring to when he means you have to decide which is more important: design or speed.

We have tried to compensate for the dullness of the Hershey bar shape and size, by carving designs into the wood, and routering, or using a forstner bit to drill holes in the car. This definitely broadens your designs options with the Hershey bar shape. Google [no advertising for this vendor]' Nellie Faye cars. They are pretty cool designs and have world class speed as well (due to many factors besides shape, of course).

Scrollsawer

[pgosselin]

I expect your questions will generate lots of interesting discussion. To start...
Yes, it is a factor, but not an overwhelming one. That is, a thick car could beat a thin one if the thin one has poor alignment, improper lubrication or inadequate weight placement. The thinner the car, the more control over how the weight can be distributed horizontally (there's less wood weight that needs to be countered). A thin car, by design, also forces the weight to reside vertically lower (close to the axle line), which seems just about optimal.

FS is exactly right. Thinness is merely a response to optimizing the mass of the car. However, I will say this: it also depends on who your son is racing against.

We won the Pack 4 times, brought home two 2nd place division trophies from District, and had the 2nd fastest car in Louisville Metro last year. All the cars we won with, were dog-bone-shaped with very thick back ends, but thin in the middle. Some, even had lead in them instead of tungsten.

Center of mass, wheel prep, axle prep, and alignment can carry you a long way. Unless you have a heavy concentration of Pinewood Derby nerds in your District.

I've seen lots of thin cars with tungsten weights in them that looked like they would beat us hands down. But usually their alignment was off and their wheel prep not good enough and we left them in the dust.

So, no, thin doesn't always win. But in the hands of an expert Pinewood Derby builder, it does.

Hope that makes sense.

Paul

[Speedster]

All your questions have been answered. We all know you cannot change the Laws of Physics. However, don't give up. You can still get an advantage (maybe) over the competition. Let's say your District uses a 42' Best track so you now know what you will be racing on at the District race. Rush out and buy a 2 lane 42' Best track so you can tune your car on what you will be racing on at District. You really don't need two lanes but the kids in the neighborhood will want to build cars and race each other.
You will probably win your Den race or take Second place because you have followed all the Laws of Physics. You're now going to District. Hopefully at District the Elapsed times will be shown so now you know what times the fastest cars are running. You now need to build a car that will beat that time and since you have the exact same track you've got an advantage. Even if elapsed times are not shown, you're watching the race and you can tell how much faster another car is then yours, assuming you don't have the fastest car. If you happen to have the fastest car you and your son still have to build a faster one for next year because everyone is coming after you. Also, everyone else is going to find out, somehow, you bought a track and you have it hiding in your garage. They are now going to do the same thing because they want to win also. Also, they somehow find out you read and ask questions on Derby Talk and now they're going to do it too. That's what makes those "nail biting" finishes. Isn't this exciting ?
Cheers
Speedster

[Vitamin K]

Oh, I'm not giving up. I know you can't break the laws of physics, but sometimes you can minimize their impact.

My thinking is that the next car I work on, I will make it reasonably thin, but reduce the wood weight as much as possible, via hollowing, so that I can concentrate the center of mass low and close to the rear axle. I still want to have an actual 'shape' to the car...something I can actually carve. Building a surfboard sounds like so much of the pleasure of woodworking is lost.

Those "[no advertising for this vendor]" cars are quite inspirational. Thanks for mentioning them, Scrollsawer.

[sporty]

you can always do a routed out thin flat one and add ontop of it a balsa shaped car design. Some have had some success with this. and it usually is okay with the rules of most packs.

Sporty

[Scrollsawer]

Sporty,

For our Webelos 1 race next year, we are considering that approach. There's a R/C airplane shop near my office with lots of different airplane balsa shapes to choose from. The stuff is so soft, I imagine a wood rasp and some sandpaper is all you would need to shape it. Balsa pieces only weigh in at a few grams usually. I have also considered craft grade styrofoam as body panels, but balsa seems easier to work with, so we save the craft foam as port and starboard boat ballast on our raingutter regatta boats, so they won't tip over easily.

But that's another topic entirely!

Scrollsawer

[Vitamin K]

Balsa sounds like an interesting option. I wonder if it would 'firm up' a bit after a few coats of primer and enamel. I think I shall have to buy a bit to do some experimenting with.

[Noskills]

Vit K,
Yes balsa does firm up nicely with 5-6 coats of primer which is also need to get a good even paint finish on it.
Noskills,
P.S. I used to work in Montgomery county, miss their awesome library system.