Thoughts on "stock" wheelbase

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Stan Pope
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Thoughts on "stock" wheelbase

Post by Stan Pope »

Just went through a body build using 1/4" sintered tungsten cubes to get "optimum" CM location at 1/4" body thickness on an extended wheel base car.

I've never been able to get 5/8" CM with rear axles 9/16" from the rear using lead unless the thickness of the rear end reaches around 1/2". There just isn't enough volume available to fill!

Here's some thoughts:
1. Comparably skilled builders will benefit, perhaps decisively, from the ability to reduce the body thickness to 1/4".
2. Optimum ballast for a 1/4" thick car, when the rear wheels are flush with the rear of the car, is tungsten.
3. 4 ounces of tungsten cubes are more expensive than less dense ballasts.
4. Alternative, cheap sources of tungsten, such as left-over tungsten weld rod ends, being round, don't pack well, so their density suffers.

So, rather than encourage all of the builders who want to be competitive to go buy tungsten, I'm thinking that the cost aspect becomes more managable if the rear wheels must be in "stock" locations. Other types of ballast would become competitive. It still takes skill to build a competitive car, but the $ become less of a factor.

Thoughts????
Stan
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Re: Thoughts on "stock" wheelbase

Post by Speedster »

Hi Stan,
I'm new to this forum which I'm ashamed to admit since this is my 27th year racing the BSA. My various tracks have been used in our Pack since 1985. I get to start the cars and I get to race the 1st place winner of each grade group. I offer the scout $5.00, win or lose, to race me. I've had some mighty close races but haven't lost a race yet. I build a new car every year to comply with the rules. This is a great forum.
I appreciate you thinking of the folks pocket book but I think your #1 says it all. This is an excellent lesson. I would tell my scout he will have to do (?) to earn money because he needs supplies for his derby car.
According to Doc Jobe (Page 40 of the big Green book) we want the CM as far up the Arc as possible to take advantage of the Higher Velocity it gives us and also the advantage of the Front End Extension effect (That Cycloid of Constant Time Thingy). We must keep the stock wheelbase in our District. I always cut off the back of the car behind the rear wheels and move it to the front since our district has no rules regarding length from axle slot to end of car for either end. This gives me an advantage before the race even starts. If you build your car perfect and I have the back end of my car sticking out using cheaper weights, you are going to WASTE me. I'm afraid I can't allow that to happen, Mr. Pope. Perhaps my wife will give me some money if I do the dishes for a week. Ha, Ha.
I have a question. Even though it gives me a tremendous advantage because folks probably follow it, why do the Scouts show, year after year, the car on the box using the wrong end for the front? I've always wondered that.
Thank you for all you do, and for all you have done, for the Pinewood Derby and Scouting.
Cheers,
Bill
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sporty
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Re: Thoughts on "stock" wheelbase

Post by sporty »

Stan,

I have seen fast cars with lead. and 1/4 thick or just a tad thicker.

But they took the time to route out the wood under the car to fill in with hot lead.

But then not many people have melting lead pots and then we have the whole issue of exposed lead fumes to the kids.

Sporty
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Re: Thoughts on "stock" wheelbase

Post by Stan Pope »

Bill, your rep is on the line every year! The pressure must be intense! And I can tell that you love it! Way to go!!!

I've been wondering the same thing about that picture. I think it ceased to be a competitive design when tracks went from constant slope to single curve! But tradition is tradition, and some traditions are hard to change. On the other hand ...

I wonder the pic is intentionally bad ... to advance the learning process ... maybe early discovery of that anachronism and the design compromises it carries is one of the first steps toward the learning that we expect PWD to produce. (Not just the reversed wheelbase, but also the questionable aerodynamics and the color ... everybody knows that red cars are faster than yellow cars... at least to the unaided judge's eyes!)

There are a few tracks on which it might be competitive ... the double curve which has a very gentle slope (3 to 5 degrees) at the starting line for a foot or so and then a steep slope (30 degrees) down to the flat. That might be a fun track to design a car to run well on! If it were my track and I ran the races, I'd change the starting slope every year just to make their lives interesting and avoid "cookbook solutions"! :)
Stan
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Re: Thoughts on "stock" wheelbase

Post by Stan Pope »

Sporty,

Using lead in an extended wheelbase car, how thick does the rear have to be in order to have the same weight distribution (5/8" CM) as with tungsten? About 60% thicker, 0.4" if the lead is solid (no glued-up sections), doesn't it? Reducing the thickness requiries increasing the CM distance.

So, with equally skilled builders, the lead user must make more compromises with either energy availability or energy waste. The lead user can be fast, but if he used tungsten he would be faster. Of those two, it sounds like the guy who uses tungsten ballast beats the guy using lead ballast. If the guy using lead really wants "first chair" sounds like he must improve his skill way above that of the tungsten user OR must "pop for" tungsten and improve his skill just a hair.
Stan
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Re: Thoughts on "stock" wheelbase

Post by whodathunkit »

Stan,
Is melted lead heaver the tungsten ?
Not that try useing molten lead do you know if this is a myth or a fact.
What type of automobile can be spelled the same forwards & backwards?
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Stan Pope
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Re: Thoughts on "stock" wheelbase

Post by Stan Pope »

whodathunkit wrote:Stan,
Is melted lead heaver the tungsten ?
Not that try useing molten lead do you know if this is a myth or a fact.
Solid lead (density 11.34) takes 60% more volume than an equal weight of sintered tungsten (density 18.1) whch I'm told is the makeup of tungsten cubes, and slightly more than that for cast tungsten.
Stan
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sporty
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Re: Thoughts on "stock" wheelbase

Post by sporty »

What I have seen at council finals.

Is the ones who are pooring the lead, are having the lead lower in the car. They compromise with using standard axle height, versus what i use is the raised axle height. So the lead is thicker.
Because it is less dense, It does not seem to effect the center of gravity as much as the tungsten does. with in regards to going to low in the car.

They also seem to poor more in the axle area center.

Sporty
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Re: Thoughts on "stock" wheelbase

Post by FatSebastian »

sporty wrote:Is the ones who are pouring the lead, are having the lead lower in the car...
:thinking: Could this be an argument that melting / casting lead provides a performance advantage relative to not casting lead?
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Re: Thoughts on "stock" wheelbase

Post by sporty »

I think so.

I think melting / casting the lead does provide a advantage over just adding in lead. But sometimes If they use better shaped pieces of lead or thick pieces of lead you can do just as good as a job.

But when i think of lead, Its the standard stuff out there for sale, the links and sinkers.

You can get 1/4 thick sheet of it and thinner.

Just like the steel and tungsten plates you see for sale. U can get that n lead too.

They dont beat us, but you can built a fast car with equal balance point with lead.

I prefer to stay away from the fumes. lol.

Sporty
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Stan Pope
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Re: Thoughts on "stock" wheelbase

Post by Stan Pope »

sporty wrote:...
They dont beat us, but you can built a fast car with equal balance point with lead.
...
But to get the equal balance point, they gotta sacrifice sleekness .... those cars are FAT!
Last edited by Stan Pope on Tue Feb 21, 2012 6:50 pm, edited 1 time in total.
Reason: Make the post nice.
Stan
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Re: Thoughts on "stock" wheelbase

Post by Darin McGrew »

Stan Pope wrote:But to get the equal balance point, they gotta sacrifice sleekness .... those cars are FAT! (and not in the good sense of the word.)
FWIW, the "good sense" is usually spelled PHAT.</digression>
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Re: Thoughts on "stock" wheelbase

Post by Darin McGrew »

Stan Pope wrote:
Darin McGrew wrote:FWIW, the "good sense" is usually spelled PHAT.</digression>
Ohhhh.... When was that word born?
Well, certain subcultures have been using it a lot longer than I've been aware of it. And originally, it seems to have been used only with sexual connotations. But now, it seems to be used more generically, especially in the culture at large.
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Re: Thoughts on "stock" wheelbase

Post by Stan Pope »

OH-ohhh... I better edit my post and delete a couple others ... don't want to get into trouble with "da boss."
Stan
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