Racing by weight division (4 oz and under, over 4 oz)

Discussions on race planning, preparations and how to run a "fair" and fun race.
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MERuhl
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Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

Greetings all. It's been a few years since I've posted. Good to see some familiar names.

My 9-year-old daughter is competing in an AWANA Grand Prix at a church that is new to us. This group is doing something I've not seen done before: they organize the cars into 2 different "Speed Categories", based on weight. Cars 4 ounces and under in one group, cars over 4 ounces, up to the standard 5 ounce limit, in the other.

I haven't had an opportunity to ask why they do it, but I suppose the answer may have something to do with balancing out the competetion. I can see how it might also cut down on last-minute, pre-race weighting of cars at the maintenance table, although this group requires all cars be submitted the week before the race, presumably to give them time to inspect. All in all, they appear to be trying to address some common race-time issues, in the name of fairness and expediency.

Of course, I'm wondering if an 'optimized' 4 ounce car stands a better chance of winning its division than a full 5 ounce car. :idea:

They also started selling the car kits last night, a full 3 months in advance of the mid-January race. Another good idea.

Thoughts?
Last edited by MERuhl on Thu Oct 15, 2009 4:57 pm, edited 1 time in total.
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FatSebastian
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by FatSebastian »

Welcome back, MERuhl.
MERuhl wrote:Cars 4 ounces and under in one group, cars over 4 ounces in the other. [...]Of course, I'm wondering if an 'optimized' 4 ounce car stands a better chance of winning its division than a full 5 ounce car.
I'm sorry if I'm misreading what you're saying, but "over 4 oz" sounds open ended. Are you saying that you are limited to 5 oz in the other division?

By definition, I suppose an 'optimized' 4 oz car has the best chance to win its division because it is optimal. ;) In the quest for optimality, I might be concerned about the official scale reading 4.01 oz and pushing you up into the other division.

It's definitely a different way to run a competition - I kinda like it!
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by Stan Pope »

MERuhl wrote:I'm wondering if an 'optimized' 4 ounce car stands a better chance of winning its division than a full 5 ounce car. :idea:
...
Thoughts?
I think you asked an insightful question! The reason is that a 4 ounce car needs to be better prepared than a 5 ounce car just to get down the track! Why? Some of the energy losses don't go down in proportion to car weight the way wheel friction goes down. They are about the same whether the car is 5 oz or 4 oz or, even, 1/2 oz! The two that come to mind immediately are aerodynamic losses (function of velocity, cross section and shape) and wheel rotational inertia losses (function of velocity).

What that means is that improvements in wheel inertia or in aerodynamic drag provide more benefit for a 4 oz car than for a 5 oz car.

All that said, there will probably be good builders in each category that will take care of all the little things that need to be done to perform well. Then your builder must be among them to have a chance! If, on the other hand, the other "4 oz'ers" are just those who didn't know enough to be close to 5 oz, then your chances improve greatly.
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MERuhl
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

FatSebastian wrote:Are you saying that you are limited to 5 oz in the other division?
Sorry, I wasn't clear. Yes: the 5 oz limit applies to the "over 4 oz" division.
FatSebastian wrote:I might be concerned about the official scale reading 4.01 oz and pushing you up into the other division.
Ugh. Hadn't thought of that. :thinking:
FatSebastian wrote:It's definitely a different way to run a competition - I kinda like it!
It is different. I'll try to find someone to explain their rationale to me.
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MERuhl
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

Stan Pope wrote:All that said, there will probably be good builders in each category that will take care of all the little things that need to be done to perform well. Then your builder must be among them to have a chance! If, on the other hand, the other "4 oz'ers" are just those who didn't know enough to be close to 5 oz, then your chances improve greatly.
Agreed. We'll probably build a 5 oz'er, just because that's what we know how to do! Or maybe we'll make one ounce of weight removable, then if we win the 5 oz group, we can remove an ounce and challenge the 4 oz champ.

Not lacking for confidence, are we? :oops:
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by FatSebastian »

MERuhl wrote:Or maybe we'll make one ounce of weight removable, then if we win the 5 oz group, we can remove an ounce and challenge the 4 oz champ.
That's an interesting idea: build a 4 oz. car and add weight, or a 5 oz. car and subtract weight, should you eventually want to change the division. Two 1/2 oz. tungsten plates (the kind available from most online suppliers), screwed onto the bottom below the COM, seems ideal for that. If the area-to-mass ratio of the entire car gets smaller by adding tungsten plates (a lot of mass in exchange for a little bit of area), there would seem to be no aerodynamic penalty adding that type of weight.
Stan Pope wrote:If, on the other hand, the other "4 oz'ers" are just those who didn't know enough to be close to 5 oz, then your chances improve greatly.
We sometimes see where kids didn't think (or care) to add weight, or built purely for looks and the weight just gets in the way. My guess would be that this type of construction motivates the existence of the lower weight class. If this is the case, then chances may improve greatly, but would you want to compete hard against kids that may not be trying to compete? :thinking: Discovering the rationale sounds like a good idea - let us know what you find out, MERuhl.
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

FatSebastian wrote:We sometimes see where kids didn't think (or care) to add weight, or built purely for looks and the weight just gets in the way. My guess would be that this type of construction motivates the existence of the lower weight class.
That's my thinking, as well.
FatSebastian wrote:If this is the case, then chances may improve greatly, but would you want to compete hard against kids that may not be trying to compete?
In a word, no. But, like Stan, I suspect there will be a few who build speedball 4-oz'ers. That would make it fun to experiment with the variable-weight option.
FatSebastian wrote:Discovering the rationale sounds like a good idea - let us know what you find out, MERuhl.
Will do!
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by Darin McGrew »

MERuhl wrote:although this group requires all cars be submitted the week before the race, presumably to give them time to inspect.
FWIW, we require all cars to be submitted the Wednesday before our race (which is on Saturday night). It has nothing to do with having more time to inspect the cars, because all the inspection is done with the car owner present when the car is submitted on Wednesday night. IMHO, it would be unfair to disqualify a car when the owner isn't there to do something about the violation.

The main advantage of registering the cars early like this is that it reduces the chaos of derby night. Derby night is now just the race. Sure, you have tools and supplies available to deal with emergencies, but all the last-minute work to get the cars ready to race (weight adjustment, lubrication, mounting wheels, etc.) has already been taken care of.

Another advantage is that it is easier to arrange for impartial judges to select the winners of the design awards. Before, the judging was sandwiched awkwardly between the end of registration and the beginning of the race. Now, there are two whole days for judging, and no one is anxious for the judges to hurry up so the race can begin.
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

Makes sense.
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by engineer101 »

Our Church Summer Race Season just finished our last race. Our format is a little different than most.

Car eligibility is standard stock class - Out of the box

We qualify each car individually on a 2-lane 40 foot homemade wooden track. The performance requirements of the car must be both speed and free rolling capability to win.

Each car qualify's from a starting height of 24" and is measured how far the car free rolls and is measured to the nearest 1/4 inch. Each car makes 3 qualification runs, alternating lanes. The total length of each run then added together to determine their total qualification Score. The Top Qualifier is the car that totals the highest distance to the nearest 1/4". This is how we pair the cars for the final heats. Each final heat lane choice is determined by a coin toss, as sometimes lane choice makes the difference between winning or losing.

The advantage of being the Top Qualifier is that the car earns a Lane Choice Bonus Card that gives the holder an automatic lane choice in only one of the Semi-Final / Final Races.

The Semi and Final heats are a little different. We run the first semi-final car to car heats and then end up with a winner's and losers bracket. Each bracket runs semi-final heats until they have the top three in each bracket. Then the top three cars of each the Winners and Losers bracket go head to head for the race championship

The final heats are launched from a 48" elevation on the 40 foot track. The car building strategy is to have a car that has a reasonable amount of speed but is also a free rolling, straight running car. We have had some really fast top cars qualify but when it came to the long, level straight away they got inched out by a slower car that free wheeled a little better. This format tends to make some very interesting races and the outcome is sometime very suprising and the kids and the parents both enjoy the format. This seems to make all racing more competitive. :nervous:
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by Stan Pope »

Thanks for posting that!
engineer101 wrote:This is how we pair the cars for the final heats.
This procedure ranks cars. Is pairing by "top rank against bottom rank", "second from top against second from bottom", ...? Or "top ranking two cars against each other", "next two highest ranking"...?
engineer101 wrote:The Semi and Final heats are a little different. We run the first semi-final car to car heats and then end up with a winner's and losers bracket. Each bracket runs semi-final heats until they have the top three in each bracket. Then the top three cars of each the Winners and Losers bracket go head to head for the race championship
So, this would require a quadruple elimination (or triple elimination in each bracket) to do reasonably accurately. Is that what you do? If not, what?

Also, is this part done on the 24" track or on the 48" track?

How is pairing done with the 6 cars in the finals?

The procedure is unique enough that I would like to see it documented in detail and made available.

Have you evaluated the accuracy of the process through any formal procedure? If so, what is the result? It appears that if you award more than three race place trophies, that the accuracy of 4th through Nth place may get pretty "iffy", depending on the details of the initial pairing.
Stan
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

Going back to my original post, we turned in our car this past Wednesday, 1/19/10. The race is next Wednesday evening, 1/26/10. As we stood in line, I noticed several folks talking about whether they built a 4 oz. or 5 oz. car. So it seems that there is an awareness of the weight rules among those who have participated here in the past. Should be interesting to see how they run the racing next week. I'll report back afterwards.

And btw, we used the tungsten plates for the first time. Those are nice! They weren't available the last time I built a car.
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Re: Racing by weight division (4 oz and under, over 4 oz)

Post by MERuhl »

Tonight is race night! Just got the following in an email from the Race Director:

"This is our largest Grand Prix ever! We have 109 cars racing tonight. All cars will run 2 races. Cars will advance to the final rounds based on their average race times. In each category the 8 fastest cars will go to the Semi-Finals followed by the 4 fastest cars going to the Championship Races.

This year car race times will be recorded for each heat. Those times will be averaged giving each car their final race time. If time allows, round 3 of racing will be run."


Should be interesting to see how the times compare between the two weight divisions. Updates to follow...
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