Can weight be too low in the body?

[davet]

The lower it is the higher it starts and longer it stays on the incline correct? Anybody drill their holes up high to get the absolute minimum clearance between center rail and bottom of the car?

 

[pony express]

Drilling the holes high results in lower speed from either wind friction or the roll couple being too low. 5/32 is the limit from the bottom. 6/32 is very very slow. Most guys drill them in the range of 4/32 from the bottom. Pinewood derby is always a compromise.

 

[Kinser Racing]

Within the about 1/8" you can vary the weight it doesn't really make any difference for a scout car. Other set up factors have a far great effect on the car.

 

[Crash Enburn]

In answer to your question, and looking only at potential energy, yes, the lower your weights are, the better.

That is, weight as far back in the body, and as low as possible/practicable.

 

[davet]

We were thinking of drilling our holes then cutting out the center of the car. We would then add the 1/64" plywood to the bottom for strength then cut our weight pockets 1/4" deep from the bottom up. This would place the weight 1/64" lower in the car and would put the axle holes right about in the middle of the weight cubes.

 

[bracketracer]

1/64" lower will not make a measurable difference in time. You are moving the weight up the hill a microscopic distance. Better to move the weight farther back in the body up to the point where it becomes unstable.
If you are going to drill the rears higher then make sure you drill the fronts higher also. As Pony said, drilling only the rears higher is slow slow slow. Never drill the fronts lower than the rears.

 

[Vitamin K]

So, ideally, you want the bottom of the car parallel to the track, is what I'm hearing?

What kind of speed decreases would you see if, say, the rear was 1/8" lower than the front? Are we talking a few thousandths, or something more drastic? I'm seeing "Slow slow slow" but I'm curious as how to quantify that.

 

[bracketracer]

In my testing, drilling the front 1/8" lower than the rear (which would raise the nose) slowed the car by .011. Unfortunately, going the other way didn't net any speed! Only picked up .002 when the axle hole height was optimized. So the rule of thumb of drilling the fronts the same as the rears basically held true for me.

 

[Vitamin K]

In my testing, drilling the front 1/8" lower than the rear (which would raise the nose) slowed the car by .011. Unfortunately, going the other way didn't net any speed! Only picked up .002 when the axle hole height was optimized. So the rule of thumb of drilling the fronts the same as the rears basically held true for me.

Wow, that's an incredible drop. Hard to imagine that's all wind resistance.

Somebody want to explain this 'roll couple' thing?

 

[B_Regal Racing]

In my testing, drilling the front 1/8" lower than the rear (which would raise the nose) slowed the car by .011. Unfortunately, going the other way didn't net any speed! Only picked up .002 when the axle hole height was optimized. So the rule of thumb of drilling the fronts the same as the rears basically held true for me.

Question - if the nose being higher than the rear is slower (as in your situation), how do you account for the bend in the FDW? I do drill at the same height (front and rear), but my nose is always higher do to the bend.

 

[bracketracer]

Ed, I used to do a test drill on a blank body identical to the car I was building then a trial assembly with the wheels and axles I was going to run. Then I looked at how far off the nose was and drilled the actual car with the required change to get the body where I needed it. Once I got a feel for where everything needed to be I didn't need to do this anymore.

 

[Vitamin K]

In my testing, drilling the front 1/8" lower than the rear (which would raise the nose) slowed the car by .011. Unfortunately, going the other way didn't net any speed! Only picked up .002 when the axle hole height was optimized. So the rule of thumb of drilling the fronts the same as the rears basically held true for me.

Question - if the nose being higher than the rear is slower (as in your situation), how do you account for the bend in the FDW? I do drill at the same height (front and rear), but my nose is always higher do to the bend.

Do you lose speed when the rear is slightly higher than the nose? One could always bump the front axle holes up maybe a 1/16" or so, to try to accommodate for that bend.

Bracketracer's "test body" is probably a good idea, though.

 

[Vitamin K]

So it kind of dawned on me that I was overlooking a basic fact about canted axles. They only hold the wheels parallel provided that there is no rotation of the body up or down. So if you have negative cant, nosing the body up will produce a toe-out effect, while nosing the body down will give you a toe-in effect.

So, the takeaway is that if you're running canted rears, a body that isn't parallel to the track will destroy your alignment. Duh.

 

[txchemist]

That is why I have the older Cubs use my jig and get the bottom of the car parallel, then put drift and offset into car front part without messing up back wheels. Hex nut will go up & down and get car bottom correct even if Cub drilled front axle wrong.

All 3 axis set with drift, offset, and lifted wheel and bottom parrellel,
Then glue or epoxy for perfect rail runner