thin car estimates, Pro and Cub
- Thread starter txchemist
- Start date
Your standard COG graph can't be right. It's saying a .3125" thick cars COG only loses .03 sex from .5" to center of car? So basically it's saying your COG doesn't really matter on a standard car.
Kingdoms come and go over .03 sec. (actual car difference is 0.0245 sec.) and it's not a lot different on other cars. Good prep drops the difference down to 0.021 sec.
Do you have a different gravity where you are? I am using 980.27 cm/sec^2 for the track in Johns location. Not much difference on the wood short tracks most dens use.
I do allow for the air to warm up in his garage, so I use 0.001036 g/cm^3.
I don't see any mistakes. Perhaps this is starting to have a desired effect, If your are slow, you will not get fast with just thin and far back.
What would you like to see next?
I apologize if I went all BGB for a while.
Do you have a different gravity where you are? I am using 980.27 cm/sec^2 for the track in Johns location. Not much difference on the wood short tracks most dens use.
I do allow for the air to warm up in his garage, so I use 0.001036 g/cm^3.
I don't see any mistakes. Perhaps this is starting to have a desired effect, If your are slow, you will not get fast with just thin and far back.
What would you like to see next?
I apologize if I went all BGB for a while.
The best place to discover wheel impact is to review what DD4H has for sale. His numbers let you figure out the relative improvements with the different design wheels.
For example: The 1.8 gr. Cheetah extreme gives you 0.08 sec. improvement over std wheel. Even if you are not perfect in your wheel prep, if you put both a standard wheel and the Cheetah Ex through the same prep- you will still get this big improvement. Now not all 1.8 wheels are alike, the moment of inertia plays a big part in speed, and if you can still make a strong light wheel ( which the Cheetah Ex is), it's unbeatable. I can not do a simple model of a different wheel. Each wheel needs a lot of "fudge factor"" to account for it's performance. Some wheels made by a different process will have a bigger bore- that will be slower. It can be made faster with using a bigger diameter axle, but not ever get up to the top speed you can get with the Cheetahs and the 0.092 axles.
So a rough guess would be if you were running DD4H product and getting 2.95 as an example, then cars using standard wheels would be running at 3.03 sec. ( assuming they were also making a good car like yours- way slower if just slapping stuff together.)
For example: The 1.8 gr. Cheetah extreme gives you 0.08 sec. improvement over std wheel. Even if you are not perfect in your wheel prep, if you put both a standard wheel and the Cheetah Ex through the same prep- you will still get this big improvement. Now not all 1.8 wheels are alike, the moment of inertia plays a big part in speed, and if you can still make a strong light wheel ( which the Cheetah Ex is), it's unbeatable. I can not do a simple model of a different wheel. Each wheel needs a lot of "fudge factor"" to account for it's performance. Some wheels made by a different process will have a bigger bore- that will be slower. It can be made faster with using a bigger diameter axle, but not ever get up to the top speed you can get with the Cheetahs and the 0.092 axles.
So a rough guess would be if you were running DD4H product and getting 2.95 as an example, then cars using standard wheels would be running at 3.03 sec. ( assuming they were also making a good car like yours- way slower if just slapping stuff together.)
OK, I need to dial it back a bit and not pitch one over the head. Let's try again - I now plagiarize from
Pinewood Derby Times
Volume 5, Issue 10
February 8, 2006
Testing for the best horizontal COG location for a given track is fairly easy if you have a track timer. Build a lightweight car without added weight, but with three dowel rod pieces sticking up out of the car (one in front, one in back, and one in the middle). Using steel washers weight the car in the front, back, and middle and compare the results. Mix and match to find the best COG for the track.
I ran time trials with this type of test car on a 32 foot ramp-flat track and found that rear-weighted cars outperformed front-weighted cars by up to one car length. Other testing results show similar results.
(translation: if you get a 1 car difference with COG in front compared to COG in back, you get 1/2 car difference if COG in the middle.)
In addition, Michael Lastufka used a computer model to generate data and reached similar results he got a 0.025 second improvement
That works out just about on the money with my 0.0245, right?
Another way to look at it is when you move the COG back just over 2 inches, you only lift it up about 1 extra inch above the ground, so in the equation of velocity, recall v=SQRT(2gh)
where g in ft/sec/sec is 32 and h is 4 ft for the first car we shall call CAR A,
v= 16 ft/sec. (that would be with no friction in a vacuum)
now when we add 1 inch to the height, we now are 4.0833 ft above the flat and that gives a velocity of 16.1658 ft/sec. for CAR B and that is only a 1% speed improvement. It will be less when we toss in all the real effects of rolling down the track. Now the big news is- this is true for ALL cars thick, thin, low friction, high friction, 1%- that's it. You can argue with me, but you can't argue with math [Foghorn Leghorn]
Volume 5, Issue 10
February 8, 2006
- and copy just this part of the article
Testing for the best horizontal COG location for a given track is fairly easy if you have a track timer. Build a lightweight car without added weight, but with three dowel rod pieces sticking up out of the car (one in front, one in back, and one in the middle). Using steel washers weight the car in the front, back, and middle and compare the results. Mix and match to find the best COG for the track.
I ran time trials with this type of test car on a 32 foot ramp-flat track and found that rear-weighted cars outperformed front-weighted cars by up to one car length. Other testing results show similar results.
(translation: if you get a 1 car difference with COG in front compared to COG in back, you get 1/2 car difference if COG in the middle.)
In addition, Michael Lastufka used a computer model to generate data and reached similar results he got a 0.025 second improvement
That works out just about on the money with my 0.0245, right?
Another way to look at it is when you move the COG back just over 2 inches, you only lift it up about 1 extra inch above the ground, so in the equation of velocity, recall v=SQRT(2gh)
where g in ft/sec/sec is 32 and h is 4 ft for the first car we shall call CAR A,
v= 16 ft/sec. (that would be with no friction in a vacuum)
now when we add 1 inch to the height, we now are 4.0833 ft above the flat and that gives a velocity of 16.1658 ft/sec. for CAR B and that is only a 1% speed improvement. It will be less when we toss in all the real effects of rolling down the track. Now the big news is- this is true for ALL cars thick, thin, low friction, high friction, 1%- that's it. You can argue with me, but you can't argue with math [Foghorn Leghorn]
I think what you are forgetting what science and math cannot account for is the concept of synergy. You are over thinking this. What looks good on paper in most cases fails in practical applications because of variables that cannot be held constant. Listen to what is said on this board because ultimately, the clock does not lie and the pros, through trial and error not math and science, have cracked the nut on speed in all conditions. Each car's com, wheel prep, design are totally unique and balancing each element individually to maximize synergy is more art than science.
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