COG and COM?

[jbkennypa]

OK, I have to admit, I am a rookie to this sport and already addicted. I run cars for my kids in AWANA races only with our church.
I am seeing the terms COM and COG used an awful lot, and forgive my ignorance, but what do they mean? (I'm assuming Center Of Mass and Center of Gravity, but likely I'm wrong.)
I have even seen measurements of these things - how is that done?!
Thanks for the help!

[derbydominator]

Yes, you have it right and they are essentially the same thing. One can measure it a number of ways but basically you are looking at the balance point on the car and seeing how far that balance point is from the rear axle. You can balance the car (with axles and wheels on but not necessary to push in all the way) on the edge of a ruler or even on the edge of another derby block. Depending on your car setup and the type of track, you can be more aggressive on the COM, say 3/4 or 7/8" in front of the rear axle to a more conservative COM around 1 to 1 1/8" in front of the rear axle. The more aggressive the COM, the faster the car but the more susceptible the car is to speed wobbles. You can increase the stability of the car via various other advanced setups such as a rail rider, off center weighting or lower moment of inertia as well as better tracks, metal vs. wood as an example. However, in general, if you are looking for a basic setup of the car, try to stay around 1" on the COM. Don't be shy about asking questions. That is primarily what the board is for. Best of luck to you!!!

Darryl