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Nanu
06-14-2003, 01:45 PM
I am thinking of entering a gravity car race (cars pushed only by the force of gravity down a hill) in my university and I wanted to know what was the best strategy for constructing one of these (how many wheel , what type of wheels, a light car or a heavy car, ect...)
If anyone has some good tips, I sure would appreciate it.

trabi
06-14-2003, 02:35 PM
I'd say you want to try and achieve the best combination of maximum weight with minimum friction. Ways to reduce friction could be to use the narrowest possible tyres and use ballraces to attach the wheels to the axles. Also, aerodynamic bodywork will cut down wind resistance - one way to make it more aerodynamic is to have the 'pilot' in a lying position rather than sitting.

I'm no great expert though, these are just the first ideas that popped into my head after reading your post.

Sock Munkey
06-14-2003, 02:53 PM
You also want you wheels to be as big around as you can fit on your car. This lets the wheels turn slower at any given speed causing less heat friction and allows them to travel over the bumps with less drag.
(this is why the wheels on covered wagons were so big)

trabi
06-14-2003, 03:11 PM
Big wheels will also make it more stable (due to the gyroscopic effect created as they turn), but maybe the extra ground clearance would lead to more wind resistance.

Also, have you considered how many wheels it will have? Four is more stable, but three means less friction. If three, maybe it would be better to have two at the front and one at the back, which should make it less likely to topple over when cornering.

Rick
06-14-2003, 03:12 PM
Assuming that your gravity car race uses regular cars, you will be limited to what you can do.
However inflating the tire way up will make it roll easier as it will have less surface area in contact with the ground.
Retracting the brake pads, and backing off the rear drum adjuster will also reduce drag. NOTE This will also cause the car to be harder to stop, and could be dangerous. Always restore the brakes to full functionality before driving the car away.
If you really want to go crazy, remove the driveshaft of a rear wheel drive car. (check the rules, some gravity drags require the car to drive to the start line.
Good luck and have fun

Sock Munkey
06-14-2003, 03:34 PM
Since the car is to be powered by rolling down a hill it's unlikely that there will be more than a few degees of side-to-side turning.