Physics of moving a car

[vega]

I have been doing a lot of reading lately to come up with something as close to perfect as possible for my current project - that is an entirely different conversation on its own. I found this link in the pursuit of trying to figure out friction losses/aerodynamics and power correlation. I don't believe that the common understanding of how tq moves a vehicle is well understood. Most people think that its all about tq, I give you the rotary motor for analysis. It makes little tq but spins high to make hp (which yes is a function of tq. Anyhow, I was trying to figure out how much "power" (more or less) it takes to move a specific weight with tire friction loss, and with gearing involved. I found the coefficient of rubber on dry concrete to be 1.0 (0.8 on wet concrete). F = f x W/R

 

f= coefficient of ROLLING friction (which is 0.01-0.02 for rubber on concrete)

W=weight of cylinder (car in this case)

R= radius of cylinder

 

PROBLEM: how does having four 'cylinders' effect this calculation? The equation as it stands is for calculating force on a single rolling cylinder. Also, how can it be applied if the front two wheels of the car are on the platform that is doing the pulling??

 

http://craig.backfire.ca/pages/autos/horsepower

[getoffmyinternet]

Since weight and surface area are at odds, in theory the net force for four wheels is the same as one. You're distributing the load over a larger area, the net friction force is the same.

 

Your formula doesn't seem correct though, how did you come up with 1.0 (looks like 1.0 lbs/in which I can only correlate to a spring rate). I'm not an expert on the subject but it looks like you're interchanging the coefficient of rolling friction as a simple constant with the rolling resistance as a distance. I don't think the force needed depends at on the radius of the tires. Unless I'm misunderstanding the variables you're using... Are you looking for F as in Force or are you looking for rolling resistance? If you're looking for rolling resistance I don't think it depends on the weight either. That said, I'm not sure how the rolling resistance helps get you to the force needed to overcome it (I'm not sure what the rolling resistance would be good for, it's probably over my head.).

 

It seems to me that all you need to figure out how much force is used up by the tires is the coefficient of friction (which can be estimated) multiplied by the weight of the car. Again, the surface area or size of the tires doesn't make much difference.