Rolling Friction

Basic physics book.

Try it?

• A rail vehicle has significantly lower rolling friction per unit weight than anything with a rubber tyre.
• A single horse will pull with ease a canal barge weighing tens of tons.
• Brunel discovered that the ratio of wheel diameter to axle diameter was important, and then someone invented the roller bearing.

Try this site:

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

Tom

Remember: If the vehicle is at rest initially, you have to overcome some static friction first before you can calculate the rolling friction or force resistance whilst moving.

The most important info you will need is the rolling and static coefficients of friction for the surface you are travelling on.

The Website provided by TVP45 has a good list of rolling friction coefficients. However, if your wheels are made of any material that deforms significantly and/or has low resilience, the actual drag will be a strong function of speed and load. This is because the contact area is being deformed to fit the (assumed rigid) path. This requires an input of energy to create the deformation. All materials have a certain amount of hysteresis, which means that not all the energy gets returned. Some is lost as heat. What is really happening is that the "leading surface" of the wheel requires energy to squeeze it into the shape of the path. Then the "trailing edge" of the contact surface returns a portion (never 100%) of this energy as it pushed against the path (road).

Some materials "rebound" slowly, such that their "trailing Edge" does not push very hard against the pathway. The rate of recovery can become slower than the speed at which the deformation is traveling around the wheel. This means that for some materials, the "drag" will increase very significantly with the speed of the wheel. As an example, Natural Rubber rebounds relatively fast, with minimal hysteresis compared to many commercial "rubber" formulations. The affect can be a difference in drag by 3 to 5 times!!!

Therefore, be aware of your speeds and choices of materials. You will definitely have to do some testing to determine what the "rolling friction" is for your application.

You might what to check out the test: ASTM D 1054 Standard Test Method for Rubber Property - Resilience using a Goodyear-Healey Rebound Pendulum. Try this link:

http://engineers.ihs.com/document/abstract/YPQOBBAAAAAAAAAA

How would you be pushing the vehicle? From the bumper in nuetral? Years ago I had a short stint in an auto repair shop. One of the tricks I learned was to move the car by turning one of the tires with your hands. It took much less effort to roll the car around by a tire rather than pushing on it from the front or back.

I doubt this helps you but I was amazed when taught this little nugget. Although thinking back on it I believe it had to be one of the drive wheels with the vehicle in nuetral(of course) and I'm guessing the gearing in the drive differential is why this happens and the different diameter of the tire and axle.

Not much help I think..

Lots of variables would go into this equations but it grows from the deceivingly simple F=ma.

If the vehicle is a car or truck, then the Bosch Automotive Handbook provides details. If you need only a rough estimate: the rolling friction coefficient for radial tires averages about .013, and the curve is pretty flat for speeds from 5mph to 70 mph. So a 2000 lb car will have 26 lbs of drag due to tire rolling friction. (Usually, you can consider the wheel bearings as part of the transmission inefficiencies, but if you were pushing the car by hand, you'd feel this drag, too.)