Tires: tires and fuel efficiency, automobile tires, fuel efficiency

Question
For safety reasons, I am writing for my 7th grade kid. He has to come up with a science project. He wants to test how automobile tires affect fuel efficiency. How do the experts test tires for fuel efficiency? How would he be able to replicate some of that at home?

Answer
Irene,

Tires are tested for rolling resistance using a machine dedicated to that purpose.  There are several different types and several different test methods, the most common test is SAE J1269.  However, this is way beyond what can be done at home.

However, a simple coast down test is sometimes used by folks who don't have access to the machinery.  This is a test where repeated runs are made over the same course and starting at the same speed, the vehicle is taken out of gear and coasted to some other speed - and timed for the length of time.  Obviously, the wind speed plays a large role in the testing so it has to be accounted for.

I would suggest that instead of doing the test yourselves, try finding published data.  A starting point would be here:

http://onlinepubs.trb.org/Onlinepubs/sr/sr286.pdf

This is pretty thick and difficult to read - even for me.  But I am sure there are some tid bits that would be helpful.

But I've written up a small article that will help:

http://www.geocities.com/barrystiretech/rrandfe.html