Crr ~= 0.0102, about right?
 

Using the roll-down test spreadsheet and data gathered last summer, I was able to load up the spreadsheet for Cd and Crr. However, I already had the Cd, 0.29, from earlier Toyota sources. So all I had to seek was Crr and that came in about 0.0102. Is this pretty much what other folks are seeing?

The spreadsheet pretty much asks for about 60-70 seconds of data but I only had 40 seconds. As a rough approximation, it seems to fit the higher speed parts close enough.

Yes, I'll go back and gather some fresh data next weekend with longer roll-down intervals. Just I thought I'd ask if 0.0102 seems about right.

Thanks,
Bob Wilson

That sounds about right. From the figures I've seen Crr goes from ~.07 to ~.12. Unfortunately, I can't recall where I've seen those numbers.

Wikipedia has numbers for Crr, and I have seen at least one guy's numbers from a coast down test on instructables. You can see how he did his test here, and use his spreadsheet if you like. According to co_driver, you can include Cv (coefficient of viscous [skin] drag) also, and just approximate it at 1 Newton per Meter/second. You can see his equation in this thread if you like. Like I said, you have to approximate the skin drag, since the solver function will blow the skin drag number way out of proportion.

The author of that instructable estimated his '92 Metro with 145/r12 (I think) tires inflated to 45 psi: Crr = .0106