[TexasCotton]

Originally Posted by sidecar

Ive been looking over a few older threads, there seems to be a popular disconnect.

Over at the prius forums people have been experimenting with larger than OEM rims (but important to stress same rolling diameter) just for the 'looks' of it. The experience is, that even with tyres with good RR data, the fuel economy rises some 3-4 mpg shifting up from the very light 15" OEM wheel to something in the area of 17-18" diameter rims.

The problem is, we have been unable to establish a common RR formula for both standard size and larger diameter tyres. We have been unable to

It always seemed logical to me that very small sidewalls would create a lower weight tyre, which would offer better sidewall control, and therefore better mileage. But experience has proven this to be flawed, and I think because as lower tyre weights are apparently more than offset by heavier wheels. Add to that generally taller wheel diameters always seem set to wider than conventional rims, generally adding to the aero drag and generally behaving different to stock diameter footprint.

This could also mean, you might be tempted to do this for the additional contact patch at similar psi. IOW reasons of safety in more marginal driving conditions. Which is ok, options are good, but it isnt a like with like comparison if fuel economy was of interest to you.

We also found that, it mattered if summer or winter driving conditions, but have been unable to establish if this is because the tyres themselves are warmer and less brittle on the road or if winter driving conditions just made general fuel economy suffer.

I think we desperately need to know some things, like a common RR for tyres of different diameters. And establish rim/tyre combos that come out as near equal weights. Only then will this argument be scientifically settled. But the fact remains is that despite this thinking, practical experience proves that larger diameter wheels fitted with suitable low profile tyres of the same rolling diameter will increase MPG in the area of 3-4 MPG.

I guess or assume you overlooked the horror story thread about a GEN 2 Prius owner that went from the stock oem 15 to a larger wheel/rim size and decreased their mpg. I take issue with your statement about a mpg increase on non stock oem 15 inch rims ......unless you can give more veracity to your previous statements. I have yet to see a toyota prius gen1,2 and 3 owner document any mpg increase with non stock oem rims...!!!!!!!