Quote:
Originally Posted by Old Tele man
...basically, yes, width = more Crr, tall & narrow is better for MPG.
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Actually the opposite is true. Wider = more load carrying capacity = better RRC.
But the issue at hand is if a 195/65R15 would be better or worse than a 225/45R17. That means that not only is the width changing, but so is the aspect ratio and the rim diameter.
According to the results of the Smithers study on tire size, the 17" will have about a 7% better RRC than a comparable 195/65R15.
But the key word here is COMPARABLE. Smithers also reports up to a 60% difference in RRC between tires of the same size - so careful selection is extremely important - more improtant than tire size.