The numbers I'm reporting (17/20) are the ones calculated by the overhead console electronics in my 2008. My truck is bone stock running 265/70/17's and I don't have a lead foot. Yet.
Maybe I should start hand calculating my mileage??
Anyhow, thanks for the replies so far. I'm sure I should expect 1-2 mpg loss if I increase a tire size or so.
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2008 QCSB 6.7L 4X4 2500 6-speed Mineral Gray