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One of the first things that I did was try to reduce the highway RPM a bit. It was running pretty high at 70-80mph, and the 285/70/17 Grabbers are 15.6% larger circumference than the OE 225/75/15s. So 3000rpm => 2600rpm. Interestingly enough, this made NO change to fuel economy. I was averaging around 13.6mpg before the change, and the two tanks afterwards were 13.6 and 13.7mpg. This is probably due to a couple of things:
1) Unknown rolling resistance changes by a few percent, 225 vs LRR 285s.
2) Substantially higher aero drag, both due to section width and due to a big chunk of the tire sticking out of the fenderwell further.
3) Lower engine speed = closer to torque converter stall speed = possibly higher losses.
4) Lower engine speed might not = to significantly better engine economy, even though it is in the "sweet spot" in the torque curve.
You can see how bad the aero performance is in the photo in the previous post. The wheel does actually stick out a bit, I had to hammer-roll the inner fender well so it didn't cut down the sidewall when heavily loaded!
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