Actually, I have 285/70/R17's.
In terms of the ride, you are correct that it would be stiffer. This is because it is a LT (light truck) tire vs. the stock P (passenger car) tire. The main differences are that the LT tire is inflated to a higher pressure (~45-50 psi), vs the P tire's 28-30 psi. Also, the LT tire has more plys to it which give it a higher load rating. It is still a good ride to me, and the wife says she couldn't really feel a difference.
The mpg does not seem to be effected. I was actually hoping to see a slight increase, due to lower rolling resistance, but the fact that it is slightly taller than stock means I am lowering my gear ratio so that I guess it calcels each other out.
The speedometer seems to be close to actual, as the tire is only 1 inch taller, or only a 1/2" taller rolling radius. See the following like for exact tire specs.:
http://www.bfgoodrichtires.com/assets/pdf/all_terrain_ta_kd.pdf
Here is the following advice for anyone thinking of upgrading their tires, or even with the set they currently have:
1) New aftermarket shocks. Especially with new tires. Your shocks greatly effect how the truck rides and how the tires wear. Worn shocks will quickly turn $800 dollars of new tires (you can expect to pay ~$200 installed per BFG) into crap. I also put on a steering shock.
2) When balancing the tires, use "tape weights". I found that the stock rims (which I really like) throw the usual rim weights. This in turn caused me to go thru a set of tires real quick (the OEM Wranglers - scalloped them). It is not obvious that some of the weights are missing, so it took awhile to hone in on that being a problem. Tape weights cannot be thrown of as they are held against the rim via centrifugal force.
3) Alignment. Note that the Exby's (at least the '98) do not have camber adjustment (it is set at the factory). Have your tire shop put the camber kit in, and really get the alignment set exactly.
I have had several sets of BFG's, and I really like them. They wear well, as in slow, and go over and thru everything. Work well in sand and snow, and are quiet on the highway.
