[hispeed6]

If it were my truck then here is what I would do. First I'd buy 5 tires of the same size. Come on guys, if you can afford a $35,000 (average) truck then you can at least mod it with 5 tires instead of 4. Secondly, when you rotate the tires, do a 5 tire rotation instead of 4, keeping all 5 tires relatively the same wear-wise (and diameter-wise). Never understood why someone would have a perfectly good tire to use and not use it. Besides, with 5 tires the mileage is spread over 5 tires instead of 4, thereby making the entire set last longer.

Also I think using 5 of the same size tires is a good thing since I'm not sure how one smaller tire would affect the stabilitrack (autos only) or the traction control. Both I believe sense the delta between tire rotations across 4 wheels. One tire with a smaller diameter means one tire with a smaller circumference which will have to turn faster to cover the same ground. Also, if you have the locking rear diff it's a good idea to use two tires the same size so that one axle isn't doing all the work. This also applies to running same size tires at identical pressures to most closely match tire diameters.

Just my 2 cents, take it or leave it.