right now i have 265 75 16's on my truck and in need of a replacement set of rubber. as i have 3 tires below min tread depth and one of witch blew out on me the other morning. so i threw my spare on and it was i belive a 235 85 16 looked just as tall as my other tires but narower, and in the never ending search for the best possible fuel millage, do you think this would be a good choice of sizes to replace my tires with?

 

Yes the 235/85 will help some with mileage. They aren't as wide so less rolling resistance and less weight. Might notice it in the math might not. Here is a site to help with tire size and comparison
Metric Tire Conversion Calculator - Red Rock 4x4

 

ok so it looks like the 235 85 16 works out to be
31.7x9.3/16
where the 265 75 16 works out to be
31.6x10.4/16

so just as tall but about an inch narrower i did notice it was certainly lighter than my 265 when mounting it.