265 is the tire tread width in millimeters. Though it does actually vary somewhat from tire to tire. 16 refers to the wheel diameter. 75 refers to the ratio of tire height to width. Hence a 255/85-16 is skinnier and taller than a 265/75-16.
Stock 80 wheels are 16" x 8". So, you need a tire meant for an 8" wide wheel. usually tires have a wheel width range.
It's easier to just find a tire table like on
Tire Rack - Your performance experts for tires and wheels.
For my two cents, I went from stock 31" hwy tires to 32" mud retreads to 33" BFG KM2's all in just over 1 year. My tires got skinnier and taller each time. I got a good deal on the retreads but a tread separation told me I needed something more reliable. My family and I just love the BFG KM2's in 255/85-16. They SUCK on ice, I mean smooth ice, but that's what chains are for. Otherwise, they are great, smooth riding, quiet, and we feel extra secure with how tough they are. It just drives me crazy that skinny 35's are impossible to find here. For off-road, I would really like 35's, as has been said millions of times on 'Mud. But, 33 MT's are an improvement in many ways over 31" highway tires for us.
Last summer, right after my backcountry tread separation issue, my uncle had a simple rock on a not too rough mountain road slice a gash right through his hwy tire sidewall. It was then that we decided to go with the most reliable tire we could, and we wanted skinnier for better mpg, hopefully. Sadly, I'm getting really bad mpg, but it's winter in Montana so I am (sadly) cranking up in the cold, waiting, then driving 1/2 to 3/4 mile frequently. There are reasons for the very short trips, but I think that's the cause of my 10 mpg lately. I do get better when I do hwy driving, but I don't do enough now to check the mpg. I think the short trips in town in the cold with a lot of idling is causing the mpg problem.
However, with my lift, front bumper, and roof rack on, which certainly makes some weight and aerodynamic difference, I have to switch O/D on and off to get up the slightest inclines on the hwy at 70-75 mph. So, I am planning to go to 4.88 gears for better around town performance and better hwy performance. Naturally, I intend to go to 35's eventually. If I believed I was staying on 33's, I would probably get 4.56. Still not 100% sure since I did just invest $$ in nice tire chains.
My opinion is that more aggressive tires are great. Bigger tires are nice too, but if you do around town driving like I do, you'll either pay even more at the pump or need to sink the $2-$3k on new gears. At least if you're able to wrap up the axle rebuild with the gears, you can offset some of the expense.
Anyway, hope this helps.
