larger tires

I am about to buy new tires for my stock 1998 chevy suburban. i am somewhat interested in buying slightly larger tires. What is the largest size i could buy that would fit without a lift and on 16 inch rims. also how will this effect my gas mileage?

Is it 4x4?

On those, you could go with 265/75/16 (which was a factory option over the 245/75) or the 285/75/16 without issue. A lot of people run 285 and you see plenty with the 265. I have 285/75 on a stock 1998 Z71.

The larger diameter will slightly affect your odometer. There are tire calculators online that you can see the differences. So if you're using that to figure mpg then your calculation will be off since the mileage is off.

On our 2003 Tahoe, I went from 245/75/16 to 265/75/16. They look so much better and I noticed maybe a 1/2 mpg loss. Hard to really tell...it could be due to driving habits, new tires having better resistance than the old bald ones, etc.

Not sure about two wheel drive tire sizes.

Ask the tire dealer if they can recalibrate the speedo/odo by either changing the VSS gear or by updating the ECM. There are also aftermarket tools that plug into the OBD-II port that allow you to adjust for the new tire size.