Anyone know what the biggest tire size is that I can fit on my 98 stock Trooper without rubbing? I currently have the OE size, 245/70R16s. Also, will a larger tire mess up my ABS?

A larger tire wont mess up your abs. If you want to keep the 16 inch rims and not lift the vehicle, I would go with 275/70/16 which is about a 31.5"

The calculation to convert metric to inches is:

tread in cm (27.5 in this case) times the sidewall percentage (.7 in this case) times 2 (in order to account for both sidewalls) divided by 2.54 (to convert to inches) plus the rim size (16 in this case)

i.e. 27.5 x 0.7 x 2 / 2.54 = 15.16
15.16 + 16 = 31.16

these are the tires that I am currently running on my WJ. They are a bit shorter but a bit wider than 265 75 16s

The first non-stock tires I had on my trooper were 31x10.50x15 with no body or susp. lift

The 285/75 R16 is another solution, though without any lift it will look a little strange. I run this size on my 1998 Trooper with a 1.5" total suspension lift. The lift is not required to fit the tires though, as I did not adjust any of the bump stops to prevent rubbing.

IMO the 265/75 or 275/70 solution is more practicle unless you really need the additional clearance. I really noticed the affect of the additional weight and diameter when driving the truck on the highway. The vehicle is working much harder now.

Thanks for the replies.