I´ve had a set of 30X9.50 for about half a year (on my 88). Plenty of pep, with the 3.55 gears I have. Actually seem to complement the torque range of the motor, more so than stock sizes. Occasionally drive triple digits, normally well over the double nickle. Runs well, straight, since I replaced the trac-bar.
The track of the XJ, doesn´t really fit the grooves cut by heavy trucks, on most highways, you´ll always feel it some, more so with taller tires/taller sidewalls. 16" rims help some, with the sidewall flex, add a little stability (have a set on my 95, with 29.5 inch tires).
Seems to push a little more in corners with the 9.50´s, but the XJ with that big cast iron brick out front, pushes anyway. A little more tire pressure than normal seems to help. Think most of the extra push is the sidewalls, at least on my tires, they seem to have a straighter sidewall, than say a 235X75R15. The 30´s do raise the COG a little also, which is gonna amplifly, any lateral movement a bit. The Koni shocks I have on mine, help some with the sway, seems to stay a little straighter and lean less, due to wind and uneven highways.
Don´t know for sure, but most of the problem with mine, seems to be moderate curves at say 30-40 miles an hour on a flat curve. The push, right in this area makes me a little nervous. I can really feel the wieght on the outside front tire (wet street and things could get hairy). Get the feeling an over the motor frame brace would help. Maybe raising the rear an inch so, so you could drift it, if you had too, instead of plowing with the front.
I know, way more than you wanted to know about the handleing of an XJ, narrow track, high COG, it´ll never be a sports car.
