Retrac,
The 30x9.50-15 is wider than the 235/75-15. The actual numbers depend on which manufacturer the tires come from and what model tire you are talking about - they are all slightly different. The main difference betweem the two is height.
Let me give you an example with a BFGoodrich Radial Mud-Terrain T/A.
LT235/75-15
Overall Diameter - 29.1"
Tread Width - 7.3"
Section Width - 9.3" on a 6.5" rim
Static Loaded Radius - 13.3"
Revs/Mile - 715
Tread Depth 18/32"
30x9.50-15
Overall Diameter - 29.9"
Tread Width - 7.4"
Section Width - 9.8" on a 7.5" rim
Static Loaded Radius - 13.8"
Revs/Mile - 696
Tread Depth - 19/32"
So you can see, the 30x9.50 is a larger tire. The Tread width (the part that contacts the road ) is only .1" wider but the Section width ( overall width ) is .5" wider. These differences are fairly minor.
The major difference to consider between the two is that the 30x9.50 is TALLER than the 235, .8" taller in this example. This is where the concern lies. Any time you put a taller tire on any vehicle without changing the gearing in the differentials, your vehicle will lose acceleration and power. In this case it will be slight but still apparent. So you need to look at what your priorities are for selecting a different tire. Do you want the taller and wider tire for looks or for off-road capability?
Another consideration is that with a taller tire, your speedometer will be off slightly - it will read slower than actual. This isn't hard to remedy - changing the speedo gear is very simple and the part costs about $10.00 .
I speak from experience on this subject because I ran 30x9.50's for about 40,000 miles. I liked the look and the little more ground clearance they gave but I didn't like the weaker acceleration and dropoff in power up long grades. I have progressed now to 31x10.50's because I changed the gearing from 3.55 to 4.10. By the way, check on what gearing you presently have. If you have 3.73 gears, 30x9.50's would work better than with 3.55 gears.
The main point though here is that you should consider many factors before choosing a larger and taller tire. Everything is always a matter of personal preference and there are always pros and cons. My recommendation would be to stick with the 235's unless you are willing to change your gear ratio, which can be rather expensive.
Hope this wasn't WAY too long winded. Just trying to help.
DOGMAN
