Pro Comp is noted for its tough tires, and they don't get much tougher than these 37x13.50/15 XTerrain and LT 325/80R16 (37x13.50/16) Xtreme All Terrains. How about three plies of high-denier polyester in the sidewalls covered and mixed with a special cut-resistant rubber? Then under the tread, add three polyester plies, plus two steel belts and a second belt of nylon. Yes, both of these test tires are nearly identical in construction, with the same materials, but this is where the similarity ends. Their tread designs are different, a lot different.
The XTerrain was designed for the serious four-wheeler to work well in all types of terrain, be it mud, sand, or rocks. Street performance wasn't an issue in the design; however, its highway manners weren't compromised, with the noise level and handling characteristics about equal to or better than most of the aggressive tires we've used in the past. Based on our experience, their strongest forte is loose, rocky soil.
So sure of these tires being bulletproof-or should we say, "rockproof"-we left the matching spare off our test Jeep during an extended trip to Moab, Utah. Where else is the ultimate place to test an aggressive tire that offers all the elements mentioned above, including snow? We put these tires through the worst conditions possible that included an honest 889 miles of trails at 8 psi, as well as some high-speed highway driving between the trails. We liked them so much, we kept them on the rest of the summer for our local trail rides.
If you think that a 37-inch tire isn't all that big, compare the Xtreme All Terrain on the left and the XTerrain on the right to the little 35-inch XTerrain that's in the center.
If we had to rate their lowest performance issue, it would be on icy and snow-covered roads. There are just not enough small biting edges to offer maximum traction under winter conditions. (Note that I used the words "maximum traction." They still worked quite well.) The tread rubber-to-void ratio is a bit large for snow to stay in the tread and to offer the best snow-to-snow traction. However, we wouldn't hesitate to use this tire for a winter snow trip-they should offer excellent flotation as long as one is easy on the throttle.
Visual effect, or the "cool factor," is right up there with overall performance. In fact, the truck driver who delivered them wanted to know what type of a "skidder" they were going on! From then on, during our test in Moab, the Jeep and its tires were referred to as "the skidder."
At first we mounted the XTerrains on some 15x8-inch rims-pretty standard for rockcrawling rigs-to allow for more sidewall flex and to protect the rim from damage. However, after remounting them on 10-inch-wide rims, now we feel that this is a better width for all-around use, at least for our application. Why? First, at 8 inches wide with 3 1/2 inches of rim backspacing, the tire's 13.50-inch designated width caused them to rub our springs on full turns, thus limiting our turning radius. They also rubbed our fenders under compression. A 2-inch-wider rim moved the tire's body outward and eliminated some of the bulging, as well as slightly lowering the overall diameter. Both these factors came real close to eliminating the rubbing. Second, the wider rim width improved both road and trail manners without sacrificing off-highway prowess by preventing excessive roll-under in corners or side hills.
Yes, we like to torture our tires. Even with its load-range D rating, the XAT was able to conform to these rocks for maximum traction. Note that there is almost a fold in the sidewall.
Built on the same basic "green tire design" as the XTerrain, the Xtreme All Terrain has a slightly more aggressive tread than the standard Pro Comp All Terrain, but not nearly as aggressive as the XTerrain. Designed for excellent highway manners, its flat tread and square shoulders still offer good traction in most off-pavement encounters.
For wheels, we went with a 16x10-inch rim. Because these tires would see more highway than trail mileage, we went with 16s to offer a lower sidewall aspect ratio in order to capitalize on better handling through sidewall stability. But don't let the mild tread design fool you-they worked so much better than we ever expected. These tires were built for the truck owner who wants a good-looking large tire without having to put up with noise that comes with most of the tires in this size range. We didn't realize just how quiet these tires were (or how noisy our Jeep was) until we came home from one trip on a tow strap for 50 miles.
While we didn't get to try the tires as extensively off-pavement as the XTerrain, we did put a lot of combined highway and trail mileage on them. No, they don't work on the trails quite as well as the XTs do-nor did we expect them to-but they're no slouch either. In fact, we were quite impressed with their mud performance after initially judging that the tight tread blocks would really limit their traction capabilities in loose dirt and (especially) mud. We even got to try them out in some snow and again were pleased with the performance. On gravel roads, they were a bit on the "loose" side, to use a stock-car racer's term, meaning they lack some adhesion ability-something that we pretty much figured would happen with some 11 inches of flat rubber in contact with the ground. It's interesting to note that while the rim size on our test XAT is an inch larger in diameter than the XT we used (which means less sidewall height), the tire's weight is one pound more at 85 pounds, and it carries a load range D rating. This tire was made more for the pickup owner who wants a tire with a lot of load capacity and good street manners. The higher rating does explain why the sidewall didn't flex and conform to obstacles as well as the XT's did.
While never designed as a mud tire, we were surprised at the self-cleaning ability of the XAT. Note how the center of the tire is fairly clean and outer lugs at the top of the tire have released the mud.
Yes, these tires are on bead-lock wheels, mainly because we like to run at lower pressures than most people-maybe not as low as one other fellow magazine writer, but pretty low pressure, nevertheless. And not because these tires needed the extra traction the low pressure footprint offers, but because we really like the ride quality the low pressure offers. OK, we're getting soft.
The bead-lock wheels also came from Pro Comp. No, you will never see them listed in a Pro Comp ad, but nevertheless, they are available under special order (and if you're nice enough to the sales people and swear that you will never run them on the highway as they are not DOT-approved). These quality 32-bolt bead-lock wheels are quite stout and weighed in at 40 pounds each for the 16x10s. Yep, the total package is quite heavy, especially so when combined with the 85 pounds each tire weighs.
37x13.50R15 XT 37x13.50R16 XAT Load Range C D Max load 3,000 3,525 Diameter 36.76 36.75 Overall Width (in) 13.6 13.5 Tread Width (in) 11.0 11.0 Tread Depth (in) 20.5 21.0 Rim range (in) 8-12 8-12 Weight (lb) 84 85