Choosing wheels and tires might be the most crucial decision you’ll make when building your rig.  Even when one is just replacing the stock doughnuts for an aftermarket look, many toss and turn in bed, annoy their friends with a thousand questions and search the net for months trying to find the perfect off road tire for performance and looks.  There have been a myriad of advancements in tire technology over the past five or six years and Pro Competition Tire Company (www.procomptires.com) has done their home work and turned it in on time! 

Procomp has stepped it up in the tire world and is not just the suspension company that we’ve all known for many years.  On the tire side, sure, you’ve seen their standard Mud Terrain and All Terrain tires that look like most everything else out there and perform as well. You’ve seen the X-Terrain that has proven to be a formidable competition tire amongst the hard core crowd.  Well, some are still in the dark and have not seen the new Procomp Xtreme Mud Terrain.  We were lucky enough to nab a set of 37’s to tuck under our Project JK and literally beat the rubber off of them to tell you about it.

First, why did we choose the Xtreme M/T?  We are used to running this Jeep with a very aggressive bias-ply tire and wanted something that would give us confidence in big, tire slashing rocks.  We also wanted to go to a full-time tire, rather than swapping out for the weekend from radial street friendly to bias ply rubber for the trail. 

Looking at the Xtreme M/T tells a different story than what was proven to us on the trail.  The tread pattern is visibly tamer compared to what we’ve been running. However, the sidewall and tire construction begs for abuse.  Procomp tends to get very generous with kerfs and sipes in their entire tire line up.  Kerfs you ask? A kerf is a molded sipe that allows larger lugs to flex more independently and provide huge traction on any surface.  These traction aids will also be beneficial in winter time, street driving here in Colorado.  Lastly, the Xtreme M/T’s design will also help keep the tire cool, increasing tread life, even with the semi-soft durometer measurement of 66.  We chose this tire for its versatility and spec sheet, and not just the cool looks.

Extensive kerfs and siping help give the Pro Comp Xtreme M/T excellent traction on the trail.	The three-ply sidewall with a nylon overwrap gave us the confidence to abuse the tires on the trails of Colorado.

Tire Construction is very impressive to say the least.  Procomps first tire offerings to the market used two ply sidewall construction, which is fine for the guy who hits the dirt roads and small boulder fields.  The Xtreme M/T incorporates their proven Tri Ply construction which consists of two typical radial Polyester plies and a third outer ply, angled at ten degrees.  This added third ply offers a puncture resistant sidewall, yet allows the tire to remain flexible on and off road, as well as in the hardcore rocks that we like to play in.  With this, they then combined the two outer layers of opposed angle steel belts and a “seamless” layer of spiral nylon overwrap for what might be the toughest radial tire on the market today.  These treatments give us as much confidence as we have had with our bulletproof bias ply tires.

Our wheel choice is a prelude of what’s to come for our project so when you read that we are using an 18 inch wheel, don’t run away screaming, “mall crawler!” With that said, even if we were to stay with the 37 inch tires and not graduate up to some monster 40’s, we’d still chose the 18 inch wheels.  Why?  We noticed absolutely no ill affects by using a wheel this large in off road conditions.  Air volume in the tire was still great enough to allow proper “air down” to 10 lbs and we were rewarded with a nice sidewall bulge and ample traction. In fact one of the best we’ve tested. The slightly shorter sidewall may also help in offering less exposure to the rock gods for sacrifice.  On road, the shorter sidewall improved handling tremendously with less flex but the tough, three-ply sidewall proved to dish out a somewhat harsh ride if aired up over 33 lbs. 

We mated the Xtreme M/T to Pro Comp's slick looking 8128 Alloy in the 18x9 size.

As for looks, we have never been big fans of simulated bead locks but when we saw the new Pro Comp Alloy 8128 wheels, we couldn’t resist picking up a set of the 18x9’s. (picture 4)  These wheels are beautiful and will surely be a huge hit amongst the off road crowd due to the five spoke simplicity, yet modern looks of either flat or gloss black and polished bead rings.  We’re know the 8128’s are a light weight alloy, however, with the 40 stainless steel bolts that grace the outer bead of these wheels, the weight increases quite a bit.  However, this additional weight did not seam to affect the balancing of the wheel and tire package.  The Xtreme M/T’s are an incredibly true tire, as are the Procomp Wheels, each calling for three ounces or less to zero out and might just be the most well balanced tires we’ve ever run.

Our impressions of the Xtreme M/T on the street, rocks, dirt and mud were all about the same; very positive in each area.  After airing them down to 27 lbs, pavement pounding was a pleasure, even with an E rating. The super flat tread surface allows these tires to hug the asphalt making the smooth and sure footed. While we’ve only gathered up about 4,000 miles, no visible or odd tread wear has occurred. 

On hard packed and loose dirt, the Xtreme M/T’s kicked butt!  The sharp edges of each center and shoulder lug grabbed into the terrain, making forward and lateral traction easy, even at speed.  When aired down to 10lbs, the firm sidewall kept handling manageable while quickly scooting around the fire roads.  We found it difficult to get the rear end to break free under hard acceleration on hard packed dirt.  These tires just plain hook up.  We’d love to mount a set of these up on pre-runner type truck to see what they’d do!

Mud?  Come on!  We tested these things in Colorado during the summer.  We did encounter some mud intentionally though.  One of our local trails still has some large snowy areas, usually providing enough run off to cause small mud bogs.  The tires cleared the wet Colorado mud easily but we can see how a more tacky goo might clog the Xtreme M/T’s. 

Even with their E-load rating, the Xtreme M/'T's flex well and work excellent in the rocks. The wrap around sidewall treatment also helps provide traction (and protection) when aired down.

Of course, rocks were our prime target and we found some that really bit back at the Procomp Tires.  The Xtreme M/T’s are some of the stickiest tires we’ve ever seen work and all types of rock is their natural habitat.  The tires tread and sidewall worked incredibly well in concert!  Wedging the aggressive sidewall onto rocks provided enough traction to pull the heavy Jeep up, as well or better, than using the flat tread surface. When the tires wrapped around rocks or folded over, there was always plenty of sidewall thread to keep forward progress.  Rarely did a tire slip, even on the most dusty and sandy or wet surfaces.  Each Kerfed lug was able to do its job by flexing and grabbing at what it could, to fight for traction. 

The fairly soft durometer of the tire allowed nice graining on the lug edges. However, we did get some minor to significant chunking while on some rough rocks sections, which surprised us. This could be attributed to some excessive throttle while stuck in a less desirable situation but the tires got us out in the end.  Again, with the 18-inch wheel, we felt even more control with this combination on the road and in the rocks due to less sidewall over-flex and would go with 18’s again for a 37-inch tire. 

The Xtreme M/T is now one of our new favorite radial rock tires and will be a natural choice if and when Procomp Tires reveals a 40-inch tall version.  The closest to that size currently available is the 38.5x14.50 but if you have to have a 40-inch tall Pro Comp Tire now, they do offer the Xterrain in that size.

With a softer compound we did experience some chunking on the rockier trails we tested the Xtreme M/T on

Upon inspection of the chunking that occurred during our hard rock running, we also noticed a little rock rash our new wheels had suffered.  The large outer bead that these wheels use protrude out past the rim guard molded into the tires.  The bead is thick enough to hold the recessed stainless steel bolts but puts them in harms way when spinning past the granite.  If you like to wheel in the rocks but also like to have an immaculately kept rig, these wheels might not be for you. An “immaculate trail rig” is an oxymoron anyway, isn’t it?

As said before, Pro Comp Tires did their homework when designing their Xtreme M/T and all homework leads up to the inevitable test.  It was hard to find a week spot when administering our test and we feel the proper grade for these tires is a very strong A.  These tires are right at home in the harshest conditions a true crawler can throw at them and they can still get you back home on the street comfortably and safely. Pro Comp Tires and Alloys are availabe at 4Wheel Parts (www.4wheelparts.com).

Additional Tire Specs:
Pro Comp Xtreme Mud Terrain
Sidewall Size Print:  37x12.50 18
Weight:  87 pounds
Actual Height:  36.9 tall
Tire Width:  12.5 wide
Tread Width:  10 tread
Load range E
Max Load LBS 3,970
Durometer 67