Conquering the Rocker Knocker...
Conquering the Rocker Knocker on Pritchett Canyon in Moab is not an easy task. To simply crawl up this obstacle in a short-wheelbase vehicle is pretty much unheard of. Between the capability of Kevin Hawkins' Jeep and his driving skill, it happened, but in no small part due to the special soft-compound Interco TrXus MTs. Ironically, Walker Evans, whose name is on those nice bead-lock wheels, can't always make it up the Rocker Knocker without making numerous attempts. On White Knuckle Hill, Kevin's special TrXus tires went right up, while Walker's vehicle didn't, at all.
This is not a normal tire test but a look at what happens when taking a proven performer, the TrXus MT, and using rubber compounds normally reserved for sticky drag-racing tires. Since Interco is the manufacturer of the Super Swamper and also owns M&H Racemaster Tires, the technology was available in-house. It was only a matter of relentless ragging on our part to make Interco whip up a set of experimental tires with a compound so soft that it just had to stick to rock like crazy. Of course, nobody knew exactly what the end result would become-a usable trail tire with unreal traction, or a tread that would shred itself to pieces within a single trail ride.
A tire represents a massive amount of compromise between traction, wear, and several other factors, and a gain in one aspect is generally paid for with lessened performance in another. A mud tire is already well into the traction-at-the-cost-of-wear part of the equation, so to make one with a decent life expectancy is already tricky, and throwing a soft compound into the formula is going way out on a limb.
A bias-ply would be the casing of choice to get the best possible traction through conformability, but because of time limitations, Interco opted to use the TrXus MT, which is a radial. In the 37x12.50R17 size, that also means a load-range E tire ... ouch. We certainly had our doubts about a 10-ply-rated radial on a 3,100-pound vehicle, as each tire could support over 500 pounds more than what the whole vehicle weighs.
At first, we suspected that...
At first, we suspected that Interco had pulled the two steel belts out of the experimental 37x12.50R15, because this kind of conformability is great for a radial, and especially a load-range E casing. We certainly hadn't expected a very cushy ride from these tires, and definitely not at a relatively high 10 psi of inflation pressure on a light vehicle. Kevin ended up running 10 psi for the majority of the test, and only once was there a hint of bounce, while climbing a very steep sandstone wall with moderate tire spin.
To give the experimental TrXus tires a true workout, we enlisted Kevin Hawkins-a rock connoisseur with extensive competition experience and a keen sense for details-and his "CJ2A" rockcrawler. He mounted the tires on 17x8.5 Walker Evans bead-lock wheels and headed for Moab. Twice.
As you probably know, Moab's Easter Jeep Safari was largely about mud this year, but Kevin ran even the bad spots in two-wheel drive: "Compared to my other tires ... a major difference," he said. Good lateral support in fast dirt-road driving, decent flotation in sand for a narrow tire, and low noise were also noted. Our fears about the load-range E were unfounded-at a relatively high 10 psi, Kevin felt that the "tire rides like you're driving on innertubes." So far, very good-but those are all the traits of a regular TrXus MT (Apr. '03) and had little to do with the compound.
Let's cut to the chase: "These tires slow-crawl up sandstone walls like no other tire I have run!" said an excited Kevin. "I have a test climb ... on the Golden Spike trail that with my other tires, the only way up was with spinning momentum. These tires crawled it!" Still not convinced? Neither was Kevin, so the next time he stopped halfway up the wall and still crawled it. Moving over to the even steeper side, "it crawled without spinning the tires until [both] front tires came off the ground." Well, that's about as much traction as you can realistically use, and in that respect, the tread compound worked great.
Clinging to rock is what this...
Clinging to rock is what this special-compound experiment was all about, and the result was beyond expectations. When the tire offers enough traction to keep crawling up hills until the front wheels come off the ground, you really don't need much more grip than that. Kevin couldn't pull a wheelie and shoot a photo at the same time, so this one only shows the TrXus hanging on sideways. That the tread remained quite intact despite some outright abuse was a really nice surprise, since not even all regular treads hold up well in rock use.
It's relatively easy to make a sticky tire, but also having it stay together can become a real issue. In this case, after a week of trails during Easter Jeep Safari and another full weekend of four-wheeling shortly thereafter, the tire's tread still showed no signs of chunking tread blocks or missing pieces. In an all-out effort to find the compound's weakness, Kevin did two one-minute "burnouts" on the slickrock, one in two-wheel drive and one in front-wheel drive only, but only managed to round off the leading edges of the tread blocks a bit.
So there you have it. This tire grips like glue, yet the tread doesn't readily come apart. It doesn't get much better than that, except, this tire doesn't really exist yet.
So what does this mean for the rest of us?Hopefully, within the near future Kevin Hawkins won't be the only four-wheeler on the planet with these special-compound tires. Interco is considering limited production, if the demand is there. We would imagine that there are a fair number of customers willing to run a tire like this, but it's certainly not the ideal tire for everybody. So why would you not want a tire that absolutely kicks butt on the rocks? Cost would be one reason, as specialty tires made in small numbers will be pricey compared to the regular TrXus. Legality for street use could be another issue since the soft-compound tire wouldn't necessarily become DOT-approved-or if it was, it'd make the tire even more expensive. On the other hand, you wouldn't want to drive much on the pavement anyway since the tread is so soft. Sure, it'll grip like crazy-just don't expect tire life to be even close to that of a regular compound. These are compromises you may or may not be willing to make, but at least Interco has taken the first steps towards making a tire for rockcrawling that has far fewer compromises than what the usual trail treads offer.
Tire: Special compound Interco TrXus MT
Size: 37x12.50R17 LT
Type: Radial
Load range: E
Max load (lb. @ psi): 3,640 @ 60
Sidewall: Three-ply polyester
Tread: Two-ply polyester, two-ply steel, one-ply nylon
Approved rim (in.: 8.5-11
Tread depth (in.): 21/32
Tread width (in.): 9.25
Section width (in.): 12.77
Overall diameter (in.): 37.2
Static loaded radius (in.): N/A
Revolutions per mile: N/A
Weight (lb.): N/A
Test vehicle: 3,100-pound Jeep CJ/buggy