Cooper STT Pro MudTire

Tire test­ing an old­fan­gled way

Jp Magazine - - Table Of Contents - By Brian Gabriel jped­i­tor@jp­ Pho­tog­ra­phy: Brian Gabriel

You’ve read hun­dreds of tire tests and re­views, many of them right here, but most are a snap-

shot of the tire over a mat­ter of days or weeks of use. Those are per­fectly le­git­i­mate and do yield valu­able in­for­ma­tion. How­ever, when pos­si­ble we’re go­ing to start giv­ing you long-term tire tests, dur­ing which a se­lect group of ex­pe­ri­enced Jp Mag­a­zine staff and con­trib­u­tors will put months’ worth of driv­ing, on- and off-road, on a set of tires so we can tell you how they hold up over the long haul. These long-term tire tests will be­gin with a first im­pres­sion of the tire’s per­for­mance, noise, phys­i­cal at­tributes, specifications, and if pos­si­ble de­tails about other sizes of the tire in ques­tion be­ing of­fered—that’s what you’re about to read. Short up­dates on the tires will fol­low every few months for as much as a year, de­pend­ing upon the spe­cific sit­u­a­tion.

Cooper Tire is a brand that just about ev­ery­one has seen in ad­ver­tise­ments, on the trails, and at the mall. They have been build­ing top-qual­ity tires since way back when Willys-Over­land was build­ing sedans. Old dogs can learn new tricks though. A few years ago, Cooper Tires opened its Global Tech­ni­cal Cen­ter in Find­lay, Ohio, as head­quar­ters for R&D. USA-de­signed and USA-made are nice things to see to­day.

A set of 35x12.50R15 tires soon ar­rived all wrapped in pa­per, and I stared at them like Ral­phie when he opened the Red Ry­der BB gun—in my pa­ja­mas, since they ar­rived at 8 a.m. The tire

side­wall shows 35 and the spec sheet says the ac­tual mea­sure­ment is 341⁄2 inches, but the real, in the drive­way, true, re­al­life, and ac­tual mea­sure­ment for this set of tires on my Jeep at max load pres­sure is 331⁄2 inches. We have seen this difference in a few tire brands, and it’s the same for a num­ber of “35s.” The load range on this par­tic­u­lar size is 113Q, which trans­lates to: 113 = 2,535 pound max load (per tire) and Q = 99 mph max­i­mum speed. There is no doubt we will never get near the lim­its of ei­ther of those specs with this old Jeep though. Weigh­ing in at 67 pounds of rub­ber, this tire seems to be about av­er­age for the size. The tread depth is nice and deep (ad­ver­tised and ac­tual mea­sure­ment) at 21⁄32 inch.

Over­all, the early im­pres­sions of this tire are pos­i­tive. This is a real-world, long-term test on these tires. We will be re­port­ing back pe­ri­od­i­cally for up­dates on our ex­pe­ri­ences with ter­rain per­for­mance, road man­ners, wear pat­terns, and ro­bust­ness. They will in­deed be put to the fire.

Our trusty test lab is this 1979 CJ-7 pow­ered by a 258ci in­line-six with a 4.0L head swap, NV3550 trans­mis­sion, Dana 300 trans­fer case with 4:1 gears, AMC 20 rear axle with Warn full-float axlesand ARB Air Locker, nar­rowed Dana 44 front axle with ARB Air Locker, and a three-link front sus­pen­sion. Weigh­ing in at around 4,750 pounds loaded for bear, the Jeep has wheeled the mu­dand moss-cov­ered rocks around the moun­tains of Penn­syl­va­nia, and now spends time in the desert dirt and slick­rock of Utah. It also sees snow in the harsh Utah win­ters, and lots of top-down, around­town, and high­waydriv­ing too.

As soon as the 35x12.50R15 Cooper STT Pro tires were mounted on the Jeep, we were headed to Easter Jeep Sa­fari 2018 to start test­ing the new rub­ber in Moab, Utah. New tires are stiff and need some flex­ing to break them in for the best trac­tion. In this pic­ture it seems like the tires are at street pres­sure, but they are ac­tu­ally aired down to around 12 psi. By the end of the first day on the trail the tires were wrap­ping around the rocks. Since we have the con­ve­nience of se­lectable ARB Air Lock­ers in the CJ-7, we drove un­locked off-road as long as we pos­si­bly could so that the tires would show their worth unas­sisted. The tires met a va­ri­ety of ter­rain from solid slick­rock, larger boul­ders, loose rub­ble, and silt in Moab, and im­pressed us in all of these sit­u­a­tions. The lock­ers did have to be en­gaged on some in­tri­cate ob­sta­cles a few times through­out the week, but in gen­eral, the Cooper Dis­cov­erer STT Pros met our ex­pec­ta­tions.

One of the more chal­leng­ing areas in the gen­eral Moab area is the White Sand Dunes. Cruis­ing along the beach is one thing—blast­ing around the dunes is an­other. Sand re­quires ex­pe­ri­enced driv­ing tech­nique as well as special adap­ta­tions to the tire. The STT Pros were aired down to 10 psi to spread the load over a larger foot­print, and that made a big difference, but a lit­tle too much throt­tle and wheel­spin on this climb and the lugs on the tires dug the Jeep in deep. Thank­fully, the flota­tion char­ac­ter­is­tic of the tires al­lowed for easy re­ver­sal out of trou­ble.

Once the tires “broke-in,” they adapted to the en­vi­ron­ment well, grap­pling the ob­sta­cles as they came. Even the ag­gres­sive side­wall biters got in on the ac­tion here. The rub­ber com­pound was re­designed for this tire for bet­ter trac­tion in wet con­di­tions, but I think it’s safe to say that change pro­vided trac­tion ben­e­fits in most sit­u­a­tions.

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