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Long-Term Tire Test: Cooper STT Pro

We put these Jeep feet “to the fire” to see how well the Cooper STT Pro tire holds up

Brian GabrielPhotographer, Writer

You’ve read hundreds of tire tests and reviews, many of them right here, but most are a snapshot 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 your 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 Finlay, 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 34 1/2 inches, but the real, in the driveway, true, real-life, and actual measurement of these tires on my Jeep at max load pressure is 33 1/2 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.

A quick look at some popular tire size specifications of Cooper Tires Discoverer STT Pro tires:

Tire SizeService DescriptionUTQGLoad RangeSidewallApproved Rim WidthMeasured Rim WidthSection WidthOverall DiameterTread WidthTire WeightMax LoadTread Depth (1/32")
30X9.50R15LT104Q CRWL6.5 - 8.57.59.629.577.7244198519
31X10.50R15LT109Q CRWL7 - 98.510.730.758.548227020
32X11.50R15LT113Q CRWL8 - 10911.731.579.0954253520
33X12.50R15LT108Q CRWL8.5 - 111012.232.729.860220521
35X12.50R15LT113Q CRWL8.5 - 111013.134.5710.0867253521
37X12.50R17LT124Q DBLK8.5 - 11101336.7710.275352522
37X13.50R17LT121Q EBLK8.5 - 111113.336.7710.9884319522
40X13.50R17LT121Q CBLK8.5 - 111113.639.7610.9892319522