Cooper Tires’ Discoverer S/T MAXX has been my favorite commercial traction/hybrid tread design since its introduction. I have experimented with four sizes on four different truck platforms, and suggested them to many friends and acquaintances. Two of my four-wheel-drives are still running the S/T MAXX, including the built, 2006 V-8 Toyota 4Runner with 4.88:1 gears in this video.
After a whopping 7,436 miles before the first rotation, mostly road miles, these LT285/75R16 Discoverer S/T MAXX are wearing impressively well and evenly. From their original, generous depth of 18.5/32″, the fronts are down to 16/32″, and the rears 16.5/32″, 2.5 and 2/32″ respectively. That’s an average of 3,300 miles per 1/32″ of tread, and excellent wear from a fairly aggressive, moderate-void tire on a full-time four-wheel-drive car. They were rotated using the rearward cross pattern.
All thirty-threes are not created equal, because they’re not all exactly thirty-three inches tall. The very common 285s are typically 32.8-inches tall while 255/85R16s are almost always 33.3+ inches; the Toyo M/T is 33.5-inches! Removing the Dick Cepek F-C II 17-inch 285s, slapping-on the 18-inch Cooper S/T MAXXs, and taking a few measurements showed that the taller 275/70R18 MAXXs were good for 3/16″ of additional clearance under the rear differential. Nice.
My initial S/T MAXX drive was on a test loop I typically travel after any tire, wheel, air pressure, alignment, or other drivability changes are implemented. It’s several miles long and includes city streets, rural highway, interstate freeway, and sometimes just a minuscule amount of dirt for photos. The route and terrain are familiar, as is the vehicle platform, what’s being evaluated is the change, in this case, tires.
LT275/70R18E Cooper S/T MAXX, slightly taller than most 285s.
Noise
What noise? Articulating tire noise can be a challenge, as vehicles have different levels of insulation and sound deadening, and drivers have their biases and tolerance or lack thereof for noise. With several back-to-back tire tests under my belt the S/T MAXX is clearly one of the quietest traction tires I’ve ever had the pleasure to drive on. The volume and tone is similar to my beloved Dick Cepek F-C II, but a bit quieter, and the MAXX is certainly quieter than the standard Cooper S/T. Comparing the S/T MAXX to the super popular BF Goodrich A/T is tough. While I currently have a set of used BFG A/Ts, I have few personal miles on them and I’m not a BFG A/T fan. I’ll go out on a strong limb and say the new S/T MAXXs are louder than the BFG A/T, but not much. For a tire that offers as much traction and void (much more than the BF Goodrich A/T) the Cooper S/T MAXX is an amazingly quiet tire and well worth the little noise it makes.
LT275/70R18 S/T MAXX on Tundra SR5 wheel
Stiff
As noted in my introduction, the ArmorTek3® carcass construction and 3-ply sidewalls of the S/T MAXX are stiff. This can be great if this is a feature you are looking for, or a negative if you prefer a more compliant ride and/or a lighter tire. (If you are new to this blog or subject, read Wheels, Tires, and Sidewalls from Jan. 30, 2012.) In addition to the intentionally rugged design of the S/T MAXX, using 18-inch wheels with only a 33-inch tire adds to the lack of sidewall flex.
One of my strong dislikes for tall wheels on light-trucks is manifested by this situation: a relatively tall tire (33+), with a relatively short sidewall doesn’t offer the same off-highway flex and performance available from a taller sidewall. The same height tire on a 16-inch rim would yield an additional inch of sidewall to drive and flex on; this is not a small difference. If you already use and like the firmness of a load-range E sidewalls then the stiffness of the S/T MAXX (similar to the Toyo M/T) may not bother you, particularly if you don’t have to run it on a tall wheel. However, if you prefer a more compliant ride or a lighter tire you might reconsider the MAXX. What do you want, and what do you need for your application?
S/T MAXX with Old Man Emu (OME) suspension.
Pulling To The Right
Several years ago I rarely experienced tire pull problems with my trucks, however they are all live-axle 4WDs. Starting with my 2006 V8 4Runner and now continuing with this Tundra, I’ve experienced a pull (or drift) to the right with certain tires but not with others. Both of these IFS four-wheel-drives have alignment settings and geometry that are equal to or better than when new.
Aftermarket upper-control-arms are employed and expertly adjusted, though invariably some tires cause a very noticeable drift or pull to the right. I’ve spent countless hours and dollars to try and understand, identify, and combat this situation on these Toyota 4WDs. In short, my work involved many trial-and-error alignment adjustments, tire & wheels swaps, rotations, and tire pressure changes, all of which did not correct the problem. Some tires would still pull right, some terribly so.
How bad is the pull or drift? On a straight section of freeway with little road crown, at 65 miles-per-hour, releasing the steering wheel will result in crossing the right lane-line in about 3-seconds. Three seconds! I’m a strong advocate of keeping one, if not two hands on the wheel, and paying attention to the task at hand when driving. But I also like my vehicles to have very neutral handling, heading straight down the road unless instructed otherwise. Modified or not, I require my vehicles to drive almost perfectly on-highway. For comparison, depending on the road, wind, and other variables, with the same alignment settings Dick Cepek F-C II tires would continue straight for 8–10 seconds with no-hands.
Some readers may observe that the wheels are not identical. OE 17-inch forged TRD wheels are being used for the F-C II, while the MAXXs are mounted on 18-inch SR5 wheels, and there is probably a slight difference in backspacing. Is that part of the problem? I doubt it, though I did consider of this difference, and have a plan.
After an interlude, there will be more Cooper S/T MAXX commentary in the future—first we have to drive there.
After deciding the LT275/70R18 was my perfect 33-inch tire for an 18-inch wheel, and seeing there is a nice selection of tires in this size, a tread had to be chosen. This was relatively easy as I’m familiar with most of the popular light-truck traction tires. I’m a fan of Cooper Tires and their subsidiaries, and the new S/T MAXX design was already on my to try list, offering the type of any-terrain tire I prefer—not too biased toward on or off-highway. Cooper calls this a 50/50 tire (on/off pavement) and I’d say they are very close to hitting that mark.
LT275/70R18E Cooper S/T MAXX
After some online shopping, my local Discount Tire matched a price from TireCrawler, a mere $242 each delivered. (This was a few months ago; tire prices change, usually increasing.) Discount ordered the tires and a few days later I hauled my 18-inch wheels to their shop for mounting and balancing. Cooper says the LT275/70R18E MAXXs are 33.35 x 11.2 inches and my scale said they weigh 60.5-pounds each. Combined with the relatively heavy, 30-pound, 18-inch cast aluminum SR5 Tundra rims, each tire/wheel combo weighed 91-pounds!
Stout Construction
Once you get your hands on one, there will be no doubt the S/T MAXX is a super stout tire. The scale tells part of the story, though not all load-range E or 3-ply sidewall tires are created equal (see Wheels, Tires, and Sidewalls). Grab an unmounted ArmorTek3® sidewall and give it a good jerk back and forth, they’re stiff, similar the Toyo MT, and more substantial than the 3-ply sidewalls on the very common BFG All-Terrain. The MAXX sidewalls are much stiffer than the older and lighter-duty Cooper S/T, which offers flexible sidewalls and very little sidewall tread. Similar name, and I like both treads depending on the intended application, but they are very different tires. Try not to confuse the S/T MAXX with the S/T, or the Cooper STT… maybe Cooper needs some new letters?
The S/T MAXX has beefy sidewall lugs/tread.
The S/T MAXX is an impressive looking tire. The sidewall lugs are attractive and thick, more impressive in person than in the photos I’d seen, and possibly the most aggressive sidewalls I’ve seen on a tire in this class (not a mud-terrain). The tread is a hybrid 4–5 rib design with a bit less void than the older 4-rib S/T, the center circumferential groove is noticeably missing. There is a moderate amount of siping and the cut & chip resistant compound is studdable. Cooper describes the MAXX as a “commercial grade traction tire”, an accurate description.
S/T MAXX 4-5 rib hybrid tread design.
Mount & Balance
Mounting a 275/70R18 S/T MAXX on Tundra 18 inch SR5 aluminum wheel.
Mounting the first tire and giving it a spin on the balancer showed it wanted 3.25-oz. inside and 4.75-oz. outside for a dynamic balance. Eight ounces is not much weight for a 91-pound spinning mass, but I generally like to add less weight to my wheels when possible.
While dynamic balancing is the technically the best as it balances in two planes, I’ve had many positive experiences using the single plane static balance method for heavy RV tires (an old term). Static spin balancing counters vertical imbalance (hop) of a tire & wheel, and I don’t run very wide tires where dynamic balancing can be more important. Generally, I see how the first couple tires in a set balance and if they can be dynamically balanced with moderate weight, that’s what we do. If they are going to ask for substantial weight using the dynamic method, I choose static.
Modern balancing machines are very good.
Sometimes this difference can be very dramatic. A few months ago a heavy, high-quality tire wanted about 9 ounces for a dynamic balance, but only 1.5 ounces for a static balance. Guess which one I chose? The S/T MAXXs were single pane balanced and the road force (RF) was also measured—which was very low—another indication of quality. For more thoughts on tire balancing you can read Static Balance Details.
Static Balance Numbers
#1) 4.75-oz. RF .002″.
After seeing this low road force number the kid doing the balancing commented “Wow, that’s like a Michelin.”
#2) 4.25-oz. RF .008″
#3) 5.50-oz. RF .007″
#4) 1.50-oz. RF .009″
Cooper Tires’ website lists the tread depth for every S/T MAXX currently made as 18.5/32″, which it probably is. But it would be pretty easy to call this 19/32″ as measuring down to one-sixty-fourth can be a challenge. The original tread depth is important, more is better for most truck tires, though the long-term wear rate is also important. Combine deep tread with a low rate of wear and you have a long-lasting tire.
LT275/70R18E COOPER S/T MAXX tread depth.
Because my original 17-inch Tundra TRD wheels use tapered lug nuts, which are uncommon for modern Toyota trucks, I needed new shank-style nuts for the 18-inch wheels. Searching online I found a source for the Gorilla brand lug nuts and locks, a complete set was delivered for about $110. I’ve been using an impact-gun on Gorilla wheel locks on my 4Runner for years, and they have held up to my intense use. I wish they would fit on the OE 17-inch TRD Tundra wheels.
Shank style Gorilla locking lug nuts needed for SR5 wheels.
