Tread Matters: Tire Selection and Fuel Economy

2014 Ram mpg test platform.

Tread Matters: Tire Selection and Fuel Economy

Tires have been a popular subject in magazines for decades, and forums continually see new threads seeking information and expertise. This is partly because they are expensive. They can also provide dramatic style and performance improvements and are an easy upgrade. With so much talk, it is surprisingly difficult to get unbiased, detailed, and authoritative information.

Fuel economy is another perpetually popular topic. Since tire choice affects mpg, or so we have always believed, the subjects are intrinsically linked. Some folks don’t care about mpg, but many care a lot. Except for the purchase of a new(er) truck or major repairs, fuel is our biggest operational expense.

What if it was possible to improve your highway mpg by 5 or 10%? Not a possible increase from the latest magic program pushed by a snake-oil salesman, but simply by choosing a different tread design? An improvement that could be measured and verified, repeatedly, with real world testing, not just theory or laboratory results that are difficult, if not impossible, to replicate.

What Affects MPG?

In the enthusiast truck world it is commonly accepted that bigger rubber reduces miles-per-gallon. Maybe, but bigger is not specific, sometimes it means wider, taller, or both. Taller tires will increase the overall final-drive-ratio, which can help or hurt efficiency depending on the platform and usage.

Previous tests with my 3.42:1-geared, 2014 Ram/Cummins 2500 used for this article indicate that taller meats up to 35” helped economy, or at least hurt mpg less than one might expect when unloaded. Tradeoffs include less torque and slower acceleration from higher final-gearing, though current generation trucks make plenty of torque and horsepower for most reasonable loads. My sense is that stepping-up to 37s would require lower differential gears for optimal performance.

When folks upgrade their tires, particularly on a four-wheel-drive, they often switch to a higher-void pattern; sometimes the more aggressive tread is chosen simply for looks. Even if we don’t mind the road noise or faster wear of an aggressive pattern, how much fuel does looking cool consume if one rarely or never drives off-road? With multiple, simultaneous changes, it’s impossible to say what caused a reduction in fuel economy. Instead of belaboring what modifications can do to our trucks, or what affects what, I’ll briefly quote myself, “Modifications lead to modifications.”

Beefier tires might cost you more mpg than you think.
Three great tread choices depending on your priorities.

Controlling Variables With Cooper Discoverer Tires

With generous support from Cooper Tires, I performed a series of real-world tests to document how tread design (or pattern) or tread width impacts fuel economy. I invested a substantial amount of time and money to prove or disprove commonly accepted hearsay and to produce solid data I could not find anywhere. The pattern design tests are complete, and my procedures are detailed below together with the results in Table Two. The width results are concerning, or at least surprising, and additional work may be necessary to become comfortable with the facts.

Worth $11.
Love knowing what it really weighs.

The primary variable to be controlled for the design test was the size, but weights, odometer and speedometer error, wind, and temperatures were also logged. The bullet list below offers details.

  • Weather forecasts were monitored until several similar days were on the horizon. Because wind is common in Nevada, and typically increases with the afternoon temperatures, just one test was performed each morning, avoiding the higher winds and heat that would influence outcomes if I conducted multiple runs each day.
  • Three used sets of the same 29.8-pound, forged-aluminum (WBJ) Ram Bighorn 18” wheels were purchased from Craigslist, allowing all tires to remain mounted and balanced in case a test needed repeating.
  • Odometer error was measured for every design using mile-markers (MM) and GPS, as different treads in a certain size are not dimensionally identical. A single, constant-GPS distance was used for all mpg calculations. Road speed was monitored with GPS and corrected speedometer measurements.
  • To reduce the possibly of substantial inaccuracies during fueling, and to increase the validity of the data, the roundtrip route distance was 222.7-miles, over mostly level freeway.
  • Refueling was done at a particular pump, on the slowest fill rate to prevent foaming, and never topped-off. The freeway onramp is just one mile and three stoplights from the filling station.
  • Appropriate, not maximum, pressures were used for the modified but unloaded truck- 8,900-pound GVW.
  • The tailgate was up and the A/C was on.
  • Cruise control was used and only adjusted or turned-off briefly when absolutely necessary, and notes were logged regarding any irregularities. If an accident, construction, or other mishap would have caused stopping or a substantial speed adjustment for an extended distance, I would have aborted and repeated the test.
Same GPS distance used for all runs.
EVIC mpg info is often inaccurate, doing the math is better.

All-Terrain, Commercial Traction, Or Mud-Terrain?

When enthusiasts upgrade their rubber it’s common for choices to fit into one of three categories; all-terrain, commercial traction (hybrid), or mud-terrain. I chose the LT295/70R18E size, which is approximately 34” tall and 12” wide, with an impressive 4,080 pound capacity at 80 psi. Cooper offers three of their popular, yet distinctly different Discoverer patterns in this size: the Discoverer A/T3, Discoverer S/T MAXX, and Discoverer STT PRO.

Readers should remember than although every effort was made to limit variables, these were real-world tests using off-the-shelf products; some differences naturally exist. One easily overlooked fact is that tire compounds are proprietary, and each has its own special cocktail. Tread depth, and sidewall and tread plies also vary depending on the terrain and audience targeted. So the differences affecting performance and mpg are not just the visible patterns, but they include the compounds and the overall construction of each tire.

Cooper A/T3, S/T MAXX, and STT PRO designs.

Discoverer 295/70R18E Measurements

The differences between tires of a particular size are often small, though one should be careful when comparing those from different manufacturers and/or a vastly different pattern. Over the past decade I’ve evaluated several sets of Cooper-branded and Cooper-manufactured tires, and my measured values have repeatedly matched the published specifications. Occasional, slight variations appear to be from measuring tools, mounting on narrower rims, etc. Manufactures know precisely what they are producing; they want to be as accurate as possible. Careful measurements were made of each Cooper design, and the details are in Table One.

Reading forums leads me to believe that some consumers don’t measure accurately, and/or expect the on-vehicle dimensions to be identical as the wheel-mounted, off-vehicle measurements; these folks cry foul when they are not. That is silly, as the weight of the vehicle, psi, and wheel width all affect the on-vehicle stature, and this is something the manufactures have no control over.

If you read carefully, and do some math, you may notice that the measured weight of a solo tire, plus the 29.8-pound wheel, does not match the mounted data, there are a few extra pounds in the sums. I’ve seen this many times before, as measuring bare wheels is difficult, and generally I must hold them against my chest and subtract my body weight. The figures listed in table one are what my shop scale, a good bathroom scale, indicated, plenty accurate for weighing heavy auto parts. Emphasis should be placed on the mounted weights, as nobody drives on wheels without tires. The few pound difference between these designs is negligible on a heavy-duty truck with prodigious torque and weighing nearly 9,000 pounds.

All 295/70R18 tread designs were about 34.25” tall.
Straight edge, a rule, and a keen eye were used to record height and width.

Table One, 295/70R18 Measurements

Cooper Discoverer 295/70R18 A/T 3 S/T MAXX STT PRO
Weight (pounds) 60.2 66.4 68.8
Weight mounted (pounds) 92.0 97.4 99.8
Height unmounted 33 11/16” 33 13/16” 34”
Height mounted @60 34 4/16” 34 5/16” 34 5/16”
Tread width 9 7/16” 9 10/16” 10 3/16”
Tread depth 17/32” 18.5/32” 21/32”

Table Two, Tread Affecting MPG Test Data

Tread Matters MPG 295/70R18 A/T3 S/T MAXX STT PRO
Test GVW (pounds) 8,900 8,900 8,900
Tire PSI F/R 60/40 60/40 60/40
Date 9-28-16 9-27-16 9-29-16
Time 0832–1202 0859–1230 0837–1208
Temperatures F 54-59-72-70-76-72 52-58-67-73-75-78 58-60-56-69-79-76
Wind/Gusts 1/2-5/5-2/5-4/4-1/2 4/4-2/3-0/0-1/2-0/0 0/0-3/4-5/6-3/8-0/0
Odometer 27,241–27,459 26,950–27,168 27,503–27,721
Trip Odometer 217.6 217.7 217.5
Odo error % MM & GPS 2.24/2.34 2.17/2.29 2.28/2.39
GPS (miles) 222.7 222.7 222.7
MPH indicated 64 64 64
MPH GPS 65.0–65.5 65.0–65.5 65.0–65.5
RPM Tach/Edge Insight 1,700/1,677 1,700/1,680 1,700/1,677
Fuel used (gallons) 10.380 11.033 11.533
ECM indicated MPG 23.2 22.4 21.0
MPG calculated 21.45 20.18 19.30
The less aggressive Cooper A/T3 delivered much better mpg.

Tread Results Commentary

Choosing the Cooper S/T MAXX over the STT PRO mudder offers a 4.6% bump in fuel economy. Running the A/T3 instead of the S/T MAXX delivered a 6.3% increase. The leap from the STT PRO up to the A/T3 is 11.1%. Wow!

It’s impressive that a modified, heavy-duty, 4WD pickup with prodigious capabilities, weighing 8,900 pounds empty, with 34” x 12” tires mounted, can still reach or exceed 20 mpg during highway travel. Obviously most driving involves at least a few and stops and starts, but these repeatable tests demonstrate what is possible if speed and idling are minimized. If I picked the Discoverer A/T3, it appears that long distance highway runs, even with a couple pit stops, could top 20 mpg.

If one needs the extra grip offered by the STT PRO or S/T MAXX, choosing the A/T3 all-terrain might not be an acceptable tradeoff. Yet, if one is so inclined and has the space, these numbers seem to reinforce the practice of having two sets of tires and wheels. Whether they are all-terrains and mudders for your truck, or highway and winter rubber for your car, strong arguments can be made about picking the right tool for the job. We don’t wear flip-flops to go mountain climbing, and our clodhoppers are out of place in a gymnasium.

Off-highway traction is great with a mudder, but you will pay at the pump.

Does Width Matter?

The initial primary platform for measuring how tread width affects mpg was my modified, heavy, and low-geared ‘06 V8 4Runner, because I already had one of two desirable sizes. One might think the results would be relevant for most light-truck platforms. The conditions and procedures were the same as those for the different tread patterns.

I used Cooper’s S/T MAXX in 255/80R17, and 285/75R16, both 33” tall, but the 285s are substantially wider. The 255s are about 10” wide and the 285s about 11.5”; conventional wisdom says the 285s would consume about 1–2 mpg. Without creating another table, the short story is that theses tests delivered ambiguous results, there was very little difference. I was shocked! Followup runs might indicate these results were a fluke, but there were no obviously problems or procedure inconsistencies. The narrower 255s delivered 18.34 mpg, and the 285s 18.22 mpg.

I thought wider treads consumed more fuel, not so sure anymore.
On the car or dismounted, the 285s are much wider than 255s.

Ram Width Comparison

Two sets of tires and wheels for my ‘14 Ram partially met the width criteria, meaning they were very similar height with the identical tread pattern, yet the width difference was small. I had them, so test I did, using the same parameters, during the same week, weather conditions, etc.

One set were the 295/70R18 S/T MAXX in table one. The other were 285/75R17 S/T MAXX mounted on 2015 (WFV) forged aluminum Power Wagon wheels, which weigh 28.6 pounds each. These 285mm-wide Discoverers are also 34” tall, but just fractionally shorter than the 295s. The mounted, measured tread width difference between these two sets is only about 3/8”.

The seventeens were evaluated at the end of six consecutive days of testing, and the weather started to change, with 22 mph winds near the end of this last trip. This was noteworthy, but I’d argue that there was not enough wind during most the run to impact the outcome. The data appear to support that opinion. For the slight difference in width, the results appear appropriate. There simply was not enough difference to influence economy, 20.18 vs. 20.22 mpg. I call that a draw.

295/70R18 vs. 285/75R17. Not a huge width difference but still easy to see.
Forged 17” Power Wagon wheel on the left, forged 18” Bighorn wheel the right.

Table Three, 285/75R17 Measurements

Cooper Discoverer 285/75R17 S/T MAXX
Weight 64
Weight mounted lb. 93.4
Height unmounted 33 11/16”
Height mounted @60 34”
Tread width 9 1/4”
Tread depth 18.5/32”

Table Four, Ram Width Matters 285/75R17

Width Matters MPG S/T MAXX 285/75R17
Test GVW lb. 8,900
Tire PSI F/R 60/40
Date 9-30-16
Time 0759–1130
Temperatures F 55-59-69-71-73
Wind/Gusts 0/0-3/4-5/5-5/14-22/22
Odometer 27,780–28,000
Trip Odometer 219.0
Odo error % MM & GPS 1.57/1.68
GPS miles 222.7
MPH indicated 64
MPH GPS 65.2–65.7
RPM Tach/Edge Insight 1,700/1,690
Fuel gallons used 11.011
ECM indicated MPG 20.9
MPG calculated 20.22
Good traction with a tolerable mpg penalty, I prefer a hybrid/commercial traction tires like the Discoverer S/T MAXX.

The Ram results were not a big surprise. The lack of separation between the 4Runner’s width test mpg numbers, and to a lessor extent the Ram’s, have me questioning how much tread width alone impacts fuel economy. Much taller tires, with the corresponding overall gearing changes, combined with more aggressive tread patterns may be the main story behind fuel economy losses when fitting aftermarket rubber. Sometimes testing answers questions.

James Langan

Copyright James Langan/RoadTraveler/Turbo Diesel Register. All Rights Reserved.

 A version of this article was also published in the Turbo Diesel Register magazine.

Source:

Cooper Tires: coopertire.com

 

TRD Tundra Wheels a 17 MPG Rock Warrior Solution?

Several weeks ago I posted about purchasing a set of OE 17-inch TRD wheels which included the original BF Goodrich All-Terrain 285/70R17 tires (17″ Tundra Wheels & BFG A/T Tires). However those were not the first, nor the best, set of TRD Rock Warrior wheels I have purchased. The Cooper S/T MAXX trial started last summer and has drug on for a while.

Cooper Discoverer S/T MAXX LT275/70R18E with Tundra SR5 18" wheel

The reasons for buying the 18-inch Tundra SR5 wheels was because I wasn’t enthralled with the fake beadlock rings on the Rock Warrior wheels (Goodbye Bling Rings), and because finding a set of  17-inch TRD second generation Tundra wheels for a reasonable price seemed nearly impossible. Most of the sets on Craig’s List were almost new, with almost new tires, and guys wanted almost new prices, upwards of $1,500 for the tires and wheels. No thanks. In addition to being far more than I was willing to spend, because I’m not a BFG A/T fan (not a hater, just not a fan) I really didn’t want to pay anything for BFG A/T take-off tires.

There were two issues with the 18-inch Cooper S/T MAXXs: the drifting to the right, and the stiff ride from the rugged, short sidewalls. I could seek alignment solutions for the pulling—which I doubted would work—but how could I soften the ride of the stiff, short sidewall tires without letting too much air out? The stout construction of the S/T MAXX appeals to me, there is a time and application for these tires and I wanted a set, but the 18-inch 275s were rougher that I cared to drive on.

After deciding I wasn’t going to keep the 275/70R18s, and to take advantage of Discount Tire’s excellent exchange policy, the question was exchange them for what? Another set of F-C II? That seemed a bit silly, since my existing set was almost new, and I’d rather have one set of mild treads and another more aggressive. Though I knew a second set of F-C II wasn’t going to pull to the right and wouldn’t be a waste of money. Since I’d been down this road several times with the 4Runner, I was confident I knew the unhappy ending.

Summer I80 Road Construction

The First Set of TRD 17-Inch Rock Warrior Wheels

Knowing my dissatisfaction with the 18-inch sidewalls, early one morning my friend Frank inquired about finding a second set of 17-inch TRD wheels. I quickly dismissed his idea, telling him via email I had looked and they were all too expensive… But I decided to look again, and hidden among all the ridiculously expensive was one reasonably priced set at an independent tire dealer in Sacramento, just a couple hours away (thank you Frank). I was the first person to contact the seller, told him I’d be there in a couple hours if he would hold them for me.

A rural road side trip in search of Dutch Bros. Coffee

Though there was summer road construction in the Sierras, and the several thousand vertical feet lost and gained during the 228 miles of travel, careful use of my right foot allowed the Tundra to squeeze 17.88 miles from each gallon.

TRD beadlock ring scuffing

The wheels were not perfect, but in hindsight they are the best set I’ve purchased thus far. There were a few scuffs on the fake beak lock rings from careless handling (which helped me to negotiate a lower price), and three of four spring clips that secure the center caps were missing, which I didn’t notice until I was home. But overall they were a very nice set the will likely stay with the Tundra as long as it lives in my barn.

TRD Rock Warrior 17-in. beadlock ring gouges.
TRD Tundra Rock Warrior 17-in. take-offs

With another set of 17s in the shop I didn’t know what I was going to exchange the S/T MAXX for, but I knew they were not going to be 18-inch tires.

Copyright © 2012 James Langan

Tire Pull Diagnosis

Looking For The Offending Tire 

Conventional wisdom regarding radial tire pull says that if a tire is the source of the pulling problem it can be diagnosed by using a specific procedure.

-Rotate the front tires side-to-side. If the vehicle goes in the opposite direction, it’s one of the front tires. If the vehicle goes in the same direction the pulling is from one of the rear tires, or is not a tire-related problem. There are more steps, but you can read them on The TireRack’s Pulling Tire Diagnosis PDF.

Though I have been through this procedure a few times before, I printed the PDF to insure I was following the steps exactly and made notes during the process. Guess what? The Tundra still pulled to the right, so I jumbled the position of the tires again and adjusted the tire pressure. Regardless of the position of the tires or PSI, the truck still drifted to the right rather quickly. So is there a chassis or alignment problem if there isn’t a tire problem?

Based on my experiences with my 4Runner I was quite confident that my alignment settings were fine, and not the source of the pulling problem, at least not directly. After numerous alignment adjustments attempting to redirect tire pull on the 4Runner (mostly cross-caster adjustments) some tires would still pull right while others would not. In fact depending on the tire and/or tread pattern, some tires required relatively high cross-caster while others needed very little. Using OE wheels, and in the case of the Tundra, OE sized tires, removes another variable that can make tire pull diagnosis difficult on modified vehicles. Are my modified chassis bent or broken, or are there simply compatibility issues with some tires and platforms?

Toyo M55 and Toyo M/T. Two tires that have caused tire pull on my 4Runner, but not on other trucks.

The Toyo M/T is known to cause a pull or drift on Dodge trucks, are these trucks broken too? My point is that even though the standard and accepted tire-pull diagnosis procedure might indicate the problem is not with the tires, that doesn’t mean there is a problem with the chassis. Having a second set of mounted and balanced tires has helped me confirm this a couple times. The tires may not be defective, but they may still cause a pulling problem on your truck and that doesn’t necessarily mean your truck is damaged or out of adjustment.

My favorite all-around tire remains the Dick Cepek F-C II. The Tundra’s alignment settings were working reasonably well with the F-C II and I was not willing to make changes that might improve the pulling with the S/T MAXXs at the cost of hurting drivability with the F-C IIs. Having two sets of tires isn’t practical if you need different alignment settings for each set.

What Next?

Copyright © 2012 James Langan

Cooper S/T MAXX LT275/70R18E Part 2

A Minor Lift

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.

S/T MAXX 275s on the Tundra

RoadTraveler.net – Rollin’ Forward

Copyright © 2012 James Langan



Cooper S/T MAXX mounted

Today I’ll be working on continuing this series. Until the words are ready here is a little taste.

Cooper S/T MAXX LT275/70R18E

RoadTraveler.net – Rollin’ Forward

Copyright © 2012 James Langan

Cooper S/T MAXX LT275/70R18E Preview (Traction Tire Part 2)

The Cooper S/T MAXX 

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.

Driving Impressions

To be continued…

Copyright © 2012 James Langan