MPG, Fuel Economy, Tire Width, and Treads No. 1

Newer, detailed article, click here: Tread Matters

 

Will The Most Efficient Tires Please Drive Forward

It’s often stated that narrower, lighter, less aggressive tires are more efficient and will yield better fuel economy, but how much better? To properly compare apples and pears one must take care to reduce the variables that are always present during real-world tests. In this case I used the same vehicle, same gas pump, during similar weather conditions and time of day, calculated the odometer error, and used the same section of freeway. The GPS-confirmed road speed was 64-MPH and was maintained by cruise control. The tires were inflated to 35-PSI in all but the last test with the Dick Cepek F-C II treads where I goofed and only used 32-PSI. The F-C II tires performed so well I doubt they could have provided better economy with an extra 3-PSI.

Cooper S/T 255/85R16D on Toyota 4Runner, @ 15 PSI.

If you think the fuel economy numbers listed below are too high you are partly correct, the tests involved almost zero city driving. The variables of in-town driving are not repeatable and won’t yield consistent data. What these tests do show is the fuel economy potential of this vehicle and establishes a baseline against which other tests can be measured. For each test the modified 2006 4.7L V8 4Runner was fueled and then driven a few blocks to the same freeway onramp, onward to a specific exit, and then the route was reversed and terminated at the same gas pump where the engine was promptly turned off.

Dean SXT Mud Terrain & Cooper S/T, both 255/85R16. Two of the narrowest 255/85 tires made.

All the tires used were close to the same diameter, about 33-inches, and they were all mounted on Toyota FJ Cruiser TRD 16 x 7.5-inch aluminum wheels. Because of the slight differences I tire height, one corrected odometer reading of 56.76-miles was used for all the tests. Listed below with the figures are the weights of each tire/wheel combination.

Results:

Cooper S/T LT255/85R16D: 75-lb  3.027-gal. = 18.75 MPG

Maxxis Bighorn LT255/85R16D: 82-lb  3.017-gal. = 18.81 MPG

TreadWright Guard Dog LT285/75R16E: 87-lb  3.331-gal. = 17.04 MPG

Dick Cepek F-C II LT285/75R16D: 83-lb  3.121-gal. = 18.18 MPG

Maxxis Bighorn 255/85R16D, TreadWright Guard Dog 285/75R16E, Cooper S/T 255/85R16D

Commentary

I was a little surprised that the very narrow and light Coopers consumed more fuel than the heavier, more aggressive Maxxis Bighorns. Though when filling-up after the Cooper test the gas-pump didn’t stop normally and a little gas spit from the filler, possibly contributing to the lower reading. Longer distance tests would likely be more accurate, but this type of testing is very time consuming and expensive.

It was expected that the heavier, wider TreadWright Guard Dogs with their aggressive lug tread would use more fuel. The Cepek F-C II tires impressed me by splitting the difference and topping eighteen MPG!

Cooper S/T 255/85R16D, Dick Cepek F-C II 285/75R16D

Surely tread design, width, and weight all make a difference. My theory is that width and tread design have a larger impact on fuel economy than tire weight, at least when there is only a few pounds difference. There is five pounds separating the Maxxis Bighorn 255/85R16 and TreadWright 285/75R16, but I don’t think those additional few pounds account for the 1.77 mile-per-gallon difference. There is a seven pound difference between the Maxxis Bighorns and Cooper S/Ts, but the results for these two 255s were so close you could call it a tie.

Your mileage will vary.

Copyright © 2012 James Langan

Dick Cepek F-C II Review No. 1

This blog will not always be so tire centric, but it seems a popular topic so I’ll continue in this vein for now.

Dick Cepek F-C II

This is a review about one set of Dick Cepek F-C II tires I have been tracking. Longevity is only one consideration when choosing a tread, and needs to be balanced with other criteria, but everyone always asks about wear. Some might argue that long wear is the most important characteristic, however that really depends on how you want your tires to perform. Some off-highway enthusiasts care much more about traction or noise.

Hummer H2 with 38" Dick Cepek F-C II

A few years ago this Hummer H2 was lifted several inches, and at the same time these 38×15.50R20LT Dick Cepek F-C II tires were mounted. I’m aquatinted with the owner and he’s not a conservative driver, or maybe he is now but he didn’t used to be. Admittedly this H2 is a street queen, though it has traveled a few fire roads when goin’ fishin’. The tires were rotated with each oil change, about every 5,000 miles.

When doing the photo shoot the owner knew the tires had logged several thousands miles, though not exactly how many. After he confirmed the date and mileage of the installation, I had the data I needed for this story.

Dick Cepek F-C II 38x15.50R20 with 20/32" tread depth.

The F-C II is no longer offered in this size, but came with 20/32″ of tread, as seen here on the still new spare.

Dick Cepek F-C II after 40,000 miles, with 10/32" of tread remaining.

Slow Wearing Tread Design

After 40,000 miles of driving, the rate of wear was nothing less than exceptional. Four thousand miles per 1/32″ of tread wear on a heavy, modified utility wagon running a fairly aggressive traction tire is outstanding.

Still plenty of tread and siping after 40,000 miles on a 38" F-C II.

Without prompting, the owner shared that the F-C II is a great winter tire, which is a common accolade. While not a dedicated winter design, the shape and density of tread sipes, combined with the layout of the center tread blocks helps make the F-C II an outstanding winter performer. This tire does well many places, that’s why Dick Cepek Tires calls it an any-terrain radial.

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


Traction Tire Preview Prelude

For several years I’ve been a fan of what are often called aggressive all-terrain tires. Labels and classifications can be difficult, sometimes neither descriptive nor adequate as there is much crossover, gray-area, and blurred lines with tread designs. These tires are not as open as a mud tire, but offer much more void than the typical all-terrain or all-season tire. Current examples include Mickey Thompson ATZ 4-rib, Dick Cepek F-C II, Cooper S/T Maxx, Goodyear DuraTrac, Dean SXT Mud Terrain/Cooper S/T, and the Toyo M55. These treads are also called traction or commercial traction designs.

Limited Terrain SUV Tires

When marketing types decided that utility vehicle was no longer an adequate description for 4WD utility wagons, the Sport Utility Vehicle (SUV) appeared, surged, then dominated the light-truck utility market. Lighter-duty all-terrain tires that offered less void and less traction became popular on the increasingly soft SUVs over the past two decades. It’s understandable that SUV tires became so road-biased, as invariably that’s where many log all their miles in their SUV trucks, but many of these conservative “all-terrain” treads would be more accurately described as all-season tires.

Michelin Cross Terrain SUV tire, properly labeled an all-season highway tire.

Despite the 4WD SUV becoming the modern on-highway station wagon for much of the U.S. if not most of North America, there are still those that want their 4WD wagons to be body-on-frame truck designs, shod with better, higher void traction tires. These folks include hunters, sportsmen, off-highway adventurers, people who live or work in rural areas, and those who travel in serve climates. For a variety of reasons a mud terrain tire may not be preferred (less MPG, longevity, and less traction on wet roads, with more noise) but a low void all-season tire labeled and masquerading as an all-terrain often doesn’t do the job either.

More void is desirable to absorb debris and let it escape. The wetter the material the more void you might want, and open, lug designs are typically louder, though modern tire design has reduced the noise penalty for some traction tires.

Toyo M55 & Multi-Mile TXR LT255/85R16D

What Size

I’ve never been a fan of needlessly wide tires, but wide tires have dominated the enthusiast 4×4 truck aftermarket for several years. Fat tires work well for some applications, but have many limitations for common usage, particularly on-pavement, where even the most active off-highway explorers travel thousands of miles each year. A slight correction seems to have occurred, where not every enthusiast 4×4 tire needs to be over 12-inches wide; 285 mm wide tires have caught on.

While I’m currently using and have accepted 285s, in my mind they are still a bit wide, roughly 11.5-inches depending on the tire—narrower tires track straighter and offer better MPG. Drivers are at least aware of fuel economy because of the cost of fuel, though I don’t see many people driving for fuel economy, bad habits are prevalent and it seems we’re often in a hurry.

The days of much narrower 33-inch enthusiasts tires like the LT255/85R16 are disappearing fast. Thankfully, if you don’t want such a tall tire, there are many 235–265 mm wide treads in the 31–32-inch range that can deliver better fuel economy.

Great traction tires: LT255/85R16D Cooper S/T & LT285/75R16D Dick Cepek F-C II

Eighteen Inch 33s

Not knowing much about 18-inch tires or wheels, but owning a set of take-off eighteens, I studied the options and was pleasantly surprised to discover the LT275/70R18 size. This size is just slightly narrower than the common 285 mm treads in either a 16, 17, or 18-inch, but with a reasonable aspect ratio of 70 percent. Most 275/70R18s are 33.3-inches tall, very similar to the tall 255/85R16 size that I’ve loved for fifteen years.

Eighteen-inch wheels are two inches taller overall, so tire sidewalls are a full inch shorter at the bottom (the part we feel and drive on). Historically 255/85R16s were flexible and pleasant riding load-range D designs, though load-range E is becoming more common in a 255/85, but 275/70R18s are almost all load-range E rated. Not all load-range D or E tires are created equal, some are stiffer than others, but shorter load-range E sidewalls on a 275/70R18 are going to be stiffer in almost every application. Again, stiff sidewalls can be a positive or a negative, depending on your needs and preferences, refer to this Wheels, Tires, and Sidewalls article for more on this subject.

To be continued…

Copyright © 2012 James Langan

LT255/85R16 Tire Delivery Part 3

Long before my route was paved there were much hardier travelers who passed this way. I stopped for a brief photo and took a moment to reflect. Lately I’ve been reflecting on how thoroughly spoiled we are with easy, efficient, convenient long distance travel. Several decades ago vehicles were not as low-maintenance and relatively trouble-free as they are now. Before the transcontinental railroad, traveling across The States was a serious, life-threatening endeavor. As modern motorized backcountry travelers there is always the possibility that our machines and computers will fail and we will be reunited with primal overland travel; walking.

Beckwourth Trail

Below is a poor grab shot through windshield glare and at a substantial distance  as I drove through the small town of Quincy, California. It’s not everyday that one sees an nicely restored original Bronco with uncut rear fenders, and nice, narrow original size tires.

First Generation Classic Ford Bronco, uncut fenders and small, narrow tires.

Onward further into the country where I met Brian and his family—very kind people. Brian and I visited for over an hour, talking mostly about trucks and tires, before I started reversing my path.

After several miles I drove down a dirt road where I enjoyed lunch. I really like having a tailgate for picnics, one of the advantages of a pickup over most utility vehicles.

 

Excellent Highway Fuel Economy

After lunch and enjoying the sights and smells of the forest, my fuel economy mission resumed. Theoretically, there are many ways in which to improve fuel economy. Though if your vehicle is outfitted the way you like it and your maintenance is up-to-date, the best way to increase fuel economy is to drive slower and pay attention to your driving technique—there is more to it than simply lowering your top speed.

My not-so-speedy-delivery was a 183.7-mile all highway roundtrip, on which the 3UR-FE 5.7L aluminum Toyota V8 consumed 9.761 gallons of gasoline. The math says that’s 18.81 miles-per-gallon. Excellent.

I’d love to attain this type of economy all the time, but mixed driving, living at altitude, and driving up and down mountains makes it nearly impossible. Though for a lifted truck with a big gasoline-powered V8 engine, and reasonably large & wide 33-inch LT285/70R17D tires (Dick Cepek F-C II), being able to top 18 miles-per-gallon is an accomplishment. Some of the credit has to go to the very tall sixth gear overdrive, which lets the engine lope at very low revolutions-per-minute when lightly loaded, and use little fuel.

Road Traveler – Rollin’ Forward and Sippin’ Fuel

Copyright © 2012 James Langan

LT255/85R16 Tire Delivery Part 2

With a bed and trailer full of tires & wheels I was off to see my tire guys for dismounting, mounting, and balancing so I could get my 4WDs off jack stands and rolling again. A few days later I loaded the bed of the Tundra with the Bighorns and Cooper S/T treads, as well as one old Multi-Mile Wild Country TXR so Brian would have a proper 255/85 spare.

Years ago the TXR was a big seller for the western tire chain Les Schwab. I really liked the void ratio of the TXR—not an A/T nor an M/T—and I purchased a few sets over several years. However, they were not the most rugged tire and tended to cause a steering wheel wobble. The last rig I ran the TXR on was my 2005 Wrangler, which was not as tolerant of their idiosyncrasies, so I moved on to better tires…and have yet to stop.

A load of LT255/85R16D tires, a Multi Mile TXR in the foreground.

I had a few goals for this little trip; deliver the tires, meet my new friend Brian, enjoy a country drive, and conduct a mileage test. After fueling at my local filling station and resetting the trip meter, it was time to roll with a goal of keeping my speed at 65 mph or less.

Through the cities and into the fertile Sierra Valley I drove. It cost, but one of the features I enjoy on the new Tundra is the satellite radio. There are a few stations I like, but I seem to listen to Outlaw Country often, Steve Earle came on singin’ Hillbilly Highway.

Copyright © 2012 James Langan

A New Tire or Two

Old TXR 255/85R16D spare and a Not so old Dick Cepek F-C II 285/75R16D

Several weeks ago I cut a sidewall on one of my LT285/75R16 Dick Cepek Fun Country II (FC II) tires. The story about the sidewall cut and trail will be told later, but with only three FC II treads on the 4Runner I was in need of at least one new tire. Since I had been running a close enough 255/85R16 spare, I decided to buy two FC II to insure I had the exact tire in the unlikely event I ruined another casing in the near future. My calculations indicated that if I rotated the older three tires on one side of the car, all with 3/32″ of wear, and the two new ones on the other side, the wear would even out over the next 30,000-miles.

Most tire warranties don’t cover off-road use. This is term is open to interpretation, as many state and county roads in the rural west are not paved but are still very clearly roads. Regardless, since the three older FC II treads had been purchased mail-order and were not covered under any road hazard warranty, I decided to buy the new tries mail-order as well. One of the local tire shops I do lots of business with would have mounted & balanced the new treads for a reasonable fee, but I decided to play with a little old school technology and balance them myself. It wasn’t easy.

Copyright © 2011 James Langan