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

Safety Beads on Light-Truck Wheels

A visual always helps. In these pictures you can see the circumferential raised lips, or beads, on a typical light-truck wheel which are often called the “safety bead”. They help the tire stay on the wheel. The first photo below shows a relatively new, 17 x 8-inch TRD Tundra wheel, but they are all similar. The safety bead ring is inboard approximately one inch from the actual tire bead seat.

TRD 17 inch Tundra Rock Warrior wheel safety bead rings.

Below is another example, a very well used 16 x 7.5-inch TRD FJ Cruiser wheel, which has had several sets of tires mounted.

TRD FJ Cruiser 16 x 7.5-inch wheel with circumferential safety bead rings.

Copyright © 2012 James Langan

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