Hi all. I've been gone a long time only because I had no problems with my 05 Diesel Excursion and am miserably retired. But I recently needed new tires and wheels and did quite a bit of research. I put them on the truck along with some other things and I am now reliably getting (at least) 4 extra miles per gallon. The only reason I am posting is that I have read numerous threads about bigger tires and the effect on fuel mileage.

The subject is a 2005 Ford Exursion, 6.0, 4WD, Eddie Bauer. It has a 6 inch lift. It has Black Rhino Hollister wheels, 18x9.5 -18. The current tires are (Discount Tire house brand) Pathfinder All Terrain LT295/70/18. The former setup was Black Rhino Combat wheels of the same size, and Toyo Open Country M/T 33x12.5. All tires E rated. All tires at 55 psi.

I switched wheels and tires because I bent a wheel hitting a curb (and they aren't made anymore) and my tires were just getting old and hard. I did not go into Discount Tire with the object of buying Pathfinders but I couldn't get the tires I wanted and they gave me a ridiculous discount (150 a tire) for the Pathfinders because I'm so old, nice, and persistent.

I measure my miles per gallon by hand, based on the fuel I put in versus actual miles (GPS and odometer match) and with a bullydog tuner that I got just to monitor my delta and my instant MPG. The console screen hasn't worked for years. The bullydog compensates for both gears (I have 3.73's) and tire diameter. I am not a fast driver, I always get an "A" from the bullydog driving coach, and I could probably store eggs on my accelerator pedal. I have time for these shenanigans so I've been as scientific as possible.

With the former setup I got a steady 17 miles per gallon in mixed driving, which I would say is 20 percent city and 80 percent highway. Doesn't matter what the mix was because I haven't changed my driving habits or routes at all, and now I get a steady 21 miles per gallon in the same mixed driving, over three trips to the fuel station and 98.7 gallons used.

The new tires are about two inches taller than the old ones, factoring for the diminished tread on my old Toyo's. The new tires are also about an inch narrower. Finally, and maybe most importantly, the new wheel and tire combo beats the old one by about 11 pounds per corner.

In full disclosure I also replaced all rotors and pads just because I had the truck on jacks and had the stuff laying around. Since I was doing that, I also replaced the front hub assemblies with Timkins because my originals have over 200,000 miles on them and I had the Timkins laying around. I heard an occasional clunk before but my tires rotated freely so I don't think the hubs made any miles per gallon difference.

The reason I think my increase in miles per gallon is significant is that in doing my research I saw many opinions that taller tires hurt miles per gallon. However, there are also occasional mentions that miles per gallon drop off a cliff over 70mph. Combining the two, I wondered if larger, lighter tires keep you close or under 2000 rpms, then miles per gallon would increase. They do. A lighter, taller tire seems to help quite a bit. I should have mentioned that the Pathfinder has a lower rolling resistance than the Toyos (I was told). Of course I mentioned it is a little narrower and significantly taller.

So, there you go. At 75 mph I am now just a hair over 2000rpms (65 is just a hair over 1500rpms) and getting much better miles per gallon on the straight and flat than before. I am also getting 4mpg better than before when I pull a fairly light, but aerodynamically bad, tandem 18 foot trailer with solid ramp on the back (18 versus 14).

Okay, poke holes in it. I'm ready. I think I've done all can to verify these results but if I'm wrong somehow, let me know. If I'm right my cheapie tires pay for themselves well before they need to be replaced.

Charlie V

 

Great post. You said there is an 11 pound difference between new and old tires. What percentage difference does that represent? In other words, what is the weight of the new tire?

 

I'm so glad you asked that question because there is an additional weight savings that I did not know until I checked in order to answer.

The Pathfinder tire weighs 63 pounds. The Toyo weighs 74. However, what I did not realize is that the new wheels weigh 33 pounds and the old ones weighed five pounds more.

So, the old combination was 112 pounds per corner. The new combination is 96 pounds: a 16 pound difference.

So much for my "science" since I remembered the wheels weighing the same. They have the same weight rating, but they weigh different.

That is about fourteen percent weight savings (tires and wheels, or just tires) resulting i(in combination with the taller and slightly narrower tire keeping RPMs at about 2000 in 75mph driving) in approximately 20 percent better mileage in mixed driving. That is really astonishing; maybe 2000 rpms really is a magic number.

Now I am wonderong whether tire size or tire weight is more significant for fuel savings, but I'm going to have to be content for now with knowing that a taller, lighter tire is a good change.

In my case, the new tires were also quite alot cheaper than direct replacement of the Toyo tires would have been. I thought of the difference as helping pay for the wheels. But they also are saving me money at the pump.

For simplicity let's say I drive 10,000 milea a year. At 17mpg that would be 588 gallons. At 21mpg it is 476 gallons. At 2.75 a gallon that's 308 dollars saved a year, and assuming I hadn't been a ninny and bent an irreplaceable wheel, my tires pay for themselves in roughly 2 years or 20,000 miles.

I could probably improve a tiny bit by changing my diffeerential oil.. I could also save a tiny bit by removing my heavy aftermarket brush guard and the solar panels (see Solar Powered Exursion post a few years ago). I might get an improvement by removing the lift but then I would be back with smaller tires and who has ever removed a lift?!

A sixteen year-old, 7,800 pound, lifted, 4wd truck with 213,000 miles getting over 20 mpg makes me pretty happy!

 

If you think that truck is 7,800 lbs, best think again!

 

He must have been looking at his registration paperwork!! LOL

 

Im lost. Does it weigh more than that? Less?

 

Ah, did some looking and apparently it weighs alot more than 7800 pounds with around 46 gallons of fuel, aftermarket wheels and tires, and bumper. Not to mention the solar batteries, people, and all of tools and junk I generally have in the back. Geez, I'd guess closer to 8800 pounds.

This makes sense. A few weeks ago when we had a snow storm/ice event and I stopped to help a guy in a 4wd (I didn't have the heart to tell him that his front wheels never spun, despite his claims to the contrary from the driver seat) so the 4wd wasn't working) pickup who was in the ditch and had already had help from two jeeps, but the help just got him in a worse position and against a mailbox. I was aimed downhill on a hill steep enough that his back end had just gone sideways unto the ditch when he was headed uphill, and just had a tow strap and no lockers, so I had to back uphill in very slick conditions and was worried I would just slide into the same ditch due to his weight in the ditch. Shockingly, I pulled him right out and on up the hill without any tire spin or sliding. I guess the weight is a good thing in some circumstances.

Just increases my happiness with my mpg!

I have some land rovers (4) of various generations and I noticed it really doesn't matter what's in the vehicles/how much they weigh from a mpg standpoint (mpg is always horrendous in a gas powered land rover). Presumably, same for Excursion. And I can't imagine there is any aerodynamic change that makes much difference, either.

 

the taller tire can make a difference on the highway if you have the power to keep it moving as it lowers your rpm, towing you may suffer as you may hunt gears a bit more.

your right foot helps the most as the vehicle with taller tires will inevitably get off the line slower, if you were trying to match a 0-60 times with the taller tire your gas mileage may suffer.

 

Yep, makes perfect sense. Other than my light, 18 foot trailer I don't tow anymore and I only use it to carry things that should be in the back of a pickup. Our travel trailer has become a permanent fixture at the farm and since I never, ever get in a hurry driving the setup should continue to provide savings for me.

Other use cases and driving styles might go the other way.