Changed Tires today for MPG experiment.

I was reading last night about tire size and mpg and how it effects odometer. Today I bought four 2010 Toyota stock rims with stock tires (275/65/18) from Craigslist (rims in perfect condition and tires good enough for the experiment and a little time on road still). I had Discount Tire put them on my 2008 Tundra today.
Two weeks ago I pulled my small boat to 7,000 ft. up in California's Sierra Nevada all the way from San Diego. I had 3 adults and lots of gear and coolers in the bed as well. I was getting a sucky 9.5 mpg on average up and back.
I know that my tires up until today were a 305/65/18 BFG All-Terrains - E Load rated.
They are big and heavy but so dependable and capable off road. I know because I have them in my 2004 4Runner Limited AWD V8 with Bilstien 5100's and new rear coil springs (best off road vehicle EVER!!! Wouldn't take it on the Rubicon Trail but almost anywhere else I would).
Anyhow, I have detailed records of my MPG on my Tundra. I will keep everyone posted as to how the stock rims and tires will (hopefully) improve my MPG. If it doesn't, I'm going to sell the beast and look for more fuel efficient trucks. I love my Tundra and will be satisfied with just 2-3 mpg improvement. I would say I've been getting 9 city / 12 hwy with the larger tires. BTW, I still have my 305's ready to go on balanced rims. I'll put them on when I need them.
Thank you. Any input is welcome!

 

Don't forget to log your speed too. Also, seems low that you get 9 and 12. How fast do you drive? I'm averaging 14.6 overall on 35s. Then again I'm not pulling a boat. Since you plan to sell it if the MPGs don't improve, does that mean you are looking for fuel efficiency vs capability? Cause it sounds like the Tundra is capable . . .

 

Very cool!
Interested to see how this turns out!

 

COMiamiFan, thanks for the input. I'll register the speed. I stick to the speed limits such as 70mph on posted hwys. I can't explain yet why the milage sucks so badly. The truck runs like new.
I had my 4Runner before the tundra and bought the tundra thinking I would use it off road. I came to the conclusion that big trucks can't go where 4Runners go. I have upgraded my 4Runner and have done some awesome four-wheeling in it and wouldn't think about taking my Tundra. I use my truck like a truck should be used such as ladders and tools and camping gear and anything else needing power and towing and space for lots of stuff in the bed.
I really don't use my truck much but would if it was more economical. The answer is yes, I want economy from my Tundra. I would rather keep it instead of buying another truck.
BTW, last year I bought a new 2016 RAM 1500 EcoDiesel. At 1700 miles new, a check engine light came on. After 5 engine lights and visits to the dealer and a total of 30 days in the shop, I made them buy it back as a lemon. I'll stick to Toyota.

 

If you are considering selling the Tundra for a 2-3 MPG improvement, me thinks ye protest too much. Sounds like you're just looking for a reason to go a different direction. Consider that the money you save in gas will most likely go towards maintenance on a lesser truck.

Lets do some napkin work. Assuming 15k miles per year and going from say 10 to 12 MPG, you're saving about $625 per year if gas price averages 2.50 per gallon. If you paid More than 625 for those tires + rims + install, Its already going to take you over a year to break even, assuming the expected 2 MPG improvement.

Now all that said, I have gnarly tires and 3.5" lift on my 4WD '08. I'm getting 14.7 on average (mostly highway). My guess is your tires are not the problem, but I'll be very interested in what you find out.

 

When you calculate mileage, are you correcting for the fact that you are traveling farther than your odometer says due to the larger tire size?

 

Ding ding ding.

 

The question is not if but how much.

If you want to maximize the mpg gain, you need to take out the leveling kit. A bigger air drag under the body of the truck negatively impacts the mpg (even though the impact may be small). Disconnect the battery to reset the ecu. Drive gingerly to let the ecu learn this style of driving. I've gotten 18+ highway mpg (stock), driving through PA mountains hauling stuff in bed (not trailer). I lost 3+ mpg when I lifted my truck and mounted larger and heavier tires.

 

To add one more:

Do I regret modding my truck for losing 3+ MPG? Absolutely not. But to be fair, this is one of reasons why I don't. I fueled up yesterday.

 

My average is right at 10.2 for quite some time now with city and going up to the mountains combined. On long highway trips I've gotten around 15 usually with a few hundred lbs of camping gear and fencing supplies. City is always around 10. Lift, heavy tires, topper, heavy grille all combine to hurt MPG but I don't care. I bought Shell mid grade 87 for $2.15 a gallon this morning. I'll take capability over MPGs any day of the week.

 

Took 476 through the PA mountains yesterday (one leg of our trip back to NY from VA/NC) and got 17.77mpg hand calculated. Bed loaded with about 600lbs, plus family of 4 in the cab. 275/70r18 LT e-load tires. Felt like I drove uphill from Philadelphia to Scranton

 

Speaking of, how do you fix that? Does the dealer do that for you?

 

I only meant to calculate the added miles by comparing the revolutions per mile of stock sized tires to the larger size.

To the best of my knowledge, there are aftermarket speedometer calibrators for our trucks to correct the speedometer and odometer, but not a parameter for tire size that the dealer can change. I have no experience with them, but I'm sure there are members that do.

 

Easy way is to use Hypertech speedometer calibrator, as mentioned.

You could do simple calculation if you don't want to spend $$.

If you are running a 35 inch tire (let's assume that stock tire of 32 inch gives the correct odometer reading), you just have to multiply the distance on your uncalibrated odometer by (35/32).

So if your uncalibrated odometer reading is 100 mi, then the actual distance is
(35/32)x(100 mi)=109.4 mi

 

Are there any legal implications by not having your odometer read the correct miles? Because with larger tires I'm under calling the actual miles of the vehicle.

 

Technically, it is illegal to make any change that affects accurate recording of mileage. That said, I don't think I've ever heard of anyone getting dinged for running taller tires or different gear ratios.

 

Apparently, a little deviation is okay. Most manufacturers make the speedometer to over report the speed. So when the stock speedometer reports 55, you are actually going a couple of mph under.

 

Uh, sure about that? Not sure that would hold in court if I got caught with radar going over the speed limit. And usually the speed I'm showing matches what I get on those speed trailers on the street.

 

I wasn't talking about that, haha. I am sure it's the owner's responsibility to know how fast he is actually going.

Pennsylvania has yearly inspection and I haven't heard of anyone not passing due to a different tire size, etc. I haven't heard any manufacturer getting into legal trouble for little speedometer inaccuracy. As far as I know, in our Tundras, 33 inch tires make the speedometer more accurate than stock 32 inch tires.

By the way, the speedometer deviation becomes more noticeable at higher speed.

 

Update: Today I traveled 40 miles on a full tank. I believe I'm seeing a 3mpg increase by using stock tires over the Big BFG's. This is very early but I will keep you all updated.

 

That sounds promising. Be sure and do the math on the tire size change so you're comparing the right numbers. Also be wary of self fulfilling prophesies. If you expect better mileage, you may subconsciously drive differently so as to meet your own expectations.

I tend to magically get better mileage as the price of gas increases, without really thinking about it

 

@bobeast
I'll keep that in mind and agree about your statement.
Thanks

 

Also, ensure that you drive on both tires with the same amount of fuel in the tank. Don drive stocks with less than half a tank and BFGs with full tank as an example.