LOOOONG Road trip Gas Mileage Experiment

[Synister]

OK, so I obviously bought my truck not really caring about gas mileage (cant take a Civic wheelin' can you?) but I still track it every tank and thus far in the 5k Ive owned it Im in the 17-18 range running premium mixed city/hwy. This month, however, Ill be driving a 6k mi marathon with the varied types of terrain you would expect covering that much distance. Ill pretty much be doing the speed limit up to + 5 or so so I dont expect going much faster than 75. Cruise control as often as possible except for big hills. Premium gas only. Fuel receipts will be kept at all fillups with the mileage for that tank written on each one. When I tally it all up at the end I will add 6% for the larger circumference of my tires over stock. I could potentially be towing a trailer for 1500 mi of this little adventure so I will tally those separately. Stay tuned.

 

[thirstyturtle]

in for results :0)

 

[Synister]

Results thus far with no trailer involved:

4023.5 mi on the trip meter
222.96 gallons of premium gas purchased


Trip meter corrected reading ( 6% correction factor correlating to 6% larger circumference over stock tires) of 4264.91 mi.

4264.91 / 222.96 = 19.13 mpg..... 95% hwy, 5% city mix, read signature for vehicle configuration.

Keep in mind Im on cruise control 99% of the highway time at no more than +- 3 mph from the posted speed limit at all times. So far my trip has taken me through most of the south western states....that means hills. My next 1500 mi leg will involve a 2000 lb box trailer through the south so a tad bit flatter all around. I will be towing at 65 mph as that yields a no weight trailer gain of close to 2.0 mpg over 70 mph towing the same empty trailer.
__________________
2009 4runner Trail Edition, Daystar 2.5/1.5, GYSA 255/75r17, ProComp 7098's, Carbon Filter eliminate mod, KurtFab diff bracket, Husky floor mats throughout

 

[CJ3Flyr]

Bump/move

 

[LogwoodInnMan]

cool! I monitor my gas mileage religiously... im a big advocate of the KandN air filter.


Miles

 

[S p a r k y]

Results thus far with no trailer involved:

4023.5 mi on the trip meter
222.96 gallons of premium gas purchased


Trip meter corrected reading ( 6% correction factor correlating to 6% larger circumference over stock tires) of 4264.91 mi.

4264.91 / 222.96 = 19.13 mpg..... 95% hwy, 5% city mix, read signature for vehicle configuration.

Just curious how you got the 6%?? I didnt do any figuring myself, just using tire calculators. I thought the 255/75 was 4.5% diff. I will be putting 265/70/17 on next week will my diff be 3.4% or somehting different.

Thanks for the updates Synister

 

[clint616]

Sparky:
I'm assuming your Sport has the 17" wheels, and if so you have 265/65/17 stock.
265mm*65%*2 = 344.5mm = ~13.55 in
pi*(13.55in + 17in) = ~95.99in tire circumference

With your new 265/70/17 you get:
265mm*70%*2 = 371mm = ~14.61 in
pi*(14.61in + 17in) = ~99.29in tire circumference

Since % change is (final-initial)/initial you get
(99.29in-95.99in)/95.99in = .03447*100% = 3.447%

So yes, your % difference will be ~+3.4% or if you really want to get accurate, it's +3.4469428317%. (This of course also doesn't account for tire wear)

Synister:
I'm unclear how you got a 6% differential. Your sig states that you have an 09 Trail, which IIRC has 265/70/17 stock, which you have replaced with, again according to your sig, 255/75/17 (I am a little curious why you chose to go to a slimmer tire). According to my math you should only be getting a 1.4% differential.

265mm*70%*2 = 371mm = ~14.61 in
pi*(14.61in + 17in) = ~99.29in tire circumference

255mm*75%*2 = 382.5mm = ~15.06 in
pi*(15.06in + 17in) = ~100.72in
in tire circumference

Since % change is (final-initial)/initial you get
(100.72in-99.29in)/99.29in = .01432*100% = 1.432%

 

[S p a r k y]

I'm assuming your Sport has the 17" wheels, and if so you have 265/65/17 stock.
265mm*65%*2 = 344.5mm = ~13.55 in
pi*(13.55in + 17in)/2 = ~47.99in tire circumference

With your new 265/70/17 you get:
265mm*70%*2 = 371mm = ~14.61 in
pi*(14.61in + 17in)/2 = ~49.65in tire circumference

Since % change is (final-initial)/initial you get
(49.65in-47.99in)/47.99in = .03447*100% = 3.447%

So yes, your % difference will be ~+3.4% or if you really want to get accurate, it's +3.4469428317%. (This of course also doesn't account for tire wear)

Thanks Clint your the man. For those of you who want to know other sizes, I use this calculator Tire size calculator it works great and even shows a comparison

 

[clint616]

No problem. Those online calculators are pretty good, just make sure (this is mostly for everyone else that might read this) that you get the initial(Stock) and final(new) tire sizes in the right order, as mixing them up will change the % differential.

 

[Synister]

Hey guys sorry for not getting back to this thread earlier, works' been busy. I just recalculated the above numbers and 6% is a little optimistic, I actually came out to 5% increase over stock diameter. This is how I got it.

TireRack lists my stock 265/70r16 AT20's as having a diameter of 30.6"
30.6*3.14=96.08" circumference

TireRack lists my new 255/75r17 GYSA's as having a diameter of 32.1"
32.1*3.14=100.79" circumference

This means a difference of 4.71" over stock.
4.71/96.08=.049 or 4.9% increase from stock diameter.

If you carryover this correction to my road trip my corrected mileage is 4220.65

4220.65 miles / 222.96 gallons = 18.93 mpg corrected.

I can now comment on the remainder of the trip as well, however not in decimal point detail. I ended up hauling 3200 lbs approx 1600mi in my V6. When I originally picked the trailer up and was towing it home empty I did a little experimenting and found a huge difference in gas mileage simply from drag at 60, 65, and 70 mph. The difference from 60-65 was minimal, maybe 2 mpg. From 65-70 though, there was an ADDITIONAL 5 mpg drop, down to around 12. I ended up towing the rest of the trip around 65 and average out in the 14-16 range depending on how many hills each tank encountered.

I chose to go with a 255/75r17 tire because a) they were very inexpensive for a well reviewed a/t tire b) were lighter than a 265 c) have less rolling and wind resistance than a 265 while being a little taller overall d) actually look really good on the vehicle. I was worried about the pizza cutter look but that is not the case at all and the offset provided by the backspacing on the new wheels pushes the whole wheel/tire assembly out flush with the wheel well. Also, the only rubbing was on the front mudflaps and it was an easy fix.

 

[CO_FlyFisher]

As you found out in your experiment, drag increases as the SQUARE of speed.

D = 1/2*Rho*V^2 * Cd

Simplifying, drag is 17% higher at 65mph than 60mph, and 16% higher at 70mph than 65mph. However, that is NOT the whole story.

The power required to overcome that drag increases as the CUBE of speed. Take that basic equation above and multiply by velocity yet again. Your mileage results bear out that difference pretty closely.

 

[Yogi4]

Synister--why premium gas?

 

[Synister]

I run premium for a couple reasons. When I first got the truck, I had to drive it 750 mi home with a decent headwind most of the way. At 75mph on the freeway I was getting an abysmal 16 mpg bone stock. The next several tanks were driven around town, to and from work etc and the average was in the 17's. Not what I had expected from a V6 in 2wd mode. I switched to premium for the next several tanks to give the ECU a chance to adjust. Without changing my driving style my average went to 18 around town and 19 on the highway. Even after the lift and tires highway mpg is right around 19 and on flat stretches even breaks into the 20's with 22 being my highest. Additionally, Lexus uses this engine but the output is higher. Wikipedia's article on this engine states the following;

"The 1GR-FE is the 4.0 L version, designed for longitudinal mounting in RWD and 4WD pickup applications. It has a 94 mm bore and a stroke of 95 mm. Output is 236 hp (176 kW) at 5200 rpm with 266 lb·ft (361 N·m) of torque at 4000 rpm on 87 octane, and 239 hp (178 kW) at 5200 rpm with 278 lb·ft (377 N·m) at 3700 rpm on 91 octane"

So, I get a slightly higher torque peak and a little lower rpm as a kind of "freebie" in addition to the mpg bump I mentioned. Now, I know lots people get great mileage with 87 but that simply was not the case with me. I crunched some numbers and the added price of premium offset by the better mileage I experienced means running premium costs me roughly $75 a year over 87. I have no probs paying that.

 

[Yogi4]

I run premium for a couple reasons....
So, I get a slightly higher torque peak and a little lower rpm as a kind of "freebie" in addition to the mpg bump I mentioned. Now, I know lots people get great mileage with 87 but that simply was not the case with me. I crunched some numbers and the added price of premium offset by the better mileage I experienced means running premium costs me roughly $75 a year over 87. I have no probs paying that.

Synister: thanks for the explanation. Sounds logical and well-thought out. I might give it a try. (Also, it's nice to know that there is at least one other '09 TE on the boards.--even if mine is still stock.)
Bill W

 

[joeveto]

Just to tag on...

I'm currently on a thousand mile trip, with 6 adults (I have the 7 passenger seating) and a roof top carrier. For my first fill, after sustained speeds over 80mph, the truck returned 14.37. I've been averaging 17.36.

For those who don't know...the dashboard mpg readout is far, far from accurate. I often saw mileage as high as 27, even 30! 18-20 is more realistic, at more legal speeds.

I also have a scan gauge connected. It automatically runs the average mpg of every trip I make, and I've found it to be a lot more accurate.

I'd like to find a gas station that sells honest to goodness gasoline, with no added ethanol to see how that impacts my mileage. I'm guessing I'd see a 5% improvement.

 

[Ridger]

Great info and reading guys, interesting.

I read many times on here about the onboard gauge being about 10% off, and I recently started tracking my mileage (see signature) and so far mine has been about 4-6% off of the readout with mostly city driving.

But Joeveto, your readout seems to be significantly more off then that.

 

[Koz]

Save your money and use regular. There is NO difference in mileage.

note: The biggest increase in mileage under your control is the tires you use and maintain the proper air pressure.

Koz

 

[Ridger]

Save your money and use regular. There is NO difference in mileage.

note: The biggest increase in mileage under your control is the tires you use and maintain the proper air pressure.

Koz

Ummm.... and of course, how hard your tramping on that gas pedal. :wink2:

 

[Koz]

Ummm.... and of course, how hard your tramping on that gas pedal. :wink2:

This is why I have never and will never get the advertised gas mileage. I have a serious problem with my right foot. No matter how hard I try to be gentle on the pedal, this serious foot problem persists.

Koz