TFL: 2016 Tundra vs Tacoma, towing mpg

[itguy08]

Originally Posted By: hattaresguy

You also have to remember that TFL tests their trucks at pretty high altitudes so they really are kind of worst case numbers.


Wouldn't it even itself out? Less air at altitude means less fuel needed for a given throttle opening? At WOT you're burning less gas at, say 5200 feet vs at 0 ft?

 

[MNgopher]

For a given throttle setting, sure, less fuel consumed at altitude.

Issue is you aren't using the same throttle setting pulling a trailer at altitude. Guaranteed, loaded (or unloaded for that matter), your foot is likely heavier on the go pedal than pulling the same trailer at sea level...

 

[supton]

Originally Posted By: itguy08
Originally Posted By: hattaresguy

You also have to remember that TFL tests their trucks at pretty high altitudes so they really are kind of worst case numbers.


Wouldn't it even itself out? Less air at altitude means less fuel needed for a given throttle opening? At WOT you're burning less gas at, say 5200 feet vs at 0 ft?


ECU will adjust and keep the air/fuel mixture the same ratio.

But at altitude, since there's less air, less fuel goes in; and thus less horsepower. I believe the effective compression ratio goes down too, thus they can run with lower octane (hence the comment about 85 octane at the pump--I've never seen less than 87).

 

[itguy08]

I get that you would use more throttle but you still need the same amount of power to move that load. (ok, maybe less because the air is less dense)

If it takes 100 hp to move a load up a hill at sea level it will still need that same 100hp to move that at 5200 ft. But while at sea level that could be accomplished with 1/2 throttle at altitude I need 3/4. But at 3/4 I'm flowing the same amount of O2 as before and using the same amount of gas because the air is thinner.

Does that make sense or am I way off?

Edit: Did some Googling and found a discussion from BITOG: https://bobistheoilguy.com/forums/ubbthreads.php/topics/741816/2

Also the general consensus is that you do get better mileage on the flats at altitude but the trip up the mountain to get there kills it.

 

[MNgopher]

Exactly. The best fuel mileage I've ever recorded in nearly all of my vehicles has come on the downhill run out of Denver back across Nebraska or across the high plains of Wyoming.

Driving in the mountains uphill, its tough to keep your foot out of it enough...

Of course, if the wind is blowing, all bets are off!

 

[hpb]

Would've been interesting to see the result if they'd thrown a diesel engine vehicle in the mix.

 

[rslifkin]

Originally Posted By: itguy08
I get that you would use more throttle but you still need the same amount of power to move that load. (ok, maybe less because the air is less dense)

If it takes 100 hp to move a load up a hill at sea level it will still need that same 100hp to move that at 5200 ft. But while at sea level that could be accomplished with 1/2 throttle at altitude I need 3/4. But at 3/4 I'm flowing the same amount of O2 as before and using the same amount of gas because the air is thinner.

Does that make sense or am I way off?

Edit: Did some Googling and found a discussion from BITOG: https://bobistheoilguy.com/forums/ubbthreads.php/topics/741816/2

Also the general consensus is that you do get better mileage on the flats at altitude but the trip up the mountain to get there kills it.


You've got it. In theory, being at altitude won't hurt your mpg at all, unless you're finding you don't have enough power and are at WOT and asking for more. In that case, being forced to get up to speed more slowly can end up being less efficient.

 

[hattaresguy]

Originally Posted By: itguy08
Originally Posted By: hattaresguy

You also have to remember that TFL tests their trucks at pretty high altitudes so they really are kind of worst case numbers.


Wouldn't it even itself out? Less air at altitude means less fuel needed for a given throttle opening? At WOT you're burning less gas at, say 5200 feet vs at 0 ft?



Yep the ECU will adjust but unless you have something making up for the loss of air density your going to lose power.

Off the top of my head because TFL has calculated it, they are about 30% down on manufacture rated HP. IMHO the way they test on TFL is really good, its real world, loaded up, and literally about the worst case scenario. A lot of truck manufactures paint rosy pictures under optimal conditions.

With turbo engines like the Ecoboost for example if you put them on a dyno they are probably down until the turbo's get spooling. Once they have boost they have boost so HP loses are minimal.

For example the Pentastar in my truck is rated for 305 at sea level, all motors are rated at sea level. For a TFL test its probably putting out around 210-215, less at the rear wheels maybe 180ish. So throw on the rated 7k pound load which they do and your foot is to the floor most of the time. Its why you see trucks struggling with loads even on flat ground that around here they yank around with no issue. Your fuel burn will actually probably be pretty close though, it simply just takes energy to move mass. No way around that, only so much energy in a gallon of gas.

This is an area where it pays to have a diesel, the 1 ton trucks with the gas motors always run out of breath when they tow up Ike Gauntlet. They simply don't do that in my area because I'm at sea level. This is why guys love the high HP Cummins, it will simply out pull the gas jobs at that altitude, the HP difference is over 100!

 

[wirelessF]

TFL released a new video and tested a 2016 Silverado High Country 6.2L 8spd and they calculated 10.1MPG which was close to the 10.4MPG on the truck readout.

 

[Bladecutter]

I've never cared for the way they do some of their comparisons.

What they should have done was used the same exact fuel in all three trucks, to eliminate that factor.

They should have also used a standalone gps device to ensure that all three trucks are driving down the road at 70 mph (hello, speedo error).

And finally, all three trucks should have been tested on the same day with the same conditions.

I've met Roman and Nathan in person, quite a few years ago, when they were comparing three cars there for a review, at the Left Hand Trailhead park. Nice guys.

BC.

 

[itguy08]

Originally Posted By: hattaresguy

This is an area where it pays to have a diesel, the 1 ton trucks with the gas motors always run out of breath when they tow up Ike Gauntlet. They simply don't do that in my area because I'm at sea level. This is why guys love the high HP Cummins, it will simply out pull the gas jobs at that altitude, the HP difference is over 100!


That's why I wish Ford would put a Ecoboost in the F250/350. Best of both worlds - low cost of Gas in both fuel and maintenance and the constant power at altitude. Turbos are awesome - be them on Gas or Diesel!

 

[rslifkin]

Originally Posted By: itguy08
Originally Posted By: hattaresguy

This is an area where it pays to have a diesel, the 1 ton trucks with the gas motors always run out of breath when they tow up Ike Gauntlet. They simply don't do that in my area because I'm at sea level. This is why guys love the high HP Cummins, it will simply out pull the gas jobs at that altitude, the HP difference is over 100!


That's why I wish Ford would put a Ecoboost in the F250/350. Best of both worlds - low cost of Gas in both fuel and maintenance and the constant power at altitude. Turbos are awesome - be them on Gas or Diesel!

Agreed. The 3.5 TT V6 would be a much better gas option for the super duties than the 6.2 V8, IMO. But it might sway a few too many customers away from the diesels if they don't tow anything huge.

 

[supton]

Originally Posted By: wirelessF
TFL released a new video and tested a 2016 Silverado High Country 6.2L 8spd and they calculated 10.1MPG which was close to the 10.4MPG on the truck readout.





Interesting! I will have to watch later and see if it was same temperature etc. Toyota's mill is long in tooth, as is their transmission.

 

[Anthony]

I feel like something was off in this test. I wasn't there, but it doesn't look like they are going up hill the entire time... 5600 lbs should have been easy for the Tundra. It was over 3000 rpm cruising on the hwy.

I towed 6500+ lbs 200 miles with my less powerful ( on paper ) Titan with one less gear in the trans. I towed in 4th gear with the speed around 65mph. RPM's were around 2100, and the truck not once had to shift even climbing some of the hills on the hwy. MPG readout showed 15 mpg.

I know I wasn't in Colorado when I towed, but even the Tacoma should have had an easier time I think.

 

[hattaresguy]

Again those trucks are at high altitude, they are producing at least 20% if not 30% less power than in GA...

 

[Anthony]

Originally Posted By: hattaresguy
Again those trucks are at high altitude, they are producing at least 20% if not 30% less power than in GA...


True. Lets just say the Tundra now has 300HP, and 300 ft lbs vs its rated 381/401 figures. That should be enough to haul that load down the hwy pretty easily with the Torque Converter locked in 5th gear. I'm guessing they didn't lock out 6th gear, and the transmission was hunting a bit.

 

[rslifkin]

Originally Posted By: Anthony
I feel like something was off in this test. I wasn't there, but it doesn't look like they are going up hill the entire time... 5600 lbs should have been easy for the Tundra. It was over 3000 rpm cruising on the hwy.

I towed 6500+ lbs 200 miles with my less powerful ( on paper ) Titan with one less gear in the trans. I towed in 4th gear with the speed around 65mph. RPM's were around 2100, and the truck not once had to shift even climbing some of the hills on the hwy. MPG readout showed 15 mpg.

I know I wasn't in Colorado when I towed, but even the Tacoma should have had an easier time I think.



It may just depend on what the gear spread in the trans is. With my Jeep (4 speed auto), 4th is too tall for pretty much any towing (1800 rpm at 60). 3rd (2600 at 60) is lower than needed for all but the steepest hills, even at the max trailer weight the chassis can handle safely. But I'm pretty much stuck with running in 3rd with a trailer at that point. A gear half-way between them would be perfect for flat ground cruising and mild hills, but it's just not there.

 

[Anthony]

Originally Posted By: rslifkin
Originally Posted By: Anthony
I feel like something was off in this test. I wasn't there, but it doesn't look like they are going up hill the entire time... 5600 lbs should have been easy for the Tundra. It was over 3000 rpm cruising on the hwy.

I towed 6500+ lbs 200 miles with my less powerful ( on paper ) Titan with one less gear in the trans. I towed in 4th gear with the speed around 65mph. RPM's were around 2100, and the truck not once had to shift even climbing some of the hills on the hwy. MPG readout showed 15 mpg.

I know I wasn't in Colorado when I towed, but even the Tacoma should have had an easier time I think.



It may just depend on what the gear spread in the trans is. With my Jeep (4 speed auto), 4th is too tall for pretty much any towing (1800 rpm at 60). 3rd (2600 at 60) is lower than needed for all but the steepest hills, even at the max trailer weight the chassis can handle safely. But I'm pretty much stuck with running in 3rd with a trailer at that point. A gear half-way between them would be perfect for flat ground cruising and mild hills, but it's just not there.


The Tundra has a 6 speed. It should have handled that load comfortably in 5th at much less than 3,000 rpm. I'm no expert though. I would have to tow at High Altitude to really know what it's like I suppose.

 

[supton]

5.7L Tundra, at 3,000rpm, is:
1st: 20mph
2nd: 34mph
3rd: 49mph
4th: 67mph
5th: 91mph
6th: 113mph

and at 70mph it's 1,862rpm in 6th, 2,304rpm in 5th, 3,155rpm in 4th and 4,260rpm in 3rd (actually it'll be ~5% higher due to no torque convertor lockup in 3rd).

2,300rpm is like 150hp on the 5.7L--subtract out 30% and it's maybe 100hp. That's at full throttle though, which the trans programming won't allow--it'll just downshift. That trailer probably needs 100hp at 70mph. Ergo, I suspect that truck wanted to just sit in 4th.

[Eons ago I downloaded a pdf from Caterpillar about how to spec out hp required for truck, taking into account grade, road surface and frontal area. I spent some time playing with grade, frontal area etc when truck shopping--and basically came to the conclusion that more hp is generally better. Anyhow... 70mph for 60 square feet at Cd=0.38--total guesses--gets us upwards of 100hp at 70mph with a very slight grade.]

 

[rslifkin]

Looking at those speeds, 4th to 5th is definitely a big enough drop that I could see it not wanting to stay in 5th on a hill climb at altitude. 5th is probably a good flat ground cruising gear with a trailer like that.