Real world towing MPG with Ford 5.0L V8?

[Bill and Earline]

Originally Posted by H46Driver

We have the F-150 V-8 5.0 with 3.55 and I've got to show my ignorance with regard to 3.55 vs 3.92 rear ends as I didn't even know enough to ask when we bought the truck. Can someone, in 8th grade level terms, explain advantage/disadvantage of each so I'll know something when it's time for my next purchase. We almost exclusively tow having logged almost 31K of our 35K miles with a trailer hooked up. Thanks in advance. BTW we got 14.5 to 15.5 towing our 3500lb Casita - no data yet on the Escape 21.

Nearly every vehicle has one or two differentials. That is the large lump in the center of the rear axle you see if you are behind a truck. In the differentials are a set of gears that direct the power from the driveshaft (and engine) to the individual wheel axle shafts.
In a higher number differential, the engine and drive shaft turn more often that a lower number differential. Think in terms of your first 10-speed bicycle. In a lower gear, you pedal very quickly and seem to have more power, but don"t go that fast.
Thats what any gears can do--whether in the transmission or the differential. Unlike the transmission the ratios in a differential don't change, unless you take it apart. So if you have a higher number than someone else, you will feel like you have more power, but the engine will turn faster and burn a little more fuel. This is often desirable if towing, and if the extra fuel isn't that much.
Hopefully simple enough without being insulting.
I'm sure others will elaborate.
Bill

[H46Driver]

Originally Posted by Bill and Earline

Nearly every vehicle has one or two differentials. That is the large lump in the center of the rear axle you see if you are behind a truck. In the differentials are a set of gears that direct the power from the driveshaft (and engine) to the individual wheel axle shafts.
In a higher number differential, the engine and drive shaft turn more often that a lower number differential. Think in terms of your first 10-speed bicycle. In a lower gear, you pedal very quickly and seem to have more power, but don"t go that fast.
Thats what any gears can do--whether in the transmission or the differential. Unlike the transmission the ratios in a differential don't change, unless you take it apart. So if you have a higher number than someone else, you will feel like you have more power, but the engine will turn faster and burn a little more fuel. This is often desirable if towing, and if the extra fuel isn't that much.
Hopefully simple enough without being insulting.
I'm sure others will elaborate.
Bill

Thanks Bill. So the 3.92 is going to be way better for climbing hills and such, correct? And the 3.55 will do just fine if you're mostly towing on level ground or gentle hills?

[War Eagle]

Dave, I'll add my understanding to what Bill said. The differential ("rear-end") adds what's called a final drive ratio (something to one). A 3.31 differential final drive ratio means the crankshaft has to revolve 3.31 times in order to turn the tires one revolution. A 3.92 ratio means the crankshaft has to turn 3.92 times to get the same one revolution of the tires. So, if you're carrying light loads and fuel efficiency is important, then advantage goes to the 3.31 - fewest crankshaft turns to get the tires to turn. But load it down with a lot of weight, and the engine will start to struggle. To use Bill's analogy, when you try to peddle a bicycle uphill in high gear, you don't have to peddle fast, but your leg muscles start burning from the power it takes your legs to turn the peddles. On the other hand, if you are pulling a heavy load, and you need power to do that, then the 3.92 ratio will get you there. Kind of like peddling on the flat in low gear. The peddling will be easier, but your legs will peddle really fast and it seems like you're not getting anywhere. So in a truck, your engine will rev up to higher RPMs to turn the tires with more power, but the high RPM will burn lots more fuel. If that all makes sense, then you have to think of matching the power of your engine with the work you need it to do, and will your differential ratio help you or hurt you. In our case, we're pretty confident the 5.0L V8 will have enough power to muscle through pulling our 21' (guessing it will be around 4,000 lb loaded) with pretty much any rear-end ratio we put in it. The 3.31 rear-end would give us the best mpg on flat land hauling. The 3.73 rear-end would help take a little stress off the engine climbing in the mountains. And since we plan to do both over the life of the truck, the 3.55 seemed like a logical compromise. I hope most of that is somewhere near correct and not "TMI" (too much information). And we haven't even started talking about optimum engine RPM to maximize torque and transmission gears and gearing. If it all starts to seem like much ado about nothing - just go to the dealership and pick out the best looking truck. It's all good.... Dale

[Santiago]

While I would certainly welcome more liters and higher rear end ratio for towing purposes, I chose truck specs that balances our use of the truck, meaning daily uses in town as well as non-towing trips to visit in-laws 400 miles away. This last trip from Anaheim to Oakland CA yielded 27mpg north ( 60-65 mph ) and 28.4 mpg southbound both at 60-65 mph. No AC use, no wind. Now that we are retired, we find 60-65 mph relaxing and trips are a lot more enjoyable and definitively less stressful. Will do a 70mph ( no tow ) trip in future to see how much the V6 drops in mileage over the same 800 mile round trip route.

Only Escape 21 foot towing so far I reported on this site 11/06/2016 titled "2016 RAM 1500 3.6L towing 21ft - my experience" and that yielded 15.8 mpg with windy conditions covering 1,300 miles.

Our truck is: 2016 RAM 3.6L V6 aspirated - Quad Cab - 8 speed - 305hp, 269ft-lb 3.55 axle ratio with SnugTop camper shell, 32 gal fuel tank.

[cpaharley2008]

The higher rear end gives a lower ratio thus allows for more owing capability but at the expense of economy. So that option is available for those with heavier trailers not expecting a economical towing experience but expecting performance.

[escape artist]

Originally Posted by cpaharley2008

The higher rear end gives a lower ratio thus allows for more owing capability but at the expense of economy. So that option is available for those with heavier trailers not expecting a economical towing experience but expecting performance.

Hi: cpaharley2008... At $1.12/L ($4.35/US G.) for gas after happy new year... I'll have more "Owing" capability too!!! Alf
escape artist N.S. of Lake Erie

[steve dunham]

When I purchased my 2014 Ram 1500 Hemi V8 there was 2 available rearend ratios 3.21 and 3.92 . The Ram Eco diesel had 2 available rear end ratios 3.55 and 3.92. The 3.21 was designed for economy , the 3.92 was designed for towing and the 3.55 was the compromise rearend ratio. When Ford or Chevy or Dodge advertise that their 1/2 ton truck is the towing leader or can tow 6 TON's they aren't doing it with the 3.21 rearend. The fuel mileage in my 2014 Ram V8 with the 3.92 rearend is better than my 2011 Ram V8 with the 3.55 rearend for a variety of reasons.

I bought my truck for towing not commuting to work .
Over 75% of the miles on my truck are towing miles . We were planning a trip to the mountains so for us the 3.92 was the better choice especially with the Ram's 8 speed transmission.
Everyone's vehicle performance expectations are different.

[cpaharley2008]

We have the same truck Steve, but different rear ends. Be interesting to compare numbers....

[emers382]

Originally Posted by escape artist

Hi: cpaharley2008... At $1.12/L ($4.35/US G.) for gas after happy new year... I'll have more "Owing" capability too!!! Alf
escape artist N.S. of Lake Erie

That's why Alf I love our 36 gallon tank. Since we go from home to our son's in Thunder Bay by cutting through MN south of Lake of the Woods we always fill up there, and unless we're running around a lot in TBay (as we did this time being here nearly two weeks) we have sufficient gas to get us back to MN to fill up at 2.20 a gallon as opposed to the 1.10/L I had to pay here.

For explanation of Alf's comment, Ontario is putting into place on Sunday a cap and trade system which will add 4.3 cents to a litre of gas plus home heating fuel up as well as everything else that has to get to a stop by truck, i.e. anything you buy at a store. Just glad we don't live anymore in Ontariowe

Adrian

[Loren & Cathy]

A friend of mine bought a new Chevrolet Silverado and it is almost like my GMC except for the rear axle ratio. His has the 3.42 rear end and mine is the 3.73. We did some comparing last fall to see the differences and it was like this. Highway mileage was around 21 on both. He doesn't tow, and I get 13.5 to 14 mpg towing the 21, On engine rpms, mine ran right at 200 rpm faster at 70 mph. Loren

[escape artist]

Originally Posted by emers382

That's why Alf I love our 36 gallon tank. Since we go from home to our son's in Thunder Bay by cutting through MN south of Lake of the Woods we always fill up there, and unless we're running around a lot in TBay (as we did this time being here nearly two weeks) we have sufficient gas to get us back to MN to fill up at 2.20 a gallon as opposed to the 1.10/L I had to pay here.

For explanation of Alf's comment, Ontario is putting into place on Sunday a cap and trade system which will add 4.3 cents to a litre of gas plus home heating fuel up as well as everything else that has to get to a stop by truck, i.e. anything you buy at a store. Just glad we don't live anymore in Ontariowe

Adrian

Hi: emers382... Ontari airy air I owe!!! Carp and Tirade will do nothing for the environment... but will air out our pockets a lot!!! Alf
escape artist N.S. of Lake Erie

[BCnomad]

Originally Posted by Loren & Cathy

A friend of mine bought a new Chevrolet Silverado and it is almost like my GMC except for the rear axle ratio. His has the 3.42 rear end and mine is the 3.73. We did some comparing last fall to see the differences and it was like this. Highway mileage was around 21 on both. He doesn't tow, and I get 13.5 to 14 mpg towing the 21, On engine rpms, mine ran right at 200 rpm faster at 70 mph. Loren

Loren, that's really close to what the guys are reporting on the Ram forums too.

I just lock out overdrive and manually help the gear selector in hill country on my highway geared truck.

[Brian B-P]

Originally Posted by steve dunham

When Ford or Chevy or Dodge advertise that their 1/2 ton truck is the towing leader or can tow 6 TON's they aren't doing it with the 3.21 rearend.

True, and not just in final drive ratio. The "best in class" claims are typically based on the ideal configuration of engine, transmission, cab, box, drive configuration (4X2 vs 4X4), payload and towing packages, tires, and other options (mostly by omitting them). The same ad will often have a fuel economy claim, based on a very different configuration. That makes sense - if something is important to a buyer, that person should configure the truck for that attribute.

Originally Posted by steve dunham

I bought my truck for towing not commuting to work .
Over 75% of the miles on my truck are towing miles . We were planning a trip to the mountains so for us the 3.92 was the better choice especially with the Ram's 8 speed transmission.
Everyone's vehicle performance expectations are different.

I think it's important to understand how the vehicle is to be used and choose appropriately, as Steve has. For a lot of people who use their truck mostly for non-towing driving (especially on highways), the tallest (numerically lowest; 3.31:1 for an F-150) axle ratio may be the best choice, despite having the lowest towing rating.

[andraycho]

I have 2016 f-150 5.0 SCrew 4x4 3.31 with 36g tank.

I'm getting 23mpg on highway without towing and 14+ mpg with towing 5.0TA half fresh water tank.

[rbryan4]

Originally Posted by andraycho

I have 2016 f-150 5.0 SCrew 4x4 3.31 with 36g tank.

I'm getting 23mpg on highway without towing and 14+ mpg with towing 5.0TA half fresh water tank.

That sounds about right Andray, since it's the 4x4. About 2 mpg less than my 2WD.

[H46Driver]

Thanks to all who have enhanced my understanding of rear end ratios - and thank you for being patient in bringing it down to a level a P.E. major could understand! Also apologies if I sorta hijacked this thread but it was great info!

[Brian B-P]

This post is full of numbers to systematically illustrate a technical issue under discussion. If that doesn't interest you, I suggest just skipping the post.

I found the Ram final drive ratios, in the downloadable specs buried in the towing and payload tables: 3.21 and 3.92 are available for the 5.7L engine and 8-speed transmission.

• The Tundra's 0.59:1 sixth gear and final drive ratio combine for an overall engine speed to axle speed ratio of
  • 2.31:1 (with the 3.91:1 final) and
  • 2.537:1 (with the 4.30:1 final).
• The 5.7 L Ram 1500 with 8-speed has a 0.67:1 eighth gear and final drive ratio which combine for an overall engine speed to axle speed ratio of
  • 2.15:1 (with the 3.21:1 final) and
  • 2.62:1 (with the 3.92:1 final).
• The F-150 with 5.0 L V8 and 6-speed has a 0.691:1 sixth gear and final drive ratio which combine for an overall engine speed to axle speed ratio of
  • 2.29:1 (with the 3.31:1 final),
  • 2.45:1 (with the 3.55:1 final), and
  • 2.58:1 (with the 3.73:1 final).

If they had the same size of tires, then engine speeds for a given road speed are only a few percent apart between all three brands of truck, for the corresponding final drive choice. Each company offers final drives to complement the transmission gearing. Ford does offer a middle choice, unlike the others.


Just as importantly, the Ram's 8-speed has a much lower first gear...

• The Tundra 5.7's 3.33:1 first gear and final drive ratio combine for an overall engine speed to axle speed ratio of
  • 13.0:1 (with the 3.91:1 final) and
  • 14.3:1 (with the 4.30:1 final).
• The 5.7 L Ram 1500 with 8-speed has a 4.71:1 first gear and final drive ratio combine for an overall engine speed to axle speed ratio of
  • 15.1:1 (with the 3.21:1 final) and
  • 18.5:1 (with the 3.92:1 final).
• The 5.0 L F-150 with 6-speed has a 4.171:1 first gear and final drive ratio combine for an overall engine speed to axle speed ratio of
  • 13.8:1 (with the 3.31:1 final),
  • 14.8:1 (with the 3.55:1 final), and
  • 15.6:1 (with the 3.73:1 final).

Having more gear ratios in the transmission lets Ram go with a lower first and still keep the spacing between gears close. Getting a heavily loaded rig moving quickly enough and efficiently takes low enough gearing, so any taller (lower numbers) final drive ratios probably wouldn't be appropriate for the Tundra.

Ford and Toyota both use 6-speeds which limits their range of ratios; since Ford's transmission gearing has more reduction (in both high and low gears), their final drive has less reduction, and the overall result is very close in top gear, and not as close in first gear.

Ford's spread of transmission ratios is wider than Toyota's (6.04:1 versus 5.65:1) which gives Ford more pulling ability off the line than Toyota with the same highway cruising gearing, but will mean bit bigger steps between gears along the way. Since Ford's spread is already so wide, they didn't go much wider with the 10-speed (which you can't get yet with the 5.0 L V8).

Unfortunately for Tundra buyers, Toyota has not yet put an 8-speed (or higher) into their trucks; their Aisin AW division has made an 8-speed for longer than anyone else (for a decade now), but it only appears here in Lexus models... and the Cadillac CTS.

[Bill and Earline]

Very well done, Brian.

My Ram Eco-Diesel with the 3.55 fits nicely into your chart.

Your next mission, if you choose to accept it, is to see what the various torque ratings are at engine rpms of 1,000, 2,000 and 3,000 for the Tundra, Ford Eco-Boost 2.7, 3.5, and non-boosted 5.0, and the Ram 5.7 and 3.0 diesel. To make is even more interesting, some Fords get their 10-speed for 2017.

Bill

[cpaharley2008]

Thanks Brian for the report, very informative for those comparing other trucks.

[War Eagle]

Do any of the current 8 and 10 speed automatic transmissions out there have more than one over-drive gear? Or are all those extra gears just starting lower and/or narrowing the gaps in under-drive to help optimize engine RPMs?