Tow Vehicle Fuel Consumption

[Bigfoot Mike]

About the milage on your Dodge diesel. My brother first bougt a Dodge V-8 Hemi as a TV for his RV (32 ft. stick built). After 3 months at 8-9 MPG (55 MPH) he took it back and got the very same truck with a diesel engine, I don't know which Model. His MPG went up to 13-14. He thinks that's pretty good.

That sounds about right for the size of the trailer being pulled.

[Ron Wrighton]

Not to make any point but I also have a 35FT diesel pusher with a turbo 5.9 cummings and a 6 speed transmision. I get an average of between 11 and 12 MPG. When I pull a trailer with a 3.9 Dakota I average about 14 MPG.

[John Perry]

Has any one towed with a small engine Toyota Tacoma 2wd? Reason I ask is I have a friend that drives super fast (130 km/h) which is about 80 MPH towing a 13' boler and claims that it hardly affects his fuel economy. I'm skeptical of his claims but would love to know if there anyone out there with a Toyota tundra 2wd 2.4L engine and what they are getting.

Cheers Russ

For the last 2 1/2 years I have been towing with an 05 Tacoma, manual transmission, 2.7 L 4 cyl.. The worst mileage I ever experienced was a trip to Arizona with my 603 pond ATV in the back of the truck and towing my 13' Scamp. I averaged 19 mpg for the trip. I am one of those that drives with the flow of traffic.
With just my Scamp I average 21 mpg. I live in the Mts. so just usual driving I get about 24 or 25 mpg.
This was my 7th Toyota. I say was because I was by a Toyota dealership today and they had one 07 Tacoma left. I made them a stupid offer and they accepted so now I have a new truck with an automatic transmission instead of a manual to break in.

You can't beat a Toyota!
John

[Pete Dumbleton]

With the big diesel pickups, I suspect that the rear end ratio has a LOT to do with mileage. A friend bought one a while back to tow a mid-sized trailer, but he's the kind of guy who likes to have a lot of tow capacity, so he got a low rear end and then was disappointed by his mileage.

[Dean & Mary]

With the big diesel pickups, I suspect that the rear end ratio has a LOT to do with mileage. A friend bought one a while back to tow a mid-sized trailer, but he's the kind of guy who likes to have a lot of tow capacity, so he got a low rear end and then was disappointed by his mileage.

Yes, I also believe this to be true. The 4.10 axle ratio over the 3.73 in the Dodge will lower your mileage. In my opinion, the low rear end is certainly not needed pulling the fiberglass trailers.

[wildbill]

Has anyone tried using a higher octane fuel while towing. I have a Honda Ridgeline, and according to the Ridgeline forums, people have said that using a higher octane while towing will increase their mileage by 2 mpg. I haven't had the opportunity to try this myself yet (hopefully winter will end soon). Curious if this applies to other vehicles, or if this particular to the Honda VTEC engine. Oh, my Ridgeline gets anywhere from 12 to 17 mpg depending on speed.

[Nancy]

Russ,

Trailer tire pressure is a loaded question.

We have original tires on our 04. They now have about 25,000 miles on them. I can't check their size or brand for quite a while. I think we run around 33 in them, but it has been a long time for that memory.

Our 13 loaded weighs around 1500 lbs.

I do know that the door side needs air often. We carry one of those 12 v air things, plug it into the cig. lighter and pump the trailer tires often. (we go up and down mountains, and sometimes drive in 100 degrees during the day and hit 60's the next day).

Here is a quote from Joy A (has a 13 that weighs over 2,000) who travels a lot and changed her tires:

"I changed to a Tow Master 6 ply (B78 -13/6 ST ply rating C). They have now been on for 3 full years logging 20,906 miles. They aren't even showing any wear. The tread depth is 1/4" deep. I keep the tires filled to 45psi. I rotate the tires side to side and pack the wheels at the beginning of each year".

Joy has been to Alaska since then so we need an update from her. This post was back in 2005. Maybe she even has different tires now.

You could probably do a search on tire pressure to get more info. But, I think this is another personal opinion thing. We all drive with different tire brand and sizes, different weight trailers, and different driving speeds. Some of us have to put up with 10 hours of 100 degree weather. We try to adjust for the driving conditions.

Hope this helps you.

Nancy

[Pete Dumbleton]

Has anyone tried using a higher octane fuel while towing. I have a Honda Ridgeline, and according to the Ridgeline forums, people have said that using a higher octane while towing will increase their mileage by 2 mpg. I haven't had the opportunity to try this myself yet (hopefully winter will end soon). Curious if this applies to other vehicles, or if this particular to the Honda VTEC engine. Oh, my Ridgeline gets anywhere from 12 to 17 mpg depending on speed.

Octane alone does not increase power; high octane fuel is associated with powerful engines, but the fuel only allows them to produce more power. Octane is the rating of fuel to NOT ignite under high compression until the spark plug fires; high compression engines need higher octane to function properly.

Notice that when in the mountains, when one would expect to need so-called "high octane" fuel for power, the octane ratings of the fuels are actually lower at the pump. That's because the compression ratios change with altitude....





That said, modern engines are computer controlled and can change the timing of the spark to suit conditions. IF an engine has the compression and computer to take advantage of high-octane fuel, then it might run more effectively or efficiently with that fuel. If not, then the money for the premium fuel (It's called premium because it yields more profit ) has been wasted.

A 2 mpg improvement is worth checking out.

[Per Walthinsen]

My ancient '99 Odyssey has a computer which automatically changes the timing to take advantage of higher octane. Probably in conjunction with a knock sensor (device used by earlier SAABs and others I seem to recall).

Now if I weren't so cheap I would already have tested this out.

[Chester Taje]

My truck which i have at present time is a Diesel 6.7liter. On my way to Chilliwack going empty i averaged 20 mpg Imperial. That was a distance of 1164KM. Most of this was highway driving and some town driving. On my way back i took the long hilly way and got 16 mpg Imperial pulling trailer. Trip back was 1429.8 Kms
Lots of my route was in mountains and at times very slow. I never drove over 100kms/60 mph.
Total fuel bill was $483.52 CDN.
Total Kms was 2593.8 Kms
Cost/Km is about $0.18

[CliveAlive]

[quote]
Attachment 12305


Nice memories, huh? $5 for 3 Gallons !!

[Pete Dumbleton]

That was taken in August 2001, on my way back to Washington from Alaska.

People were complaining loudly about the cost of fuel at that time, they are complaining now and they will be complaining in the future.

[peterh]

I just got back from Vancouver Island, towing our new-to-us 14' Surfside trailer. Our 2001 Hyundai Santa Fe (AWD, 2.7 liter V6) got about 24mpg @ 65 mph heading north to Canada, then 17.5 mpg driving back at 60 mph (in bad weather).

This got me thinking about ways I can increase my towing mpg. Here's what I've come up with:

1) You'll notice I slowed down on my way back. Driving slower has a very noticeable effect on gas mileage. With fuel costs soaring, even the big rig trucking companies are slowing down to save fuel.

2) Tires. The trailer came with standard ply-bias car tires inflated to 30 psi. Not only are the tires on the trailer now not designed for towing, they have much higher rolling resistance than a radial tread trailer tire inflated to 50 psi. Replacing the tires should have a measurable effect.

3) Tires on the tow vehicle, too! The Santa Fe tires will need replacing this fall, so i have an opportunity to fix this problem, too.

When you add load to tires they spread out on the ground, increasing rolling resistance without substantially increasing traction. (The weight-bearing part of the tire is at the outer rim of the tire's imprint on the ground; the center section of the tire's imprint bears less weight than the edges do. This is why chronically under-inflated tires wear out at the edges, not in the center of the tread. When the tire's load spread away from the center tread the load moves to the part of the tire designed to handle cornering and turning forces that come at an angle to the tire's direction of rotation. Increasing inflation moves that load back to the center of the tire, which is the part that's designed for traction on the direction of roatation.) The back tires on my Santa Fe have a standard inflation of 30 psi; I could also improve my towing gas mileage and my braking traction by jumping to a tire with a higher load and max inflation pressure rating. Then I could increase my cold tire pressure from 30 to 34 psi.

Tires are rated as temperature range A, B, or C, with "A" being the high rating, "C" at the low end. Tires with "A" ratings generally have harder rubber in the tires and additional structures in the sidewalls that allow them to pass heat up the sidewalls faster to help cool the tires. Both features reduce rolling resistance and improve gas mileage, so replacing my range "C" tires with "B" tires will slightly improve gas mileage, too.

4) Axle maintenance. The last owner never re-packed the axle bearings, so I'm guessing that there's a low-level rolling resistance on the wheels due to poor maintenance. Re-packing the bearings is high on my must-do maintenance list.

5) Air dam. This is something I may have to experiment with: Add a fairing on the top of the Santa Fe that deflects air up and over the trailer the same way that air dams on the roofs tractor-trailer rig cabs deflect air over their trailers. They wouldn't put them up there if they didn't reduce fuel costs.

--Peter

[Pete Dumbleton]

If the bearings are a problem they should be heating up and be detectable.

Umm, something wrong with your numbers -- They don't match your conclusion about slowing down, which of course, they should.

From WiKi:

QUOTE
Power

The power required to overcome the aerodynamic drag is given by:

P_d = \mathbf{F}_d \cdot \mathbf{v} = {1 \over 2} \rho v^3 A C_d.

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

It should be emphasized here that the drag equation is an approximation, and does not necessarily give a close approximation in every instance. Thus one should be careful when making assumptions using these equations.
END QUOTE

[Chester Taje]

OK Pete---Put that in lay mans terms

[Pete Dumbleton]

Buried in the middle of that is:

"the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW)."

Double speed, increase power need by eight times!

However, that relationship is less true for lower speeds -- I recall reading somewhere that the air drag factor really starts to come into play at something like 45 mph.

Maybe someone with a consumption readout in their buggy can look at 45 mph compared to 90 mph and give us some real-world readings (without trailer, of course). A lot might depend on the speed at which the car may have been designed to give the least drag.

[Steve L.]

Some comments about tires:

Radial tires have a significant advantage over bias and bias belted tires in terms of rolling resistance. Changing over to radial is a good move from a fuel economy perspective although they tend to be harsher (not a particular issue with the trailer) and more flexible side to side.

Peter's observations about inflation pressure versus tread wear and tread wear patterns are particularly pertinent with regards to bias tires but less so for radials. For radials, decreasing the pressure tends to lengthen the contact patch rather than widen it. However, the decreased bending at both the front and sides of the sidewall work the rubber more and the rubber’s hysteresis properties consume more energy and thus fuel.

Rolling resistance versus pressure is not a linear relationship. Once you’re in the design range of the load/inflation pressure table, increasing inflation pressure has a relatively trivia impact on rolling resistance.

Friction is a function of normal load, but again, the friction versus load curve is not straight. Doubling the load does not double the friction. Tread wear generally occurs at the relatively lighter loaded sections. Tread wear occurs at the instant when the tread block just leaves the contact area and it scrapes the road as it snaps from flat contact with the road to it’s radial position.

Higher speed ratings are generally obtained by delaying (increasing) the speed at which standing waves occur. Generally this is done in the tread area by altering the resonant frequency of the tread band by adding material such as nylon plies. Standing waves generate heat faster than the tire can shed it and eventually the rubber reverts, adhesion suffers and finally centripetal force does it’s thing. Sidewalls are generally kept thin to help them shed heat and it’s debilitating consequences.

Lastly, inflation carries the load. The sidewall’s just keep the air in. Tires designed for increased inflation pressure generally have stronger sidewalls, are generally heavier and both are bad for rolling resistance.

I know that (some of the rest) of the moderators frown at excessively technical posts but I'm not above tweaking things once and awhile.

FWIW, I have 17 years with a tire company (a technology manager) and for the last 10 years have been a tire engineer for a major auto company.

[peterh]

Umm, something wrong with your numbers -- They don't match your conclusion about slowing down, which of course, they should.

I read your post three or four times before I realized where you thought my numbers were off, then I realized: You were assuming I drove the trailer both ways, so . . .
Leg 1: I drove the Santa Fe northward without a trailer at 65mph (average) and got 24 mpg
Leg 2: I drove the Santa Fe southward with the trailer at 55-60mph and got 17.5 mpg

The loss in gas mileage was not because I slowed down, it was due to hauling 2000 lbs of trailer behind me.

--Peter

[peterh]

Some comments about tires:

Thank you Steve . . . You need to teach a class in Trailer Tires for us!

[Pete Dumbleton]

I read your post three or four times before I realized where you thought my numbers were off, then I realized: You were assuming I drove the trailer both ways, so . . .
Leg 1: I drove the Santa Fe northward without a trailer at 65mph (average) and got 24 mpg
Leg 2: I drove the Santa Fe southward with the trailer at 55-60mph and got 17.5 mpg

The loss in gas mileage was not because I slowed down, it was due to hauling 2000 lbs of trailer behind me.

--Peter

OK! Got it!