truck milage for 1ton+

[tcartwri]

5.13 nice. i saw that on the ford list. really glad I don't have those..

Well, on the upside, you could leave 4 black stripes on the pavement when the trailer was empty!

 

[scoutcub]

I wouldn't go with a bigger tire size. It may or may not help you. While the taller tire will effectively reduce your axle ratio, the taller tire will exert more leverage against the axle. The result is often a crap shoot. Think of picking up a small car battery with one hand and holding it by your body. Then extend your arm out full length. That's the leverage.

Hmmmm....thanks K7, I've never heard or considered this. Now I definitely will..

 

[sld]

A couple things to think about as far as MPG.

No matter what gears you have, it takes the same amount of H.P. to move a truck down the roads. Doesn't matter if you have a 5.00 rear end or a 3.00 rear end. Its a matter of a engine having a particular sweet spot in the RPM range where it gets the best mileage.

Not entirely accurate IMO. Put a truck on a dyno that has the 3:73 gears and swap them for 4:10's and it will show quite a bit more rear wheel horsepower. The engine will not work as hard with lower gears. The low gears can definitely help around town mileage. On the highway, they can hurt mileage, but that is only one of many variables. In some cases they could help it.

 

[Renze]

From Europe: a Mercedes Sprinter 518 (similar to Dodge Sprinter 3500 just tuned to 185 instead of 150 hp) with a single axle 5th wheel on 17.5" HD duals, 8ft wide, 9ft high curtainsided trailer with a GCVW of 8.75 ton, does about 6 km to the liter, which is about 14 miles to the gallon. the GCVW of 8.75 ton is 19.290 pounds.

You do have to go back to 5th when pulling into the wind... small price to pay.

p.s. changeing rear end gears has no effect on the max. rear wheel hp... just on the speed at which they are available. When you reduce speed, you'll increase torque. Power is torque x speed. With the right gears to the intended load, you have the best match of speed and torque in relation to the given load. When driving high speeds at low resistance (unloaded) your engine has the power to pull higher gears which saves fuel. Hook a trailer to it, the engine load will increase and you'll be more fuel efficient with lower gears, because you'll also be able to use 6th speed with a little incline.

 

[slowzuki]

No it won't. It has almost no effect on the rwhp. The torque available at the rear tires will change, but your dyno will calculate the rwhp from the torque and roller speed.

Not entirely accurate IMO. Put a truck on a dyno that has the 3:73 gears and swap them for 4:10's and it will show quite a bit more rear wheel horsepower. The engine will not work as hard with lower gears. The low gears can definitely help around town mileage. On the highway, they can hurt mileage, but that is only one of many variables. In some cases they could help it.

 

[SPYDERLK]

I wouldn't go with a bigger tire size. It may or may not help you. While the taller tire will effectively reduce your axle ratio, the taller tire will exert more leverage against the axle. The result is often a crap shoot. Think of picking up a small car battery with one hand and holding it by your body. Then extend your arm out full length. That's the leverage.

Hmmmm....thanks K7, I've never heard or considered this. Now I definitely will..

Assuming the two tire sizes have equal rolling efficiency the size change is just the same as an axle ratio change. And much cheaper. You WILL see a decrease in measured mileage because youll be travelling further per indicated mile.
larry

 

[dodge man]

Tire size can work in your favor if you don't like your rear gears. You can go bigger or smaller to help you out.

 

[SPYDERLK]

The low rear really does not hurt as much as people seem to think. I had 2 F-150's that were identical. 4x4, short bed, 5.4, ect. One had 3.73's and one had 4.10's They were only 1 mpg apart week in and out.

Now if you were to take them on say a 1000 mile highway trip the 3.73 would do maybe 3 mpg better but for most driving they were very close.

Chris

The only other things I am considering is opening up the exhaust and going to a bigger tire size, to get a little better mpg....especially with diesel prices....

I wouldn't go with a bigger tire size. It may or may not help you. While the taller tire will effectively reduce your axle ratio, the taller tire will exert more leverage against the axle. The result is often a crap shoot. Think of picking up a small car battery with one hand and holding it by your body. Then extend your arm out full length. That's the leverage.

Assuming the two tire sizes have equal rolling efficiency the size change is just the same as an axle ratio change. And much cheaper. You WILL see a decrease in measured mileage because youll be travelling further per indicated mile.
larry

Guess you didn't understand the battery analogy. It will also take more twisting force to turn the taller tire. Put a 32" tire on a truck, and then change to a 35" or 38" and see what happens. It's really a crap shoot as to what the end result will be as to mileage, but you can bet the performance will go down the tubes on the taller tires. Your increased radius creates a longer lever. Unfortunately, the power is being applied at the axle and not the tire tread.

What I really dont understand is why you think I didnt. There is a lot involved that I did not specifically mention, but most of these were mentioned elsewhere in the thread ..ie engine sweet spot, stop and go traffic, etc. In general as revs go up so do the pumping and windage losses inherent in the mechanics. Absent a sweet spot rpm where the eng produces more HP hrs per gallon, the inherent engine losses will cause poorer mileage with a low geared [hi ratio] rear. So it would be at least marginally beneficial the lower the cruise rpm. ... In the case of a sweet spot it can be quite beneficial to go to higher gearing to get cruise speed and sweet rpm to correspond. What I did not see mentioned was how larger circumference tires might produce a different effect than a corresponding axle ratio. Many times when going to larger tires youll go to a fatter tire with a more aggressive tread. The rolling resistance of that tire will almost definitely be greater -- so in those cases you lose some, all, or more than any gain that would have come from doing an axle ratio change resulting in the same increased distance of travel per engine revolution. To complicate the comparison, with larger circumference tires you are going faster than prevously indicated unless you factor it in mentally as you read your speedo.
larry

 

[sld]

I have always been under the impression that an engine is most efficient at converting gasoline to power at the rpm level of the measured torque peak.

The may or may not give you the best mileage as there are many variables so just reducing rpms doesn't automatically give you better mileage. Engine load is a big factor. Low rpms maximize mpg in some situations but with a tail wind my V10 with 4:30's has posted its best numbers at 85mph and almost 3k rpm's.

A lightly loaded engine at 2500 rpm's can use less fuel than a heavily loaded one at 1800 rpm's. Lower rpm's do contribute to lower emissions just from fewer explosions per minute while keeping the same speed.

Within reason, higher rpm's do not necessarily mean less mpg.