[Lawdog]

Some of this has been covered I know after doing searches, but this is my new experiences. I am now hauling commercially with a 40' flatbed and my MegaCab. The truck is a 2012 with an auto and 3.73 gears with Max Tow. I towed several loads of my dedicated run with the 3.73 weight combined is 25,300 with 3/4 tank of fuel. i was getting 8-8.7 mpg loaded depending on speed and 12 empty avg.

i recently had a 4.10 gear put in the rear end, thinking the truck was working too hard running too low an RPM. We pulled the front driveshaft as well. I am now seeing 7-7.8 mpg on average loaded and 11-11.2 empty (Empty = Empty with trailer)

Trailer is about 10k empty tandem duals with Electric / Hydraulic disc brakes.

Now seat of the pants says the truck likes the 4.10 gears better, but Milage says otherwise. Should I stick with the 4.10 and suffer the milage or switch it back to 3.73. I also had a 31K gross load that was low on the deck and got 10 loaded with the 3.73. My daily load is up in the wind creating a lot of turbulance. They are steel racks. run 500 miles (250 miles each way) per day, loaded and back empty. I dont look for back loads as the dedicated route pays better to just get back to releoad each day.

Thoughts or suggestions please

 

[Lawdog]

No thoughts or suggestions?

 

[Vatalaro]

The 4:10 should give you the best towing mileage and 3:42 would give you the best empty mileage, with this test you did were you towing the exact same weight and exact same load with the 3:73 vs the 4:10, aero dynamics plays the biggest roll with towing mpg's, so if the loads were not a picture perfect match then the test was garbage. Personally I don't really care for the 4:10 gears, they are too low, I'm really loving the 3:42's, I get 20-22 empty highway and 12-14 towing a 5k travel trailer. Obviously a lot lighter but still like towing a wind sail behind you. Mathematically the 4:10 will have better towing mpg and lower empty highway, the taller the gears the lower the towing mileage goes and the higher the highway mileage. I think the 3:73 is a good happy medium between the 3:42 and 4:10.

 

[wixthedog]

Were you towing at the same speeds? RPM difference will play a large factor here.

 

[NC4stroker]

FWIW, my 12 mega has 35" tires, 3:73s, auto tranny, I and was considering a "regear", as I pull a 5th wheel toy hauler.

I downloaded an RPM vs gear vs tire size chart, and realized there are so many variables. To justify a regear cost, you have to decide on a permanent tire size, and a dedicated tow speed, or towing RPM.

After looking at the chart, ad nauseam, I decided to keep the 3:73s and I just tow in 5th until getting up to 65 or 70, which I can tow in 6th on level ground. When towing I shift manually on the stalk.

In other words, if you can find a tranny gear which will give you the towing RPM, and the towing speed you want, that's obviously the cheapest way to go.

 

[davisman]

Probably a silly question, Have you tried towing in a higher gear since you swapped rear end?

 

[rpage]

ran heavy loads for over 12 yrs only ran a 4:10 once and will never do it again. As far as mpg, the 4:10 on paper may seem to support better mpg but i never saw it and you lose what little you mite gain when you run empty.

 

[Destroked 450]

I agree ^^ 3.73's are the best all around tow gear with 30-35" tires

 

[bootstrap]

I have zero complaints about 3.54. No problem starting off on a hill with 15000+ hooked up.

 

[Holybubba]

Gear Ratio Calculator

you can plug in your truck with different gears and see if the RPMs look better to you..

 

[Lawdog]

Truck goes back in in 2 days to go back to the 3.73

 

[Novakane]

Lawdog, you actually did the exact opposite of what will give you better mileage. I'm not sure what your cruise RPM is, but keeping your RPMs low is what will give you better fuel mileage. This is old news in the trucking industry. 3.42s would be my choice. After all, why have a six speed if you don't use the extra gears. I'd rather have 3.42s and drop a gear to pull a hill than to have 3.73s and limit my empty or cruise fuel mileage... That's what 6 speeds are for. 3.42sssss

 

[Destroked 450]

I believe 3.73's are the best all around tow gear, but your area dosen't have a lot of big hills and with half of your miles running empty you mite want to look at 3.55's. They will lower your rpm 100-150 in top 2 gears over 3.73's.

IMO for heavy towing find a gear that will get you 1800-2100 rpm in 5th or direct at 65 mph so that on your return trip empty you can run in 6th or OD at 15-1800 rpm, remember your still pulling a trailer. Gearing to tall may get you lower rpm's but will cause the trans to down shift more often on grades. When the trans down shifts the rpm's go up and mpg's go down so gearing it up to where it down shifts on a simple overpass can cost you up to 1 mpg or more on the round trip.
There for the best gear is one that gets the job done at the LOWEST MAINTAINABLE rpm with the fewest down shifts.

 

[Lawdog]

It had the 3.73 and it runs 1700 at 70 where I got the 12.2 mpg with empty 10k trailer flat bed. with the Auto, I don't think I would want 3.42 towing everyday Empty with no trailer they would be great.

 

[Destroked 450]

Off topic
My fire dept bought an old 89 Pierce pumper about 6 years ago that came from Clinton Twp.. I picked it up in Toledo, but while I was there I went on up to Dundee to the big Cabela's store. If they had a Jerky Shop down here like the one I went to I'd be broke all the time.

 

[Novakane]

It had the 3.73 and it runs 1700 at 70 where I got the 12.2 mpg with empty 10k trailer flat bed. with the Auto, I don't think I would want 3.42 towing everyday Empty with no trailer they would be great.

If you don't want to take advice from the trucking industry then you'll pay for it per mile I suppose...

Before the fuel hike post 9/11, it was common practice to run 4.11s 3.90s, and 3.70s in trucks (semis). Mainly because they pulled great. But now that fuel is triple the price most of the time, It's common to have 3.36s but never higher than 3.55s. If you think there is no rhyme or reason for that... then

 

[Vatalaro]

I love my 3:42's whether towing or not, plenty of power to tow in 1-5, then you have that extra gear 6 to drop the rpm on the highway and get good mileage too. But the heaviest I've towed with it is 10K since that's my sticker limit from factory, but it would tow 20K if you wanted, plenty of power with 3:42's and I sit at 1650rpm going 70 on the hwy getting 22+ mpg with my own custom tuning.

 

[Novakane]

I love my 3:42's whether towing or not, plenty of power to tow in 1-5, then you have that extra gear 6 to drop the rpm on the highway and get good mileage too. But the heaviest I've towed with it is 10K since that's my sticker limit from factory, but it would tow 20K if you wanted, plenty of power with 3:42's and I sit at 1650rpm going 70 on the hwy getting 22+ mpg with my own custom tuning.

What size tires do you have? 265/70r17s?

 

[Destroked 450]

If you don't want to take advice from the trucking industry then you'll pay for it per mile I suppose...

Before the fuel hike post 9/11, it was common practice to run 4.11s 3.90s, and 3.70s in trucks (semis). Mainly because they pulled great. But now that fuel is triple the price most of the time, It's common to have 3.36s but never higher than 3.55s. If you think there is no rhyme or reason for that... then

Be carefull how you throw the word Trucking Industry around, you have one opinion and I have another and I started my trucking career in 1978 before the big fuel hike in 79 (fuel went from $.63 to $1.01 over a weekend), thats over 60%. Try that at todays prices, $4.00 to $5.00 is only 25% increase.

New 14-15 liter engines with 1800 lbs of torque need higher gears to operate in the lower 1100-1600 rpm range they are designed for.
An engine less than 1/2 the size designed to operate at 1600-2100 rpm pulling half the weight will need a slightly lower gear to operate efficiently.

We haul regional with less than 25% interstate, so our trucks have 475 cat, 18 spd, 3.70 rears.
Running a hundred rpm more and not down shifting will get better mpg than running lower rpm and down shifting on every grade. (been there proved that)

 

[Holybubba]

I am going to blow everyone's mind here..Ready!?!?!? You can get 20mpg with a 4:10 and you can climb the biggest hills with a 3:25.. It is all in how you drive it. Changing your rearend gears is at most going to give you a 1-+ mpg and get you up that hill 5-10-+ sec at BEST. IF you want real change you are going to need to change your driving habits.. You have got to decide what you want out of your rig and adjust for that..You want POWER your mpgs and rig's longevity will suffer. To get all 3 your going to have to dump a lot of money into your rig. IMO you pick one and drive accordingly .