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Tow Gearing - Real World Experience -

8K views 41 replies 23 participants last post by  norfla71 
#1 ·
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
 
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#3 ·
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.
 
#5 ·
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.
 
#6 ·
Probably a silly question, Have you tried towing in a higher gear since you swapped rear end?
 
#8 ·
I agree ^^ 3.73's are the best all around tow gear with 30-35" tires
 
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#12 ·
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
 
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#25 ·
class 8 semi's also have 10:1 or even steeper 1st gear transmissions.. unless your throwing your transfer case into low range, your not really comparable to a semi, since the lowest gear range you can get in a pickup is the G56 and that's less than 6:1 1st gear..
 
#13 ·
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.
 
#14 ·
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.
 
#16 ·
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 :doh:
 
#15 ·
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.
 
#17 ·
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.
 
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#18 ·
What size tires do you have? 265/70r17s?
 
#20 ·
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 .
 
#21 ·
It Is back to stock with the 3.73 rear. It worked well before my experiment with the 4.10. I understand that the 3.42 is better for economy in some instances but running speeds with lower rpm where the 3.42 would run, my truck will not hold the gear with the load. Thanks for the insight
 
#22 ·
A friend has a 2012 quadcab, 6.7 auto, 3.73's that gets 16 average no trailer, 12 empty trailer and 8 or less loaded in the hills. He said they can do a stealth delete, a programer and maybe some exhaust mods that could have the truck getting 20+ but it would void his warranty so he hasn't tried it yet.
 
#23 ·
We had an 08auto with 4'10s, and it could pull a house over.

I think that the argument between 3'55s 3'73s and 4'10s is dependent on the transmission, the build and what you do.
 
#24 ·
I think that the argument between 3'55s 3'73s and 4'10s is dependent on the transmission, the build and what you do.[/QUOTE]


I agree

Just think, if you had a 4500 or 5500 it would have 4.88's like my F-450 has. They SUCK and it cost over 2 grand to regear.
 
#27 ·
I have 3:42 with 68rfe and I stopped posting my mileage cause no one would believe me, IT GETS BETTER WAY BETTER MPG than 4:10 gears. I don't understand why your even talking about first gear, I get about 2mpg in first gear and it's still low and slow with the 3:42. Now heavy towing I think the 4:10 will do better mpg wise cause after 5K lbs my engine is working way harder than a truck with 4:10 and my mpg drops fast. I've gained a lot of mpg by playing with my tuning and getting it perfect for the 3:42 setup.
 
#28 ·
Slow down some as well. Using right lane only with fewer acceleration and deceleration events plus less braking is a win. Fewer steering corrections is also measurable.

Find your average trip mph. Slowing down may not change it appreciably. But it will sure as hell add to tire, brake and vehicle longevity. The aero penalty is too high. Running dedicated loads makes it easy.

Percentangei improvements to the annual fuel bill is the FE game. Component and vehicle longevity is what really pays.

Good luck
 
#29 ·
i am by no means smart in this area, i just got done pulling 11k pounds with stock 3.55s. truck was kinda sluggish pulling up a 8% grade(about 5 miles) about 35-40mph. But i have done alot of reading on here and most of my problem was my 35s throwing my gearing out of wack. If i was running stock size tires i would stick with my gears, but having 35s on my truck i think i am gonna go to a 4.10. my advice is if ur staying with stock tires i would keep the gearing the same. im only changing to do larger tires. i hope im right and if im wrong please chime in and correct me, im all about learning.
 
#31 ·
I think You're thinking along with the correct lines. My 3.55 is Ideal with the stock tire sizes. I tow more than you do and I never have any problems going up any hills. That is because I have stock tires. If I had bigger tires I would have to gear correctly for the tire size that I had.
 
#30 ·
My truck has 12,000 miles on it now, and 8,000 of those miles are towing a fairly heavy 5th wheel trailer, and I have 3.42 gearing. on the interstate with moderate grades I keep it in 5th gear , and in cruise control. Some will say OMG your going to blow your rear end and trans up using CC. I say BS. I've climbed darn near every extreme pass in the entire western U.S.. When the grades get real steep on secondary roads or even the interstate I use 4th gear, and will keep in cruise control unless I have to slow down below 55 mph.

I use the shift selector like a manual trans when entering the on ramp, then once it settles in, I use the cc in either 5th or 4th gear. I like to keep the rpm's around 1600-2000. Works for me. The only problem I have is when its hot outside and I have to drive through the city, or traffic jams. With the 3.42 I find that if you manually shift the trans in these situations you can keep the trans fairly happy ( below 180 Degs).

Do I wish I had 3.73 gearing for towing ? Hell yes, but this is how it worked out for me, and thats what I have to work with. After 8,000 miles towing I'm getting 11 mpg when hooked up. I have no idea what it gets without the 5er attached.
 
#32 ·
Not sure if this would help or not but thought I would throw this out there as I have though of it for myself also but don't know if it would help or hurt. What about a overdrive unit like the ones gear vendors sells. I know you aren't supposed to tow in double overdrive but empty it should help mileage and gives more gears to get a load rolling.
 
#33 ·
The consensus on those is that they're expensive, can be a weak link in the driveline, and never pay for themselves. :)
 
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