Good Sam Club Open Roads Forum: Truck Campers: Rear end ratios
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mt-ed

Montaha

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Posted: 12/21/19 09:42pm Link  |  Quote  |  Print  |  Notify Moderator

I've read where some truck campers specify the ratio of gearing in the differential of their trucks used for truck camping. Would anyone out there be so kind so as to explain to me what the advantages/disadvantages are to these different configurations?
Thanks in advance!

bwlyon

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Posted: 12/21/19 10:48pm Link  |  Quote  |  Print  |  Notify Moderator

The higher the gear ratio numerically (3.55, 3.73, 4.10, 4.30, 4.44, 4.56) the more revolutions your driveshaft has to turn to make the tires go 1 Revolution. This increase in gear numerical gear ratio decrease effort required to turn the tires thus making it easier for a vehicle accelerate and pull a load. If you have a light vehicle that does not pull heavy loads you can use a numerically lower gear like 3.08 which decreases the rpm of an engine at speed and thereby increase fuel economy. On the other hand, if you have a heavy vehicle that frequently pulls heavy loads you’d want a higher numeric gear ratio to make it easier to accelerate and pull heavy loads.

time2roll

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Posted: 12/21/19 11:09pm Link  |  Quote  |  Print  |  Notify Moderator

Generally the modern 6 to 10 speed transmissions have made changing rear gears obsolete.
Now if you have an old 3 or 4 speed and you feel like you are often in the wrong gear then consider a change.


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wnjj

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Posted: 12/21/19 11:49pm Link  |  Quote  |  Print  |  Notify Moderator

time2roll wrote:

Generally the modern 6 to 10 speed transmissions have made changing rear gears obsolete.
Now if you have an old 3 or 4 speed and you feel like you are often in the wrong gear then consider a change.


With 10 speeds perhaps but at least some 6 speeds aren’t that different than older 4 speeds when it comes to towing heavy. Our 6 speed Yukon will top 60 in 2nd gear so it would definitely need lower gears in the rear if I wanted to tow anything substantial with it. The 2 added gears allow for lower RPM when cruising in the 40-70mph range for better mileage.

Kayteg1

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Posted: 12/22/19 12:36am Link  |  Quote  |  Print  |  Notify Moderator

Final gear ratio is always a balance between engine torque and differential gearing.
For years I drive European vehicles, who I love for high differential ratio as they take most of the grades without downshifting.
My family members on other hand drive Toyotas, who I get to drive occasionally.
It gets really annoying when Toyota needs to downshift with each wind gust or freeway overpass. But then Toyotas get better mpg.
Same with trucks, but here, on this forum you will find "conservative" members who drove trucks with high differential ratios for decades and can't comprehend changes combustion engines made in last years.
Most of the members will advise you to get high differential ratio for camper.
I educated myself and for my 440 HP dually - have chosen the lowest differential ratio Ford would install, yet still the truck takes all those 15-17 miles grades we have with 6000 lb camper never dropping from overdrive at 1600 rpm.
Frankly I wish I could get even lower than 3.55 differential ratio for fuel economy. It doesn't make sense to gear truck for hauling 20,000lb rigs without downshifting.
Transmissions have gears for a reason.





Lwiddis

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Posted: 12/22/19 07:52am Link  |  Quote  |  Print  |  Notify Moderator

X2, Kayteg. My new Silverado with the eight speed transmission and 3.24 rear end pulls better than my 2015 Tahoe with the six speed and 3.42.


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phillyg

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Posted: 12/22/19 08:10am Link  |  Quote  |  Print  |  Notify Moderator

Sticking my neck out a bit as I'm going from memory, but a 3.55 geared vehicle will have less pulling power than a 4.10. But good luck finding, let's say a new one ton vehicle, with more than 3.73 gearing. The reason is the newer vehicles compensate with up to 10-speed transmissions. Back in the day, a 4-speed tranny might have 4.10 gearing in a one ton. Bottom line is any of the newer one tons can handle most, if not all, truck campers sold today, especially if DRW.


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jaycocreek

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Posted: 12/22/19 08:29am Link  |  Quote  |  Print  |  Notify Moderator

Quote:

Back in the day, a 4-speed tranny might have 4.10 gearing in a one ton.


Mine does with the old 460 and it does quite well on gas mileage if you keep it around 2000 rpm's... That is the problem with higher ratios, Fuel mileage at higher speeds..


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ppine

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Posted: 12/22/19 08:38am Link  |  Quote  |  Print  |  Notify Moderator

I agree with the above posts.
Run your engine under load with careful attention paid to your tachometer and you will be fine no matter what gear ratio you have.

RCMAN46

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Posted: 12/22/19 08:41am Link  |  Quote  |  Print  |  Notify Moderator

" But good luck finding, let's say a new one ton vehicle, with more than 3.73 gearing."

I may be wrong but I am almost sure the new GM one tons with the Duramax and 10 speed Allison has a 3:42 rear gear as the only option.

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