Axle ratios limit towing?

[Kukailimoku]

Some of you owners please post factual data about the different axle ratios and the towing limits please. (No speculation please, actual facts)

I read in another thread that wasn't about towing, some tangent about the 3.21 can only tow 7,000 or 8,000.
???

The 3.92 can tow 11-12,000.

Is the basic premise true - that lower ratios tow less? If so, what is the actual breakdown?

I'm asking about manufacturer's rating and limitation, not what your granddad did when he tow the horses.

 

[crazykid1994]

Lower ratios less torque. A 3.21 gear ratio at 375 ft lbs is 1200 ft lbs to the ground due to the 3.21 multiplier. 3.92 at 375 is 1470 ft lbs to the ground due to the multiplier. Therefore the 3.92 gearing will make it easier to get a larger load moving
Edit: changing the ratio does not change your vehicles load capabilities though because that vehicle was specd by the manufacturer for such weights

 

[Kukailimoku]

Lower ratios less torque. A 3.21 gear ratio at 375 ft lbs is 1200 ft lbs to the ground due to the 3.21 multiplier. 3.92 at 375 is 1470 ft lbs to the ground due to the multiplier. Therefore the 3.92 gearing will make it easier to get a larger load moving
Edit: changing the ratio does not change your vehicles load capabilities though because that vehicle was specd by the manufacturer for such weights

Thanks. I get it that different ratios affect torque (or mileage, but this is a truck forum so the mileage is less than the torque in importance). I get it that a truck with one ratio will more easily tow a given weight than a truck with a different ratio.

But "more easily" and "easier to get a larger load moving" is not the same thing as saying WHAT the max load is for each ratio.

So did the manufacturer tell owners of ratio X that they can only tow up to Y and owners of ratio A that they can tow all the way up to load B?

 

[pacofortacos]

The steeper ratio is able to tow more due to strength and load, less stress on the actual gears on the 3.92's vs. the 3.21 due to the torque multiplying effect.
Yes ratio A can tow X lbs, ratio B. can tow X lbs. etc

https://www.ramtrucks.com/towing-guide.html

The only one it doesn't seem to change is the ecodiesel, maybe due to the torque curve of the diesel?? Or that there isn't much difference between the 3.55 and 3.92 capacity which is all that is available?

 

[crash68]

Part of the SAE J2807 testing to determine how much a truck can tow is not only how fast a vehicle can a load up to speed but also within the thermal operating limits of the vehicle itself.
The lower gear ratio will get the larger load moving faster and less load while traveling. Depending on the terrain your traveling, you can go over the "rated" weight for the tall axle ratio but expect the performance to suffer.

 

[BWL]

If you follow the link a couple posts above you'll see a 4x2.bighorn is rated 8510 towing with 3.21 vs 11610 with the 3.92, but both have the same payload rating since both axles are rated to carry the same weight.

 

[hounddog]

The simple way to understand;

The lower the number the fewer the times the transmission propeller shaft spins. The higher the number the more times it spins.

That means if its 3.92 the engine and transmission need to work less hard to get the rear axle to turn because the axle spins more quickly, so more easily.. Which isnwhy you get higher revs on "higher" gear ratios- theyre actually lower gear ratios. It acts like a reducer, essentially.

It is opposite to how we think it should work, but the higher the number the harder working the gear actually is. I hope this helps.

 

[Kukailimoku]

Thanks all. But I was not asking for the "why" behind any of it. Just wanted to know if ratio Z was limit to Y pounds by the manufacturer.

Pacofortacos posted a wonderful guide exactly showing that it is true, manufacturer issues weight limits by-ratio. Manufacturer also limits weight based upon wheelbase*, too.

Interesting.

(*more properly said, manufacturer builds all the trucks to carry X pounds total, and some versions have more of their own heft to carry around, taking away from the overall total - which means for every extra pound of its own self, it carries a pound less of cargo.)

 

[dhay13]

It isn't necessarily about bed length but more the overall weight of the truck, which obviously the long bed weighs more than the short bed. But a short answer to your question...definitely. Take 2 identical trucks, 1 with 3.21 and 1 with 3.92. Everything else with those trucks are the same. Same axles, same springs, same brakes, etc. The only difference is the gear ratio so yes, gear ratio does matter.

 

[Kukailimoku]

It isn't necessarily about bed length but more the overall weight of the truck, which obviously the long bed weighs more than the short bed. But a short answer to your question...definitely. Take 2 identical trucks, 1 with 3.21 and 1 with 3.92. Everything else with those trucks are the same. Same axles, same springs, same brakes, etc. The only difference is the gear ratio so yes, gear ratio does matter.

roger that. And the reverse: same axle ratio and the bigger cab and longer bed will have a lower useful load.

This is all not much more different than aeroplanes - load up a full load of gas and you cannot load up a full load in the fuselage. Fill up the fuselage and you cannot carry full fuel. Powerplant being equal of course...

 

[392DevilDog]

The difference is GCWR. GVWR is determined by configuration. Cab, bed, engine, 4x system. GCWR is then decided by gear ratio.

For instance using 5th Gen numbers. Note: V6 is different,just saying before it is asked

Crew 5'7 Hemi 4x2 is 6900 GVWR

The same but 4x4 is 7100 GVWR

3.21 gear ratio is 13900 GCWR

3.92 is 17000 GCWR.

This is why a 3.21 will have the same payload as a 3.92...but will have 3100 lbs less towing.

See the SAE J2807 for why and how

 

[crash68]

The difference is GCWR. GVWR is determined by configuration. Cab, bed, engine, 4x system. GCWR is then decided by gear ratio.

Technically a vehicle GCWR is determined by the state regulations. Some states have a set limit for a particular vehicle classification, others you pay for how much the vehicle/trailer combined can weigh(Elected Gross Weight).

 

[392DevilDog]

Technically a vehicle GCWR is determined by the state regulations. Some states have a set limit for a particular vehicle classification, others you pay for how much the vehicle/trailer combined can weigh(Elected Gross Weight).

That is all wonderful and good I suppose, but he was asking why there is a difference. I posted what the difference is.

We could be here for days going by what each state says.

And, I will gladly admit that I am wrong, but the state only cares what you are towing when they stop you. If you are over the rate you pay registration on...that has not a thing to do with the factory rating of the truck.

GCWR OF THE TRUCK, buy the manufacturer states what they have tested the truck to for warranty and saftey.

GCWR by your state is what you decide to pay for. It is what you have decided will be the most you will tow combined and the most you want to pay for. Some people do not even register their GVWR right. New ram is 7100...but I guarantee in Pennsylvania most are rated Class 2...which isn't right...but is cheaper.

 

[dhay13]

My 1500's were class 2. My 2500 is class 3 but they still have not sent me the sticker. I called them and filled out a form MV44 and they claimed they sent a new one but I still have not got it. I called them to confirm the address and they said that is where they sent it. My son bought the same truck and never received his weight class sticker either. PA is horrible to deal with.

 

[pacofortacos]

It will say on your registration card what weight class you are - or at least what you registered it at.
I haven't put my class 2 sticker on in either truck for the past 18 years - it just sits in the glove box.


I am surprised they haven't done away with the weight class sticker yet like they did the registration sticker - since many cops now have the system to scan plates and spit out all of your info.
They actually scan entire parking lots and I have seen them at off ramps.

 

[dhay13]

So the saga continues. Filled out another MV44 and sent it in again requesting a weight class sticker. Today I get a new registration card in the mail with the same expiration as my other card (April 2020). Still no weight class sticker. The registration cards say Class 3 on them but also say 'Registered Gross Weight' 9000?

 

[Ratket]

So the saga continues. Filled out another MV44 and sent it in again requesting a weight class sticker. Today I get a new registration card in the mail with the same expiration as my other card (April 2020). Still no weight class sticker. The registration cards say Class 3 on them but also say 'Registered Gross Weight' 9000?

Well time to Move-

 

[Elkman]

Check out specs for heavy duty trucks and you will find that those with diesel engines have taller gearing as they can provide maximum torque at half the RPM's of a gas engine. You need lower gearing to keep a gas engine in its peak power band which is going to be more than 3,000 RPMs.

Manufacturers are more concerned about fleet fuel economy and so they will sell light duty pickups with tall gears as even a 0.5 mpg gain is important to them. When you specify the tow package it will usuallly include lower gears to the gas engine powered truck.

The overall payload depends on the number of passenger seats. A 1500 with the 8-passenger crew cab configuration has a calculated occupant load of 8 x 150 lbs or 1200 lbs before anything is put into the box. That is why the trucks with the regular cab always have the highest payload and tow load rating.

 

[Rick Stevens]

hello there...

I have used the information from the site below to determine what you can tow based on your gear ratio....3:92 can tow the most based on this information....

google - 2018 dodge ram 1500 trailer towing weights (just replace the year with you vehicles year, they are different surprising)

Take care,

Rick