Tow capacity lmt factor - 6.4 Hemi

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mtofell

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I poked around the Ram tow charts a bit and have an idea about this but wanted to throw it out to my fellow Ram-aholics.

My 2500 Hemi 6.4 w/3.73 gears has a tow capacity of 12,500# - jumping up the to 4.10s bumps that rating up to 15,500#. So, what does/would going up to 4.56 gears do? Keep in mind I'm not talking payload here at all. That remains at 3000#. I'm just talking about what the truck can tow.

Could one conclude that the 4.56s would give an even higher rating? At what point is the transmission overworked? Or, what's the next weak link in the system? I'm going to guess it's the transmission as the 4500 and up start to come with the Aisin but I'm really just guessing.

And before you cranky weight Nazis jump on me I know nothing changes the sticker on the truck from it's original rating from the factory (fwiw, the door sticker on a 3/4 ton privately used truck is pretty much irrelevant anyway). I'm more thinking theoretical here.

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drittal

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2015 Ram 3500 Chassis Cab 6.4 with 4.44 and Aisin has tow capacity pushing 18k properly equipped.

Does this mean a standard 2500 with a gear change is going to be as capable? Who knows. I think the 4.44 gear ratio is for a heavier axle than what comes with a standard 2500.

An axle ratio change will not change your GCWR. GVWR of a 2500 may be for tax reasons, but stulepping up to a 3500 with 6.4 gets you over 1,000lbs GVWR, but only an additional 100lbs GCWR.
 

BoldAdventure

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Yeah; towing is based on a combo of the engine power curves in relation to the gearing and the transmission.

You might be able to increase gearing, but the truck might not actually be able to pull 20K because it would have to do so at 5000 RPM in drive. Which would be bad. I know, bad example, but hopefully you can get what I'm saying here.

You want optimal performance.
 

Stangshcky12

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While 4.56 will physically ease towing a heavier load but it will not statistically change your towing capability.
 

tjfdesmo

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At some point you reach the limit of stability with SRW.
 
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mtofell

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While 4.56 will physically ease towing a heavier load but it will not statistically change your towing capability.

Not sure what "statistically change" means.... I know the numbers on my door sticker don't change. 3.73 to 4.10 increases by 3000# per Ram engineers. My question is where does it stop? What's the next limiting factor after gearing?
 
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mtofell

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At some point you reach the limit of stability with SRW.

SRW vs DRW is payload - As mentioned in the OP I'm not talking about payload.... just towing ability. I see your point though. At some point the max payload is hit but it's really not until you have a 30,000# trailer - 10% goes to the tongue which = 3000# to max the payload. Of course this is kind of an exaggerated example as there aren't 30,000# trailers or receivers to hold them. I'm really just talking about what the engine/tranny/gears can handle.
 
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Andy578

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SRW vs DRW is payload - As mentioned in the OP I'm not talking about payload.... just towing ability. I see your point though. At some point the max payload is hit but it's really not until you have a 30,000# trailer - 10% goes to the tongue which = 3000# to max the payload. Of course this is kind of an exaggerated example as there aren't 30,000# trailers or receivers to hold them. I'm really just talking about what the engine/tranny/gears can handle.

no it's far more then just payload. having that extra rubber makes it far more stable plus you do need payload for towing anyway since there will always be tongue weight. also there are plenty of trailers that can take that much weight and more just they are 5th wheels and those generally also put a lot more weight on the truck compared to a hitch so again payload is very important

as far as the engine/tranny/gears go they will usually take far more then the trucks rating and they are really a pretty small factor in that ratings which are primarily based on safety. hell you could pull 30k with a civic if you wanted but it sure as hell wouldn't be safe
 

Lipcurl

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Not a towing guru here but don't the trucks have a GCVWR (max weight of truck and trailer combined) somewhere listed for them ?


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TRCM

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Not sure what "statistically change" means.... I know the numbers on my door sticker don't change. 3.73 to 4.10 increases by 3000# per Ram engineers. My question is where does it stop? What's the next limiting factor after gearing?



He probably means, that even tho the gears may let you go higher, other things won't.....MY guess would be tires/rims are next, as in capacity as well as ability to maintain traction.

I was surprised to find out I could get e rated tires for my dually that were rated higher than the rims on the truck.
 

BoldAdventure

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Not sure what "statistically change" means.... I know the numbers on my door sticker don't change. 3.73 to 4.10 increases by 3000# per Ram engineers. My question is where does it stop? What's the next limiting factor after gearing?

Nope, sorry. You're theory is wrong. Explain why one of these 4.10's then is 13K and the other is 15K. Why does the diesel tow more with less gearing.

More going on than just gears. As I said above. Transmission, engine, power, suspension are all factors along with the gearing. Where it stops is when you hit the wall in the next weakest link of the chain.
 

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cc rider

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the civic is a good example of how you cant just use those factors to determine capacity. Didnt see brakes mentioned. And Im not sure how the sae ratings work. check out the link below. Dont mean to hijack but figured its relevant. i always wondered how brakes worked. Where is the line crossed on safety. Since most trucks have the same brakes/rotors but there are huge differences in towing caps. like several thousanads of pounds . Yet they have the same brakes? Hello....emergency situation anyone? I know the trailer has its own brakes too. Just saying

SAE J2807 Tow Tests - The Standard
 
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mtofell

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Dont mean to hijack but figured its relevant. i

SAE J2807 Tow Tests - The Standard

Hijack away.... my whole question is really just theoretical. I'm not looking to haul 30K with my truck. I'm just trying to learn what the weak links are.

That's a good article. I'm generally happy with my job and feel lucky to have it. Then, I look at these guys who get paid to roll loaded trucks up and down hills all day and get very jealous. That would super fun.

What really got me wondering is I'm seeing a lot more Ram 4500+ trucks around my area, some with the 6.4 Hemi. It got me curious about what/how the various parts change as the weight ratings go up.
 

Andy578

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But the civic will probably only last a week if that

of course it wouldn't last but that wasn't exactly my point lol

the civic is a good example of how you cant just use those factors to determine capacity. Didnt see brakes mentioned. And Im not sure how the sae ratings work. check out the link below. Dont mean to hijack but figured its relevant. i always wondered how brakes worked. Where is the line crossed on safety. Since most trucks have the same brakes/rotors but there are huge differences in towing caps. like several thousanads of pounds . Yet they have the same brakes? Hello....emergency situation anyone? I know the trailer has its own brakes too. Just saying

SAE J2807 Tow Tests - The Standard


that's why trailer brakes are also required once you reach a certain weight. you can't just keep putting bigger and better brakes on the tow vehicle or you'll run into excessive wear and will run into issues with the trailer such as jackknifing
 

crash68

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Explain why one of these 4.10's then is 13K and the other is 15K. Why does the diesel tow more with less gearing.

The diesel produces practically double the torque at less than half the RPMs of the Hemi. At 3.5K rpms the CTD is pretty much redlined, the Hemi is just starting to think about making HP and torque.
Thats why the CTD is capable of pulling more with less gearing.
 

Catmandoo

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I'm not gonna study the entire spread sheet but if you are basing anything on numbers you can clearly see that the Aisin transmission and/or gearing makes a difference. If you just want to know what people think is the next weakest link, then the even more limiting factor in towing in my opinion would be the rear axle. The axle sizes goin from 2500 to 3500, then to 4500 get bigger as you go up. When you get to the 4500 They have bigger ring gear size but also more fluid capacity, larger axle shaft size, and then higher lug number. I've had buddy's blow up rear axles in 3/4 ton trucks trying to tow things, granted it towed it for a few years but eventually it gave up. lower gears in any truck will give you an advantage, there's gotta be so much less pressure when the axle starts twisting on a truck with 4.88's compared to 3.73's.
 

csuder99

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With regards to the initial (theoretical...) question: Lower gearing would allow the truck to tow more weight, with the caveat that the ring & pinion might not last long. I have not seen a 4.56 pinion vs. a 4.10 but typically the pinion gets smaller with lower gearing which means higher contact pressure.

The mentioned SAE J2807 specifies amongst other things 0-60 in less than 30s, 0-30 in less than 12s, 5 starts on a 12% grade and staying above 40mph on the Davis Dam grade while not overheating etc.. Meeting these requirements is a combination of engine output and gearing. For the same engine lower gearing allows more towed weight, or for the same gearing the higher output engine will tow more, which is pretty much what the RAM charts show.

As for the weak link, that would be the transmission as the torque converter generates more heat when it runs with a higher RPM differential. Hence the use of specific HD transmissions in heavier trucks.
 
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Danno

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How can we make them meet their current towing capacity with the gear hold problem? Looking to exceed the current capacity is light years away if it can't meet the advertised capacity.
 

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