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Open Roads Forum  >  Tow Vehicles

 > 3.31 gears at 40,000 lbs gross.

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blt2ski

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Posted: 05/25/21 10:02pm Link  |  Quote  |  Print  |  Notify Moderator

Roy,
If that frod with 6.15 gears had 40" tires vs standard 32" tires. Might be a good setup.
2nd setup looks kinda normal for some OTR rigs where top rpm is 2000!

Tire diam, tra s ratio's, all effect how a RA ratio should be at.
A rig with 28" tires, 3.42 gears, another with 3.73 and 30" tires, or 4.10 with 32" tires, assuming same trans, engine, all have the same shift points, should accelerate and pull the same load equally. I'm positive there will be some difference's, but in reality, nothing too major.

Marty


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4x4ord

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Posted: 05/25/21 10:58pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

RoyJ wrote:

Let's be fair to Ford and look at what Ram uses (I'm a big Mopar fan just to be clear):

3.75:1 Aisin 1st speed ratio, 4.10 axle ratio, 37,100 lbs tow rating. Works out to be 15.375 total ratio, or "2413 lbs per total gear ratio"

Ford: 4.615:1 1st gear, 3.55 axle ratio, 35,000 lbs towing. 16.383 total ratio, or 2136 lbs per gear ratio

So starting out in 1st gear, the 3.55 Ford has a 12% gearing advantage over an Aisin Ram running 4.10.


Never heard "lbs per gear ratio" unit of measure, but I'm tracking and your assumption is solid.

What you're confused about is the argument was never, is the trans (OD clutches, whatever) being overstressed. But rather higher final ratios put "more" stress on the trans, (OD clutches, driveline, whatever) and the answer is still resoundingly yes.
Oh, and I'm a Dodge guy too and they're again (sorry, still...) s ucking hind teat in the transmission department!



When a 4.30 vs a 3.31 are towing down the highway in 10th gear you’re right .... the 3.31 is putting little torque through the overdrive clutches and the 4.30 truck is putting even less torque through the OD clutches. Come to a hill and the 4.30 puts nearly peak engine torque through the OD clutches and the 3.31 equipped truck puts no torque through the OD clutches. Also if the same driver accelerates towing a trailer with a 3.31 equipped truck followed by a 4.30 equipped truck and the torque were measured on the driveline in each gear it is very likely that the torque measured would be close to identical. Torque on the axle would be higher with the 4.30 equipped truck. The thing is the 4.30 would jump up a gear and the 3.31 would now be putting higher torque to the axle until it also makes the shift.

Edit: (to bring a little more clarity) By the time the 3.31 truck is up to 65 mph in 7th or 8th gear the 4.30 truck is doing 65 mph and is in 10th. So, the driver of the 3.31 truck backs off on the accelerator and the transmission will make 2 or 3 more shifts under low torque.

* This post was last edited 05/26/21 05:37am by 4x4ord *   View edit history


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dodge guy

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Posted: 05/26/21 05:51am Link  |  Quote  |  Print  |  Notify Moderator

4x4ord wrote:

Grit dog wrote:

RoyJ wrote:

Let's be fair to Ford and look at what Ram uses (I'm a big Mopar fan just to be clear):

3.75:1 Aisin 1st speed ratio, 4.10 axle ratio, 37,100 lbs tow rating. Works out to be 15.375 total ratio, or "2413 lbs per total gear ratio"

Ford: 4.615:1 1st gear, 3.55 axle ratio, 35,000 lbs towing. 16.383 total ratio, or 2136 lbs per gear ratio

So starting out in 1st gear, the 3.55 Ford has a 12% gearing advantage over an Aisin Ram running 4.10.


Never heard "lbs per gear ratio" unit of measure, but I'm tracking and your assumption is solid.

What you're confused about is the argument was never, is the trans (OD clutches, whatever) being overstressed. But rather higher final ratios put "more" stress on the trans, (OD clutches, driveline, whatever) and the answer is still resoundingly yes.
Oh, and I'm a Dodge guy too and they're again (sorry, still...) s ucking hind teat in the transmission department!



When a 4.30 vs a 3.31 are towing down the highway in 10th gear you’re right .... the 3.31 is putting little torque through the overdrive clutches and the 4.30 truck is putting even less torque through the OD clutches. Come to a hill and the 4.30 puts nearly peak engine torque through the OD clutches and the 3.31 equipped truck puts no torque through the OD clutches. Also if the same driver accelerates towing a trailer with a 3.31 equipped truck followed by a 4.30 equipped truck and the torque were measured on the driveline in each gear it is very likely that the torque measured would be close to identical. Torque on the axle would be higher with the 4.30 equipped truck. The thing is the 4.30 would jump up a gear and the 3.31 would now be putting higher torque to the axle until it also makes the shift.

Edit: (to bring a little more clarity) By the time the 3.31 truck is up to 65 mph in 7th or 8th gear the 4.30 truck is doing 65 mph and is in 10th. So, the driver of the 3.31 truck backs off on the accelerator and the transmission will make 2 or 3 more shifts under low torque.


You just stated exactly why lower gears are better than higher gears, even when towing marginally heavy.

Sheesh, this thread is longer winded than trying to tow a trailer with 3.30 gearing!


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4x4ord

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Posted: 05/26/21 06:30am Link  |  Quote  |  Print  |  Notify Moderator

^^^^ What gear ratio is “better” depends on what you’re trying to accomplish. If you’re worried about overdrive clutches not being capable of transmitting high torque ..... ironically 3.31s are better. If you’re towing heavy equipment up a rough logging road .... 4.30s are going to be better. If you need duals to tow your 20,000 lb rv and want a wide track front axle you unfortunately have to go to 4.30s. If you use your truck for towing some and empty some it’s like Roy said ..... The new Powerstroke with the 10r140 and 3.31 gears can pull a house off its foundation and be capable of 22 mpg running empty down the highway.

ShinerBock

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Posted: 05/26/21 09:26am Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

ShinerBock wrote:

RoyJ wrote:

The counterpoint being raised is given an enthusiast driver who cares about his truck (not a fleet driver), towing heavy with a 3.31 puts very little additional stress on components other than the driveshaft / u-joints.


This is where we disagree. I know that the added stress put on the driveshaft/u-joints is also placed upon the output shaft of the trans which in turn is being held to the input side of the trans via clutches. I don't see how anyone can say that there is added stress on the driveline, but not added stress on a clutch and output shaft that is connected to that same driveline.


I'll start by saying we're talking RV use, NOT commercial under-speed cases. In the latter case you would have higher average torque in the transmission input side, because you're purposely lowering the cruising speed. So with a fix cruising hp requirement: we drop the rpm by 25%, up goes engine torque by 25%.

In the RV case, we're locking out 9th / 10th. So if cruising rpm is identical, engine output HAS to be identical. Engine does not know what rear end there is, only the total gear reduction ratio.

If you look at my chart earlier, both 3.31 and 4.30 truck engines are putting out ~420 hp and ~800 lb-ft of torque. The only difference is the 3.31 truck in 4th, and 4.30 truck in 6th. The flywheel / TC clutch would not know the difference.


Again, I am not talking about those who manually lock out gears in order to reduce the added stress placed upon the driveline and overdrive clutches(that are directly attached to the said driveline). I am talking about those who let the computer do all the work and the computer will keep the transmission in these higher gears (as seen in the video) even when towing more weight than its rating.

Hence the reason why the fact still stands that taller rear gears put more stress on the trans and driveline gear for gear than a shorter rear gear. Gear for gear, not one 8th and the other in 10th. Gear for gear.

There is a reason that many trans manufacturers and off-road enthusiasts say you should regear your vehicles when you put larger tires that alter your final drive ratio. It puts more stress on your drivetrain(including trans) and causes premature trans failure due to the taller gearing pulling heavier weight so you need to regear to reduce this stress.

"Increasing Tire or Rim Size Can Cause Premature Wear
You Don’t Want To Reduce Your Vehicle’s Effective Gear Ratio
The increased size causes the tires to rotate slower to cover the same amount of ground. It will take more power to accelerate because your drivetrain’s mechanical advantage has been decreased. If you are running an automotive transmission this can cause some serious strain depending on the current gear ratio if you choose not to re-gear your system.
"

INCREASING TIRE SIZE CAN WEAR OUT YOUR DRIVETRAIN & TRANSMISSION

"This theory works against you, however, when you increase the radius of a tire, because it now requires more torque from your driveline to turn that larger tire. This generally does not have much of a negative effect on the engine components themselves, although it will now require the engine to work harder to maintain the same speed as before. The transmission components, on the other hand, especially the clutches and bands, take the brunt of the abuse. Clutches and bands will begin to create excessive heat as they struggle to operate under higher constant stress. Excessive heat cycles will cause the friction surfaces to start slipping, and at that point the transmission will need to be overhauled. If the core problem of the failure is not addressed — increased tire size — problems will occur again and again."

Transmissions & Oversized Tires: How Cha........r Ratios Helps Prevent Drivetrain Damage

"Q: Are there other issues beyond part fatigue to consider when you upgrade to bigger tires?

A: Absolutely. A gear ratio change is essential to achieving a good balance between the torque you want, and the efficiency of your engine and transmission. The larger tire size changes the optimization of the transmission-to-engine operation. You need to change the axle’s gear ratio, or you’ll get terrible gas mileage and wear out the transmission quicker."


Spicer-Bigger Tires Demand Related Modifications

* This post was last edited 05/26/21 12:16pm by ShinerBock *   View edit history


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RoyJ

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Posted: 05/26/21 01:01pm Link  |  Quote  |  Print  |  Notify Moderator

blt2ski wrote:

Roy,
If that frod with 6.15 gears had 40" tires vs standard 32" tires. Might be a good setup.
2nd setup looks kinda normal for some OTR rigs where top rpm is 2000!

Tire diam, tra s ratio's, all effect how a RA ratio should be at.
A rig with 28" tires, 3.42 gears, another with 3.73 and 30" tires, or 4.10 with 32" tires, assuming same trans, engine, all have the same shift points, should accelerate and pull the same load equally. I'm positive there will be some difference's, but in reality, nothing too major.

Marty


Funny enough, I just recently put the smallest, highest payload tires on my old V10 Ram, because re-gearing may cost more than the old truck! I chose 235/65/16C, off of a Transit van. Compared to the 31.5", I made my 3.54 effectively into a 4.00.

My point though, was folks only look at rear end ratios. The 4R100 has a 2.75:1 1st, and the 10R140 a 4.615:1.

I bet if we did a random poll of what's better for towing: old 4 speed Ford with 6.10 rear end, or new 10 speed Ford with 3.31. 9 out of 10 would pick the 6.10 rear end without thinking twice.

RoyJ

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Posted: 05/26/21 01:19pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

Hence the reason why the fact still stands that taller rear gears put more stress on the trans and driveline gear for gear than a shorter rear gear. Gear for gear, not one 8th and the other in 10th. Gear for gear.


If gear-for-gear was the strict condition, then sure, I'll absolutely agree the 4.30 truck will have lower engine stress, converter stress, transmission internal stress, driveshaft stress, and equal axle torque.

But that's unrealistic. Why shouldn't the 3.31 downshift twice and match rpm-for-rpm? Ford must agree with me somewhat to make the tow ratings so close.

Also, I'm limiting my statement to modern HD pickups only. i.e. vehicles with power similar to a semi, and transmission ratios better than an Allison BR500. If we include Jeeps/ 4runners with barely adequate gearing for stock 32s, and then putting on 37s, that's an entirely difference story.

See my post above, I made it clear my old Ram very much need a re-gear, and that's just to tow a 10k dump trailer. If I tried a 30k trailer I'll need 4Lo just to nudge it! So my statements weren't meant to be a 1 size fits all for all vehicles / situations.

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Posted: 05/26/21 01:26pm Link  |  Quote  |  Print  |  Notify Moderator

dodge guy wrote:

Sheesh, this thread is longer winded than trying to tow a trailer with 3.30 gearing!


Better not read trucking news then, Volvo is talking about (gasp!) 1.95 rear end ratios on their semi [emoticon]

https://www.ttnews.com/articles/rear-axle-ratios-still-moving-downward

ShinerBock

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Posted: 05/26/21 02:00pm Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

ShinerBock wrote:

Hence the reason why the fact still stands that taller rear gears put more stress on the trans and driveline gear for gear than a shorter rear gear. Gear for gear, not one 8th and the other in 10th. Gear for gear.


If gear-for-gear was the strict condition, then sure, I'll absolutely agree the 4.30 truck will have lower engine stress, converter stress, transmission internal stress, driveshaft stress, and equal axle torque.

But that's unrealistic. Why shouldn't the 3.31 downshift twice and match rpm-for-rpm? Ford must agree with me somewhat to make the tow ratings so close.

Also, I'm limiting my statement to modern HD pickups only. i.e. vehicles with power similar to a semi, and transmission ratios better than an Allison BR500. If we include Jeeps/ 4runners with barely adequate gearing for stock 32s, and then putting on 37s, that's an entirely difference story.

See my post above, I made it clear my old Ram very much need a re-gear, and that's just to tow a 10k dump trailer. If I tried a 30k trailer I'll need 4Lo just to nudge it! So my statements weren't meant to be a 1 size fits all for all vehicles / situations.



Did you see the OP's video? His 3.31 axle with large tires was in 10th towing a combined 40k. He locked it out of 10th and 9th, unlike many people who just let the computer do the work which will leave it in 9th or 10th. My 2014 Ram 2500 Cummins with a 3.42 rear gear and 34-inch tires will do the same in 6th. It will hold 6th in many scenarios where it should downshift into 5th to put less stress on the trans. I just lockout 6th, but many people like my brother don't and wonder why they have transmission issues.

The computers in these trucks will be more than happy to keep you in the highest gear possible even though it is not the best thing for your transmission. And just because I have enough engine power to tow in 6th or the OP can tow in 10th, doesn't mean that we should especially with taller rear gears.

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Posted: 05/26/21 05:40pm Link  |  Quote  |  Print  |  Notify Moderator

RoyJ wrote:

dodge guy wrote:

Sheesh, this thread is longer winded than trying to tow a trailer with 3.30 gearing!


Better not read trucking news then, Volvo is talking about (gasp!) 1.95 rear end ratios on their semi [emoticon]

https://www.ttnews.com/articles/rear-axle-ratios-still-moving-downward


LOL, I vaguely remember reading something about that a while ago. But they are also using a completely different type of trans.

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