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 > How critical is axle ratio?

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philh

Belleville MI

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Posted: 06/15/21 04:54pm Link  |  Quote  |  Print  |  Notify Moderator

on my ordered 2022 F350, I went with 3.31 instead of 3.55. I'll take the lower RPM when not towing. For towing, the transmission will determine proper gear

Grit dog

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Posted: 06/15/21 05:38pm Link  |  Quote  |  Print  |  Notify Moderator

ShinerBock wrote:

valhalla360 wrote:

ShinerBock wrote:

The need for a low or high number rear gear ratio boils down to how the truck is being used and how often. If it is unloaded most of the time and you occasionally tow closer to its max ratings then it is probably best to get a lower number rear gear ratio and just select lower trans gears as needed when towing. If it is towing most of the time then it is probably best to get a higher rear gear ratio.

Getting a lower rear gear ratio to get better fuel economy on a truck that is towing 75% of the time makes no sense just as getting a higher gear ratio for a truck that is unloaded 75% of the time it is used.


Back in the days of 3 or 4 speed transmissions, you really had to choose what you wanted to optimize (towing or not towing) when selecting the rear end ratio.

This is the beauty of the 8/10 speed transmissions. Even up near the tow limits, the engine can stay in it's ideal RPM range by selecting an appropriate transmission gear.

Loaded or empty, if you stay within ratings, the overall gear ratio is good with the lower (numerical) gear ratio.

The only time you need to consider using a higher (numerical) gear ratio, is if you are over the tow rating of the lower gear ratio.


I have to disagree here. The more frequent you tow closer to your upper limits, the better you are in getting a higher numerical gear ratio to keep added driveline stresses low that a lower gear ratio brings.

It is similar to the half-ton versus HD debate. Towing close to a half-ton's 10k rating on a rare occasion does not warrant getting an HD, but if you do it on a regular basis then you are better off getting an HD because the added stress will cause premature wear on the half-ton as to where an HD is built to handle it.


Easy does it Shiner....this has a Shiner/4x re-match written all over it! LOL


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Grit dog

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Posted: 06/15/21 05:41pm Link  |  Quote  |  Print  |  Notify Moderator

philh wrote:

on my ordered 2022 F350, I went with 3.31 instead of 3.55. I'll take the lower RPM when not towing. For towing, the transmission will determine proper gear


But the difference at 80mph is like 1650rpms vs 1800rpms. Really nothing to write home about. Unsure why there's even an option anymore unless its a big jump in final drive ratio.

Terryallan

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Posted: 06/15/21 06:53pm Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:

dodge guy wrote:

Huntindog wrote:

Groover wrote:

Bottom line is that drive shaft RPM is irrelevant. What really matters is whether the engine is in its power band when you need it to be. Back when truck transmissions only had a 2.5 to 1 spread between high and low axle rations where much more important than they are with the newer transmissions that have a 7 or 8 to 1 spread.

The op is correct, unless you find yourself in first gear wishing that you had a deeper gear or in 10th gear wishing that you had a higher gear you get the same effect by simply changing gears.

I do suspect though that axles built with higher ratios may also be built to handle higher torque to the wheels, at least in some cases.
We have a winner. Rather than write all of this again, here is the readers digest version.
GM was late to the party of increasing their HD lines tow ratings. Ford and Ram were first, and they required higher (numericially) ratios to do it. When GM tried this approach, the Pinion gears would not live behind the Dmax. For those that do not know: as the rear end gears increase numericially, the pinion gear engages less of the ring gear, and thus is weaker.
So though the Dmax was more than capable of a higher tow rating, the gear set to make the performance acceptable was out of reach.
Enter GMs new Allison 10 speed. With lower gears available in the tranny, the rear gearset could actually be changed in the direction that would make it stronger. So that is what they did, and for good measure they increased the size of the ring gear on the duallys as well.


What I get out of that is that GM’s axles are weak. No other manuf had that issue with lower gears.
That is one possibility. But it is unlikely....I do not know who the axle suppliers are for the different brands and for what years, but I have read that for some years/models the same supplier sells to more than one manufacturer,,, even so, I doubt that one brand of axle is much stronger than another. A 11" inch ring gear is the same size in any brand, and the steel will be the same as well.
What is more likely is the Dmax actually puts out more power for longer.

There is a lot of evidence to back this up over the years.... If one chooses to look at it.


Actually that is not true. I made ring, and pinion gears for 23 years. each company has different specs for the steel used in their gear sets. There are a infinite number of metal combinations, and each one has a different heat treat spec. How long it is heated, how hot, and how it is quenched.
It is true that one supplier, supplies many different manufacturers, and each manufacturer has different quality demands. Different metal combinations, and different tolerances for quality.

Dana Axle makes the majority of American truck gear sets, and axles. Or they did 2 years ago. GKN Driveline makes axles for SUVs, and vans, and some passenger cars. They supply BMW, Ford, GM, Fiat/ Jeep/Chrysler, and Maserati. And yes, some are weaker, and some are stronger than others. it all depends on the application. after all the axles in a Chevy Equinox, don't need to be as strong as the axle in a Maserati.

Fun fact. Many ring gears are no longer bolted on. They are welded. However you still have to change both the ring, and pinion if you ever need to replace one or the other. They are married together through a process called Lapping.. During which they are run together with a abrasive compound spraying on them, under high torque to "wear" them together, so that they will run quietly. Then they are put into a testing machine to see if they indeed make noise. If they pass they go to the next step, if they fail. they are scrapped, and sent back to be melted down.
Then when they are put into the axle, they are tested for noise again. It is a very interesting process, well at least for the first year.
So if you have one of the makes we made axles for.. and it moves when you press the gas. You can thank.... me. LOL

BTW. Each gearset has 2 sides. A Drive side, and a Coast side. and they are exactly what they say. But in general. One side is always harder to get right. If your vehicle is quite going down the road, but roars when you let off the gas. You have a problem on the coast side.


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Huntindog

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Posted: 06/16/21 02:58am Link  |  Quote  |  Print  |  Notify Moderator

Terryallan wrote:

Huntindog wrote:

dodge guy wrote:

Huntindog wrote:

Groover wrote:

Bottom line is that drive shaft RPM is irrelevant. What really matters is whether the engine is in its power band when you need it to be. Back when truck transmissions only had a 2.5 to 1 spread between high and low axle rations where much more important than they are with the newer transmissions that have a 7 or 8 to 1 spread.

The op is correct, unless you find yourself in first gear wishing that you had a deeper gear or in 10th gear wishing that you had a higher gear you get the same effect by simply changing gears.

I do suspect though that axles built with higher ratios may also be built to handle higher torque to the wheels, at least in some cases.
We have a winner. Rather than write all of this again, here is the readers digest version.
GM was late to the party of increasing their HD lines tow ratings. Ford and Ram were first, and they required higher (numericially) ratios to do it. When GM tried this approach, the Pinion gears would not live behind the Dmax. For those that do not know: as the rear end gears increase numericially, the pinion gear engages less of the ring gear, and thus is weaker.
So though the Dmax was more than capable of a higher tow rating, the gear set to make the performance acceptable was out of reach.
Enter GMs new Allison 10 speed. With lower gears available in the tranny, the rear gearset could actually be changed in the direction that would make it stronger. So that is what they did, and for good measure they increased the size of the ring gear on the duallys as well.


What I get out of that is that GM’s axles are weak. No other manuf had that issue with lower gears.
That is one possibility. But it is unlikely....I do not know who the axle suppliers are for the different brands and for what years, but I have read that for some years/models the same supplier sells to more than one manufacturer,,, even so, I doubt that one brand of axle is much stronger than another. A 11" inch ring gear is the same size in any brand, and the steel will be the same as well.
What is more likely is the Dmax actually puts out more power for longer.

There is a lot of evidence to back this up over the years.... If one chooses to look at it.


Actually that is not true. I made ring, and pinion gears for 23 years. each company has different specs for the steel used in their gear sets. There are a infinite number of metal combinations, and each one has a different heat treat spec. How long it is heated, how hot, and how it is quenched.
It is true that one supplier, supplies many different manufacturers, and each manufacturer has different quality demands. Different metal combinations, and different tolerances for quality.

Dana Axle makes the majority of American truck gear sets, and axles. Or they did 2 years ago. GKN Driveline makes axles for SUVs, and vans, and some passenger cars. They supply BMW, Ford, GM, Fiat/ Jeep/Chrysler, and Maserati. And yes, some are weaker, and some are stronger than others. it all depends on the application. after all the axles in a Chevy Equinox, don't need to be as strong as the axle in a Maserati.

Fun fact. Many ring gears are no longer bolted on. They are welded. However you still have to change both the ring, and pinion if you ever need to replace one or the other. They are married together through a process called Lapping.. During which they are run together with a abrasive compound spraying on them, under high torque to "wear" them together, so that they will run quietly. Then they are put into a testing machine to see if they indeed make noise. If they pass they go to the next step, if they fail. they are scrapped, and sent back to be melted down.
Then when they are put into the axle, they are tested for noise again. It is a very interesting process, well at least for the first year.
So if you have one of the makes we made axles for.. and it moves when you press the gas. You can thank.... me. LOL

BTW. Each gearset has 2 sides. A Drive side, and a Coast side. and they are exactly what they say. But in general. One side is always harder to get right. If your vehicle is quite going down the road, but roars when you let off the gas. You have a problem on the coast side.
So do you think there is an appreciable difference in the HD truck axles among the big 3?

It doesn't really matter in this conversation if a Maseratti has stronger axles than a Yugo. I would expect that to be the case.



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valhalla360

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Posted: 06/16/21 04:26am Link  |  Quote  |  Print  |  Notify Moderator

If you are within the trucks ratings, talk of increased stress is a red herring.

The manufacturers have designed to account for it.


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Lynnmor

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Posted: 06/16/21 05:43am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

If you are within the trucks ratings, talk of increased stress is a red herring.

The manufacturers have designed to account for it.


Is that why all trucks last forever? [emoticon]





ShinerBock

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Posted: 06/16/21 06:30am Link  |  Quote  |  Print  |  Notify Moderator

Lynnmor wrote:

valhalla360 wrote:

If you are within the trucks ratings, talk of increased stress is a red herring.

The manufacturers have designed to account for it.


Is that why all trucks last forever? [emoticon]


Yeah! Like the current half-tons will last the same as an HD with the 14k tow ratings they have these days. Right...

valhalla360 wrote:

If you are within the trucks ratings, talk of increased stress is a red herring.

The manufacturers have designed to account for it.


Not really. Even Dana-Spicer, one of the largest driveline manufacturers in the world, states that the life expectancy of driveline components decreases with lower axle ratios.

[image]

[image]

The above images are from research done by Dana-Spicer on their driveline products in the heavy-duty truck market where trucks typically cruise at around 1,400 rpm. Keep in mind that this is using their product well below the truck's ratings and only using 200 hp. Eaton and Meritor did the same with their transmissions and clutches, but I do not have the link.

Many times, speccing a lower axle ratio to save money on fuel economy is negated by added maintenance/replacement cost of the parts that this lower axle ratio effect. If one does not tow close to their ratings that often then it is probably better to get a lower axle ratio. However, if you are towing closer to your max ratings on a regular basis then the higher gear option is probably the best way to go for longer component life.


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deltabravo

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Posted: 06/16/21 07:04am Link  |  Quote  |  Print  |  Notify Moderator

Terryallan wrote:

So if you have one of the makes we made axles for..

Who is this "We" you speak of?


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Terryallan

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Posted: 06/16/21 07:19am Link  |  Quote  |  Print  |  Notify Moderator

Huntindog wrote:

Terryallan wrote:

Huntindog wrote:

dodge guy wrote:

Huntindog wrote:

Groover wrote:

Bottom line is that drive shaft RPM is irrelevant. What really matters is whether the engine is in its power band when you need it to be. Back when truck transmissions only had a 2.5 to 1 spread between high and low axle rations where much more important than they are with the newer transmissions that have a 7 or 8 to 1 spread.

The op is correct, unless you find yourself in first gear wishing that you had a deeper gear or in 10th gear wishing that you had a higher gear you get the same effect by simply changing gears.

I do suspect though that axles built with higher ratios may also be built to handle higher torque to the wheels, at least in some cases.
We have a winner. Rather than write all of this again, here is the readers digest version.
GM was late to the party of increasing their HD lines tow ratings. Ford and Ram were first, and they required higher (numericially) ratios to do it. When GM tried this approach, the Pinion gears would not live behind the Dmax. For those that do not know: as the rear end gears increase numericially, the pinion gear engages less of the ring gear, and thus is weaker.
So though the Dmax was more than capable of a higher tow rating, the gear set to make the performance acceptable was out of reach.
Enter GMs new Allison 10 speed. With lower gears available in the tranny, the rear gearset could actually be changed in the direction that would make it stronger. So that is what they did, and for good measure they increased the size of the ring gear on the duallys as well.


What I get out of that is that GM’s axles are weak. No other manuf had that issue with lower gears.
That is one possibility. But it is unlikely....I do not know who the axle suppliers are for the different brands and for what years, but I have read that for some years/models the same supplier sells to more than one manufacturer,,, even so, I doubt that one brand of axle is much stronger than another. A 11" inch ring gear is the same size in any brand, and the steel will be the same as well.
What is more likely is the Dmax actually puts out more power for longer.

There is a lot of evidence to back this up over the years.... If one chooses to look at it.


Actually that is not true. I made ring, and pinion gears for 23 years. each company has different specs for the steel used in their gear sets. There are a infinite number of metal combinations, and each one has a different heat treat spec. How long it is heated, how hot, and how it is quenched.
It is true that one supplier, supplies many different manufacturers, and each manufacturer has different quality demands. Different metal combinations, and different tolerances for quality.

Dana Axle makes the majority of American truck gear sets, and axles. Or they did 2 years ago. GKN Driveline makes axles for SUVs, and vans, and some passenger cars. They supply BMW, Ford, GM, Fiat/ Jeep/Chrysler, and Maserati. And yes, some are weaker, and some are stronger than others. it all depends on the application. after all the axles in a Chevy Equinox, don't need to be as strong as the axle in a Maserati.

Fun fact. Many ring gears are no longer bolted on. They are welded. However you still have to change both the ring, and pinion if you ever need to replace one or the other. They are married together through a process called Lapping.. During which they are run together with a abrasive compound spraying on them, under high torque to "wear" them together, so that they will run quietly. Then they are put into a testing machine to see if they indeed make noise. If they pass they go to the next step, if they fail. they are scrapped, and sent back to be melted down.
Then when they are put into the axle, they are tested for noise again. It is a very interesting process, well at least for the first year.
So if you have one of the makes we made axles for.. and it moves when you press the gas. You can thank.... me. LOL

BTW. Each gearset has 2 sides. A Drive side, and a Coast side. and they are exactly what they say. But in general. One side is always harder to get right. If your vehicle is quite going down the road, but roars when you let off the gas. You have a problem on the coast side.
So do you think there is an appreciable difference in the HD truck axles among the big 3?

It doesn't really matter in this conversation if a Maseratti has stronger axles than a Yugo. I would expect that to be the case.


I merely answered your statement that all manufacturers used the same steel, and all have the same quality . Short answer is. they do not. There is a vast amount of difference in the steel used by each company. Some steel is brittle, and some isn't. some have to be shotpeened to relax the steel so it doesn't break. It isn't all the same.
Could it be that one company or the other used a more brittle steel for a while? Yes it is entirely possible. Ford had a recall on the ring, and pinions in the 2004 F150s, because of bad steel.

* This post was edited 06/16/21 07:33am by Terryallan *

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