Why 4.1 axle?

[solismaris]

I tow an 8000 pound trailer with a GMC 2500 with 6.0l engine, 4 speed transmission, and 4.1 axle ratio. I rarely need 3rd gear on the highway; only on steep hills.

For my next truck, why not get similar engine but a 3.7 ratio? (For better economy when I'm not towing.) My reasoning is I can just use a lower gear if necessary. With the new 6-speed transmissions now common there should be plenty of gears to chose from. If that would work, why suffer the lower economy of the 4.1 ratio when I'm not towing?

[Grit_dog]

^Except those 2 engines have never been in a HD GM truck and the Ford 6.2 I don't believe has AFM either. 6.4 Ram does, but he!!, the wife's 6.4 SRT Charger can't get 20 mpg commuting. Barely over 20 just driving the speed limit on a flat road!
And 17-18mpg in any HD is either a pipe dream, your commute is 52 mph down a straight farm road in a 2wd or you're a moving traffic hazard!

Love people's mpg claims.
Remember there's 3 things most men lie about... The size of their ____, the size of the fish they caught and the fuel mileage of their truck!
Of course we are on geezernet. A guy might be able to get 17mpg on occasion in a HD by hyper miling with the wind at your 6. The rest of the world has to get somewhere before they have another birthday, so 17mpg in a 3-4ton pickup is not happening anywhere but in someone's mind.

[blt2ski]

If you can get the 6.2 or 5.3 with the cylinder shut off in a 2500, then you should be able to get 20 mpg in cruise at 60-65mph. Without that option, you will be a bit short, probably 17-18.x frankly.

Marty

[Grit_dog]

Only way you’ll get anywhere near 20mpg commuting in a HD pickup is downhill or hyper miling a diesel.
Seriously.

[solismaris]

So many responses! TMI - almost!
Seriously, this is all great. I'll definitely do the math and work through all the ratios (engine, transmission, axle, tire size). These new many-speed transmissions may change things a lot!

But the irony? My question was to help me decide which axle ratio to order, only to have it pointed out to me that GM has taken away the option and only delivers the gas 6L in a 4.1 ratio! Decision made!

The hope was I'd be able to drive a single vehicle, getting 20 average mpg commuting while still dropping to the necessary 8.5 when towing. (I get 14 commuting now with my 2004 GMC 2500.) And maybe the right axle would help achive that. Doesn't look like it though.

[K3WE]

After having fairly similar vehicles with 3.42, then 4.10, then 3.57: I noticed relatively little performance differences in them. I do not deny that there is a slight mathematical and mechanical advantage and RPM difference, but the message here is that the final drive tends towards hair splitting and fine tuning.

It DOES depend- I was towing near the vehicle's maximum capacities- and we spent a lot of time downshifted with the gas engine at 3000 RPM- I actually MISSED the 3.42 to make that 3000 RPM a little slower...Your experience may vary.

Indeed, new multi-speed transmissions make the choice of the final drive much less critical and even more in the hair-splitting / fine-tuning realm.

[valhalla360]

JRscooby wrote:


Like I have said before increasing the number of gear ratios in the transmission helps keep the engine in the preferred RPM range. At say 60 MPH, you have more choices of gears. But to increase the speed, from say 0-5 or 55-60 the whole driveline other than engine takes more stress with the higher speed gears. Now if under the rating, the increase in stress will not be a issue, but it is still there.

Again, yes they can increase the ultimate towing load (I've said this at least half a dozen times now)...but that does assume you've looked over the entire truck and made sure there isn't another weak link limiting the capability.

Bigger point for 99.99% of this discussion: assuming you are within limits, no it doesn't improve the towing experience on newer trucks. The new transmissions are better able to create the ideal gear ratio to match the engine and load as opposed to trying to manually beat it by swapping out the rear end and no you don't have to worry about the stress causing a failure.

[JRscooby]

BenK wrote:
Folks should go out and ride a bicycle with multi speeds/gears

"You" are the power source, with a rating/specification that has a red line and max torque


You wish to cruise at 10 MPH

On the flats...a higher gear ratio (lower numeric) is best

On an incline...a lower gear ratio (higher numeric) is best

Then there will be many gear choices in between those low and high gears...a personal choice and dependent on your physical abilities...

Sure wish more folks cycled...

Bicycle can work to make my point. Put the chain on the smallest sprocket on the rear wheel. Now find a hill that takes every pound of force you can muster to start the bike moving. Now move the chain to the largest sprocket, you can't make the bike go on that hill. On less of hill, but a bike in less good shape, say the rear axle a little loose. With the chain on the small sprocket, the bike takes off fine. But if chain on the large sprocket, if you try to force the bike to move, the axle is likely to slip.

valhalla360 wrote:

Grit dog wrote:
8 pages in, those that still do t understand torque multiplication should drop this thread and go back to playing soduko and tending to their muffler bearings!

But their grans pappy put in a different rear end to make his 1949 pickup tow more, so it must still be true today.

Not exactly. I have personally changed rearend ratios to make the truck tow more. And once because it cost less than rebuilding a rearend I put a higher ratio in a truck, and found I had to reduce load to go where I had gone before, and broke parts. Rebuilt and reinstalled, had no more issues.

Unless you are exceeding the tow ratings, all the blather about drivetrain stress is irrelevant as the engineers already designed it to handle that stress.

I guess the FACT the engineers call for a lower speed gear to increase the tow rating shows they understand that it is not "grandpa's science".

valhalla360 wrote:

Grit dog wrote:
Fwiw, granpappys 1949 philosophy is still 100% applicable today, so you don’t understand either. Thank you please play again soon!

No it's not the same by a long shot.

Yes, the basic physics of gearing is still true but the new 8/10speed transmissions drastically change the overall picture.

Like I have said before increasing the number of gear ratios in the transmission helps keep the engine in the preferred RPM range. At say 60 MPH, you have more choices of gears. But to increase the speed, from say 0-5 or 55-60 the whole driveline other than engine takes more stress with the higher speed gears. Now if under the rating, the increase in stress will not be a issue, but it is still there.

[valhalla360]

Grit dog wrote:
Fwiw, granpappys 1949 philosophy is still 100% applicable today, so you don’t understand either. Thank you please play again soon!

No it's not the same by a long shot.

Yes, the basic physics of gearing is still true but the new 8/10speed transmissions drastically change the overall picture.

[Grit_dog]

Fwiw, granpappys 1949 philosophy is still 100% applicable today, so you don’t understand either. Thank you please play again soon!

[valhalla360]

Grit dog wrote:
8 pages in, those that still do t understand torque multiplication should drop this thread and go back to playing soduko and tending to their muffler bearings!

But their grans pappy put in a different rear end to make his 1949 pickup tow more, so it must still be true today.

Unless you are exceeding the tow ratings, all the blather about drivetrain stress is irrelevant as the engineers already designed it to handle that stress.

[blt2ski]

Scooby,
The OP is not going to be cha going out gears etc as you are implying. His only thing he may be able to change, is axle ratio from the factory. Either 3.73 or 4.10. Everything else is the same. With 3.73, his overall low is around 24.5-1. With 4.10s, 27-1 overall low.
4.10 he has 10,800 ft lbs of torque hitting the pavement, with 3.73 9800 ft lbs. Any and all of the components speed by GM engineers should handle the torque etc produced by his motor, trans, rear gears etc.
He has around a 30-31% max grade at 20,000 lbs gcw with 3.73 gears before stalling out. With 4.10s around 33-35%. @ 60 mph, in DOD with 3.73, rpm ~1400, w 4.10rpm ~1600. Current setup @ 60 ~1800 rpm.

Marty

[BenK]

Getting lost in the weeds of detail...PM asking for explanation because you guys have lost them in the weeds

HP = torque x RPM / 5252 is the formula to figure HP (and is how much work it can do)

Gear boxes...from the tranny connected to the ICE, to the transfer case (if there is one), to the differential all have gear ratios that play with each other...or modifies their input shaft torque/HP by the gear ratio and some times changed direction of that rotation

Example using an even number for discussion : 100 ft/lbs of torque at the ICE flywheel or flex plate

1st gear of any tranny is, say 6:1. Means that 100 ft/lbs is multiplied by 6, to have 600 ft/lbs at the tranny output shaft

To the transfer case, but let's say there isn't any for this discussion

To the drive shaft that connects to the diff input shaft with 600 ft/lbs of torque

The diff has a 3.73:1 gear ratio. Means that 600 ft/lbs is multiplied by 3.73, to have 2,238 ft/lbs as it's output, plus this gear box changed direction by 90* and splits it to two axles, both having the same torque...that will change if open or LS or locker, but forget that to keep it simple...

This is the OP's topic/question...why a higher numeric ratio...it provides more torque because it has a higher numeric multiplier 4.1:1, which will provide 2,460 ft/lbs

I'm planning to go to a 5.3:1 on when update my Sub, which will provide 3,228 in this example

Each of these gear boxes also changes their input RPMs to the diff by their gear ratios. Therefore, an increase in HP, reference the formula posted above

Just using 1st gear. The other gears inside any of these gear boxes will have different ratios and might have an over drive, so the gear ratio might be 0.7 or something like. So multiplying the torque or RPM by that number will have less torque and less RPM at the output shaft


So what these guys are talking about are various tranny's (gear boxes) and their different gear ratios that then has different ft/Lb multiplications from their input shaft to output shaft.

Another point being discussed is the 'spread' of ratios from 1st to 2nd to 3rd...etc. This is to keep the ICE spinning in it's best RPM range (often referred to as 'power curve'). This varies from type of ICE, to the architecture of that ICE. Most ICE's for this discussion spin up to around 5K-7K, whereas an ICE with a Desmodromic valve architecture (no springs or rocker or push rod) can spin up to or well over 16,000 RPM. There are some very specialized ICEs with OHC that can spin up there, but they are F1 types, which cost in the $1Million per engine range


So in 1st...it has the highest multiplier ratio, but will run out of RPMs (red line) and then the tranny needs to shift into 2nd, a higher (lower numeric) ratio to continue the process...all the way up to the top gear (1:1), then into OD if your tranny has one or them...

[JRscooby]

blt2ski wrote:
Scooby,
Yes your overall low of 36-1 example of a 3 @ 12-1 setup will have more stress on given components than any of my 4 examples totaling 24.x-1. Yes 36-1 will get a given load moving easier, up a steeper grade etc. My 10.08 trans with 4.33s in my Navistar will get things moving easier than any of yours or my examples. The OP does not have these options.
I did give the two final drive ratios for the 3.73 @ 4.10 option the OP is looking at, either will not stress his setup. One barely meets grade I mentioned, the other will. If he only need to pull a 25% grade, both will do so with cushion!
At the end of the day, what will or will not work for your needs is what one should pick from a drive train standpoint.
Marty

Ok, you want to keep the overall ratio at 24-1. Let's use a 6-1 trans, 4-1 rear compared to 8-1 trans 3-1 rear and 12-1 trans and 2-1 rear. All will take the same engine torque, and multiply it by the same amount. But if say the drive shaft turning the 4-1 rearend is handling all the torque it can, but moving the load, change to the 2-1 it will break. But if you instead change the trans, and keep the 4-1 rear there will be no more strain on the shaft, because the load moves

[blt2ski]

Scooby,
Yes your overall low of 36-1 example of a 3 @ 12-1 setup will have more stress on given components than any of my 4 examples totaling 24.x-1. Yes 36-1 will get a given load moving easier, up a steeper grade etc. My 10.08 trans with 4.33s in my Navistar will get things moving easier than any of yours or my examples. The OP does not have these options.
I did give the two final drive ratios for the 3.73 @ 4.10 option the OP is looking at, either will not stress his setup. One barely meets grade I mentioned, the other will. If he only need to pull a 25% grade, both will do so with cushion!
At the end of the day, what will or will not work for your needs is what one should pick from a drive train standpoint.
Marty