4.10 vs 4.56

[gmartin1215]

I am going to upgrade my front and rear differentials from the 3.42s next spring after I save up so money. I was originally thinking 4.10. I was chatting with a local diff builder - one who has great reputation - and after we discussed my vehicle and what I plan to do with it, he has the strong opinion that I should consider 4.56. My truck is no longer stock and is running larger tires with aftermarket steel bumpers, plus I do tow a boat. The below list is what I sent to the builder, and after that he said go with 4.56. To me, that seems like it is too high and my engine will be revving higher at the 70-75 highway speeds, but he could be right with the weight of my vehicle and also that I am towing, and aerodynamically it's a brick.

Anyway, looking for some opinions on this 4.56 idea.

• 2009 Tahoe
• 5.3L
• 6L80, 6-speed transmission
• currently has the GU6 option code, 3.42 gears front and back
• No G80, but I do have the AAM Trac-Rite LSD.
• 285/75/17 tires, BFGoodrich KO3. Documented specs say this tire is 33.8". The actual diameter I measured is right at 33" from the ground to the top of the tire. The top of the tire was found by using a level and then crossing it with the measuring tape.
• Each tire weighs 63 lbs
• Each wheel weighs about 30 lbs
• Front after-market steel bumper with winch weighs about 250 lbs
• Rear after-market steel bumper weighs about 150 lbs
• The Tahoe has a 4" BDS lift
• The truck does get driven a lot in the city, but it also gets dirty.
• I do take it on some rough trails, but nothing really narrow and super bouldery that only a Jeep can do. I mean, it's a Tahoe, so it's big and wide and has limitations! Basically, just overlanding, and sometimes I take a small high-clearance trailer with me (like a small utility trailer). But it does go on rutted, rocky dirt roads with decent grades.
• I also use this truck to tow a large river raft and trailer. Sometimes I have a heavier load when heading out on a multi-day raft trip and taking a lot of gear.
• I do spend time on the highway with this truck, too. Sometimes towing my trailer. Last summer, I took the truck and two passengers while towing a multi-day raft on I-70 through the mountains. It was tough getting up to the Eisenhower tunnel and the tranny was screaming on a low gear in tow mode. Big trucks were passing me! But I am on the interstate with the truck on other times, so I do hit the 75 speeds (sometimes towing the trailer).
• Most of the time it is city or dirt road travel, but I do use the highways to get to other places.
• I do not have or plan to in the near future, tow a bigger RV camper, but that is not totally out of the question.

 

[intheburbs]

Only real downside to going to 4.56 is crappier gas mileage. Everything else is in the positive column.

I don't know the specifics of your truck with your tires, but if my math is correct, taking my Denali from 3.42 to 4.56 gears would change my engine speed at 80 mph from 2000 to 2700(ish) RPM. It's a 33% increase. Again, given the upsides - less stress on the transmission, better towing performance, better offroad performance - seems like a no-brainer to me to go to 4.56.

Besides that, the LS loves to sing. I've had my 2500 many times on I-70 in the mountains in 2nd gear, at 4000 RPM and 40 MPH up the steep grades.

 

[89Suburban]

@Marky Dissod

 

[RST Dana]

My vote 4.10 4.56 will have you really humming at 70 mph. Someone will chime in with great ratios/tire height comparisons before long I’m sure.

 

[Foggy]

33" tire. 75 mph. 6th gear 2500 rpms
4.56 ratio = 80 mph
4.11 ratio = 89 mph

 

[Foggy]

2100 rpm @ 75 mph with the 4.10 's

Of course if you are towing a boat or hilly you'd want it stay
in 5th gear instead of 6th. But this gives you an unloaded idea.
There's a bunch of diff gear/rpm calculators on line to compare.

Your 6L80 has trans gear ratios of: 4th 1.15, 5th .85, 6th .70 To 1



Now I want new gears... shhhhhhsshhhh
Been trying to figure out the differences for me too. I'd like to tow
in 5th gear at about 65 ish mph. Right now with 3.42 it's very hard
to keep 5th gear unless going downhill.. So I'm usually in 4th which
kinda sucks for mph towing... (my camper is a big brick!)

 

[Marky Dissod]

Sorry I'm late. Jus checkin ...
285/75R17 = 33.83" tall ... 6L80 ... 4.10 ... 80MpH
6th gear = 2185RpM . . . 5th gear = 2770RpM

285/75R17 = 33.83" tall ... 6L80 ... 4.30 ... 80MpH
6th gear = 2295RpM . . . 5th gear = 2910RpM

285/75R17 = 33.83" tall ... 6L80 ... 4.56 ... 80MpH
6th gear = 2430RpM . . . 5th gear = 3085RpM

The more axle gear it has, the better it'll tow, the better the city & towing MpG will be when you're easy on the go pedal, the more time it'll spend in 6th,
and the less time it'll spend in 5th or 4th, which also means the transmission will last longer with more gear.

Decide between 4.30 & 4.56 ...

 

[rdezs]

Just a note, your method of measurement of the tire height neglected to include the natural squat from the way to the vehicle. I think if you raise that tire off the ground and actually measured the diameter it would be as advertised.

Headed up to the Eisenhower tunnel....OMG... Yeah, I used to run that in a semi. Can't remember for sure, but what is that, 10 or 12,000 ft altitude? One hell of a long pull. If you do that a lot, or similar passes with 7% grades, the 4.56 will be a huge help. I wouldn't worry about the RPMs on the flatland doing 75.... Yes it will burn more fuel, but you kind of expect that anyway towing and whatnot. And I think the engine, transmission and cooling system will be much happier.

 

[Marky Dissod]

Just a note, your method of measurement of the tire height neglected to include the natural squat from the weight of the vehicle.
If you raise that tire off the ground and actually measured the diameter it would be as advertised.

It's a precaution to ensure that the speedometer always reads ever so slightly faster than actual.
No speedometer should ever read slower than actual.

 

[Joseph Garcia]

I am going to upgrade my front and rear differentials from the 3.42s next spring after I save up so money. I was originally thinking 4.10. I was chatting with a local diff builder - one who has great reputation - and after we discussed my vehicle and what I plan to do with it, he has the strong opinion that I should consider 4.56. My truck is no longer stock and is running larger tires with aftermarket steel bumpers, plus I do tow a boat. The below list is what I sent to the builder, and after that he said go with 4.56. To me, that seems like it is too high and my engine will be revving higher at the 70-75 highway speeds, but he could be right with the weight of my vehicle and also that I am towing, and aerodynamically it's a brick.

Anyway, looking for some opinions on this 4.56 idea.

• 2009 Tahoe
• 5.3L
• 6L80, 6-speed transmission
• currently has the GU6 option code, 3.42 gears front and back
• No G80, but I do have the AAM Trac-Rite LSD.
• 285/75/17 tires, BFGoodrich KO3. Documented specs say this tire is 33.8". The actual diameter I measured is right at 33" from the ground to the top of the tire. The top of the tire was found by using a level and then crossing it with the measuring tape.
• Each tire weighs 63 lbs
• Each wheel weighs about 30 lbs
• Front after-market steel bumper with winch weighs about 250 lbs
• Rear after-market steel bumper weighs about 150 lbs
• The Tahoe has a 4" BDS lift
• The truck does get driven a lot in the city, but it also gets dirty.
• I do take it on some rough trails, but nothing really narrow and super bouldery that only a Jeep can do. I mean, it's a Tahoe, so it's big and wide and has limitations! Basically, just overlanding, and sometimes I take a small high-clearance trailer with me (like a small utility trailer). But it does go on rutted, rocky dirt roads with decent grades.
• I also use this truck to tow a large river raft and trailer. Sometimes I have a heavier load when heading out on a multi-day raft trip and taking a lot of gear.
• I do spend time on the highway with this truck, too. Sometimes towing my trailer. Last summer, I took the truck and two passengers while towing a multi-day raft on I-70 through the mountains. It was tough getting up to the Eisenhower tunnel and the tranny was screaming on a low gear in tow mode. Big trucks were passing me! But I am on the interstate with the truck on other times, so I do hit the 75 speeds (sometimes towing the trailer).
• Most of the time it is city or dirt road travel, but I do use the highways to get to other places.
• I do not have or plan to in the near future, tow a bigger RV camper, but that is not totally out of the question.

Great discussion here, with some great responses, from technical to practical perspectives. Time for you to decide which way to go.

I decided on 4.10 gears, but I don't overland or tow anything significant. The front differential and rear axle are currently being built, and I anticipate the project to be completed in the next 2 weeks.

My truck is a street machine, so for me, it will be more smiles per mile/gallon.

 

[Foggy]

I think the OP has left the chat or doesn't have his little notifications
set up to know people are helping !!!

 

[gmartin1215]

Thanks everyone who has provided the good feedback to consider.

@rdezs , yeah Eisenhower as at about 11K feet. I live along the Front Range, so I am always pulling through the mountains if I am trying to go west. I started looking at other passes to drive through, even if it takes me a longer to get there. I hate I-70, but sometimes it's unavoidable.

The diff builder was telling me that he thought 4.10 to be on the low end of the power band and 4.56 would be more optimum. But that had me wondering about performance at highway speeds (most highways I drive are at 65, except for the interstates at 75). I get that it's a trade-off; eIther have better low end for towing/climbing, or better mileage for the flats. Anyway, I wanted to get all of your opinions since everyone here is more familiar with these trucks than the diff builder. I have seen many on other posts mention 4.10s, but I had not seen discussions about anyone running 4.56s, so that also had me wondering why there has been a preference to 4.10s.

Having 4.10 for street use makes sense, or even 3.73. I know @Tozan mentioned he had 4.88s at one time and hated them, and then decided to go down to 4.10s. His truck build is not too far off from my build.

 

[gmartin1215]

Just a note, your method of measurement of the tire height neglected to include the natural squat from the way to the vehicle. I think if you raise that tire off the ground and actually measured the diameter it would be as advertised.

Headed up to the Eisenhower tunnel....OMG... Yeah, I used to run that in a semi. Can't remember for sure, but what is that, 10 or 12,000 ft altitude? One hell of a long pull. If you do that a lot, or similar passes with 7% grades, the 4.56 will be a huge help. I wouldn't worry about the RPMs on the flatland doing 75.... Yes it will burn more fuel, but you kind of expect that anyway towing and whatnot. And I think the engine, transmission and cooling system will be much happier.

Good point, about my measurement method. I had not considered that! Will jack it up tonight to take the load off and remeasure with my method. I know there is also the method of marking the tire and ground, and then rolling one full rotation to get the circumference that is likely more accurate than my quick and dirty way of measuring. Anyway, you are probably right about the tire actually being at the documented specs.

 

[Marky Dissod]

If you'd like to really get cute, the more air pressure you use, the more the tire can POTENTIALLY grow as speeds increase.
This is why the precaution is to use the unloaded inflated tire dimensions, to prevent the speedometer from reading slow.
If it reads a lil bit fast it's ok.

 

[gmartin1215]

@swathdiver

 

[swathdiver]

The chart on the left is how your truck was originally configured from the factory rpms wise. On the left is how she is now with the same gears and taller tires:

Below are with your current tire running 4.10 and 4.56 gears respectively.

The 4.10 gearset with those tires is only about 50 rpms more than GM trucks with the NHT package: 6L80 and 3.73 gears and P265/70R17 tires. So 4.10s with your tires is similar to 3.73s and stock tires. The truck will handle the 4.56s with ease and like it, not for fuel economy, but less strain on the running gear and more tractive effort. Most guys running tall tires and 4.10s wish they would have gone steeper.

 

[gmartin1215]

The chart on the left is how your truck was originally configured from the factory rpms wise. On the left is how she is now with the same gears and taller tires:
View attachment 472467

Below are with your current tire running 4.10 and 4.56 gears respectively.
View attachment 472468
The 4.10 gearset with those tires is only about 50 rpms more than GM trucks with the NHT package: 6L80 and 3.73 gears and P265/70R17 tires. So 4.10s with your tires is similar to 3.73s and stock tires. The truck will handle the 4.56s with ease and like it, not for fuel economy, but less strain on the running gear and more tractive effort. Most guys running tall tires and 4.10s wish they would have gone steeper.

Thanks, man!

 

[Joseph Garcia]

@swathdiver IS the MAN!

 

[kbuskill]

@swathdiver IS the MAN!

It would seem James @swathdiver has a spreadsheet for everything... lol

 

[j91z28d1]

on much simpler terms, drive for a week in 4th gear and then drive around another week in 5th gear. if 4th doesn't bother you, then 4.56 will probably be fine.