# Axle Ratios: 3.7 Vs. 4.1.....



## WhiteSoxFan

All,

I've been looking for a used 3/4 ton Suburban to upgrade from my 1/2 ton (we pull the 28 RSDS). Boy are the 3/4 tons hard to come by! I have found one or two of the 3/4 ton with the 3.7 rear end and I'll I've heard about on this site is how the 4.1 is better. My question is, is the 4.1 rear end considered a "must have" or "nice to have" when pulling a fairly loaded (with our stuff) 28 RSDS. Since the trucks are so hard to come by to begin with, I don't want to begin to exclude certain models if I don't have to.

One dealer I spoke to said that the axle ratio really only matters from acceleration to about 20 mph. Once you get over 20 mph and towing, the axle ratio makes no difference. Is that true? As I've mentioned before on this site, I know very little about cars/mechanics.

Thanks again for all the imput!
Tony


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## Zymurgist

Hi Tony,

It will depend on the engine that you couple with that rear end. Take a look at the 'Burb weight ratings in the towing section of the manual.

With the 6L engine you would want to lean toward the 4.1 rear, with the 8.1L (depending on where you are travelling) the 3.73 should probably suffice.

We have a new (to us) '04 Yukon XL 2500 with the 8.1L 3.73 Rear, we are getting 11.5 normal and about 9.5 towing MPG, and it handles our 28 rs-ds well. Of course I haven't pushed it hard as we don't really have BIG hills or mountains in this part of the state.

Clear as mud isn't it? If you need the ratings we can take a copy out of our GMC manual, those numbers should at least get you close. I can copy and PDF them to you if you want.

Good luck in your search
Carl


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## map guy

Depends on the year and engine/tranny combination. Trailer Life website has tow rating guides for current and past years available -might want to check it out. Generally speaking factory installed towing packages with the 6.0 engine have the 4.10.

Map Guy


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## battalionchief3

I have the 8.1 with the 4.10 rear and I get the same gas mileage as the 8.1 with the 3:73 more or less. I have no problem on hills. 20mph???? Yeah good gears and torque get you off the line but come on.....why do vehicles slow down going up hill then? I can pick up speed going up hill, yeah, gears are important along with a big engine. No replacment for displacement. I learned the hard way about buying to small just to get by. Find the biggest, baddest truck or suv you can find, that way you can tow anything at anytime and you will never be sorry.


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## California Jim

I would say that the 8.1 engine with the 3:73's would do fine if you can't locate 4:10's. Although I would not wan't the 6.0 with 3:73's.

I currently have the 6.0 and 4:10's in my new Burb and feel that this combo is making acceptable but not impressive torque.


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## campmg

I agree with the others and Cal Jim. I have a 3/4 ton Yukon XL. When I went looking the dealer actually had two on the lot. One with the 8.1L and 3.73, the other with 6.0L and 4.10's. I didn't know what to do so picked the one with less milage and certified by GM. I have always questioned having much of a difference with the 4.10 gears. I tow a lot up the moutians and still struggle on the biggest grades. I can't say if the other set up would have worked better though. Mileage is about ~13mpg and ~9mpg towing. Maybe go with the 8.1L and 3.73 and see what you think. You can always change the gears out for about a grand if you want to later.


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## JimWilson

WhiteSoxFan said:


> One dealer I spoke to said that the axle ratio really only matters from acceleration to about 20 mph. Once you get over 20 mph and towing, the axle ratio makes no difference. Is that true?


No. The drive shaft is still turning X number of times per full tire rotation, regardless of how fast you're traveling. The benefits/liabilities you get a 20MPH are, relatively speaking, the same as when you're going 60. If you ask me, I think what he said is inaccurate.

As the others have said, engine size makes a big difference. If you can get a larger engine and higher gear ratio (lower numerically) you'll probably be happier. But depending upon what your trailer weighs the 6.0 with a 3.73 is no slouch. I don't know about pulling the Smokey Mountains, or the Rockies, but it should be strong just about anywhere else.


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## Carey

A 4.1 gear will give about a 300 rpm increase over the 3.7 gear.

BUT, next thing. The 8.1 uses a 5 speed Allison, and the 6.0 uses a 4 speed gm tranny.. I dont know the final gear ratio for these trannies off hand.

If both of these trannies are towing without overdrive, they would both be at a 1 to 1 ratio. Here you will see a 300 or so rpm difference on your tach, between 3.7 and 4.1.

The 6.0 would be the one needing to be using 1 to 1 ratio, comparred to the 8.1 which quite possibly could tow in overdrive. The 8.1 could tow in overdrive easier if it had 4.1 gears.

The 8.1 makes peak torque at 3200 rpm.

The 6.0 makes peak torque at 4200 rpm..

The 6.0 REALLY needs a 4.1 to be more tow friendly.

The 8.1 could use either. The difference in gears wont be felt as much as it would with a 6.0.

The 8.1 is a slow winding big block.. The 6.0 is a high winding small block.. Either would be fine, Its just the 6.0 will need to be kept higher in rpm's to feel its power..

Carey


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## Carey

JimWilson said:


> One dealer I spoke to said that the axle ratio really only matters from acceleration to about 20 mph. Once you get over 20 mph and towing, the axle ratio makes no difference. Is that true?


No. The drive shaft is still turning X number of times per full tire rotation, regardless of how fast you're traveling. The benefits/liabilities you get a 20MPH are, relatively speaking, the same as when you're going 60. If you ask me, I think what he said is inaccurate.

As the others have said, engine size makes a big difference. If you can get a larger engine and higher gear ratio (lower numerically) you'll probably be happier. But depending upon what your trailer weighs the 6.0 with a 3.73 is no slouch. I don't know about pulling the Smokey Mountains, or the Rockies, but it should be strong just about anywhere else.
[/quote]

The driveshaft is behind the tranny. The final driveshaft speed is controlled by the differential gears. 
Yes both sets of tires will be going the same speed, as well as the axles in the differential. But the gears in the diff control the revolutions of the driveshaft, which is continued thru the tranny, then to the engine, which will be spinning faster with 4.1 and slower with 3.7, reguardless of what gear you are in..

Carey


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## Rubrhammer

Cary gives a good breakdown of how much difference in rpm gearing makes. The other good point he makes is the peak TQ rpm of both engines. Gearing WILL make a difference at ANY speed. 4.1 gears willhelp your engine stay nearer its TQ peak in every gear.
I changed my own gears in my truck this spring. I went from 3.42 to 3.73 BUT I also went to 65 series tires on the back from 70 series. This gives me close to the equivalent of 3.90 gears IF I were useing the taller(by 1 inch) tires. I can feel the difference. Now at 63 mph I am turning 2000 rpm in OD. Previously I was turning 1604 RPM. I could alwys feel that the engine made moreTQ at 2000 rpm now cruising at that RPM it hardly ever downshifts.
My point here is this; if you find that after buying a truck you need some more grunt you can 1. change gears and or change the rear tire size. My tire change affects my spedo by 3 MPH. I checked it against my gps and some radar signs so now that I kow it I can drive accordingly. With the tire deal when you aren't towing swap the fronts to the back to regain your mileage if you want to.
Bob


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## Scoutr2

I'll agree with Carl, Jim, and the others. I have the 6.0L engine with the 4:11 rear end in my Crew Cab pickup. It pulls well, but does lose some speed toward the top of long, steep grades. It maintained at least 60 mph on any hills we climbed through KY, TN (Smoky Mountains), GA, AL towing our 29BHS a month ago, though. But with the 3:73, I'm sure it would have struggled somewhat.

The 8.1L is a brute, so you would be able to pull well on hills with the 3:73 and still get a little better fuel economy when not towing than if you had the 4:11 rear end. Either one will do fine, but the 4:11 will add about 300 engine rpm at 65 mph - which does affect fuel economy.

Now a Crew Cab Diesel with the Allison Trans. is sweeeeeet! But pricey, even used.

Good luck with your decision.

Mike


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## battalionchief3

I drive a 8.1 with the 4L80E....4 speed auto, the Allison 5 speed did not come out till later and I tow in OD, all the time with no problems. It drops to 3rd up grades and holds it but it never goes into 2nd with those 4:10 gears. I dont know about a slow winding big block, it does a good job. I actuall have been driving suburbans with the 6.0 and 8.1 with different gears for 10 years. Once again their is no replacement for displacement. 4:10 gears make a difference and I see no remarkable change in gas mileage. They are correct you can always swap the gears and fix the spedo so its correct. Buy big, 4:10 gears and pull what ever you want.......Unless you can find a diesel


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## azthroop

We also have the 8.1L with 4.10 gears. We pull a 31RQS and need everything we can get. I can't imagine going smaller and without the 4.10's. BTW, if you get a 'burb, talk to Battalionchief3, he steered me right when it came to getting the tranny cool. I copied him and added a large (and I mean large!) tranny cooler and extra deep tranny pan. Go BIG. I don't know about these other OB'ers, but I just don't even want to look at the mpg. It would make me sad and when I'm pulling I want to enjoy the trip!! I'll look at the bill when it comes a month later!


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## Humpty

WhiteSoxFan said:


> Boy are the 3/4 tons hard to come by!


Pete Moore Chevy in Pensacola, FL had 3 on ebay last week.


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## WhiteSoxFan

Thanks everyone. I found a dealer just yesterday in OH (I'm in Chicago area) who frequently has multiple 3/4 ton Chevy burbs/yukons. Righ now he has a 2005 Yukon 6L with 4.1 (48k miles) and a 2005 Suburban 8.1 with 4.1 (25k miles). The Yukon is listed for $3k less. All the features seem to be about the same on the inside and I can't tell too much about the exterior through internet pictures. I'll probably follow up with him and see if he can give more pictures.

Thanks again for all the help! I'll keep you posted on the decision. I'm heading out on vacation (without the OB) for a fishing trip to the boundary waters in a couple days. I may have some more questions later.

Thanks!!
Tony


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## WhiteSoxFan

Sorry to bump this up again, but I'm still trying to decide what combo I want to go with. I have found all combo's in either Suburban or Yukon: 3/4 ton, 6.0L with 4.1 or 3/4 ton, 8.1L with 3.73, or 8.1L with 4.1. The problems come into play as to where they are located. There is a 6.0L with 4.1 fairly close (less than 1 hour). There is a 8.1 with 4.1 in OH (I'm in Chicago). There is an 8.1L with 3.73 just north of Milwaukee (but pricey for some reason). There is an 8.1L with 4.1 in FL (priced 2500 less than the OH one and is a certified GM which comes with the balance of the factory warranty and the limited extened....the one in OH does not).

Right now, we do not pull through mountains and our trips are not too long. But at some point, we may want to take an extended trip (through mountains) and I want to make sure I have enough truck to do so. We're pulling a 28 RSDS. So, 95% of our trips are fairly short with little hills. ARGH!!

Sorry to babble, just not sure what to do!


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## campmg

I think you'll be happy with any one of those combos. The 8.1 with 3.73 or 4.10 gears will do a great job. If you get the 6.0 you should find the 4.10's. Since you have a larger Outback, you may want the 8.1 and take either gear depending on pricing and location. You never know when you may hit some big hills on a long trip.


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## NJMikeC

Somebody who tells you that the 4.10 gears only matter at 20MPH is dead wrong. They will help you maintain speed going up hills . It will inhibit the trans from shifting as much .


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## Rollrs45

battalionchief3 said:


> I have the 8.1 with the 4.10 rear and I get the same gas mileage as the 8.1 with the 3:73 more or less. I have no problem on hills. 20mph???? Yeah good gears and torque get you off the line but come on.....why do vehicles slow down going up hill then? I can pick up speed going up hill, yeah, gears are important along with a big engine. No replacment for displacement. I learned the hard way about buying to small just to get by. Find the biggest, baddest truck or suv you can find, that way you can tow anything at anytime and you will never be sorry.


x2 !!!

I won't even blink an eye when I'm ready to upgrade to a 5er.









Go big!!! If you go too small you will regret it.

Mike


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## WhiteSoxFan

Thanks again! I'm heading to pick up the new (used) TV this morning. I decided to go with the 8.1L and the 3.73 gears 3/4 ton suburban. Got a good deal and it was fairly close (Milwaukee). Thanks!


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## Travelers

The 8.1 with 3.73 will work great. Our 8.1 with 4.10 does a super job pulling the RSDS.

Other factors like if you use the AC, headwind, bikes, dogs, water in camper, full tank of gas, number of people in the vehicle, etc.. all contribute to the need for the bigger engine to pull with comfort.


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## Collinsfam_WY

Congrats on the new TV!!! You are going to love it!

-CC


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## Scoutr2

Good choice, at least IMHO. The extra wheelbase (about 18") will also help handling.

Congrats on the new TV!

Mike


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## California Jim

Good Luck !


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