Gear Ratio Change: Looking for Your Results, Comments

[Foggy]

For those of you that have changed gear ratios. What are your result/comments on what happened ??
I "think" I'd like to change out my 3.42's for some 3.73's gears in my AWD Denali..
I 'believe' this will allow me to tow in 5th gear instead of forth gear and stop the "hunting" between
4th to 5th and help my mileage and possibly keep my trans temps lower in the summer heat..
Of course with awd, I have to do 2 sets of gears (and rebuild bearings, etc) so it's quite expensive.

SO I don't know if it's even worth it at all... It just doesn't seem to be much of change % wise.
I've went thru all the gear calculators etc and it seems that the 4.11 option would be a little steep
when NOT towing and I'd hate to really screw my mpg.
I try to tow at about 62-67 mph on interstate and it's just not enough rpms to keep it in 5th gear
Of course when Not towing, My interstate speeds are 75-80 ish, so I'd hate to kill mpg as well with 4.11's

Looking for input from those that have changed gears and do some towing !!!!

 

[Marky Dissod]

THINK you'd like to upgrade from 3.42 to 3.73? Good, you DAMND WELL OUGHT TO upgrade to 3.73.
(Offset the cost of the upgrade by selling your 3.42 to someone with 3.08, they'll love you for it if they've the sense to do it)

It'll be worth it, it just won't pay off quickly. Improving your tow rating is not going to improve your UNLADEN MpGs.
It will however improve your metro/urban/city MpG, as well as your towing MpG.
More importantly, as you've already guessed, your transmission will last longer between rebuilds by shifting less often.

Your foot is responsible for how many miles per gallon you trade for however many smiles per gallon. 3.73 is definitely worth more smiles per gallon.

No, I don't tow, but I used to work with a livery service where I turned them on to the idea of replacing axles with lame@$$ gears, with axles with better gears
(and a basic tune from pcmperformance.com) for their GMT800 & GMT900 vehicles.

If you tow heavy enough, fast enough, and your tires are bigger by enough, 4.10 may not be so bad ... but definitely at least 3.73. You'll be so glad you did ...

 

[Foggy]

THINK you'd like to upgrade from 3.42 to 3.73? Good, you DAMND WELL OUGHT TO upgrade to 3.73.
(Offset the cost of the upgrade by selling your 3.42 to someone with 3.08, they'll love you for it if they've the sense to do it)

It'll be worth it, it just won't pay off quickly. Improving your tow rating is not going to improve your UNLADEN MpGs.
It will however improve your metro/urban/city MpG, as well as your towing MpG.
More importantly, as you've already guessed, your transmission will last longer between rebuilds by shifting less often.

Your foot is responsible for how many miles per gallon you trade for however many smiles per gallon. 3.73 is definitely worth more smiles per gallon.

No, I don't tow, but I used to work with a livery service where I turned them on to the idea of replacing axles with lame@$$ gears, with axles with better gears
(and a basic tune from pcmperformance.com) for their GMT800 & GMT900 vehicles.

If you tow heavy enough, fast enough, and your tires are bigger by enough, 4.10 may not be so bad ... but definitely at least 3.73. You'll be so glad you did ...

I'm def staying with the stock height tires. When I do tow, it's pretty heavy.
Even with my mods and HPTuned the mpg sucks (not as bad as when I had the SC though)
I kinda wish there was a middle ground between the 3.73 and 4.10.. my ford 9" rears in my gm car and truck have a 3.90 option... which I think would be perfect... but not offered in my front or 9.5" rear of my Yukon . ~

 

[swathdiver]

There used to be 3.90s for these but nobody seems to currently offer them. Kit bash it, 10 tooth pinion from 4.10 gear set and 39 tooth ring gear from a 4.33 or 4.88. Or look for 11 tooth pinion and 43 tooth ring gear.

I thought about that ratio too but just did what GM did with the 6-Speeds, 3.73s.

My 6.2 pickup with 3.42 gears is bone stock and tows like a beast. She doesn't hunt for gears while towing 5,000 pounds or 9,500 pounds. Neither does my other 6.2 pickup with 3.73 gears and she tows even more weight.

We did the swap to 3.73s and the 14-bolt Saginaw differential from 3.42s in the Yukon XL. She has a 5.3 motor and doesn't downshift anymore while crossing the steepest bridge in the county like she used to. Towing and getting off the line are easier and she's faster too. The gears allowed the motor to put down an additional 10 horsepower through the traps in the quarter mile at the drag strip. We've towed several times since the gear swap, over 7,000 pounds but it was all in town. It was effortless towing even still.

Is it worth it moneywise? That's a question every man has to decide for himself. It was an incremental difference over 3.42s but still a noticeable one nonetheless.

The truck has been on E85 almost exclusively since then and the difference in economy is small but still there. When you look at the chart realize that this truck now has 220K miles on it, save for the zero timed rear differential and the used front differential out of a 2008 Suburban with less than 150K on it.

After our next run to the drag strip, I'll put the truck back on gasoline for a bit to collect some more data.

At first glance, it looks like she's doing pretty good on gasoline with the 3.73s compared with the old 3.42s and with more data points, the difference is the other way but only marginally worse, what, a quarter mile to the gallon? A tenth of a gallon per hour difference in fuel burn? If I was maniacle about gas mileage the 3.42s might be the better choice.

My stock 6.2 pickup averages about a mile per gallon better fuel efficiency compared to the 5.3 in the Yukon XL. The 6.2 can make up for gears with more horsepower compared to the 5.3. But, you've already done that.

Have you talked to Dave @Geotrash ? Remember, he has the Yukon XL Denali with a cam in it that's towed a travel trailer all over the country and back.

 

[Geotrash]

Thanks for remembering, @swathdiver.

Towing a heavier camper as @Foggy does, I would be inclined to go with 4.10 gears over the 3.73's. I have the 4.10's in my 2018 Suburban 3500, and it's just enough to keep it in 5th most of the time on the highway when towing either of our campers, but I don't think that 3.73's would be - especially with a heavier camper. Yes, the 6.2 has more power than the 6.0, but only marginally so in the 2,500 RPM range (see below), which seems to be the sweet spot for towing. Fuel mileage is slightly better with the Suburban 3500, incidentally (maybe .5-1 mpg, depending on conditions).

FWIW, I spent a few hours some time ago calculating what my power output figures would be for both of my tow vehicles at 2500 RPM, from published dyno data on the interwebz. This is the best estimate I could come up with for each. As you can see, at 2500 RPM, it's about a horse apiece (almost quite literally, lol).

6.0L L96 ~ 190 hp, 370 tq @2500 RPM - w BB tune (6L90)
6.2L L94 ~ 190 hp, 380 tq @2500 RPM - w BB tune and Cam Motion Stage 2 Truck cam (6L80)

A couple of additional thoughts:

1/ I clearly remember @NickTransmissions mentioning that the weakest path through the 6L80 is 5th gear, so I tend to prefer running my 2012 in 4th most of the time, but it may not really matter. But the L94 doesn't seem to care much about the higher RPMs, so it keeps my mind slightly more at ease.

2/ The 6L90 has the same gear ratios but it has stronger internal components like extra pinion gears, beefier input/output shafts, and an extra clutch plate in each pack for increased torque capacity (up to 885 lb-ft) and higher GCVW ratings, so I'm less concerned about running it in 5th vs the 6L80.

 

[Foggy]

There used to be 3.90s for these but nobody seems to currently offer them. Kit bash it, 10 tooth pinion from 4.10 gear set and 39 tooth ring gear from a 4.33 or 4.88. Or look for 11 tooth pinion and 43 tooth ring gear.

I thought about that ratio too but just did what GM did with the 6-Speeds, 3.73s.

My 6.2 pickup with 3.42 gears is bone stock and tows like a beast. She doesn't hunt for gears while towing 5,000 pounds or 9,500 pounds. Neither does my other 6.2 pickup with 3.73 gears and she tows even more weight.

We did the swap to 3.73s and the 14-bolt Saginaw differential from 3.42s in the Yukon XL. She has a 5.3 motor and doesn't downshift anymore while crossing the steepest bridge in the county like she used to. Towing and getting off the line are easier and she's faster too. The gears allowed the motor to put down an additional 10 horsepower through the traps in the quarter mile at the drag strip. We've towed several times since the gear swap, over 7,000 pounds but it was all in town. It was effortless towing even still.

Is it worth it moneywise? That's a question every man has to decide for himself. It was an incremental difference over 3.42s but still a noticeable one nonetheless.

The truck has been on E85 almost exclusively since then and the difference in economy is small but still there. When you look at the chart realize that this truck now has 220K miles on it, save for the zero timed rear differential and the used front differential out of a 2008 Suburban with less than 150K on it.

View attachment 476537

After our next run to the drag strip, I'll put the truck back on gasoline for a bit to collect some more data.

At first glance, it looks like she's doing pretty good on gasoline with the 3.73s compared with the old 3.42s and with more data points, the difference is the other way but only marginally worse, what, a quarter mile to the gallon? A tenth of a gallon per hour difference in fuel burn? If I was maniacle about gas mileage the 3.42s might be the better choice.

My stock 6.2 pickup averages about a mile per gallon better fuel efficiency compared to the 5.3 in the Yukon XL. The 6.2 can make up for gears with more horsepower compared to the 5.3. But, you've already done that.

Have you talked to Dave @Geotrash ? Remember, he has the Yukon XL Denali with a cam in it that's towed a travel trailer all over the country and back.

Good Info ! Thank You
Yea Geotrash and I have exchanged info as well
I was mostly worried that such a small change wouldn't do enough
to really warrant the hassle and $$$$. Although I know it would be a little
peppier to drive
I've got my 14 bolt waiting in the wings. So If I do decide to change ratios, it's
already out and ready to be worked on. I'd have to take it to someone who does
gear set ups , along with the front diff of course.
Like mentioned , I think a 3.90 would be perfect - but not available

 

[Marky Dissod]

At first glance, it looks like she's doing pretty good on gasoline with 3.73 compared with old 3.42 and with more data points,
the difference is the other way but only marginally worse, what, a quarter mile to the gallon? A tenth of a gallon per hour difference in fuel burn?
If I was maniacal about gas mileage, 3.42 might be the better choice.

Carmakers are heavily incentivized by CAFE MpG test scores to think EXACTLY like this.
Every fraction of a mile per gallon matters to a carmaker, even though it's a very small price to pay for a transmission that will go longer between rebuilds.

 

[Foggy]

Thanks for remembering, @swathdiver.

Towing a heavier camper as @Foggy does, I would be inclined to go with 4.10 gears over the 3.73's. I have the 4.10's in my 2018 Suburban 3500, and it's just enough to keep it in 5th most of the time on the highway when towing either of our campers, but I don't think that 3.73's would be - especially with a heavier camper. Yes, the 6.2 has more power than the 6.0, but only marginally so in the 2,500 RPM range (see below), which seems to be the sweet spot for towing. Fuel mileage is slightly better with the Suburban 3500, incidentally (maybe .5-1 mpg, depending on conditions).

FWIW, I spent a few hours some time ago calculating what my power output figures would be for both of my tow vehicles at 2500 RPM, from published dyno data on the interwebz. This is the best estimate I could come up with for each. As you can see, at 2500 RPM, it's about a horse apiece (almost quite literally, lol).

6.0L L96 ~ 190 hp, 370 tq - w BB tune (6L90)
6.2L L94 ~ 190 hp, 380 tq - w BB tune and Cam Motion Stage 2 Truck cam (6L80)

A couple of additional thoughts:

1/ I clearly remember @NickTransmissions mentioning that the weakest path through the 6L80 is 5th gear, so I tend to prefer running my 2012 in 4th most of the time, but it may not really matter. But the L94 doesn't seem to care much about the higher RPMs, so it keeps my mind slightly more at ease.

2/ The 6L90 has the same gear ratios but it has stronger internal components like extra pinion gears, beefier input/output shafts, and an extra clutch plate in each pack for increased torque capacity (up to 885 lb-ft) and higher GCVW ratings, so I'm less concerned about running it in 5th vs the 6L80.

Good Info Geo !!!
I figure the 4.10 would always be better for towing heavy.... I am just concerned about
highway mpg as we take the Yukon on trips not towing. I'd really hate to totally kill
mpg. Although it would be a blast to drive around town with 4.10's !!!!!
I get your point about the transmission strengths. OD ratios are always way weaker
than the direct ratios. Too bad our 4th gear isn't 1:1 instead of 1.15:1...... I'd prob
be fine with stock 3.42
My trans is as beefed up as possible with over 3K of hard parts internally..
So I just don't know if this will "save" me from if I'm towing in 5th gear
IF I drive about 55-60 then 4th gear is fine. It's when I'm on interstate and
want to drive 65ish that 4th gear really rpm's up.. So I end up shifting to
5th gear on flats and slight downhills to drop rpm and up my mpg...
I was thinking that with 3.73s I could keep it in 5th most of the time and keep
my engine and trans temps down a bit too !!
This is like drag racing on my laptop !!!!

 

[Foggy]

Thanks for remembering, @swathdiver.

Towing a heavier camper as @Foggy does, I would be inclined to go with 4.10 gears over the 3.73's. I have the 4.10's in my 2018 Suburban 3500, and it's just enough to keep it in 5th most of the time on the highway when towing either of our campers, but I don't think that 3.73's would be - especially with a heavier camper. Yes, the 6.2 has more power than the 6.0, but only marginally so in the 2,500 RPM range (see below), which seems to be the sweet spot for towing. Fuel mileage is slightly better with the Suburban 3500, incidentally (maybe .5-1 mpg, depending on conditions).

FWIW, I spent a few hours some time ago calculating what my power output figures would be for both of my tow vehicles at 2500 RPM, from published dyno data on the interwebz. This is the best estimate I could come up with for each. As you can see, at 2500 RPM, it's about a horse apiece (almost quite literally, lol).

6.0L L96 ~ 190 hp, 370 tq - w BB tune (6L90)
6.2L L94 ~ 190 hp, 380 tq - w BB tune and Cam Motion Stage 2 Truck cam (6L80)

A couple of additional thoughts:

1/ I clearly remember @NickTransmissions mentioning that the weakest path through the 6L80 is 5th gear, so I tend to prefer running my 2012 in 4th most of the time, but it may not really matter. But the L94 doesn't seem to care much about the higher RPMs, so it keeps my mind slightly more at ease.

2/ The 6L90 has the same gear ratios but it has stronger internal components like extra pinion gears, beefier input/output shafts, and an extra clutch plate in each pack for increased torque capacity (up to 885 lb-ft) and higher GCVW ratings, so I'm less concerned about running it in 5th vs the 6L80.

So does your 6.0 with the 4.10's run in 5th gear while you are towing ???
Or do you keep it in 4th and rpm it ??

 

[Geotrash]

So does your 6.0 with the 4.10's run in 5th gear while you are towing ???
Or do you keep it in 4th and rpm it ??

It runs in 5th, 95% of the time when I'm towing. Occasionally I'll let it upshift to 6th when conditions are suitable. I rarely need 4th around here - especially towing the considerably slipperier (and lighter) Airstream.

 

[Geotrash]

Good Info ! Thank You
Yea Geotrash and I have exchanged info as well
I was mostly worried that such a small change wouldn't do enough
to really warrant the hassle and $$$$. Although I know it would be a little
peppier to drive
I've got my 14 bolt waiting in the wings. So If I do decide to change ratios, it's
already out and ready to be worked on. I'd have to take it to someone who does
gear set ups , along with the front diff of course.
Like mentioned , I think a 3.90 would be perfect - but not available

One more perspective that hit me this afternoon. The difference between 3.42 and 3.73 is a little over 200 RPMs at 2500 RPMs. But the difference between 3.42 and 4.10 is just over 400 RPMs.

At that RPM range, lots of things are happening. For one, you gain 35-40 HP (about 25% more) when you go from 2100 to 2500 RPM on a stock L94. Horsepower is what lets you keep your speed when going uphill. It's just enough when towing a camper with one of these things to avoid needing to downshift unless you're really climbing. And when I drop from 5th to 4th in my 2012 at 2100 RPM, I blow right past 2500 up to around 2,900. Yes, I'm making more power but I'm also making more noise and using more fuel. A 3.73 rear end would put me at around 2,300 RPMs in 5th, which isn't quite enough extra power, and then I'd be hitting 3,100-3,200 RPMs whenever I dropped to 4th, which would be more often.

When you're not towing and you're rolling 65 mph, holding 1,500 RPMs in 6th with the 3.42's, going to the 4.10's will add only around 250 RPMs in cruise because it's a ratio. So, just multiply any RPM you currently see with your 3.42's by 1.166 to see what you'd be turning with 4.10's.

Anyway, all of these observations is why I say that 4.10's are about perfect for towing with these, and the penalty when you're not towing is minor by comparison. I think I mentioned it, but my 1-ton Suburban with 4.10's gets slightly better mileage than my half-ton.

 

[Foggy]

I was towing my car/cargo trailer today.. It's about 2500 empty and 7000 full.
It's shorter and lighter than my travel trailer. But it gives me an idea of rpms/load etc
At 60 mph I'm right at 2500 rpm in 4th gear. Which as we know means that if I'm
trying to be around interstate speeds, I'd be at 2700-2900 around 65 ish.. Which
"seems" like too many rpm for extended driving (and mph sucking)...
5th gear with this trailer is decent. I can keep it in 5th on level ish ground at 60-65 no
problems.. But my camper is less aerodynamic and quite a bit heavier...
I'll take into account all the info given here and I'll have to man up and make a decision
between the 3.73 and 4.10 gear ratio !!

 

[Foggy]

And I'll add this to the equation: AS sooon as time/money permits I'll be replacing
my 6.2 L94 with a stroker LS3 which will be just a little less compression at 10.5:1
(to help with crappy gas) and 415 ci with all the 'good stuff' in it in case I want
to go back to a supercharger at some point.
I'm planning on using my current stock massaged cyl heads and my current camshaft
with the new engine. So maybe knowing that, the 3.73's would be enough with
the extra cubic inches ???

 

[strutaeng]

Run it on a lower gear and see what you think (which you already did)...2700-2900 rpm won't harm a thing. These engines absolutely don't mind the higher rpm, afterall, they come from a racing history.

I've had lengthy discussions with my buddy about HP, TQ, HP/TQ curves and RPM. I think what I came to conclude is your engine needs to operate close to, or between those peak HP/TQ RPM ranges, when towing near the maximum load...

Specifically, near peak TQ curve RPM (around 4,000 RPM) when pulling from a stop light, and near peak HP (near 5000 rpm) when trying to pass at speeds.

Look at those curves. If you try to keep your engine in the 3,000 rpm or less, it's barely "waking up" on the power department, for lack of a better term.

 

[Geotrash]

Run it on a lower gear and see what you think (which you already did)...2700-2900 rpm won't harm a thing. These engines absolutely don't mind the higher rpm, afterall, they come from a racing history.

I've had lengthy discussions with my buddy about HP, TQ, HP/TQ curves and RPM. I think what I came to conclude is your engine needs to operate close to, or between those peak HP/TQ RPM ranges, when towing near the maximum load...

Specifically, near peak TQ curve RPM (around 4,000 RPM) when pulling from a stop light, and near peak HP (near 5000 rpm) when trying to pass at speeds.

Look at those curves. If you try to keep your engine in the 3,000 rpm or less, it's barely "waking up" on the power department, for lack of a better term.

I agree with you. And, 2500 is a really nice, comfortable towing RPM. If I need to wind it out to 4000 or 4500 to get up a big hill and keep up with traffic, I have no problem with that, but I like it nice and calm and quiet when I’m just cruising along.

 

[Marky Dissod]

With that much (extra) displacement 3.73 would be perfect.

 

[West 1]

My 08 Denali with the 6.2L and 6L80 has 3.42 gears. I hate them. Even on the highway not towing when we hit inclines it downshifts right away. RPM is just too low for anything other than flat ground cruising. Wish it had 3.73 gears. I think it would help everyday and towing.

With that said I had a Tahoe with 4.10 gears, 5.3L and 4L60 so not a direct comparison but it was great but I thought I could push the MPG up if I had the 3.42 ratio. I bolted in a 3.42 and drove it for a couple months. The rig felt sluggish and i noticed zero change in my MPG. The only time I did not like the 4.10 gears was on an annual 800 mile one way trip to visit friends. On that trip across Nevada most cars roll 80-85, the 4.10s saw a big drop in MPG if I rolled faster than 75. I went quickly back to the 4.10’s and never looked back.

3.73 gears are a nice middle compromise but for all the expense needed to do this you might go straight to the 4.10 gears. You don’t want to do all this work and say it was not the right choice.

 

[Geotrash]

And I'll add this to the equation: AS sooon as time/money permits I'll be replacing
my 6.2 L94 with a stroker LS3 which will be just a little less compression at 10.5:1
(to help with crappy gas) and 415 ci with all the 'good stuff' in it in case I want
to go back to a supercharger at some point.
I'm planning on using my current stock massaged cyl heads and my current camshaft
with the new engine. So maybe knowing that, the 3.73's would be enough with
the extra cubic inches ???

That's going to make a great towing setup! Being able to run regular or even mid-grade is huge. Filling the tank with premium every 250-275 miles stings the wallet a bit more than I'd like.

I had Blackbear tune my Suburban 3500, and Justin had some helpful comments about how to run it. I had asked for a tune that would still allow me to run regular gas, and he was happy to oblige but noted that I should track fuel economy. He said I would likely find that the added mpg with mid-grade would offset the additional cost. I haven't been able to check it because I always run mid-grade.

On the gearing, all I can tell you is what I would do in the same situation. I'm sold on the 4.10's for towing duty, and I have seen no downsides when just hauling kids around.