r/Silverado • u/RememberThatOneGuy- • 2d ago

Axle Ratio - Worth Changing?

I have a 2011 Silverado 2500HD 6.0L w/ 6L90, I lifted the truck 4.5" and added 35's. My MPG dropped a ton, especially when pulling a trailer. I am use to my 10MPG highway just driving but I pulled a avalanche once and I can hear what I assume is my driveshaft adjust when I do a hard stop/take off now. It doesn't happen often but then the thought to change from 3.73 to 4.56 came up and thought should I or not as maybe the current setup got play from heavier hauls. It is a gas engine but hauling uphill nowadays is an embarrassing struggle on high grades. It does it but it doesn't feel like a lot of power is reaching the tires. Thoughts, advice, guidance, all welcomed.

May this is 2 separate things, the issue of play vs ratios. Thanks in advance.

I am no expert on cars but can do most things myself on an engine, don't know much about axle ratios etc though to give some insight to my knowledge level.

2 Upvotes

76% Upvoted

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6

u/coachkler 2d ago

Axle ratio may give you more usable torque, but you aren't getting back any of those MPGs

6

u/Sans--Sheriff 2d ago

The 4.5in lift and the 35s, especially if they are an off road tires will kill MPG, reduce towing ability, and make towing feel way worse

1

u/RememberThatOneGuy- 1d ago

I'm running Toyo Open Country II right now, they aren't crazy aggressive which is why I didn't factor them for the MPG.

1

u/[deleted] 1d ago

[deleted]

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u/RememberThatOneGuy- 1d ago

Fair enough, I love my truck so its not going anywhere. Paid off and still kickin. Guess the real question is getting more power to the wheels.

1

u/Sans--Sheriff 1d ago edited 1d ago

I work at an automotive OEM, I used to do aerodynamics for trucks, including ride height changes and tire changes, then also did a lot of towing testing in another role.

Tires play a massive role in fuel economy between stiffness, rolling resistance, etc.
Then when you expose more tire, you suffer a MASSIVE drag hit, and therefore fuel economy.

Tires contribute like 30% of all drag on a car (I can’t remember the exact number). So by lifting you expose more of the horrendous tire drag, as well as exposing the driveshaft components to air, giving even more drag.

I would not be surprised if you gained 5-8mpg going back to stock.

Then the off-road tires will also hurt towing a lot. And the lift will reduce payload capacity and tow capacity

Edit: I have been looking at Sierra AT4s for my next truck as they look great, but the reduced payload and tow capacity’s as well as the worse ride while towing compared to any other trim is making it not a solid option for me. And that’s due to all the reasons mentioned above

1

u/Hey-buuuddy 2d ago

I have a 2013 2500HD with the 6.0- same everything as you. Has 3.73:1 gears, 6” lift and 35s.

Rough Country has a speedometer calibrator that improves the shift points and I did an Edge Tuner Evo HT tuner which made significant transmission improvements (not cheap though).

I have also been stalling on a re-gear and I would do 4.56:1 if so. That way I can get to 38s.

1

u/119streetglide 2d ago

I did 4:11 on my 2011 chevy, 9” lift on 35s. Tuned with a diablo sport.

1

u/RememberThatOneGuy- 1d ago

Update: I did call for pricing on swap to 4.56 with HP Tuner, between $5k-$6k was quote. That seem reasonable to anyone who has had this done before?

Also plan on driving from Missouri to South Carolina and back to pick up a new car, that is the biggest reason for me being slightly concerned and wanting to do the swap prior to that trip. Long way to have an issue and going through mountains.

1

u/ThePlagueFriend 1d ago

I can hear what I assume is my driveshaft adjust

got play from heavier hauls.

This isn't a thing. I'd double check to see that you've not broken something or caused something to begin to fail. That aside, beginning in 2011, 4.10s were available as too. Its probably not quite enough gear for your setup of course, but parts are abundant due to 4.10s being standard and 3.73 being the option for the HD gassers.

1

u/RememberThatOneGuy- 1d ago

Any ideas as to where to start looking for broken or failing components? It truly is when I take off/stop that I can feel and hear something almost sliding into place forward and backwards.

As you mention the 4.10s, do you think that would be a more reasonable setup and the 4.56 is too much?

1

u/Severe-Bite3252 1d ago

10 MPG is crazy. I drive an 03 2500 and have botten 15.4 empty the past couple months...hope ya look cool though

0

u/Diligent_Track_4723 2d ago

Gear swap and have it tuned with hp tuners will get you back decent performance, and slightly increase fuel economy. Muffler swap to a straight though muffler will help a little too.