3.08 to 3.73 Gear ratio on 2013 Silverado with 35s??

Matt2013LT · October 17, 2023

I currently have a 2013 Silverado CCSB 5.3 2wd with a 6.5 inch zone lift kit on 2020 Silverado 20 inch RST Wheels mounted on 35 inch trail grapplers! I currently have the crappy factory 3.08 gear ratio. As you can imagine, a truck with 35's with a 3.08 is an absolute dog! Holds gears until 2500 RPM, 6th gear is totally unusable over 60MPH, and 9.5 AVG Fuel Economy. AFM/DOD has been removed from the engine also.

When I first bought the truck in July 2021, it was a mostly bone stock 1 owner truck. It had the 17 inch alloys on 265/70r17 Goodyear wranglers on stock suspension. RPM's were relatively low with the 3.08, but of course, mostly stock! Averaging 13.2 MPG

I've recently have had to do some long distance driving & the low MPG + price of fuel is costing too much! For anyone that has knowledge on this, do you think it's possible to put a 3.73 gear ratio in with a 6L80E & 35s, and have lower RPM's, or is it best to go for a lower gear ratio like a 4.10+ ?? I'm just trying to get as much fuel efficiency as possible!

Any input would be great! Thank you

diyer2 · October 17, 2023

Back to stock tires and get rid if the lift for fuel efficiency. Bigger gears will give more torque but higher rpms. I don't think it will help with fuel efficiency.

CamGTP · October 18, 2023

Did you ever tune the truck for the new tire size? I would have hoped you did, but that alone wouldn't have really helped much with the mechanical disadvantaged you already had.

Going to 3.73's will help a lot, the truck will work less hard to get to the same speed. Ideally with true 35's you'd want 3.90's or 4.10's. But with a 6 speed auto you can get away with less gear, I'd go with 3.73's or 3.90's personally in a 6 speed.

Use an RPM calculator to figure out your highway speed cruising rpm. Look up the 6L80e's gear ratios, off memory 6th gear is something like .62 or close to that. Fuel mileage should go up a fair amount because the truck will require less throttle to maintain the same speeds with more mechanical advantage. And get it tuned for the new gear ratio.

Matt2013LT · October 18, 2023

4 hours ago, diyer2 said:

Back to stock tires and get rid if the lift for fuel efficiency. Bigger gears will give more torque but higher rpms. I don't think it will help with fuel efficiency.

I totally don't disagree! That would be most optimal for fuel efficiency! But I love a lifted truck! Just my preference though!

Matt2013LT · October 18, 2023

54 minutes ago, CamGTP said:

Did you ever tune the truck for the new tire size? I would have hoped you did, but that alone wouldn't have really helped much with the mechanical disadvantaged you already had.

Going to 3.73's will help a lot, the truck will work less hard to get to the same speed. Ideally with true 35's you'd want 3.90's or 4.10's. But with a 6 speed auto you can get away with less gear, I'd go with 3.73's or 3.90's personally in a 6 speed.

Use an RPM calculator to figure out your highway speed cruising rpm. Look up the 6L80e's gear ratios, off memory 6th gear is something like .62 or close to that. Fuel mileage should go up a fair amount because the truck will require less throttle to maintain the same speeds with more mechanical advantage. And get it tuned for the new gear ratio.

I honestly never got it tuned! I've only ever got the speedometer calibrated, but I've only driven it 10k miles since August 2022 When the lift + tire's were installed!

And you are correct, a gear ratio like a 4.10 would probably be more optimal (that option is still on the table) but even the gearing with 3.73's on 35's is even slightly better than 3.08's on 265/70R17's! The 6L80E has a 1st Gear Ratio of 4.03 and a 6th Gear Ratio of 0.67, so I also agree with you that the 6 spd still wouldn't mind the 3.73! The RPM's would also be quite low with the 3.73 according to the gear charts & calculators I tried!

I also will get it tuned at the same time as the new gear ratio. I should've got it tuned to begin with, but I for sure will when the gears go in for maximum efficiency.

swathdiver · October 21, 2023

On 10/17/2023 at 7:07 PM, Matt2013LT said:

I currently have a 2013 Silverado CCSB 5.3 2wd with a 6.5 inch zone lift kit on 2020 Silverado 20 inch RST Wheels mounted on 35 inch trail grapplers! I currently have the crappy factory 3.08 gear ratio.

...do you think it's possible to put a 3.73 gear ratio in with a 6L80E & 35s, and have lower RPM's, or is it best to go for a lower gear ratio like a 4.10+ ??

4.10s will help more around town, 3.73s will be better for the highway.

I have a lifted Sierra with the same Zone lift on 35s for ten years now. It came with 3.73 gears (NHT) which are the equivalent of 3.42s now with the 35 inch tires. When we get around to it, we're going to regear for 4.10s so that it's gearing will be back to stock with the 35s.

She'll get about 13-14 mpg on the highway and averages 10 in the city. It's a 6.2, tuned with a muffler delete.