Lower Gears Higher Highway Mpg?

wicked ace · March 10, 2011

What is engine rpm at 70 mph with 6 speed and 3.08 vs 3.42?

Babyhauler

About 1600 RPM with 3:08. 3.42 I would guess about 2000 RPM.

About 1800 w/ 3:42 rear.

wicked ace · March 10, 2011

3.42's get my vote, less effort and strain to get the truck upto speed. And if your not gonna use it at all as a truck, ever think about a suv?

An SUV comes at a substantial premium in cost with out the flexibilty of a bed. For me an extended cab works just right.

Michael1 · March 18, 2011

Top gear performance without forcing a downshift is where the numerically higher ratio will improve performance and in many cases improve fuel mileage. ie. 3.42 or even better 3.73

The overdrive ratios we have in modern transmissions put the cruise RPM too low and out of the torque peak when combined with 3.08 ratio. Get those RPM's up and improve mileage without excessive downshifting

This just is not true.

1) Torque peak and engine efficiency have nothing to do with each other.

2) Increasing RPM, increases pumping and friction losses, which lowers mileage. That's why the XFE doesn't have 4.10s.

You can prove all this yourself. Get on a level road. Get up to highway speed, let it shift into 6th and hold it. Make sure you are not gaining or losing speed. Check the instant MPG, or reset your average MPG over a stretch. Now force it into 5th gear, and watch the instant MPG drop (or reset average MPG again and retest).

Now if you are towing frequently, you main concern isn't mileage. It's having the torque to get the load moving, and that means lower rear axle gears (higher numerical). That's why the tow ratings are higher for the same engine and body style, with lower gears.

Michael

Mulaka · March 18, 2011

From my experience. I have the 4.8 and 3.42 and I am consistently getting 17-18 in the city and 20-21 Hwy easy.

terzmo · April 9, 2011

There was a big conversation about this recently I believe we decided the 3.42s were the best choice for mileage. "Most" agreed the 3.08's left the truck feeling underpowered.

I'm a "disagreer"...I have 308's...5.3/6speed....tow a loaded 1 car trailer...truck has plenty of power

I wouldn't go to 342's...410's on a bet..also upgraded from 17 ijnch wheels to 18 so I'm sure someone will say "that's even worse"

want to save $$$ every day...go to 308's....My 2 cents

Matt_ · April 9, 2011

Top gear performance without forcing a downshift is where the numerically higher ratio will improve performance and in many cases improve fuel mileage. ie. 3.42 or even better 3.73
...... Get those RPM's up and improve mileage without excessive downshifting

This just is not true.

Actually, that is 100% true.

IF your ratio is too high and forces the truck to constantly downshift, you will lose performance and MPG. I'm not debating 3.08 vs 3.42 here, just stating the fact that there is such thing as too high of a gear causing issues.

Your logic for why his statements were "not true" are exactly the reason why they are true! Downshifting = higher RPMs Therefore, as was previously stated, the most efficient gear is the highest numerical number that does not require constant downshifting; thereby keeping the RPM's low. (often times when the trans downshifts, primarily for the 4spd, the RPM's are much higher than what is actually needed.)

My 2005 was a PRIME example of this. I had 35" tires with stock 4.10s and drove it 70+ miles on the highway every day. My gas mileage was HORRIBLE with the 4.10s because the truck was constantly downshifting, couldn't hold speed and couldn't accelerate worth a damn. I put 4.88s in it and it never needed to downshift, I didn't have to mash the pedal to accelerate and my gas mileage improved significantly.

Mckenzie · April 10, 2011

buy how much did your mpg's increase?

Matt_ · April 10, 2011

Went from mid to low 11's (maybe a low 12 on occasion) to a solid 14-15. Truck was straight up horrible with the 4.10s

Mckenzie · April 10, 2011

Went from mid to low 11's (maybe a low 12 on occasion) to a solid 14-15. Truck was straight up horrible with the 4.10s

Nice! Does your motor running at a higher RPM's cause any premature wear and tear on the motor?

DALE#3 · April 10, 2011

Full sz.trucks are very fortunate for drive train choices.My 011 colorado v8 4x4 1 choice take it or leave it.4.10 4 speed.With the research iv'e done, keep the 5.3 below 1900 rpm.you'll be fine with mileage.I will be putting a 6 speed in this truck not a cheap transfer but cheaper than trading and losing.Gear's warrant your particular needs,driving style,terrain,towing,commuting etc.Full sz. even has dod HS! 3.08 mostly hw,3.42 combo.driving. Full size 6 speeds really help all ratio's big time.YOU LUCKY DOGS.

ed c · December 23, 2011

My real experience with 3.08:1 ratio and 6 speed transmission in a 2011 Yukon XL is 17 mpg city and 21 highway.

jro909 · December 23, 2011

3.42 for 6 speed....3.73 or 4.10s for 4 speed

thesub265 · January 10, 2012

I recently bought a 2007 NBS Silverado VMax Crew with 4:10 gear and 140k km on the odometer. I have recorded as high as 19mpg (Canadian), and as low as 10.5mpg (Canadian). About 15.2/8.5mpg US, difference being the size of our Imperial measurement for a gallon. Driving at 60mph, our local speed limit, the engine revs right at 2000 RPM. Drivning up a steep incline the truck never shifts out of overdrive. On the flats I have to have a tail wind for the DoD/AFM to switch to V4 mode.

I just put a K&N cold air on it and some exhaust work, and plan on having a Black Bear tune done, hopefully that will improve the milage and power, not that it is lacking power in any way.

Wires · January 13, 2012

Top gear performance without forcing a downshift is where the numerically higher ratio will improve performance and in many cases improve fuel mileage. ie. 3.42 or even better 3.73

The overdrive ratios we have in modern transmissions put the cruise RPM too low and out of the torque peak when combined with 3.08 ratio. Get those RPM's up and improve mileage without excessive downshifting

This just is not true.

1) Torque peak and engine efficiency have nothing to do with each other.

2) Increasing RPM, increases pumping and friction losses, which lowers mileage. That's why the XFE doesn't have 4.10s.

You can prove all this yourself. Get on a level road. Get up to highway speed, let it shift into 6th and hold it. Make sure you are not gaining or losing speed. Check the instant MPG, or reset your average MPG over a stretch. Now force it into 5th gear, and watch the instant MPG drop (or reset average MPG again and retest).

Now if you are towing frequently, you main concern isn't mileage. It's having the torque to get the load moving, and that means lower rear axle gears (higher numerical). That's why the tow ratings are higher for the same engine and body style, with lower gears.

Michael

You both end up being right. You do get better MPG with lower revs, BUT, that's in an ideal case. Toss in some headwind/hills, and it's better to get the revs up, and you get consistant MPG day in/day out.

My '00 5.3L had 4.10's. It didn't matter what I had in the box, what wind was blowing/etc. At 70 MPH, I got 16US MPG. Raise/lower the speed by 10MPH, and the MPG would change by 2. Very consistant.

My '08 has 3.03's I think (with the 6 speed). Now, I get 20USMPG on the best days at 70MPH, but toss in a headwind, and then it's down to 13-15USMPG. Wihout the revs, it just labors the engine.

If you think about it, my 6.2L is crusing in 6th gear at something like 1200RPM. Not like there is a lot of power on tap with no throttle at that RPM.

kstruckcountry · January 14, 2012

My 06 runs about 2000 at 70 with the 4spd and 3.73's. I've found when towing it's better to kick it down slower with a lower gear and higher RPM, so you can hold one gear. Having to go in and out of gears will cost mileage. I think you'd be happy with 3.42.