MPG effect of 3.92 rear end

[Ramit392]

I have a 5.7 3.92 with etorque and bf Goodrich ko2 stock size... just finished a 2k mile trip... mostly freeway and highway miles... 15.5mpg is my average.. I have 2900miles total. seems so low for a truck that is advertised as 22highway/17city 19 combined. I’m disappointed... my 2010 ram bighorn 1500 5.7l did better...

I have 6100 Miles with 5.7 and 3.92 gear with average MPH 18.5 miles combo all the time with about 60% highway driving or so.

 

[cruz-in]

"he 3.92 helps to stop and manage any weight with push back the 3.21 will have significantly less. "

I found this interesting and don't understand. Could someone give a bit more info on why this is so?

Thanks in advance for taking your time to educate me.

 

[Zeronet]

I have 6100 Miles with 5.7 and 3.92 gear with average MPH 18.5 miles combo all the time with about 60% highway driving or so.

You’re doing very well mpg wise. On fuelly.com relatively few are AVERAGING the epa rated numbers. 15 is average, eTorques about 16. Then again the fords and GM trucks are all averaging 16 so they don’t make their numbers either.

 

[Zeronet]

"he 3.92 helps to stop and manage any weight with push back the 3.21 will have significantly less. "

I found this interesting and don't understand. Could someone give a bit more info on why this is so?

Thanks in advance for taking your time to educate me.

The 3.92 will provide more engine braking when going down a mountain and when slowing down when using lower gears. Very beneficial when towing heavy.

 

[Ramit392]

You’re doing very well mpg wise. On fuelly.com relatively few are AVERAGING the epa rated numbers. 15 is average, eTorques about 16. Then again the fords and GM trucks are all averaging 16 so they don’t make their numbers either.

Thanks.Very happy with it but I averaged the same 18 to 19 MPH combo with the 2014 Ram as well and no etorque. If I drive 55 to 60 with going threw little burgs and red lights for about 80 miles I got 20 and 20.5. Combo Average.

 

[Gondul]

Thanks.Very happy with it but I averaged the same 18 to 19 MPH combo with the 2014 Ram as well and no etorque. If I drive 55 to 60 with going threw little burgs and red lights for about 80 miles I got 20 and 20.5. Combo Average.

And it helps to clarify how fast you are driving when claiming high MPG numbers... thanks.

 

[Ramit392]

"he 3.92 helps to stop and manage any weight with push back the 3.21 will have significantly less. "

I found this interesting and don't understand. Could someone give a bit more info on why this is so?

Thanks in advance for taking your time to educate me.

The 3.92 produces more resistance with foot off accelerator against the Trailer in tow. Resistance reduces the "Push" the tow trailer can have on the pull vehicle which also will reduce sway, reduced Stopping Distance. 3.92 does less hunting for lower gears while pulling up grades on the open road as well. Towing becomes more difficult when trailer has no resistance against it any time your braking or going down grades with foot off accelerator 3/4 Ton trucks with 4.10 gears produce even more resistance thus allowing for more pull capacity both being gas trucks. Diesels even more.

The lower gears are not intended just for more take off power but do produce that as well. One can go down hills or grades not towing any thing and reduce braking much less, than one would with higher gears. IMO not sure why any trucks from 1/2 ton and up would have high gears? It makes no sense for what small MPG gain is produced with the higher gear? The benefits of a lower gear in a truck will out weigh the other in many ways for your money's worth IMO.

 

[Ramit392]

And it helps to clarify how fast you are driving when claiming high MPG numbers... thanks.

Yes it does. My 18 to 19 is usually 60 to 65 Mph....After 70 MPH drop off to 17 and 18. 80 Mph would be under that some....Not done 80 to 85 for any length of distance yet with this 19.

 

[User_3336]

I seen ALOT of gear hunting with the 3.21 (between 6-7-8)

 

[Jello0123]

I only have 1,200 on my 19. 5.7, etorque, 3.92 and I do notice that the mileage is 14-15 city which is most of my drive. It definitely slows with a noticeable pull and does not hunt for gears. I see it in 7-8 at 45 mph all the time. Makes me wish it had the 10 speed in it lol.

 

[Troop2865]

Ok. I know, don’t bring up fuel economy again. Anyway, just checked my last tank. 80% of driving was interstate traveling 60-75. There was some two lane at 55-60, and a couple short trips to town. I averaged 13.9 MPG. Not good.

I am running just under 2000 RPM (with tires I set the cruise at 69 to be going 75) and I notice it shifts down to 7th gear even going over an overpass. Seems like it should hold 8th on such a short/slight hill. Does that seem right for it to downshift?

The good news is has was $1.79 per gallon in St. Peter’s, Missouri, so the poor MPG hurt a little less. Coming back, I had a big tailwind. At 72 MPH, the computer showed 15.7 MPG.

I know I didn’t buy this truck expecting 21 MPG, but I did/do expect upper teens, not 13.9.

 

[Bram2019]

Ok. I know, don’t bring up fuel economy again. Anyway, just checked my last tank. 80% of driving was interstate traveling 60-75. There was some two lane at 55-60, and a couple short trips to town. I averaged 13.9 MPG. Not good.

I am running just under 2000 RPM (with tires I set the cruise at 69 to be going 75) and I notice it shifts down to 7th gear even going over an overpass. Seems like it should hold 8th on such a short/slight hill. Does that seem right for it to downshift?

The good news is has was $1.79 per gallon in St. Peter’s, Missouri, so the poor MPG hurt a little less. Coming back, I had a big tailwind. At 72 MPH, the computer showed 15.7 MPG.

I know I didn’t buy this truck expecting 21 MPG, but I did/do expect upper teens, not 13.9.

What was the menthod used to compute miles per gallon

 

[Jackham]

This is always such an interesting topic on all pickup forums as the the weight, options, sized tires, gear ratios, transmissions are all in such complex combinations. No way for example a Crew cab is the same weight as a supercab, etc.

What is impossible to know is how efficient of a driver you are. With the sound of those pipes its pretty hard to stay out of the hemi. On an interstate if you modulate your throttle pressure when you go up slight inclines you can keep the MDS going longer but it is a hastle so people put on the speed control and away you go. Still you would think given so many gears (8 vs 10...really?) you would think the engineers could compensate for the ratios. Why for example limit the 3.21 to 8,000 lbs....are they built lighter or of lighter stuff? Why not just leave it in 6th?

So what I noticed with my 2011 F 150 half ton heavy duty which comes with the 3.73 rear end (a rare find) absolutely nothing beat it out of the hole. It is actually a holy terror and puts a lot of sports cars to shame but you will never know that because the particular truck configuration is never in a road test. On the interstate it got 16.5 at 80 mph because it crossed the magic 2,100 RPM line. Below that in low rolling hills a t 68 mpg I could easily hit 21. But alas I live in Montana. The only place you drive 68 mph here is downtown.

However even with 11,000 lbs of bales on my trailer and the 8' box full of bales I got 12.9, no matter what I did. At that same time guys said they usually got 9.8 mpg. So who knows. Unless we can normalize driving habits. List all options and configurations and gather data into a chart I doubt we will learn much.

Just my two sense.

 

[Troop2865]

As for calculating the mileage I took the miles on the trip odometer X 1.09 (speedometer is off 9% due to going from 32 inch tires to 35’s) divided by number of gallons used to fill the truck. The number the computer gave and actual mileage were the same (this time). I set the cruise control at 69 which is 75 MPH actual speed (checked first with mathematical fornmula using tire circumference and also using GPS.

As for my driving style, I drive like an old man. Very easy when accelerating and long periods of coasting when approaching a stop sign. My brakes usually last well over 100,000 miles. I normally don’t even drive but a couple of miles an hour over the limit. Yesterday I was in a hurry so drove five over on the interstate (now that will get me in trouble). As for my MDS, I have never seen it kick in and I am sure the light is programmed to be on.

I check mileage manually every time I fill and I write it down. I write down all of my service on my vehicles.

The truck is still under 1000 miles so I know it is not broken in. Even with the stock tires it seems like the mileage has been low. Hoping it gets better.

 

[RPeezy]

I would expect a significant decrease in mileage from the 35" tires. Heavier, higher rolling resistance, and essentially adding another 1.5" of lift to your truck. Combine that with the off road group, and you are experiencing significantly more aerodynamic drag, which multiplies with speed.

 

[Bram2019]

I would expect a significant decrease in mileage from the 35" tires. Heavier, higher rolling resistance, and essentially adding another 1.5" of lift to your truck. Combine that with the off road group, and you are experiencing significantly more aerodynamic drag, which multiplies with speed.

Not only that, I can not tell you how much havoc those tires are creating because all engine, emission and transmission calibrations are now off plus the above mentioned items. Who know what the real mileage would be.

 

[Troop2865]

It was pretty poor before the new tires and wheels, but I wrote it off to being new. The best instant mileage shown has been about 18 at 45-50. Generally speaking, at 55 it was 15-16 and at 70 about 14. I do want to re-program the computer for the tire size, and I am sure that won't hurt. Heck, I had a 67 Kaiser Jeep M715 with a 6.0 Litre and 42's that got 12.5-13 driving 70 on the interstate and it was shaped like a brick.

 

[User_3336]

With a 3.21 sounds pretty typical. If you had the 3.55 or the 3.92, you would definitely not see this downshifting to 7th (or possibly 6th) in the scenario you posted.

I am running just under 2000 RPM (with tires I set the cruise at 69 to be going 75) and I notice it shifts down to 7th gear even going over an overpass. Seems like it should hold 8th on such a short/slight hill. Does that seem right for it to downshift?

 

[mhb1638]

Own a 4x4 with 3.92 and drive 52 miles daily 1 way and with 9k on the clock, I squeeze out 17.8 hand calculated. the truck is being traded in this weekend for another 2019 ram, but this time a 4x2 with 3.21 gears for better mileage and my truck is all stock. I can't do 17.8 driving 104 miles every day. No way. If it was a short trip in the city, fine. I drive 25m doing 75 and 45m doing 60-65

 

[User_3336]

You will reget getting a 3.21 axle ratio after owning a 3.92 one!

Own a 4x4 with 3.92 and drive 52 miles daily 1 way and with 9k on the clock, I squeeze out 17.8 hand calculated. the truck is being traded in this weekend for another 2019 ram, but this time a 4x2 with 3.21 gears for better mileage and my truck is all stock. I can't do 17.8 driving 104 miles every day. No way. If it was a short trip in the city, fine. I drive 25m doing 75 and 45m doing 60-65