Gear ratio

dwade · Nov 8, 2021

I've kind of cheated a bit on gear ratios. I've got a 2015 Tradesmen 1500 4x4 with 3.21 gears and the 6 speed transmission and pull a 24' camper with it. Short trips to local campgrounds I don't worry about it but recently added a set of 29" tires to equate 3.55 gears. At 60mph on the speedo I'm running 55mph by the GPS. On the upside my gas mileage per the onboard shows an improvement in mileage when running empty which IMHIO should equal about the same mileage as my stock 31.6" tires and 3.21 gears.

Even the ratio change was not drastic I did notice a big difference in power while pulling my 7000 lb camper. Driving on US70 west of Indy there are some longer hills that I would often drop to 5th gear and now it stayed in 6th gear on almost every hill and at 70mph the RPMs never went over 3 grand.

Not the best way to do things but definitely helped me at a much lesser cost than swapping gears front and back.

Bandit1859 · Nov 8, 2021

Kickboxer said:
I have a 2020 Ram 1500 with the 5.7 and the standard 3.21 rear ratio. I have been looking to trade for a new 2022
and some dealers have the 3.92 ordered. I am very happy with my current vehicle, and I am questioning why the 3.92.
I don't pull a trailer much, but when I have the current 3.21 does just fine.

Thoughts on this ?

I have a2019 with 392. 2020 with 321. I really don’t see much difference in mpg I like the 392.

scott lass 18 · Nov 8, 2021

Kickboxer said:
I have a 2020 Ram 1500 with the 5.7 and the standard 3.21 rear ratio. I have been looking to trade for a new 2022
and some dealers have the 3.92 ordered. I am very happy with my current vehicle, and I am questioning why the 3.92.
I don't pull a trailer much, but when I have the current 3.21 does just fine.

Thoughts on this ?

I had 3.21 too but replace it when new did a true track and love it ! have had no problem's all these years . I didn't use as much as I thought so maybe was just me wanting it more . maybe lost .5 mpg I really didn't see a lost ,but did see it run so much better on highway and city in the rain was better . it seems to run faster then old one so love that . oh did put 275/50/20 tiers on mine too ! Scott nov 2021 love my 3.92 glad I change it out still works great for me ! been 9 years now

scott lass 18 · Nov 8, 2021

KeithP said:
We have a 1955 Chevy 5500 with a 2 speed differential. And it wasn’t new technology then. They’ve been around a long time.

love things you do each day ! wow love it ! not many of us me I do own my screw up s sure does blow people away ! Scott

KeithP · Nov 8, 2021

scott lass 18 said:
love things you do each day ! wow love it ! not many of us me I do own my screw up s sure does blow people away ! Scott

Thank you.

zeus2120 · Nov 9, 2021

Kickboxer said:
I have a 2020 Ram 1500 with the 5.7 and the standard 3.21 rear ratio. I have been looking to trade for a new 2022
and some dealers have the 3.92 ordered. I am very happy with my current vehicle, and I am questioning why the 3.92.
I don't pull a trailer much, but when I have the current 3.21 does just fine.

Thoughts on this ?

I have the 3.92 gears. I travel a lot for work and rent 1500s from National whenever I can simply because I love riding in what I'm used to. All the rental 1500s that I've come across have the 3.21 gearing. Personally I can feel the difference and get more enjoyment driving with 3.92. RPMs turn a little higher at 70-75mph and fuel economy takes a little hit, but there's a noticeable difference in acceleration, at least to me. If I was in the market for a new truck right now and could choose either, I'd go with 3.92.

runamuck · Nov 9, 2021

the 3.92 rear end and 5.0 first gear give the truck some good grunt when towing our 6000# travel trailer. much more responsive than the '17 sierra 1500 I had with 3.42 rear end and 4.07 first gear. fun to drive when not towing too.

farout75 · Nov 9, 2021

My 17 RAM has the 392 and in my three other RAM 1500's I had the 3:21 So here is my take. The 321 does give about 1 to 2 MPG's more, the 392 you have quicker get and goes. You can tow more . With my 321 I use to get 18 to 21 mpg and with the 392 I get 17.5 to 20mpg. Not a huge difference, but if gas gets as high as Brandon wants it might make some difference. Either way I think you should look for a RAM 1500 that has all the things you want it to have and what ever gear ration it has go with it.

rvance · Nov 9, 2021

2019RamInSC said:
My Father's 53 Mercury had that overdrive handle you pulled under the dash. I was to young to realize that was a 2 speed rear. Your post reminded me of it. 3 speed on the column. I got to drive it very briefly. He upgraded to a 63 Mercury Monterey.

If I recall, it was a separate unit that mounted in front of the differential.

ramffml · Nov 9, 2021

There is no difference (when empty) in acceleration unless you're WOT; what you're noticing is the speed (time in seconds) it takes for each truck to up shift from first, since the 3.92 will reach higher rpms first and upshift sooner, it will feel like the truck is going faster/easier. Each truck has gobs of power available. If you feel the 3.21 isn't speeding up fast enough just push the pedal down harder, problem solved.

The 3.92 is not needed unless you run bigger tires and/or have the payload available to pull something > 8000 pounds.

And when I'm pulling my trailer with my 3.21, first gear is never a struggle. I have never once thought "I need more power" when towing in first. My RPMs are always very low, 2500 max. Third and fourth, that's where the weight begins to bite as I'm usually trying to accelerate on an on ramp or pass etc and they can jump up to 3500 - 4000. But first gear is literally the easiest of all gears for the truck to be in, I see no point in trying to make it even easier, that's not going to make me want to pull a bigger trailer. And quite frankly, feeling 7000 pounds behind my 5th gen I'm not sure it's even safe to go beyond 8000 regardless of what the specs say, that rear end can get squirrely at times.

runamuck · Nov 9, 2021

there is a noticeable difference in acceleration..easily felt when comparison driving the two different models. I've actually owned and towed with both gearsets. the 3.92 rear is not particularly needed for normal driving but I tow a travel trailer every now and then and the lower the rear end the better they tow..just my experience. the lower rear end combined with the 5.0 first gear make a good towing combination. I've towed too many things with too many different vehicles to set my truck up otherwise. I wouldnt go much more than 6000-7000# tho and stay under 30' as these 1500's are softly sprung and anything larger could be a case of the tail wagging the dog. IMHO

2019RamInSC · Nov 11, 2021

rvance said:
If I recall, it was a separate unit that mounted in front of the differential.

Even more interesting!

dwade · Nov 12, 2021

@ramffml and @runamuck

Squirrelly back ends. Do you not use a weight distribution hitch with sway bars? Curious and my camper is a 7000 pounder and I've never experienced that but I do use the heavy duty hitch and half the tow package on my 2015 1500 Tradesmen

runamuck · Nov 12, 2021

yes I use a Husky WDH with the 800-1000# bars. I have also switched out the oem sway bar to a stiffer Helwig bar and I run a little more air in the tires when towing. my truck has the built-in anti trailer sway and I added airbags. I run 20-22# when I'm towing. all these little things help. I dont get any sway unless I'm fighting a gusty crosswind. on roads that arent too hilly I can set cruise for 68-69 and get 8.5 -10 mpg. last month did 2600+ mile trip from DFW to south dakota and back towing our 6000# 28' travel trailer and mostly did 65-66 going up and 69-70 coming back for an average of 9.8 mpg using only reg. gas. the truck/trailer combo handled great except for a cpl. stretches of gale force winds in kansas.

ramffml · Nov 12, 2021

runamuck said:
there is a noticeable difference in acceleration..easily felt when comparison driving the two different models. I've actually owned and towed with both gearsets. the 3.92 rear is not particularly needed for normal driving but I tow a travel trailer every now and then and the lower the rear end the better they tow..just my experience. the lower rear end combined with the 5.0 first gear make a good towing combination. I've towed too many things with too many different vehicles to set my truck up otherwise. I wouldnt go much more than 6000-7000# tho and stay under 30' as these 1500's are softly sprung and anything larger could be a case of the tail wagging the dog. IMHO

The problem is when people post things like "my truck pulls harder in every gear" and then the math does not support their claim. The simple fact is, once both trucks are beyond second, there is literally no difference; both trucks have the same gear ratio multipliers available, they are just sitting in different numerical gears.

Calculate the ratio for the 3.21 in 6th. It's "3.21".
Calculate the ratio for the 3.92 in 7th. It's "3.219".

Literally identical gear ratios, just the one truck is 6 and the other 7. Very similar effect in other gears beyond second. You have to be careful to account for confirmation bias; you think the 3.92 is the better pull so therefore it is. But the math does not support that assertion.

And like I said; I have never felt down on power in first and second. My truck has the easiest time in first gear, it's never struggled, and I've rarely exceeded 2500 rpms while towing in first. Why in the world would you need an even shorter first gear??

Only when you put 8000 pounds behind both, sit at a stop, and then dump the pedal to the floor WOT will you notice a difference. That is how the +3000 pound rating is determined, how fast can they arbitrarily reach a certain speed and obviously the 3.92 will get you there first.

But in the real world? Nope, have never needed to drag race with my 7000 pound trailer. Where you actuallly need the power is beyond second gear, and at that point the gear ratio advantage is completely gone.

ramffml · Nov 12, 2021

dwade said:
@ramffml and @runamuck

Squirrelly back ends. Do you not use a weight distribution hitch with sway bars? Curious and my camper is a 7000 pounder and I've never experienced that but I do use the heavy duty hitch and half the tow package on my 2015 1500 Tradesmen

I use a husky centerline, IME it can be great one day and white knuckle the next. Depends on the wind a lot, and whether I have a full tank of water in my trailer or how much I have in my truck bed etc. I read this common theme among different truck forums, the coil spring is best for ride, but it is the trickiest/finicky-est(?) to setup with a trailer. It can be done, but it's not as forgiving of slight imbalances as the leafsprings in the Ford/GM twins. Part of the problem is that the coils are sitting closer to the middle of the truck vs the leafspings which are sitting closer to the outside so the wallow effect is magnified in the Rams.

DuallyDean · Nov 12, 2021

ramffml said:
The problem is when people post things like "my truck pulls harder in every gear" and then the math does not support their claim. The simple fact is, once both trucks are beyond second, there is literally no difference; both trucks have the same gear ratio multipliers available, they are just sitting in different numerical gears.

Calculate the ratio for the 3.21 in 6th. It's "3.21".
Calculate the ratio for the 3.92 in 7th. It's "3.219".

Literally identical gear ratios, just the one truck is 6 and the other 7. Very similar effect in other gears beyond second. You have to be careful to account for confirmation bias; you think the 3.92 is the better pull so therefore it is. But the math does not support that assertion.

And like I said; I have never felt down on power in first and second. My truck has the easiest time in first gear, it's never struggled, and I've rarely exceeded 2500 rpms while towing in first. Why in the world would you need an even shorter first gear??

Only when you put 8000 pounds behind both, sit at a stop, and then dump the pedal to the floor WOT will you notice a difference. That is how the +3000 pound rating is determined, how fast can they arbitrarily reach a certain speed and obviously the 3.92 will get you there first.

But in the real world? Nope, have never needed to drag race with my 7000 pound trailer. Where you actuallly need the power is beyond second gear, and at that point the gear ratio advantage is completely gone.

I have to laugh at this response, and am reminded why I don't spend much time on forums like this. Use your noodle. If you had 7 different ascending ratios in one vehicle to reach a 3.21 overall reduction, and 6 different ascending rations in another to reach the same overall reduction, OF COURSE you are going to see an improvement in towing performance. Because what the original poster conveniently (or naively) fails to consider is the performance curve of the ENGINE. How long is that engine spending in it's optimal torque/hp producing range, and how much of it is spent above or below it? In a properly calibrated automatic transmission, shift points are determined by vehicle speed, engine speed and load. With a wider ratio transmission (fewer gears) the engine must spend more time above it's optimal rpm range before the shift to the next higher gear, and then spend more time below it's optimal speed as the engine sweeps through the RPM range again prior to the next shift. The effect is more pronounced in gasoline engines than in Diesels, due to the wider and flatter torque curve of a Diesel. That is why when I drove two 2018 Ram 1500's, one with the 5 speed behind the Eco-Diesel, and one with the 8 speed behind the 5.7 Hemi, acceleration performance was fairly similar, with the Hemi pulling away above 60MPH due to the higher HP rating.

ramffml · Nov 12, 2021

DuallyDean said:
I have to laugh at this response, and am reminded why I don't spend much time on forums like this. Use your noodle. If you had 7 different ascending ratios in one vehicle to reach a 3.21 overall reduction, and 6 different ascending rations in another to reach the same overall reduction, OF COURSE you are going to see an improvement in towing performance. Because what the original poster conveniently (or naively) fails to consider is the performance curve of the ENGINE. How long is that engine spending in it's optimal torque/hp producing range, and how much of it is spent above or below it? In a properly calibrated automatic transmission, shift points are determined by vehicle speed, engine speed and load. With a wider ratio transmission (fewer gears) the engine must spend more time above it's optimal rpm range before the shift to the next higher gear, and then spend more time below it's optimal speed as the engine sweeps through the RPM range again prior to the next shift. The effect is more pronounced in gasoline engines than in Diesels, due to the wider and flatter torque curve of a Diesel. That is why when I drove two 2018 Ram 1500's, one with the 5 speed behind the Eco-Diesel, and one with the 8 speed behind the 5.7 Hemi, acceleration performance was fairly similar, with the Hemi pulling away above 60MPH due to the higher HP rating.

I have to laugh too, because you're wrong but so sure you're right :boxing:

You're not wrong with the theory, but you're wrong in the application; in other words, it doesn't matter because both trucks have the same gear ratios beyond second.

We're not talking about 5 speed vs 8 speed (that's a huge difference, and I would consider axle ratio to still be quite important with a 5 speed). But in our case, using the same transmission and motor with only difference being rear axle ratio, both trucks have the same gear ratios beyond second (within a small margin of difference, 100 rpms?); so they have the same torque curve, same power output, same response.

Check out the table below and note how the 3.21 in column 4 has approximately equal gear ratio found in the 3.92 in column 5, just staggered/offset by one gear (match using the colored squares, each shade of blue is a different match between the axles)

So yeah, no difference in real world towing performance beyond second, and first and second are the easiest gears to pull in with my 3.21 and I have no need for more power down below, I need it up top; accelerating on an on ramp, or passing some trucker up a hill. 3.92 ain't going to do you squat there my friend.

SouthernBornRebel · Nov 13, 2021

I have 3.92's and specifically shopped for them... it's all about what you want the truck for

Doug Ram · Nov 18, 2021

Todd Bennett said:
I'd love to see a truck come out with a variable rear, set it for fuel economy or towing.

Our rural community had an old, mid 1960s, International Harvester Scout pickup that had a set up like this. It was used as a utility and plow. It was the most complicated gear set up I've ever driven in a small truck. There were three levers on the floor and a diagram on the dash. As I recall, one lever put the truck in 4wd or rear WD. Another engaged low while in 4wd, and the 3rd engaged low in rear WD. Plus you had to get out of the truck and spin the hubs sometimes. Of course it also had a tall manual stick shift with 3 forward gears and reverse. I drove it only on our community's gravel roads to plow snow. I don't think I ever got it out of 4wd low and 2nd gear.

Gear ratio

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