Ram 3.21 rear end towing

Thank you to all that responded for the information. I am very appreciative of your efforts to answer my question.

you won't set speed records going uphill but you should be ok.

I have ram 1500 2015 with the 8 speed/3.21 transmission quad cab 4x4 and just got back from a Colorado trip. it definitely pulled better than my ram 1500 2002 with the 5.9 with 4 speed w overdrive (5th gear). not sure what the axle ratio was. pulled same 6500 lbs. loaded 26ft trailer. used tow/haul on 2015 which on the 8 speed knocked it down a couple gears. on the 2002 took one gear down (canceled overdrive).

the 2015 got 12.5 mpg compared to the 2002 which got 8.5 on the exact same trip. you will like the improved mpg's a lot, I did.

kept the speed to about 60 mph with an occasional 65.

Best advice I can provide is to get on any bicycle with gears on the rear
wheel (Cassette) and gears on the pedal crank shaft (chain rings)

That is the same setup most any vehicle has, except for 4x4's which has another
set of gears in that mix

The new automatics is like having more gears on the chain rings than before
Old 3/4 speed vs today's 6-7-8 or more speeds

The rear Cassette will make no matter how many gears, as our TV's has mostly
one (some can have two) and this is where the choice of gear used will tell

On the flats, just about any gear will do, but the higher gear (smaller numeric)
will take a bit more to get it going, but will allow higher speeds with
less pedaling

The lower gear (larger numeric) will take less to get it going, but will
top out in lower speeds because you can not pedal that fast

No difference, other than your legs vs an in-animate (ICE, internal combustion engine)
has limits on how fast any one architecture can go

To bad not enough folks actually cycle out there...

Y-Guy wrote:
I've had a truck with a 3.21 rear end, good for MPG not so good for towing. Felt like it was a gutless wonder. Next truck had a 4.10, thing could tow a trailer up a tree, but the MPG wasn't so go. Next truck had 3.73, felt like it was the right compromise for me.

Which transmission did the 3.21 equipped truck have? If it was a 4 speed of 10-15 years ago, we're comparing apples to kumquats. The rear axle ratio is only half of the equation.

Take a look at this spreadsheet I did.

After 2nd gear you will notice the rpm required to go 55 mph is very close when the 3.21 gear is down by one transmission gear compared to the 4.1 gear.

I would expect with a trailer in tow there is very little difference from the 3.21 from 2nd gear to 7th gear and the 4.1 from 3rd gear to 8th gear.

With the 8 speed and the next generation of 10 speed and CVT transmissions rear gear ratios will be closer to 3.0 than 4.0.

With the eight speed it might actually be decent. You may not hit eighth gear while towing depending on conditions but if you're within your towing AND payload limits you'll be fine. Lots of folks get get stuck on the rear axle ratios, myself included but that was before we had 6 to 10 speed automatics. The funny thing is the 8 speed's 1st gear x 3.21 is a lower ratio than either the old 645rfe with 3.92's or the 66rfe with 4.10's. Go drive one and see if it's what you need. You can get a 1500 with the 8 speed and 3.55's or 3.92's. Might have to do. Factory order. Same with a 2500 6.4 and 4.10's.

Have you tried Dave Smith in Kellog, ID? The drive from Kellog to Stockton, CA isn't too bad. You still pay your local taxes. The sell a lot of Dodge trucks.

I've had a truck with a 3.21 rear end, good for MPG not so good for towing. Felt like it was a gutless wonder. Next truck had a 4.10, thing could tow a trailer up a tree, but the MPG wasn't so go. Next truck had 3.73, felt like it was the right compromise for me.

rjstractor wrote:
Considering that the truck in question has an EIGHT speed transmission, the 3.21 gears may be suitable for your application. Many get fixated on the rear axle ratio alone, which hearkens back to the days when transmissions had only 3 speeds. Towing the load in question, this truck with 3.21 rear axle gears may cruise the freeway in 6th gear instead of 8th, but may otherwise provide decent performance. Having said that, trucks with a numerically higher gear ratio will have higher tow ratings, but that doesn't mean that a 3.21 axle ratio will not provide good performance with the 8 speed transmission.

X2

You will most likely have to pull the hills in a gear lower than 8th even with the 4.1 gear.

You will find the overall ratio for the 4.1 in 8 th gear will be almost the same as the 3.21 is in 7 th gear.

So when pulling the big hill it does not matter if you do it in 3 rd gear with the 3.21 vs 4 th gear with the 4.1.

This is true as the overall ratio in 3 rd gear and a 3.21 is almost the same as 4 th gear with the 4.1.

You will be putting about the same horsepower to the ground as the engine rpm will be very close in both cases.

Considering that the truck in question has an EIGHT speed transmission, the 3.21 gears may be suitable for your application. Many get fixated on the rear axle ratio alone, which hearkens back to the days when transmissions had only 3 speeds. Towing the load in question, this truck with 3.21 rear axle gears may cruise the freeway in 6th gear instead of 8th, but may otherwise provide decent performance. Having said that, trucks with a numerically higher gear ratio will have higher tow ratings, but that doesn't mean that a 3.21 axle ratio will not provide good performance with the 8 speed transmission.