An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio
Interesting read, but man, the data could've been laid out better.
Basically, the first 3 gears of the 3.92 vs 3.21 are:
18.46 vs 15.12
12.31 vs 10.10
08.23 vs 06.74
From there-on, the 3.21 can match the 3.92 by dropping into the next lower gear, and the 3.21 has one final gear ratio for super-low highway RPMs.
I'm a Mechanical Engineer, myself. I'm a noob on this forum, but I feel like I'm about to break your long-running guide, because I kinda disagree with his assessment. I appreciate his calculations and time, but he lost me at this conclusion:
The 3.21 gear ratio isn't good for towing at 58-70mph, nor could it reach 70mph on an uphill grade.
That statement seems completely wrong when you consider he just got done saying that the 3.21 has the same 5 upper gear ratios as the 3.92, if simply dropped 1 gear lower on the 3.21. At highway speeds, the 3.21 and 3.92
should feel exactly the same, all you need to do is gear limit to lock out 8th.
If the 3.92 can easily tow in 8th gear going 70mph, why is he claiming that the 3.21 couldn't do the same in 7th? (gear limiting)
-7th on the 3.21 would work, feel, sound, burn, cruise, and accelerate exactly the same as 8th on the 3.92.
-Dropping 1, 2, 3 and up to 4 gears on the 3.21 would be EXACTLY the same as dropping 1, 2, 3 and up to 4 gears on the 3.92 (again, you'd be 1 gear lower)
-Since we're already 1 gear down: 1st and 2nd gear on the 3.21 are actually better than gears 2 and 3 on the 3.92.
-The only thing the 3.21 is really missing is that super-low 1st gear that would get you 18% more final torque off-the-line.
The EcoDiesel revs to, what, 4600rpm?
Midnight edition has 284/45-22 tires (32.1" OD).
1st 18.46 vs 15.12 G/R.
2nd 12.31 vs 10.10 G/R.
3rd 8.23 vs 6.74 G/R.
1st gear on the 3.92 would top me out at 23.8mph
1st gear on the 3.21 would top me out at 29.8mph
2nd gear on the 3.92 would top me out at 35.7mph
2nd gear on the 3.21 would top me out at 43.5mph
3rd gear on the 3.92 would top me out at 53.4mph
3rd gear on the 3.21 would top me out at 65.2mph
Standing start with the throttle buried (shifting at redline):
The 3.92 has the advantage from 0.00-23.8mph
The 3.21 has the advantage from 23.8-29.8mph (because the 3.92 has now changed to a higher gear ratio)
The 3.92 has the advantage from 29.8-35.7mph
The 3.21 has the advantage from 35.7-43.5mph
The 3.92 has the advantage from 43.5-53.4mph
The 3.21 has the advantage from 53.4-65.2mph
From here on out, it's basically the same truck, just 1 gear lower, and assuming you're not drag racing your EcoDiesel with a 10k trailer on the back, technically, the 3.92 only helps from 0-24mph (EcoDiesel)....end of story.
Going back to the Fact that it's an EcoDiesel and the 3rd gen EcoDiesel makes 480ftlbs of torque at 1600RPM, I'm not that concerned about not being able to get off the line with the 3.21, even if I have 18% less torque at the tires. Lastly, because I'm looking at the EcoDiesel and Diesel engines are designed to run more at lower RPMs. I'll probably appreciate that 3.21 at highway speeds:
71mph = 1600RPM at a 2.15 final drive ratio. 1600RPMs is the EcoDiesel's 480ft.lb sweet spot.
Meh, it's not ridiculous if you don't tow or haul anything heavy. If I needed more payload I would have gotten a loaded Limited HD. I really don't like towing anything with a truck that's at the edge of its capability.
1000lb payload is ridiculous when you consider that 4 adults and some very basic daily-carry is your capacity.
I joke about seating capacity vs. payload/cargo...especially when I talk about 3-row SUVs. If your vehicle has the ability to carry 7 or 8 people, it better have enough room to carry their stuff. The Ram can comfortably seat 5 adults, It should have enough payload to carry 5 adults and 5 suitcases.
The Ramboxes will also eat into my payload, unfortunately, but I'm thinking that's the only option that might be worth the cost. I want to have a dry place to store/lock stuff, plus it has a 115V outlet.
See my sig for my upcoming truck. Lots of decisions, and I did consider the Tundra. Even waited for it to come out before ordering the Ram. But, the powertrains and no air suspension confirmed I was going Ram Ecodiesel. Nothing in the Jeep lineup has enough towing and I tried once to have no truck and that only lasted a few months.
I like the rebel look better. But one of my personal goals was to not give anything up that I have in my 2012 f150; one of which is a 6'6" bed. Rebel only coms with the 5'. Can't remember if rebel can go 6 passenger, but I got it in my Laramie just because my center console only collects junk and having seating for 6 gives both my kids options to invite friends on trips.
Thanks for the info. I also like the look of the Rebel, but the Laramie seems to have more options. I didn't realize I could get a long bed.
Also, same boat, I was waiting to see the new Tundra before pulling the trigger. I didn't realize builds were so far out.