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An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

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That’s already been posted a few times in this thread by people who owned both.


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Half ton gassers and gear ratios...

thor-petty.gif


:LOL:
 
HSKR R/T said:
You need the higher alcohol content to drink your sorrows away from having inferior gears. :p
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I’ve got some clear for those special occasions, so I’ve got the higher alcohol content.
Don’t make narry difference in my opinions on trucks.
Ive got both sets of gears. I drive them both at different times.
I honestly like the 3.21 better for hauling *** on the expressway. Country roads and in town, it makes no difference.
 
Road trip. ~700+ miles. Stopped 3 times, had about an hour of traffic. Average speed: 61mph. 11 1/2 hours, all in.

(Hmm, stops and traffic? Stops...45 minutes. Traffic. Say it slowed me by 30 minutes (bumper to bumper, stopped.) So, 11:30 minus 1:15...means 10:15 driving. Actual driving average about 70.)

Mileage...29.3 mpg.

Gotta love this diesel, this transmission, and, of course, the 3.21. ;)
 
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Op did a great job here but there are 2 things missing. He explains you'll get better towing and acceleration with 3.92. It sure would be great to know with the same empty weight, how much faster 0-60?

With the 3.21, how much better mpg at 60? Is it .1mpg or is it 1 mpg?

Without performance facts we're still guessing that one ratio or the other makes enough difference to be worth it, for our paticular use.
 
Driver said:
Op did a great job here but there are 2 things missing. He explains you'll get better towing and acceleration with 3.92. It sure would be great to know with the same empty weight, how much faster 0-60?

With the 3.21, how much better mpg at 60? Is it .1mpg or is it 1 mpg?

Without performance facts we're still guessing that one ratio or the other makes enough difference to be worth it, for our paticular use.
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0-60 times depend more on traction, curb weight, how many shifts you need to reach 60, etc. Also a better way to think of the gear ratio difference is HP to the wheel vs torque to the wheel. Both have the same engines, but applied wheel torque and horsepower will be different for each gear ratio. So 3.92 gear ratio will give you more torque to the wheel. This means the gears are shorter, engine RPM builds quicker with 3.92 gears, but also means you may have traction issues. On the other end of it 3.21 gears means you'll require less engine RPM at highway speeds. I can hit 104mph in like 4th gear.

I have 3.21 gears and spin my tires in 2wd, traction on or off. If traction control is on, then I spin less when flooring it from a stop, but also get power restricted so 0-60 times aren't that good. Traction control off and I can spin a little more but then 0-60 times don't really improve as i'm just spinning too long and not going anywhere. Best I could reliably get was 5.8 seconds when my truck wasn't leveled and had stock tires. Put in 4wd auto or 4hi and do a bit of power breaking then flooring it.

With 3.21 gears and 35" tires I shift into 3rd gear right at 59 or 60 miles an hour. So I just have 1 shift from 0 to 60. 3.92 gears you'd shift into 3rd before reaching 60 so that might slow down your 0-60 time. But wheel speed equals distance travelled so good traction with 3.92 gears should mean better 0-60 times.

With my truck unloaded at 60mph I get around 19mpg with cruise set. Will be in 8th gear. I can also set cruise at 80 and get 18mpg. This is with 35's.

If you plan to tow or haul stuff frequently (including people) then 3.92 should be the choice. If you use your truck occasionally to tow and haul stuff and mostly just commute alone for work, then 3.21 would be the better choice. If you want a street truck then either works, but 3.92 will let you do better burnouts than 3.21. But tires are expensive so 3.21 may be the better option there if your okay with 15ft burnouts vs 30 ft. lol
 
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