4:10 or 3:73 ?
Possible upgrading to Ram dually. I'm pulling 12,500# gvw with SRW and 3.42 rear end. Usually lock 6th gear out. Plan is to move up to new 15,000# gvw 5th. Not sure if I want to get 4.10 or 3:73. Wh...
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TxGearhead wrote:
3.73, Aisin in 5th at .77 overdrive, equals 1900 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1555 rpm at 65 mph.
3.42, Aisin in 5th at .77 overdrive, equals 1743 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1426 rpm at 65 mph.
385 HP at 2800 rpm and 900 ft lb torque at 1600.
I guess if you want to get higher HP the 3.73 looks better. The 3.42 in 6th gear is well under max torque.
My 3.42 works OK locked out of 6th, but the 3.73 looks like it would have higher HP. Something of a trade-off between more HP/torque and lower rpm for fuel mileage.
The problem with using most gear calculators is they do not use static load radius, and just ask for tire diameter. When the 15.5 static load radius for a LT275/70R18E is used, then your numbers come out much closer to what I see on my tach of around 1750 RPMs at 60 MPH. I used 31" as diameter not 33.1 with is the listed diameter.
So your number become when I applied the use of static load radius x2:
3.73, Aisin in 5th at .77 overdrive, equals 2023 rpm at 65 mph.
3.73, Aisin in 6th at .63 overdrive, equals 1656 rpm at 65 mph.
3.42, Aisin in 5th at .77 overdrive, equals 1855 rpm at 65 mph.
3.42, Aisin in 6th at .63 overdrive, equals 1518 rpm at 65 mph.
Chris
