I have 3.92 rear gear in my Laramie with 20" wheels. My rpm seems very low for this gear at highway speeds. Just wanted to know what other gear combos with 20 wheels were getting?

2200 rpm=80mph

2500 rpm=90mph


So theoretically my truck is geared for 180+mph? so you guys with 3.21 rear gears should be good for 200+mph! All we need is another 1000hp and we should be good to go.


I ask because my 01 2500 CTD i ordered with a 3.54 posi and then I pulled the rear cover I saw it was an open diff (one legger) I asked WTF happened as it was on my build sheet. I was told some times they run out of certain parts and use others. He said do you expect them to stop the assembly line to wait for your posi? no they throw in what they have on hand... an open diff.


So that being said what is your gear, RPM & MPH with 20" wheels.

 

With 3.92 gears, stock 33" tires on 20" wheels.... 80mph = 2108rpm (calculated)

 

Stock 275/60-20 with 3.55 rear:
70mph = 1750rpm
80mph = 1950rpm

Speed and RPM readings assume gauges are correct.

 

My RCSB 5.7, 3.92, 30.5" tall tires on 17" wheels equates to 70 mph @ 2000 RPM. And no matter what these trucks are geared for, we will never see past 150 mph no matter what your calculations add up too, he he!

 

I'm getting about 1600rpm at 60mph with 3.92's and 20's. The gearing is always a compromise between fuel economy and power. Some cars with 6 speed transmissions will actually get the highest top speed in 5th gear. The 6th overdrive gear is for improved gas mileage.