TestPilot57
Senior Member
As you said, breaking in. 17.5 is fantastic with your specs, JMO.Our new truck has about 800 miles on it. So it's still breaking in. Current mileage is 17.5 mpg which is lower than I would like. Here's the spec's.
2021 Laramie 4x4 Crewcab 5'7" bed
5.7L V8 HEMI MDS VVT Engine (no e-Torque)
Curb Weight: 5241 lbs.
Gross Vehicle Weight Rating: 7100 lbs. / Payload: 1860 lbs.
Max. Towing: 11320 lbs. / Gross Combined Weight Rating: 17000 lbs.
8–Speed Automatic 8HP75 Transmission
1st 4.71
2nd 3.14
3rd 2.10
4th 1.67
5th 1.29
6th 1.00
7th 0.84
8th 0.67
Reverse 3.30
3.92 Rear Axle Ratio
275/55R20 OWL All–Season Tires (Circumference 100.2", Width 10.8", Height 31.9")
In 8th Gear, the engine turns once for every 3.179 feet traveled.
=1/(0.67*3.92)*(100.2/12)
With a 3.92 Rear Axle Ratio at 75 mph, engine RPM is approx. 2076.
=(75/60)*(5280/3.179)
With a 3.21 Rear Axle Ratio, the truck would travel 22.12% further at 3.883 feet traveled.
=(1/(0.67*3.21))*(100.2/12)
With a 3.21 Rear Axle Ratio 75 mph, engine RPM would be approx. 1700.
=(75/60)*(5280/3.883)
To get the same travel distance with a 3.92 Rear Axle Ratio, the tire height would need to be increased to approx. 38.9".
A set of 320/75R20 tire would get you there, but I doubt the truck would have clearance for them without modification.
A '60s vehicle with the same specs wouldn't even have DREAMED of breaking 10. More like 6-7.
What are you expecting?
I really don't get people who buy a 2.5 ton truck with a V8 and expect Prius mileage.