07' Ram Top Speed?
09-18-2006, 06:41 PM
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07' Ram Top Speed?
07' CC LB dually. G56 w/ 3.73 and stock tires. I feel like i need 7th gear on the highway
! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??
! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??
09-18-2006, 09:43 PM
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07' CC LB dually. G56 w/ 3.73 and stock tires. I feel like i need 7th gear on the highway ! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??
! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??At 65 your getting good mpg. so don't go waisting fuel at 85+, the mpg really goes down hill at those speeds.
09-18-2006, 11:23 PM
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Wow, that's sad. My '02 with NV5600 and 3.55 gears ran 2000 rpm at just over 70, which seemed perfect. I know the truck would easily go over 110. My '06 with 48RE runs about 2000 at just over 70. Sounds like these new axles need some 3.55 gears (or lower!).
Tad
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09-19-2006, 12:31 AM
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07' CC LB dually. G56 w/ 3.73 and stock tires. I feel like i need 7th gear on the highway ! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??
! Truck is at redline at 100. @ 80 she sits around 2500rpm. 65 is approx. 2200. I know bigger tires would offset this a little bit but something seems off. This def is affecting fuel mileage. What are the options? any O/D kits??Anyway I found this a week or two ago & thought about it but .. 3k buys over a thousand gallons of diesel
http://www.gearvendors.com/dmanual.html
With 265's and a 6th over at .57 you're right on 1800 rpm at 80 mph. 2500 you'd be turning 111 mph.
09-19-2006, 05:56 PM
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A BIG component of the mileage drop at higher speeds is increased air resistance, which is a second-order function (i.e. increases with the square of velocity). Our trucks are not very aerodynamic, and from my experience it appears that air resistance becomes the dominant factor above ~60 MPH. It happens that with a G56 transmission and 3.73's you also go above 2000 RPM right about there, and Cummins says that mileage drops above 2000 RPM. So there's two factors right there that conspire to drop your mileage above ~60 MPH.
I considered going to larger tires to improve the final ratio, but numerous studies have shown that increasing the height of the truck makes the aerodynamics worse. I suspect that the few percent you might gain from slightly larger tires would be offset by increased aerodynamic losses. I seem to recall reading that folks here on this site have actually tried that and found it to be true.
FWIW, I seem to get the very best mileage in the 40-55 MPH range. Up to 60 MPH doesn't seem to hurt much, but above that the effect is very noticeable. It then becomes a simple decision: Fuel cost vs. clock time. Generally, if the speed limit permits, I'll spend the fuel and save the time.
I considered going to larger tires to improve the final ratio, but numerous studies have shown that increasing the height of the truck makes the aerodynamics worse. I suspect that the few percent you might gain from slightly larger tires would be offset by increased aerodynamic losses. I seem to recall reading that folks here on this site have actually tried that and found it to be true.
FWIW, I seem to get the very best mileage in the 40-55 MPH range. Up to 60 MPH doesn't seem to hurt much, but above that the effect is very noticeable. It then becomes a simple decision: Fuel cost vs. clock time. Generally, if the speed limit permits, I'll spend the fuel and save the time.
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10-03-2006, 01:51 PM
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I am at 1900 at 70 with 285s and 3.73s behind a 48re. Do those high rpms get on your nerves? I drove an 06 and I really didn't like that needing another gear feeling.
Joe
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