Originally Posted by randomid25
Doesn't have anything to do with vehicle speed. Has everything to do with engine speed. With the right gearing, a diesel will be happy at 85mph all day long.
This is true, but as I stated, I haven't been in or owned a diesel that had gearing tall enough to be happy at 85 mph.
They all seem to have gearing that makes them happiest at 70-75.
And my current diesel is a German made car, intended for autobahn blasting.
I've had it into triple digit speeds on the open road a couple times for brief periods, and it seemed fine, but it's definitely not a relaxed drive at that speed.
You seem to be able to hear and feel a "change" in engine note around 75 mph where prior to that, at 70 mph you basically can't even hear or feel the engine.
I've know a couple people with diesels too and they have all said the same.
BMW's diesel may be an exception.
In the 5500-6000 lbs Ram with a small 3.0 liter V6, pushing that heavy truck with a large front through the wind with only 240 hp, i'm guessing the 3.55 will be a needed axle ratio for acceptable acceleration and towing power, but may have that diesel engine humming a bit at 75+ mph.
Get a 3.92 in there and I am even more sure that little 3.0 diesel pushing that heavy truck will be humming along at 75+ mph.
I've been in Ford's big diesel 2500's and Dodge's Cummins and both were also most comfortable at 70-75 mph, and they have a much better power and torque weight ratio than the 1500 RAM will have with the 240 hp 420 tq 3.0 liter.
Time will tell.