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Axle Ratio & High Speed Towing

7412 Views 9 Replies 7 Participants Last post by  Accused
Fourwheeler had this to say about a test of a Crew Cab ecoDiesel pulling a ~7300 lb trailer:

"Our 3.0L backed with the eight-speed transmission and 3.55 axle gears was always able to maintain a minimum of 55-60 mph on our brutal test route. While ascending the steepest areas on the route, which included the 6 percent grade of the Grapevine, we had our foot to the floor and the V-6 was spinning at 4,000 rpm for several minutes in order to maintain 55 mph. On less steep sections the little diesel quietly motored along between 2,000 and 3,000 rpm, and still had enough reserve power to make passes."

When Fast Lane Trucker tests the ecoDiesel next month on the Ike Gauntlet, at higher elevation and slightly steeper 7% grade, I have doubts that the Ram will hold 55mph. This won't look good vs. the F-150 ecoBoost which easily maintained >60mph on the Ike Gauntlet. The higher altitude may not be too bad, because the single turbo will compensate some for the lower oxygen levels. It's the lower horsepower of the Ram that might hinder high-speed towing at the extremes.

Question: Will switching to the 3.92 only help low speed (0-50mph) acceleration and towing power, or will it also help to maintain speed at say 60 or 65 mph? If so, let's hope the 3.92 is used on the Ike Gauntlet for a real test of this truck's capabilities. The answer may not be easy, and may depend on how Ram has programmed the ecoDiesel to stay in its power band in combo with the 8-speed transmission and the different axle options.
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Other way around. They're really 3.55:1 so With 3.55 the motor turns(crank shaft) 3.55 times to the wheels 1 revolution. With 3.92 the motor spins 3.92 times to the wheels one so for a given road speed (number of tire revolutions) the higher the engine speed.
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