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Old 03-02-2012, 08:49 AM   #16 (permalink)
Join Date: Oct 2009
Location: Fort Worth, Texas
Posts: 2,442

2004 CTD - '04 DODGE RAM 2500 SLT
Team Cummins
90 day: 19.36 mpg (US)
Thanks: 1,422
Thanked 735 Times in 555 Posts
I accelerate my 3300-kg, 5.9L turbodiesel truck quite easily. Shift at 1,500-rpm or a touch lower (peak torque at 1,400-rpm, IIRC). Even with a trailer weighing somewhat more I don't find that harder acceleration is beneficial. On big trucks (lorrys) we don't ever give it more throttle than necessary to get to the next gear. "Rhythm" is what matters. Consistency. On those 10 thru 18 speed transmissions one would look up and learn (then practice) progressive shifting. Think of it as learning to waltz.

As a general rule-of-thumb, the highest gear at the lowest rpm is the best choice. So long as the truck does not "lug" one has made the best choice (especially on grades: don't downshift too soon).

So, "it" isn't about the throttle, but about the transmission gear. The single importance of the throttle is that it moves me between gears. And the gear choice is everything. I barely "use" the throttle, IOW.

The truck really needs nothing from you but strict attention to the road to determine shift points. The truck is "better" than you in the matter of greatest mpg is another way of viewing this. We work for the truck rather than the other way round. You might consider adding an Exhaust Gas Temperature gauge, and a Manifold Pressure gauge to be able to better listen to what you're being told. Low numbers of 600-F and 6-psi are good numbers for FE on my truck, for example.

Also, I'd analyze the times/distances your truck spends at highway speeds. While aerodynamic concerns are valid at lower speeds, the loss of utility may yet be present and cancel removal of the roof rack . . after all, a truck not used as a truck might be better replaced with another vehicle. To this end I recommend being able to calculate average kmh at the end of a tank-full (and on a calendar basis).

You might also contact the editor of - Big Lorry Blog and ask if he knows of a link or a source to your stated interest. He's a very wide range of readers and contacts across the Commonwealth.

Now, I can't say comparing my truck to your has great equivalence, but if it is of help, then:

* With six forward speeds, and First being extra-low (a granny gear) I use it almost exclusively to get the truck in motion and am out of it almost instantly (unless crossing a roadway, etc). Getting all the mass in motion is my thinking (debate-able, according to other owners), but I prefer to set up that rhythm mentioned above. After all, the engine rise between gears is only a few hundred rpm.

* As Overdrive is the top gear -- and with the short axle gears of this truck -- most cruising in town is in Fourth or in Direct. As the goal of shifting is to arrive in the chosen "top" gear quickly, the "place" to shift (that point ahead on the roadway) must be amenable to such. Loss of momentum hurts, IOW. The weight of the vehicle, the mass, favor an even slower acceleration if a blind spot is ahead, traffic slowing, a turn is coming up, etc.

* Planning the trip I am making is beneficial. Delivery services here in the States use routing software to eliminate turns across traffic and to travel as many miles as possible at a steady speed. So a few miles out-of-route on longer trips is beneficial to this, and even in travel around town is an extra half-mile a good thing if it avoids several full stops or traffic lights. (I may think I "know" the best route, but have been proven wrong by consulting this form of GPS aid prior to travel).

* Most of all, note military or other convoys that are heavily loaded. They take no account of other traffic as their weight and gearing preclude the rapid acceleration to which we civilians are accustomed. A steady pace that emphasizes longest life (drivetrain ease) is therefore beneficial. Etc.

I see that my fuel consumption is about an average 10.6L/100-km. Look forward to what yours can do and how you've improved it in percentage terms.


Last edited by slowmover; 03-02-2012 at 09:38 AM..
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