MPG There must be more to it

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10-31-2006 | 06:52 AM

#16

cskal

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Joined: Jun 2006

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I have never gotten below 20 mpg (hand calc) since day one. I have noticed a slight drop in mpg lately, not sure if it is cooler temps, ULSD, or a little of both. I plug in when temps hit 40 or below, I hit the highway just about when the t-stat opens so I'm at op-temp. Truck has 15K. I drive 130+ miles per day to work and back via interstate, 60 mph. I keep my tires inflated as per the placard on the door with 60 in the front and 45 in the rear.

For guys running 80 psi in the front, how's your tire wear?

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10-31-2006 | 07:13 AM

#17

v8440

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Joined: Oct 2004

Posts: 934

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From: Alabama

Quote:

Originally Posted by 04ctd

that beat you up bad on ride? roads in SC are "historic" - in other words, about the same conditions as Columbus found them, when he came over here looking for a CTD

roads here about beat your teeth out your head.

I honestly haven't noticed much of any difference in ride quality between 55 or so and 80, in the fronts. I guess the weight of the engine forces the tire to give a little regardless of pressure. The rears are a different story-run those at 80 with no load, and you'll bounce all over the place while wearing out only the center of your tires. I'll put it this way-try the fronts at 80. If you don't like it, it's easy to let them back down.

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10-31-2006 | 07:39 AM

#18

Totallyrad

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Joined: Nov 2005

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From: Birmingham, Alabama

As always, tire pressure is as varied as the truck we each drive. I have to run 75 in the fronts to carry the loads I do. When I towing my front axle weights are a little over 4450. I tow about 70% of the time. The rears only need about 35-40. All pressures are based on "what it takes" to make the tires wear evenly across the tread. As long as I can stay above 30 and below 80 I'm good.

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10-31-2006 | 07:43 AM

#19

v8440

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Joined: Oct 2004

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From: Alabama

There's not much ambiguity in FRONT tire pressure. Run 75 or 80 is pretty much a good rule to follow for mileage. You won't prematurely wear out the centers on the fronts with any normal size tire, as the front is just too heavy for that. Now, optimum rear tire pressure can swing all over the map depending on both load and whether it's a SRW or a dually.

I feel I can safely say that if you're running much less than 80 in the front tires of a dodge truck with a cummins, you're screwing up. (assuming you don't have huge mudders or something else far from stock)

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10-31-2006 | 08:02 AM

#20

Totallyrad

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Joined: Nov 2005

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From: Birmingham, Alabama

Quote:

Originally Posted by v8440

Another thing that probably plays a role in mileage differences is slight manufacturing tolerances in the crank position sensor pickup and tone wheel assembly. I've seen at least one or two people comment on how they did the tone ring mod, and in the process discovered that there was a bit of slack in there from the factory. I can't remember exactly where the slack was, but it was enough to make a degree or two of difference in timing from one truck to another. That's enough to account for noticeable differences in mileage.

I don't know if this last thing is common at all, but it is also possible for one or more injectors to be bad in an insidious way, in this case meaning that the truck seems to drive fine, but just never gets good mileage. It does not have to result in fuel being dumped into the crankcase or billowing clouds of white smoke.

I have to say I agree with this. When time permits, I'd like to check the slack/proper alignment associated with the timing components of my truck. I, like you, think there is 1 or 2 degrees of timing there to be had. Call it a no mod bomb, just tuning, but two degrees of advance can do good things to mileage and low end torque. As to injectors, they are all supposed to be in spec. when they're installed but the guys that go and buy "performance" injectors that are more closely matched usually report their trucks run smoother. There's got to something to it. I have allot of black sooting on my truck. I don't have any bombs other than an AFE torque tube. I believe I could gain from the timing tuning since I have unburned fuel going out the tail pipe.

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11-01-2006 | 08:06 AM

#21

madhat

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Joined: Jun 2006

Posts: 14,965

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From: Jacksonville, NC

Quote:

Originally Posted by bluebull

Have you recalibrated your speedometer for bigger tires?

I did, I think that it's still 3-4 off, according to the cop that stopped me the other day. I thought of that a while back, took me from 12-13 to 14-15.

Thanks fot the help, bluebull...

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