"Real World" diesel fuel mileage on Duramax

[jeffster]

What is the ratio of DEF to Diesel?

No idea yet. I have heard some guys on the dmax forums that are using about a gallon to every thousand miles or so, but there was one guy who has over 10k or something and still hasn't added any. My DIC just says OK for DEF level (they added that in 2012), until it gets somewhere around 40% and then will report percentage. I haven't gotten confirmation but it seems like the Insight CTS may be able to report more accurately than the DIC (though presumably getting the same info of course).

 

[dodge man]

Nice truck and I like the color. When you buy a vehicle like that, I wouldn't worry about the mileage, it is what it is. For some reason though, I always check the MPG of my truck on every fill up, I don't know why. Hand calc a couple of tanks and see how good the computer mileage is also.

 

[sparc]

My guess is the 20" wheels are killing the mpg. They effectively change the final gear ratio versus the standard 17" one that come on it.

Chris

Its more about the radius of the tire than the wheel diameter isn't it?

My '12 f-350 4x4 sc srw is showing 18.2 MPG on the computer since mile 1. Right now i'm at ~3700 miles.

 

[timswi]

Its more about the radius of the tire than the wheel diameter isn't it?

My '12 f-350 4x4 sc srw is showing 18.2 MPG on the computer since mile 1. Right now i'm at ~3700 miles.

The OD of the tires on my GMC OEM 20" wheels are exactly the same as the 17" OEM combo on my brothers Chevy.

 

[Diamondpilot]

Its more about the radius of the tire than the wheel diameter isn't it?

My '12 f-350 4x4 sc srw is showing 18.2 MPG on the computer since mile 1. Right now i'm at ~3700 miles.

Yes it is and you can up or down size rims and get the appropriate tire to get the same rolling diameter but unsprung weight with heavier wheels always seems to hurt MPG in my experience and also hurt stopping distance while making the ride a tad worse.

Chris

 

[hodge]

Its more about the radius of the tire than the wheel diameter isn't it?

My '12 f-350 4x4 sc srw is showing 18.2 MPG on the computer since mile 1. Right now i'm at ~3700 miles.

Do you hand calculate your mileage, to see if the computer is telling the truth?

 

[timswi]

Yes it is and you can up or down size rims and get the appropriate tire to get the same rolling diameter but unsprung weight with heavier wheels always seems to hurt MPG in my experience and also hurt stopping distance while making the ride a tad worse.

Chris

After rotating my 20's a couple of times, I really don't notice any material weight difference...The ride might be slightly more harsh, but I can't honestly say I've noticed...As far as braking, my GMC stops like a Corvette.

 

[jcmseven]

The 20" wheels are lighter on that truck than are the 18" ones. They use higher grade materials and more material is removed during machining, so the mass of this particular wheel is less than its smaller counterpart. I think one would probably experience a bit BETTER braking in this scenario due to the contact patch and the stability/profile of the wheel, but the difference is likely small. With a diesel truck, especially one having this much power, it is unlikely that wheel size such as this would make any real difference in economy or performance. The manufacturers carefully calibrate the rollout on these wheels and the effect on steering/suspension geometry when designing wheels such as this. This is one reason that one almost never gets the same feel, economy and performance from aftermarket wheels/different sized tires bought down at the ol' tire ship as he does from a factory combo. Factory=almost always better.

John M

 

[timswi]

The 20" wheels are lighter on that truck than are the 18" ones. They use higher grade materials and more material is removed during machining, so the mass of this particular wheel is less than its smaller counterpart. I think one would probably experience a bit BETTER braking in this scenario due to the contact patch and the stability/profile of the wheel, but the difference is likely small. With a diesel truck, especially one having this much power, it is unlikely that wheel size such as this would make any real difference in economy or performance. The manufacturers carefully calibrate the rollout on these wheels and the effect on steering/suspension geometry when designing wheels such as this. This is one reason that one almost never gets the same feel, economy and performance from aftermarket wheels/different sized tires bought down at the ol' tire ship as he does from a factory combo. Factory=almost always better.

John M

I can't disagree with anything you said John.

 

[jeffsw6]

Yes it is and you can up or down size rims and get the appropriate tire to get the same rolling diameter but unsprung weight with heavier wheels always seems to hurt MPG in my experience and also hurt stopping distance while making the ride a tad worse.

Wheels and tires aren't just unsprung weight, they are rotating mass. angular momentum