Better mileage with higher speed.

[cgreen]

Just went to SC and back. Going there, I set my cruise at just under 70 to try and maximize mileage. I ended up getting 17.5 that tank. On the way back, I ran around 75-77 the whole way and got a personal best of 19.25. I know it defies the laws of physics, but for some reason my truck gets beter mileage at higher speeds. Not bad for the dually I think. :cornut:

 

[cgreen]

Oh yeah stock except for Predator on 85 and a drop in AFE filter. :yesnod:

 

[stacks04]

cool. that is good for sure on dually.

 

[Jasondt2001]

That just can't be right... I'm trying this!! Thanks!

 

[Sparky8370]

My truck seems to get a little better mileage when I romp it a little. If I just drive it around normal it does ok, but if I drive a little spirited it def does better. It gets better when I drive than when my wife does. I found the "sweet spot" to be in the 70-75 range.

 

[Tow Master]

Thats pretty dang good especially for a dually!

I just went on a trip and did about the same speed out and back yet got 20mpg out and 17 comming back :frown2:

 

[btfarm]

Whatever speed you're at when running about 1700 rpm seems to be about optimum. Drafting a semi is of course a huge bonus:yesnod:

 

[BudTX]

<pssssst> <there was a 40 mph tailwind on the return trip>

 

[MACKIN]

<pssssst> <there was a 40 mph tailwind on the return trip>

That and it was all down hill :lol:


Were those numbers hand calculated or ? I've gotten 17-18 with my dually before when it was stock.

 

[RYDNHI4X4]

I ran my Predator on the 120 tune and got better mileage then tuned with the 85. With the 120 I was getting 20-21mpg. Towing a boat and trailer weighing apx. 4500lbs. I got 16.5mpg on the 65 tune.

 

[Ed HD]

Best on our 05 has been 19.1, and that was me driving a little spirited as well

 

[cgreen]

<pssssst> <there was a 40 mph tailwind on the return trip>

shhhhh... :coolgleamA: Actually the trip there was in the dead of night, and the return trip, if anything would have been back into the wind. Don't know but it sure is a lot better than my Isuzu at 8 mpg. :nonod:

 

[RayMich]

I hope you all are hand calculating your mileage when figuring your miles/gallon and you have calibrated your speedometer/odometer with a GPS or something just as accurate. Otherwise you may be fooling yourselves.

From what I've seen with the Predator, is that if you set your tire size to the same size as shown in the tires sidewall, your speedometer/odometer will read way high (almost 4% too high). This means that for every 104 miles shown on the odometer, the actual distance is only 100 miles.

Also keep in mind that all tires are not created equal; some will flex more than others when loaded, as well as have different tread depth. Ultimately the determining factor is the revolutions per mile for each tire, which will make a difference on how fast the truck will go or how far it will travel for a particular indicated speed on the speedometer or miles on the odometer.

You'll need to experiment with a GPS and tire settings in order to get your speedometer/odometer to read correctly.

Example:
For the Nominal Tire Size: 265/75R-16
...................................................NEW Tire
Tire Make and Model........SIZE.......Load Range...Revs/Mile
BFG All Terrain T/A KO..LT265/75R-16......E..........654
BFG All Terrain T/A KO..LT265/75R-16......D..........656
Goodyear Wrangler SA....LT265/75R-16......D..........656
Goodyear Wrangler SA.....P265/75R-16......SL.........660
Michelin LTX A/T2.......LT265/75R-16......E..........657
Michelin XC LT4.........LT265/75R-16......E..........652

At 70 MPH, ONE Rev/Mile will equate to approximately 0.11 mph for this nominal tire size - So the Michelin XC LT4 LT265/75R-16 will actually run 0.88 mph faster for the same speedo/odometer reading of 70 MPH compared to the Goodyear Wrangler SA P265/75R-16 ---That is 70.9 vs 70.0 MPH or 1.3% faster for the same basic tire sizes.

These two conditions can add up to more than 7% error in fuel economy numbers and when you combine that with the DIC error, the MPG figures can become totally meaningless...

Obviously, as the tire wears down, the revs/Mile will go up and the actual speed and distance will go down.

Even after you set your speedometer to read right on the money, the DIC will read higher and higher for each of the higher HP tunes. This makes the DIC's MPG numbers quite useless.

In the past, I have seen the following errors:

...TUNE
SETTING.............DIC Error
.40 HP.....>2.1% Too High
.65 HP.....>4.8% Too High
.85 HP.....>9.5% Too High
125 HP.....>More than 20% Too High in some instances

So, ultimately, I would recommend checking your speedometer calibration with a GPS and hand calculating each fill-up, making sure to fill the tank to the same spot on the filler neck.

 

[cgreen]

Ray, what I did was run the mileage on Yahoo maps and ran the exact same route and the mileage matched. I always hand calculate, my DIC is always off one way or the other by a little bit, but it does give a reference so that I can get an idea of when I will have to stop for fuel. I may be going to 235's soon, so I will have to figure out how to get the tire size right. Do you guys think going to 235's will hurt mileage?

 

[RayMich]

I also use the DIC as a "rough" gauge to determine when I should stop for fuel. But I've had instances when the DIC in my truck was OFF by almost 1 gallon compared to the actual number of gallons from the pump. That can make a big difference in your actual miles per gallon. I also try to use the same fuel stations and if possible the same pumps as much as possible.

The problem I've seen with going by the mileage on Yahoo Map or Google Map or any computerized map is that those are really approximations; they also don't include any side-trips you may need to take for fuel, food, lodging, groceries, etc. They are often very close, but many times they are not. That is why any time I change tires, or change anything that might affect my speedometer accuracy, I re-check my speedometer with a GPS and against a previously verified distance on the highway; that way I can calculate a correction factor for those tires, etc.

I guess all those years as a vehicle test engineer have made me pretty anal about trying to get the best accuracy out any instrumentation I use. But if your method works for you and you're happy with it, that's the important thing for your use.

EDIT: I don't have any experience with 235 tires, so I can't tell you for sure. Keep in mind that no two tires are the same. Tread design, tire flex, revs/mile, rolling resistance, tire pressure, etc. can make a difference in fuel economy.

 

[Sparky8370]

I have 265/75/16 tires on my truck. With the stock speedo calibration it was almost exact. When I got efi live I entered this tire size and it was way off. I did just like Ray was saying, I got out my gps and checked my speed. Then I went into efi live and did the fine speedo adjust. It brought my pulses per mile back to almost stock, pretty close anyway. And it was almost 4%.

 

[BIGR]

Seems like real good mileage for that speed? For some reason I had it in my head that my fuel mileage had went down, so I just got through doing a fuel run (checked mileage) around the house in the mountains. At speeds from 55 to 65 MPH some four lanes I got 19.855 MPG hand calculated, filled to the top each time. I took off easy at stop lights and did have some city driving mixed in. I might could improve it if I would get rid of that 250 pounds in the bed of the truck, but heck I need my tools and spare fuel filters and junk. Dang its hard to stay out of the fuel, especially when some jerk wad gets beside of you and just drags along. Out west in 2006 I got over 19 MPG with the cruise set on 70 MPH. In the past I have got as high as 22.8 MPG hand calculated.

 

[jettech]

Mine does nothing but go down after you break 60mph.

 

[cowdoc]

I hope you all are hand calculating your mileage when figuring your miles/gallon and you have calibrated your speedometer/odometer with a GPS or something just as accurate. Otherwise you may be fooling yourselves.

From what I've seen with the Predator, is that if you set your tire size to the same size as shown in the tires sidewall, your speedometer/odometer will read way high (almost 4% too high). This means that for every 104 miles shown on the odometer, the actual distance is only 100 miles.

Also keep in mind that all tires are not created equal; some will flex more than others when loaded, as well as have different tread depth. Ultimately the determining factor is the revolutions per mile for each tire, which will make a difference on how fast the truck will go or how far it will travel for a particular indicated speed on the speedometer or miles on the odometer.

You'll need to experiment with a GPS and tire settings in order to get your speedometer/odometer to read correctly.

Example:
For the Nominal Tire Size: 265/75R-16
...................................................NEW Tire
Tire Make and Model........SIZE.......Load Range...Revs/Mile
BFG All Terrain T/A KO..LT265/75R-16......E..........654
BFG All Terrain T/A KO..LT265/75R-16......D..........656
Goodyear Wrangler SA....LT265/75R-16......D..........656
Goodyear Wrangler SA.....P265/75R-16......SL.........660
Michelin LTX A/T2.......LT265/75R-16......E..........657
Michelin XC LT4.........LT265/75R-16......E..........652

At 70 MPH, ONE Rev/Mile will equate to approximately 0.11 mph for this nominal tire size - So the Michelin XC LT4 LT265/75R-16 will actually run 0.88 mph faster for the same speedo/odometer reading of 70 MPH compared to the Goodyear Wrangler SA P265/75R-16 ---That is 70.9 vs 70.0 MPH or 1.3% faster for the same basic tire sizes.

These two conditions can add up to more than 7% error in fuel economy numbers and when you combine that with the DIC error, the MPG figures can become totally meaningless...

Obviously, as the tire wears down, the revs/Mile will go up and the actual speed and distance will go down.

Even after you set your speedometer to read right on the money, the DIC will read higher and higher for each of the higher HP tunes. This makes the DIC's MPG numbers quite useless.

In the past, I have seen the following errors:

...TUNE
SETTING.............DIC Error
.40 HP.....>2.1% Too High
.65 HP.....>4.8% Too High
.85 HP.....>9.5% Too High
125 HP.....>More than 20% Too High in some instances

So, ultimately, I would recommend checking your speedometer calibration with a GPS and hand calculating each fill-up, making sure to fill the tank to the same spot on the filler neck.

What he said!

 

[cgreen]

Just knocked down 18 unloaded coming back from Memphis with the cruise set at just under 75. My odometer is dead on with mileages from yahoo maps with stock tires.