Shovelhead

Little test.

In February, I drove from Norfolk/Virginia Beach area.
Filled up to the neck, reset trip odo, drove home with cruise set at ~2100 rpm (approx 65 mph).
Refilled to the neck near the house.
Using a 4% error factor to compensate milage for the taller 235 tires achieved 20.5 mpg.
Today,
Filled up to the neck, reset trip odo, drove ~320 miles @ speeds averaging about 75 mph.
The only difference was speed and the fact that today I had Wifey with me.
(That explains the higher speeds....she hates it when people aren't in the fast lane at full-boogie)
Refilled to the neck near the house.
Using the same 4% error factor to compensate milage for the taller 235 tires achieved 17.9 mpg.

Speed Kills (fuel milage)

Also noticed that the same fuel station that had diesel priced @ $2.69 gal at 10:00 this morning had dropped it to $2.59 gal by 7:00 this evening.

edwinsmith

Yep. More speed = More drag. More drag means more power to overcome the drag. More power takes more fuel.

Wheels and tires make a big diff also. Duallys get worse mileage because there are two more tires on the road and a little more air drag. The width of the tire makes a difference too. This is why racing bicycles have those skinny tires. Easier to pedal.

But then you already knew that.

infidel

Cummins gets technical about the effects of speed and other factors here
http://www.everytime.cummins.com/eve...Whitepaper.pdf

Begle1

You drove at 65 MPH for 320 miles?




You can even set the cruise at speeds that low?

I get 16 averaging 80 on the freeway and I get ~14 driving as recklessly as possible around town.

Even at 80 with the 1st gen body, 16 MPG with a 3.07 rear end always strikes me as a bit low...

Shovelhead

Now add two more wheels on the ground, and the extra weight of the quad-cab, coupled with an auto trans and a 4.10 gear.

bluebull

I've often wondered about those 2 extra wheels. Do they actually decrease fuel mileage?

I have not sat down and figured it out but.
If you take stock trucks the duallies come with narrower and shorter tires than what are on stock SRW trucks. Now if you take the the actual rubber from each tire and rotational size differences is there really that much difference between duallies and none duallies as far as mass and power to drive each set?

Geico266

What were the wind dirctions when you were traveling? Wind has a huge effect on milage also. Going 65 MPH with a 20MPH head wind is like going 85MPH.

crobtex

I always bust 20+ on the highway when I keep it just below 65 mph. Anything above that and it degrades with the higher speeds.

Did you say the price dropped?

Shovelhead

You also have the additional wind drag from the wider combined cross section of the tires and the wheelboxes.
Wind was not really a factor either run <5 mph (slight breeze)

WideOpenThrottl

I've noticed apprx. the same difference in milage going from 60 to 75-80mph. but now with the dynomite injectors I've been able to pull a hair over 20mpg at 75-77mph. I never could get that before at them speeds with stock injectors.
Tim.

Chrisreyn

I've noticed that if I drive at 60-65mph, turning about 1800-2000 rpm, I get MUCH better mileage than if I drive 70-75 mph turning 2250-2500...
I have decided its worht the $$ to take my time getting places...

A 500 mile trip( Topeka to Denver) at 70 mph will take 7.1 hours...
at 65 mph it takes 7.6 hours...not that much of a difference....