Best speed for Mileage? Find out

bbertram · **Joined:** Mon Dec 19, 2005 4:17 pm **Posts:** 144

Yesterday I had time to kill while driving back from an out of town visit. It was a sunny day with very little wind and a nice 25 degrees out. I found a nice straight stretch of highway with very little traffic so I did some tests with my ScanGuage II. The results:

I also did some testing in 2wd, part and full time 4wd. No difference in mileage from what I can tell. They all varied to the same degree. It wasn't as scientific as my first test but I concluded the results were all very similar between the three transfer case settings.

Jeger · **Posted:** Thu Jun 14, 2007 1:44 pm

Thanks for sharing, nice to see I need to slow down a bit :twisted:

ATXKJ · **Posted:** Thu Jun 14, 2007 1:56 pm

Yeah check the horsepower vs road speed on page 5

http://www.everytime.cummins.com/every/pdf/MPG_Secrets_Whitepaper.pdf

The problem is that I don't want to drive 80mph not 80kph - but I still want to get 30mpg.....

Threeweight · **Joined:** Mon May 14, 2007 5:57 pm **Posts:** 679

bbertram, are you running the stock tires?

Wobbly · **Posted:** Thu Jun 14, 2007 3:16 pm

Wonder how pre- and post- F-37 data compare.

Cowcatcher · **Posted:** Thu Jun 14, 2007 3:19 pm

I had not been on a lengthy drive since ORM so I was looking forward to a 100 mile freeway drive on Wednesday. Unfortuntely I was late for the meeting and there was a 35>40 MPH headwind. I started out at 75 MPH and the EVIC was running about 22.6 MPG. I finally made up the late time and dropped down to a little under 70 and the last 40 miles the mileage popped up to an average of 25.5 for the 100 miles. The wind and the speed were making a huge difference.

Of course the wind was down to about 10 MPH on the return so not much boost on the way back running at the 70 MPH limit or under. I got 33.12 on the return and a 31.2 overall. I would like to test it without wind going either

bbertram · **Joined:** Mon Dec 19, 2005 4:17 pm **Posts:** 144

Threeweight wrote:

bbertram, are you running the stock tires?

Stock size but not stock tires. I'm running no name brand tires which are much grippier and tougher, 10 ply I think. I run about 34 psi, want to try more sometime when I get a chance.

bbertram · **Joined:** Mon Dec 19, 2005 4:17 pm **Posts:** 144

Wobbly wrote:

Wonder how pre- and post- F-37 data compare.

I have a spreadsheet with mileage from day one till today, 186 fill ups I believe, over 10,000 liters of fuel used, almost 100,000 kms. I can make it available to you all, its pretty cool. The average has not changed much in either direction since the F-37.

Sir Sam · **Posted:** Thu Jun 14, 2007 3:49 pm

kilometers? WTH? I am simply incapable of keeping tracks of two measurement systems!

dgeist · **Posted:** Thu Jun 14, 2007 4:11 pm

Not too much surprise there, peak MPG (or KPL or whatever you metric folks use...) is right at the peak torque point (~1800 rpm). Interesting, nonethesless, though. It's always good to have empirical evidence backing up your scientific theory (and otherwise, alter your datapoints...).

DarbyWalters · **Posted:** Thu Jun 14, 2007 5:26 pm

I always hve agot the best MPG at 1825 to 1900 rpm. Just set the cruise and know I am getting better mpg for almsot every car/truck that passes me.

vtdog · **Joined:** Fri Sep 30, 2005 11:27 am **Posts:** 640

Problem for me is that if I tried running at 1800rpm for best mpg I would end up with a semi through the rear hatch. Most traffic moves along at 70-75mph

Endurance · **Posted:** Thu Jun 14, 2007 10:39 pm

Thanks for sharing this, awesome. If I go 120 kmh, which equals 75mph, I get 100% the exact same mileage you get. 23.6mpg

bbertram · **Joined:** Mon Dec 19, 2005 4:17 pm **Posts:** 144

Here is my CRD spreadsheet, you will need MS Excel 2003 or some other program to view it:

http://www.bbertram.com/gallery2/main.p ... temId=9751

BiodieselJeep.com · **Posted:** Fri Jun 15, 2007 11:02 am

Hmmm, 100kph (your optimal) is only 62 mph. A little slow for around here...

I drive at around 70 mph (112 kph) just to live and get 25, just like your chart. I calculate by hand, so that's good to see.

oldnavy · **Posted:** Fri Jun 15, 2007 11:46 pm

Best speed should be what ever the slowest you can drive with TC locked up. I don't drive the CRD enough to know/remember what that is, but I think it is about 50-55 mph on level highway. My guess is that speed would get you 35 to 38 mpg range depending on quality of fuel.

DarbyWalters · **Posted:** Sat Jun 16, 2007 5:46 am

35-38 might be a little optimistic...but if you could go 65 and get the last OD to lock up and then back down to 55 and hold the last OD you would most likely get 30+ (like at 80KPH-30+ @ 1679 rpm)

oldnavy · **Posted:** Sat Jun 16, 2007 8:31 am

DarbyWalters wrote:

35-38 might be a little optimistic...but if you could go 65 and get the last OD to lock up and then back down to 55 and hold the last OD you would most likely get 30+ (like at 80KPH-30+ @ 1679 rpm)

I managed slightly over 33 MPG's cruising at 66-68 MPH, so I figure I coulld get another 3 to 4 if I were able to drop the speed another 10 to 12 MPH and still have final gear TC lock up. I seem to remember our CRD will stay locked up on level roads down to about 50 MPH, if that is so and I was filled with 47 to 50 cetane fuel I feel that I could hit the 36-37 MPG mark if I still had OEM size tires. I now have wider and lower profile tire that is same height as OEM tires, but contact patch is wider and tire is a low pressure non energy tire unlike what came OEM on the Jeep. OEM were 44 PSI rated and we kept about 38 PSI in town and 40 PSI for trips, the current tires are max 36 PSI and we run 35 PSI in the tires. That in itself will make probably 2 to 3 MPG at the very least on the highway, tire inflation can make a big impact, more then most realize, because after change over to the new tires the MPG's dropped from 21-22 to 18-20 MPG in town.

Jeger · **Posted:** Sat Jun 16, 2007 10:14 am

Wow....mine kicks out of HI OD at anything under 60

oldnavy · **Posted:** Sat Jun 16, 2007 10:20 am

Jeger wrote:

Wow....mine kicks out of HI OD at anything under 60

Like I said I do not drive the CRD on a regular basis, it could very well be 60 MPH or even higher. The point is the slowest you can drive in high gear with TC locked up is your best MPG point. :wink:

Best speed for Mileage? Find out

Who is online