Community Forums

roscoesdad · 12-04-2010, 02:35 PM

Last Saturday I drove from Las Cruses, NM to Benson, AZ, in 40 mph winds with gust to 50 mph. It was mostly a head wind. My fuel burn was 5.98 mpg. Drove from Buckeye, AZ to Indio, Ca with no wind and fuel burn was 8.59. Wind is the biggest obstacle to fuel milage in a MH.

Mike Canter · 12-04-2010, 02:44 PM

I think you will find it all explained here.
http://www.rvtechlibrary.com/engine/...erformance.pdf

and

http://cumminsengines.com/assets/pdf...whitepaper.pdf

It has a lot of effect on MPG

Superslif · 12-04-2010, 02:44 PM

Even with my trailer (24') I can get 13mpg with a tail wind and struggle to get 11 mpg in a head wind. I also will loose 1mpg traveling at 65 instead of my normal 58mph.

WOODYDEL · 12-04-2010, 05:13 PM

Quote:

Originally Posted by roscoesdad

Last Saturday I drove from Las Cruses, NM to Benson, AZ, in 40 mph winds with gust to 50 mph. It was mostly a head wind. My fuel burn was 5.98 mpg. Drove from Buckeye, AZ to Indio, Ca with no wind and fuel burn was 8.59. Wind is the biggest obstacle to fuel milage in a MH.

I posted several times links to how and why about fuel economy.

Headwinds and driving too fast have exactly the same effect. Now if you are attempting to drive too fast AND have a headwind you will get the double whammy.

That's all I'll say because no matter what scientific evidence is presented you will still get the obstinant individual that will doubt it and think it's OK to drive 75 MPH or there abouts.

I participate on the ECOMODDER site and conversations there about fuel economy are much more fruitful.

FleetMan · 12-04-2010, 06:04 PM

My war story towing a 7,000# travel trailer with a Ford F-250 Powerstroke Diesel - no chips or tuners. I-94 across North Dakota with 40+ mph headwinds, could not maintain speed in overdrive, had to use third gear all the way, 9 to 9.5mpg. Another trip westbound on I-80 across Wyoming with similar winds but on the tail this time - an honest 17.5 mpg from Evanston to Cheyenne. Tail winds sure are nice!

W4RLR · 12-04-2010, 09:05 PM

Fighting head winds all the way last week from San Antonio to Crestview, got 8.5 mpg towing my Jayco fiver. On the trip out, I managed 10.5 mpg. It was a struggle on the way home to keep the engine in the sweet spot, 1850 rpm to maintain 63 mph. I finally abandoned the effort.

LewF · 12-05-2010, 06:29 PM

Mike, very good info on the links you provided. I was surprised, but shouldn't have been, at the impact the driver has on fuel economy - as much as 30%. Thanks for finding this information.

Lew

Mike Canter · 12-05-2010, 06:58 PM

Yea, the Cummins data is interesting. On a Thanksgiving trip I was driving a long flat stretch of road and had zero wind, at 500ft altitude and it was 70 degrees. I put the cruise control on 55 mph and let it go for 40 miles and was getting 8.0 mpg average on the Aladdin computer (no stopping or accelerating). Then I upped it by 2 MPh on the MPG dropped to 7.8. So I increased by another 2 mph and again it the mpg dropped another 0.2 mpg. So during the test the MH started at 8.0 mpg at 55 mph and dropped 0.1 mpg for every 1.0 mph increase in speed. Then I re-read the Cummins Whitepaper and that is exactly what they say right on the money. I am not sure how accurate the Aladdin is and my 8.0 mpg maybe 7 or 9 but the change in average mpg would be accurate.

I think when Cummins say that the driver can change the economy by 30% would make be believe they are talking about a manual transmission and no cruise control and the speed the truck is going. Other than the speed the MH is going we are pretty well locked in to what we see is what we get. Now the way we accelarate coming on to the freeway or around town can make a difference.

WOODYDEL · 12-07-2010, 07:01 AM

Quote:

Originally Posted by Mike Canter

Yea, the Cummins data is interesting. On a Thanksgiving trip I was driving a long flat stretch of road and had zero wind, at 500ft altitude and it was 70 degrees. I put the cruise control on 55 mph and let it go for 40 miles and was getting 8.0 mpg average on the Aladdin computer (no stopping or accelerating). Then I upped it by 2 MPh on the MPG dropped to 7.8. So I increased by another 2 mph and again it the mpg dropped another 0.2 mpg. So during the test the MH started at 8.0 mpg at 55 mph and dropped 0.1 mpg for every 1.0 mph increase in speed. Then I re-read the Cummins Whitepaper and that is exactly what they say right on the money. I am not sure how accurate the Aladdin is and my 8.0 mpg maybe 7 or 9 but the change in average mpg would be accurate.

I think when Cummins say that the driver can change the economy by 30% would make be believe they are talking about a manual transmission and no cruise control and the speed the truck is going. Other than the speed the MH is going we are pretty well locked in to what we see is what we get. Now the way we accelarate coming on to the freeway or around town can make a difference.

I posted the info needed to save fuel in several posts and it seemed to be hopeless to convince the readers. Your on the road results might help to sway habits. Glad you took the time.

Mike Canter · 12-07-2010, 07:18 AM

Well if they don't believe us then they should believe the CAT and Cummins reports in my earlier post. The CAT report is all about motorhomes. The Cummins Whitepaper does include a data on big rigs but there is a lot of good data that applies to MHs also. The Cummins report talks a lot about specific operating RPMs which we call the "Sweet Spot" . Each engine has it and it appears that the motorhome gearing and size tire all puts the "Sweet Spot" around 60-62 mph regardless. I know at 62 MPH my Signature is at 1450 rpm which is the Sweet Spot for the Detroit Series 60 motor. Now it is obvious that one can improve the MPG if you go even slower but I believe that mainly applies if the road is real flat because if you get the RPM down too low on a hilly road then the motor is on the down side of the torque curve and will have to downshift on the hills which will result in more fuel being used.

WOODYDEL · 12-07-2010, 07:21 AM

Yesterday I took a 6 mile walk to the post office. Weather conditions 15+ mph wind and just above freezing. The wind was in my face going and I could feel myself working against it. Then it dawned on me that the OP's revelation about headwind is common knowledge to all runners. I did many a race where the wind was a major obstacle and if you add hills to the mix well it just makes it harder to make headway. When running away from the wind we used to put the extra speed "in the bank". That increase in speed did not always work out as planned.

I used to have the info about the effects of wind and hills handy but this link has some statistics at the bottom of the paragraph. Keep in mind that a human alters his stance but you'll get the idea of how headwinds affect everything. Notice the effects at different running speeds.

Effects of wind assistance and resistance on the forward motion of a runner -- Davies 48 (4): 702 -- Journal of Applied Physiology

So that is why I'm saying to maybe get on those sneakers to remember what the wind is doing and believe the scientific information.