Hills

[lolder]

Do hills improve or degrade mpg? I did a 6 day 2900 mile trip in Sept. from FL to AR and back on interstates at the speed limit in 70-90 deg. temps. I got 38.9 mpg. overall. The 12 individual legs mpg. varied from 37.5 to 41.4 mpg. The 41.4 came on a leg from near Paducah, KY to Chattanooga, TN that was rolling terrain with one long hill near Chatt. that fully charged the battery going down it. This is a small anecdotal sample but I have heard support for both increased or decreased hill mileage. The potential energy change of a hill is 100% efficient, much better than the battery charge/discharge. The ICE is at higher power going up the hill and should be more efficient and has no or little fuel flow going down. What do you folks up North think about this? I want to help get you out of your cold winter mpg funk.

 

Lee

Edited December 11, 2009 by lolder

[junehhan]

Do hills improve or degrade mpg? I did a 6 day 2900 mile trip in Sept. from FL to AR and back on interstates at the speed limit in 70-90 deg. temps. I got 38.9 mpg. overall. The 12 individual legs mpg. varied from 37.5 to 41.4 mpg. The 41.4 came on a leg from near Paducah, KY to Chattanooga, TN that was rolling terrain with one long hill near Chatt. that fully charged the battery going down it. This is a small anecdotal sample but I have heard support for both increased or decreased hill mileage. The potential energy change of a hill is 100% efficient, much better than the battery charge/discharge. The ICE is at higher power going up the hill and should be more efficient and has no or little fuel flow going down. What do you folks up North think about this? I want to help get you out of your cold winter mpg funk.

 

Lee

 

 

We have a ton of hills in Cincinnati and they absolutely destroy my fuel economy. 100% potential energy isn't taking into account wind resistance, rolling resistance. It also is not 100% if you are forced into using your brakes to keep you out of felonious speeds as cops love setting up traps at the bottom of long hills.

[lrymal]

We have a ton of hills in Cincinnati and they absolutely destroy my fuel economy. 100% potential energy isn't taking into account wind resistance, rolling resistance....

Definitely agree with this. My Fusion Hybrid is averaging about 38 - 40 mpg in my native area (East Texas hills), but if I am in the Galveston Coastal Plains area (very flat), my mileage is easily in the mid-40s and sometimes low 50s, depending on the traffic stop-n-go, etc.

 

But, 38 - 40 mpg surely blows away the MPG rating of an ICE-only Fusion.

[Oman]

It is going to depend on the size of the hills and the speed of travel. The ICE is *not* more efficient at higher power, it is less efficient which is why the stored energy in the battery is used to boost the ICE under high demand. Another consideration is speed descending. If you go more than 47MPH then you will be running the ICE which consumes fuel even when simply being dragged along. Then the distance down is a consideration as you can't recover more energy than your battery can hold. After that it is wasted as heat. In most all cases hills will decrease mileage.

 

Jon

 

 

We have a ton of hills in Cincinnati and they absolutely destroy my fuel economy. 100% potential energy isn't taking into account wind resistance, rolling resistance. It also is not 100% if you are forced into using your brakes to keep you out of felonious speeds as cops love setting up traps at the bottom of long hills.

[lolder]

I'll yield to the more experienced hill climbers that it's worse. Look at this article: http://autospeed.com/cms/title_Brake-Specific-Fuel-Consumption/A_110216/article.html. Scroll down to the Prius engine operation chart. It's efficiency is still good at 3500 rpm. This is very interesting. Potential energy changes due to height differences are by definition 100% efficient. The losses of the car are there all the time whether you're coasting downhill, in EV or in ICE mode. This is fun.

 

Lee

[RegGuy]

I average 39.8 mpg mostly in NJ but with some travel to DC. We took a trip to Pittsburg (350 miles each way) and a large portion of it was up and down mountain passes. The trip mpg was around 36. It was also cold that week with the temperature getting below freezing. I've noticed a drop in mpg with the lower temperature too.

[ace43]

I've seen trips recently where my mileage wasn't affected negatively by hills at all, a result, I think, of planning for them and managing the throttle carefully to prepare for them.

 

Today, however, I went over a 3000 foot mountain, up and down twice, and as careful as I was I seemed to lose more going up than I was able to gain on the way down. However, even with the changes in grades and comparatively cold temperatures (25 F), my long term mileage only degraded from 39.4 mpg to 38.7 mpg on a 175 mile trip.