Do hills help gas mileage?

[billygoat11]

Live in Colorado Springs and drive a lot of up elevations and down elevations. This seems to actually result in high mpg. Going up mileage seems to be around 40 or so. Down a lot of times 90 plus mpg over 10 miles of driving. Currently at 53.8 and mileage is slowly increasing. Am afraid to get update since car is really good and surpassed my expectations as it is. Anyway, not sure about the hill think. Hypothesis?

[Sparky]

Driving in hills forces you to pulse and glide (P&G).  At your altitude there is less wind drag and the engine will develop less horsepower.  All this contributes to better mpg.

[fotomoto]

Well you do lose more going up than you gain coming down.  If not, you've got a perpetual motion machine.   Nice summer temps and high altitude do wonderful things for hybrids.   Even if you go up a lot, finding a route with an overall drop in altitude can do wonderful things as I found out in my recent trip to the mountains of New Mexico. 

 

 

 

 

 

 

Side note:  Electric vehicles are now setting the fastest times at the historic Pikes Peak hill climb event because they don't lose power as they gain altitude like the gassers do.  

[fbov]

Well you do lose more going up than you gain coming down.  If not, you've got a perpetual motion machine.  

At the system level, yes, but looking only at the ICE alone, the situation is reversed; you get more energy per gram of gasoline going uphill than you do going down. The reason is engine load.

 

I haven't seen a Ford-specific BSFC chart, so I'm pulling this from Tim Gulden's analysis. The contours are equal fuel usage per kilowatt hour supplied. The optimal operating point for this engine is where fuel usage is minimized at 220g/kWh. Move outside the "puddle" at the minima and energy costs increase in the form of greater fuel consumption per kWh.

 

The trick, of course, is that you don't create of destroy energy, just move it from one form to another, with finite losses at every step. The gas burned going uphill gets stored as potential energy for use coming back down. However, you'd need more gas to generate the same amount of energy while you're coming down because you'd be running the ICE at higher BSFC (away from the optimal "puddle") due to insufficient load. 

 

Energy balance is the first step to understanding how to operate a hybrid - knowing how to move energy around among kinetic, potential and electrical storage options, and when to use ICE. The next step is optimizing energy transfers, like learning 100% re-gen braking, and how to load the ICE to minimize BSFC. It's what Jus's MPG tips are all about. When climbing hills: "...I stick to the right lane, power bar up to the second level where the battery charges and climb..."

 

Have fun,

Frank

Edited September 4, 2013 by fbov

[Bob999]

My experience is that modern cars with fuel injection, oxygen sensors and computer controls cars get better mileage at higher altitudes--there is less air resistance because the air is thinner and the modern control systems still allow the engine to operate efficiently.

[HannahWCU]

 

Well you do lose more going up than you gain coming down. If not, you've got a perpetual motion machine.

Actually, if the hill is steep enough, in a hybrid, you use almost no energy (except to power the accessories), and most certainly no ICE on the downhill. So, this would make the CMax MUCH more efficient at using the potential energy of the hill. I believe but can't prove that the CMax gets better mileage in hills than flat ground if used correctly.

Edited September 4, 2013 by HannahWCU

[viajero]

I get 10-15% better mileage at 75 mph on the interstate in Colorado than in Texas, in this and my previous non-hybrid car.

 

Altitude definitely makes a difference.  Here's a nifty air density calculator:

 

http://www.altitude.org/air_pressure.php

 

At 6000 feet the air is 81% the density of air at sea level, so the drag due to air resistance is also 81%.  Of course there are other losses besides air drag, but that's one of the big ones, especially at highway speeds.

 

The effect of going up and down hills is hard to prove conclusively, but it makes sense as an enforced pulse and glide.  Even on my non-hybrid car, going up and down a really steep mountain (Beartooth Pass) gave me very good overall mileage because on the downhill the fuel cut off completely and I used almost no gas the whole way down.  I suppose on the way up I was in the sweet spot of that BSFC graph.

[billygoat11]

Great answers and responses. It all seems to help my mileage.

[fbov]

How'd you get yours to run on hot air?

[billygoat11]

fbov dont understand your point.

[fbov]

Trying to be funny... our answers improve your mileage, but we're just full of hot air, at least in my case. I never claimed to be a comedian!

Frank

[billygoat11]

Get it, guess I am a bit slow.

[SnowStorm]

I still think hills save gas.  See my topic here:

http://fordcmaxhybridforum.com/topic/2113-can-hills-save-gas/

 

Everyone seems to believe in kinetic P&G but some still argue against potential P&G.  Its a lot easier to set EcoCC and ride the hills than work your foot off doing kinetic P&G on a flat.  I don't see whet conservation of energy has to do with it and its certainly not perpetual motion.  As mentioned, its all about that BSFC graph we can't get a hold of!  (Higher altitude is a separate issue but quite an interesting one.)  My undocumented experience is that I get 51 to 52 mpg on the flat at 55 mph (high ICE) but more like 55 mpg with EcoCC on hills at the same speed.  At this point I've done thousands of miles on 55 mph roads.  Ideally, I would think, the hills shouldn't be so steep that the battery starts recharging on the way down.

[Jus-A-CMax]

Hmmmh....it the rolling hills are net down, then you get more - and its hard to tell. East Los Angeles Ave has rolling hills and 50-55mphs through farm lands and one section I get great MPG but the way back, I lose some and visually I can't tell but the CMax can in the MPG readings.

[mnrobitaille]

One thing I've noticed about hills & the C-Max is that the hill assist can help with FE on steeper grades when going downhill.

[fbov]

 

This is my way to work. My high point is a gentle bend in the road with a very slight rise. Needs some ICE every time. Very subtle, but then, the whole route only moves ~100 ft. peak-peak... and I can feel each of the gentle hills in how long EV lasts. That little blip in thie middle has an S-turn at the bottom that's reminded me how to take a turn!

 

Have fun,

Frank

[MacGyver]

One thing I've noticed about hills & the C-Max is that the hill assist can help with FE on steeper grades when going downhill.

 

Right, confirmed in an engineer chat too, so people can have confidence in that statement.

 

but "Low" gearshift transmission mode does NOT; "Torque" my android app that shows engine revs shows that results in engine braking, which is gonna suck SOME gas through, so...

 

Whereas hill assist engages regeneration only- anyone know if that regeneration is equal to / greater than / less than brake regeneration?

[MacGyver]

Live in Colorado Springs and drive a lot of up elevations and down elevations. This seems to actually result in high mpg. Going up mileage seems to be around 40 or so. Down a lot of times 90 plus mpg over 10 miles of driving. Currently at 53.8 and mileage is slowly increasing. Am afraid to get update since car is really good and surpassed my expectations as it is. Anyway, not sure about the hill think. Hypothesis?

 

Wow, what level grade? What speed?

[drdiesel1]

Anytime the ICE is off and your car is moving, you're saving gas over a conventional car :happy feet: