Improving FE while driving uphill

[HighAltitudeFE]

I've been trying to figure out how to drive uphill efficiently. My home is at an altitude of approximately 7,000 ft. and my office is at an altitude of approximately 6,000 ft. That's a 1,000 ft. climb every evening.

My TCH (no nav) keeps track of the overall FE for the tank. With the overall FE and trip odometer readings at the beginning and end of each trip, I can derive the FE for the trip (with increasing error as I put more miles on the tank). Combined with the Eco Drive Display for my inefficient trips, I think I can get a fairly accurate estimate of the FE for any given trip. I've been using the following formula to compute trip FE:

trip_FE = (end_miles - start_miles) / (end_miles / end_FE - start_miles / start_FE).

As you might expect, I've been rather happy with my fuel economy on my way to work: usually over 50mpg, with a personal best of 58mpg. On a trip past the office to another location downtown, I managed 68.75mpg, my personal best since I started keeping track.

Driving home, however, I usually get 33-37mpg. I'd like to improve. On my best trips, I used the following techniques:

• Begin the commute at a time when traffic on the main roads is relatively light.
• Use warm-up pulse and glide for the first mile before getting onto a 55mph highway.
• Accelerate briskly, but not aggressively, to cruising speed (10-20mpg)
• Delay accelerating when speed limit increases to 65mph until road levels out a bit.
• Use DWL to trade speed for FE on steep sections.
• Recover speed lost from DWL on downhill, level, or less steep sections (again, brisk acceleration: 10-20mpg).
• Anticipate red lights.
• Use "golf cart mode" for the last mile or so through my residential neighborhood from the highway to my home.

DWL has been helpful, but because I'm gaining 1,000 ft. it's impossible to have enough speed to trade for FE. Also, because the speed limit on the steepest sections is 65mph, it's hard to give up more than about 10mph without feeling like I'm being somewhat rude to the people behind me.

? Would it be more fuel efficient to accelerate to 70mph in order to have more speed to give up or would the extra acceleration and drag reduce my overall FE?

There's a small hill (maybe 50-100ft.) that I ascend on my way to work and descend on the way home. On the way in, maybe 8 minutes and 4 mi. into my commute, I can use DWL at 45mpg and lose only 5mph from an initial speed 65mph. On the way home, I reach this hill after about 20 minutes and 11mi. and I seem to get only 40-45mpg maintaining 55mph (going downhill!). This is actually one of the better parts of my commute home, but it is puzzling.

My car usually seems to easily get 60+mpg going even a slightly downhill, but drops to 40-50mpg on level ground and it's very hard to break 40mpg going even slightly uphill (pulse and glide for small hills, DWL for slightly larger hills seems to help).

I have only about 3 weeks of experience driving a hybrid. Does anyone have any suggestions on how to get good FE going uphill? I'll try to reply to this thread as I figure out more techniques that work.

Thanks,
Chris

[BailOut]

I've never driven a hybrid but I climb mountains all the time. The only things that I have found that help while climbing are:

1) Make sure that your vehicle is set up properly. Pump up the tires, drop weight where you can, make sure the engine is operating properly, etc.

2) Find the magic, usable speed that nets the best FE and make that your permanent climbing target.

3) Get to that speed slowly. It takes me about 2 km to fully accelerate from 0 to 50 MPH on a 7% grade.

4) Maintain that speed as much as possible. Try to not slow down at all so that you don't have to re-accelerate.

5) Avoid passing if a slower speed will create less of an FE dent than the acceleration burst.


Just let me know if you have any other questions regarding mountain driving.

[desdemona]

I don't drive a hybrid but oh gee, I feel your pain!
I think the driving techniques of hypermiling are fairly consistent but there might be certain things that are different. I can't really "go golf cart mode" for instance, but a nonhybrid can go in neutral or FAS.

I have the opposite situation, so at least my car is warmed up. The other difference is the speed limits which are in the 35-40 range, which are much easier to DWL. I don't mind going a bit slower and I am usually not even the only slow driver (surprising as that may be). It may also explain a bit your lower mpg. (And my less impressive to work rates.)

My ascent might be about the same as yours. I live about 1 mile from the foothills.
I am in a little lower altitude but still can't figure out how to bake anything. :-)
These aren't exactly the Rockies but still (actually might be *part* of the Rockies?)


I have gotten fairly good (at least in my own reconning ) on DWL but it still hasn't really gotten me much better than 38.8 or so. I think your main problem is the speed, imo. How many lanes is this? If it were 3 lanes, I would take the right lane, and try and go as slow as possible (maybe 40s?). A Scan Gauge might help (or if your hybrid shows gph or TPS?)
I try and keep the gph under around 1.2 and I can do pretty nicely. There is a big drop off after 1.5 or so. (Of course obviously as it tells you what you are or aren't doing. It is easy to watch this and let up if needed. If leaving home a bit early gives you an advantage of getting to pick your lane or drive slower in one of them I'd take it. I think going close to 65 is going to be very hard to get decent mileage uphill.

I also think you need to watch where on the gas pedal you are accelerating. I have mostly seen this discussed in passing and some drivers here like to go bare or sock footed (I feel I''d like to wear something like Indian mocassins.) But the accelerator is quite sensitive and
reacts easily to little cues. I like to put my use my heel to to accelerate vs my whole foot (I don't think I could do this for long trips). I have been playing around with placing my foot in different positions than the standard straight footed pattern, for instance sideways.
You talk about accelerating quickly at some point. I've never seen where this is an advantage but there may be something there that is specific to hybrids.
But any accelerating you do uphill HAS to be slow. I have seen big falloffs in mileage if I hit the gas too hard going uphill.

Another option that hasn't been discussed is route changes. I have found a certain road that has a much more gradual incline than others. I think pretty much the older the road the more gradual the incline is. But I don't know if this is an actual option for you.
I have sometimes heard of hybrid drivers trying very odd city type routes, esp in the Prius.

And yes, I also can identify with the rather strange thing of making rather modest gains down a hill but very big loses going up. There is such a hill here and I mostly avoid it, if I have to go up it. I am always suprised at the 20 mpg I get if I go up it, and the only 45 mpg I get going down, even though I can look at the SG at a given point and see an impressive 175 mpg!


Also if this is a new car, a new engine needs "break in" (maybe 1000 miles?) to get better mileage.

--des

[tarabell]

For small hills you mentioned, I try to accelerate to slightly above normal speed on the flat part before the hill, let off the gas slightly climbing the hill, and let momentum carry me over the crest.

Another thing. Just because a hill took your FE going up, it's not a given it'll just hand it back to you on the way down. Knowing Murphy, hills are ready and willing to rip you off both ways if there should be a red light or a slowdown halfway down the slope. I'm extra vigilant approaching a downhill, watching signals and traffic in front of me because I want to ensure I get everything possible back.

[HighAltitudeFE]

I did some experimenting over the weekend and today, using Brian's suggestions (this is the first I've been able to check since I posted). I managed to get back over 35mpg going uphill today and would probably have made 36 if I hadn't made a side trip. I wound up getting stuck at a long light before the car was warmed up enough for the ICE to shut off.

Brian wrote:
Get to that speed slowly. It takes me about 2 km to fully accelerate from 0 to 50 MPH on a 7% grade.

This works OK, but FE while accelerating is pretty bad: 10-20mpg. I started resetting the accelerator every 10mph or so (just releasing it and re-engaging). This seems to let the FE rise to about 30mpg when accelerating through about 45mph. I've also noticed a range of acceleration rates at the same FE--why accelerate slowly at 20mpg when I can accelerate a bit faster and still get 20mpg?

des wrote:
I think going close to 65 is going to be very hard to get decent mileage uphill

Actually... this is where it gets surprising. I seem to get great FE between 60 and 65mph. Using my technique of resetting the accelerator, I was able to make 35mpg for most of the way home at 60-65mph, even doing DWL from 65-55mph up the steepest section at 40mpg.

des wrote:
I have mostly seen this discussed in passing and some drivers here like to go bare or sock footed

I'll try this tomorrow and let you know how it goes.

des wrote:
You talk about accelerating quickly at some point. I've never seen where this is an advantage but there may be something there that is specific to hybrids.

I read an article in one of the forums on this site recently. Unfortunately, I just can't find it again. The poster was a name I recognized, but I can't remember who. He (she?) was dissatisfied with his FE, hadn't had a >50mpg trip in his Prius recently, and went to a AAA seminar on driving a hybrid. On the return trip, he got >55mpg, I think. One of their suggestions was to accelerate briskly but not hard.

It made logical sense to me. If I remember correctly, the pulse phase of P&G involves moderate (not slow) acceleration. I noticed that accelerating moderately gets the engine into a more efficient range quicker than accelerating slowly. However, it doesn't seem to yield better results than the way I drive before reading the article.

des wrote:
But any accelerating you do uphill HAS to be slow.

Of course. I try to accelerate on downhill or flat sections and hold steady or DWL on uphill sections.

The method that seems to be developing from my experiments appears to be a combination of P&G and DWL: pulse up to a desired speed on flat and downhill sections, then hold steady or DWL on uphill sections.

des wrote:
Also if this is a new car, a new engine needs "break in" (maybe 1000 miles?) to get better mileage.

It is. I picked it up less than a month ago and it has only 1300 miles on it. I'd heard about the break-in period, and I'm seeing some improvement (39.9mpg, 40.0mpg, 40.5mpg on the first 3 tanks).

BTW, des and BailOut, I'm not dealing with mountains here. My commute is between downtown Colorado Springs and the high plains on the east. I haven't taken the TCH into the mountains, but I got a record tank (>22mpg) in my 2001 Pathfinder (EPA: 15/19) on a ski trip last year to Summit County via Hoosier Pass (11,539 ft.).

Anyone know how altitude affects FE? I picked up the car in Aurora, CO (just east of Denver) at an altitude of 5300ft. I haven't had it below about 6,000ft. since driving it home.

Thanks,
Chris

[desdemona]

Chris--
I'm not really in the mountains either. I'm at high altitude (somewhat over a mile up) with hilly terrain and towards the foothills. I drive into a valley going to work and out going home somewhat opposite of you. It sounds like we have fairly similar terrain to work with.
I'm not sure what the grade is. But I think driving in Colorado and NM would be somewhat similar. You're up a bit higher than I am I think. I'm guessing we're a little warmer here right now (average 77/44).

35 mpg is uphill is probably pretty good if the car isn't warmed up. I have gotten up to 50 (even a bit more) but not maybe at that much of a grade and not for very long either. I think the average is more on the order of 30ish, and I am fully warmed up. I think it takes quite a lot of practice and I find the most challenging thing hypermiling there is. Although it is mentioned as kind of a basic technique it is much more challenging than say NICE-on coasting, DWB, etc. Even P&G. (My going home commute is averaging around 37ish while to work is 44ish. I just started doing P&G, which isn't quite as natural as a hybrid.) There is a total upward grade but it isn't equally going up, some is relatively flat and a little bit I can actually coast downhill.

I don't know if this is ok in a hybrid (maybe someone could say) but if the car hasn't warmed up can he turn the key off at a long light? I do this, if I think that the light will be more than 10 seconds (I am sometimes wrong!), but I don't have a hybrid.

There is a point where you can't get good FE at all, I think that is supposed to be under 22-25 mph. That seems about right. You might have hit some sweet spot at your higher mph, I don't know. I have only made decent mpg going fairly slowly. OF course the speed limit isn't even close to 65 here, perhaps you have gained a certain amt. of forward push to get up the hills or something.

I was reading the various hybrid chats for awhile. They weren't as nice as this forum and besides it became apparent that I wasn't going to get one right now anyway. I think I might have read some of hypermiling with a hybrid is a little different.

Well the bare feet isn't my idea. I have read this here though. Some folks swear by it. I don't think I would like it.

I'd be curious about hypermiling and altitude as well. I wonder if it is like baking a cake!?


--des


>Anyone know how altitude affects FE? I picked up the car in Aurora, CO (just east of Denver) at an altitude of 5300ft. I haven't had it below about 6,000ft. since driving it home.

Thanks,
Chris

[PaleMelanesian]

Originally Posted by desdemona

There is a point where you can't get good FE at all, I think that is supposed to be under 22-25 mph. That seems about right. You might have hit some sweet spot at your higher mph, I don't know. I have only made decent mpg going fairly slowly. OF course the speed limit isn't even close to 65 here, perhaps you have gained a certain amt. of forward push to get up the hills or something.

I believe I was the one who said that. That's if the engine is running. If the engine is off, you get great mileage all the way down to a stop. I'm not exactly sure on the speeds, you'll have to do the math for your situation. I don't want to be the source of any misinformation.

[desdemona]

Same thing if your coasting. I can see sometimes 60 mpg at coasting at 20 mpg or under.
So I think you are right from an experimental pov. OTOH, if you go back up to speed you are going back into gear. You will flip thru the gears again, so this has limited application.

--des

Originally Posted by PaleMelanesian

I believe I was the one who said that. That's if the engine is running. If the engine is off, you get great mileage all the way down to a stop. I'm not exactly sure on the speeds, you'll have to do the math for your situation. I don't want to be the source of any misinformation.

[Skwyre7]

Just a quick note about acceleration: Try to keep your iMPG at about half of what your speed is (20 mph = 10 mpg, 40 mph = 20 mpg, etc.). Or if you get a SG, you can watch gph and accelerate at 2.0 gph. The Prius crowd thinks that this is a good acceleration rate.

[Shiba3420]

Why is it better to accelerate quickly?

While it does apply more to hybrids, it still applies to all cars to some degree. It comes down to "idling" the engine, where gas is being wasted just spinning the motor without moving the car. While is obvious that a stopped car should stop its engine, its less obvious that a moving car is wasting energy when moving too slow. Think of it this way, you burn a gallon an hour when stopped/idling. If you put your car in gear, but still just idle your way down the road (my car used to do about 15/20 on a complete flat without me applying gas, lets say it costs another gallan a hour. All things being equal, you are now burning 2 gallons an hour with half of that going to movement and the other half being wasted on the engine. All cars have an optimum spot where they move as fast as possible using ICE while burned the least fuel. Slower than that speed and you waste fuel on the engine. Faster than that speed and you waste fuel to increasing friction. For me thats about 45/47 mph where I see 35/38mpg with ICE.

When it comes to accerating you have the same deal. Accelerate too fast, and your throwing away excess gas to inefficencies, and accerate too slow and you throw away gas to the engine doing nothing. So, I'm finding that accelerating briskly (still pretty slow by hypermiling standards, say 2/3mph every second) until I hit around 20/30mph and then accelerating more slowly produces the best results for me in a conventional car. In a hybrid, I actually accelerate to about 10/15mph using just electric (if I can spare the battery/time) and then accelerate "briskly" to 30, and finally slowly to my top speed produce some of my best results.

However since I do try to be nice to traditional traffic around me, I use my own advice based on traffic flow. With heavy traffic, I try to be more consistent so others don't have to accomodate me.