Driving Tips & Techniques to improve MPG (Hypermiling)

[Ludercrz]

so since i'm probably the worst MPG CRZ driver and find that very disappointing i went looking for ways to improve myself and thought that I might not be the only one who wants to improve, so I am posting my findings in this thread and others are welcome to add their tips and techniques in here as well.

*Sticky Please*


Conserve momentum: avoid stopping

Avoid coming to a complete stop whenever possible (and when safe and legal of course). It takes much less energy to accelerate a vehicle when it's already traveling just a few kilometers per hour than it does from a complete stop.


Conserve momentum: stop sign 'stop and crawl'

When multiple vehicles ahead of you are progressing through a stop sign (or a right turn at a red light), this represents a mini 'stop and crawl' situation normally found in a bumper to bumper traffic jam.

Time your approach, to arrive at the stop sign as the last car ahead is departing.


Conserve momentum: brake hard

It sounds like a contradiction, but there are rare times when braking hard can save fuel compared to coasting or light braking: it's a "damage control" technique when faced with an unpredictable/unanticipated stop or slow down ahead and not a lot of space.

An example: approaching a fresh red traffic light that had no other indicators to predict the change (no pedestrian signal and no cars waiting on the cross street). If you brake lightly/moderately, you will cover the entire distance to the intersection and have no option but coming to a full stop.

But if you brake quite hard initially, you can potentially scrub enough speed and buy enough time to coast the remaining distance to the intersection at a low speed. With judgment and some luck, you'll arrive at a fresh green light and avoid a full stop.

Obviously, rapid deceleration isn't a safe option if there is following traffic.


Traffic light timing - 'stale' green

When approaching an intersection with a green light you can watch the pedestrian signal crossing light to help determine when it will turn yellow.


Windows up

Drive with windows up at higher speeds to minimize aerodynamic drag. Use flow-through ventilation if possible.


Hybrids: minimize regen braking

While regenerative braking in hybrid vehicles - capturing braking energy into the battery - is more efficient than braking with conventional friction brakes, it's still not as efficient as 'driving without brakes' (DWB).

So even if you drive a hybrid, you'll get better economy when you minimize use of the brake pedal.


"Drive without brakes" (DWB)

Minimize use of the brake pedal. Each time you press it, you're effectively converting gasoline into brake dust and heat.

Driving as if you have no brakes will cause you to do two things: 1) reduces 'excessive' acceleration, and, 2) extends the amount of time you spend coasting down to stops and turns.

Obviously you have to balance use of this technique against traffic conditions so as not to adversely affect other drivers.


Use the 'racing line'

Knowing how to pick the "racing line" through a corner, when safe, can help to preserve momentum. Generally, the racing line is the path through a turn with the largest possible radius. It may permit a higher speed with more comfort (less body roll and g-forces), and less tire scrub.

Note this isn't advocating high speed turns, where the cost of increased tire wear may outstrip fuel savings. Even at low speeds, choosing the "racing line" has benefits.


Manual transmission: cruise in high gear

When cruising at a constant speed, shift to the highest gear you can use without lugging the engine.


Automatic transmission: neutral when stopped

Shift automatic transmissions to neutral when stopped (assuming you're going to leave the engine running). Remaining in drive wastes fuel as the engine continues to try to creep the car forward while being held back by the brakes.



Heavy traffic: play the accordion

If faced with worst-case "stop & crawl" traffic conditions, leave as much space ahead of you as possible and continually "accordion" that space to keep your vehicle moving near a constant speed while the cars in front of you stop & start.

Yes, some people will cut into the space you create ahead of you. Deal with it.

Note that this may aggravate following drivers who can't absorb the big picture, and that must be taken into account.


When changing direction, use brakes rather than engine

When going from reverse to a forward gear (or vice versa), don't use the engine to stop the vehicle after the gear change, use the brake.


Pulse and glide (P&G)

Use pulse and glide (or "burn and coast") rather than maintaining a constant speed, where practical.
(method explained bellow)


Winter: Avoid 'warm up' idling

Don't idle your engine to warm it on a cold day. An idling engine gets zero miles per gallon.

Start to drive - under light loads - as soon as the engine is running smoothly (usually immediately). It's a more efficient way to warm the engine and entire drivetrain, including tires.

[Ludercrz]

Pulse and Glide : Explained

taken from MetroMPG.com (Driving technique: exploring 'Pulse and Glide' - MetroMPG.com)

Before going into the details, I should point out that it's not a technique that can be used all the time in real world driving. Even one member of the group who made the run stated that their feat was in no way "normal", but rather a demonstration of the potential efficiency of a hybrid when driven with ultimate fuel economy in mind.

Pulse & glide overview

Pulse and glide works like this: let's say you're on a road where you want to go 60 km/h. Instead of driving along at a steady 60, you instead accelerate to 70 (that's the pulse), and then coast in neutral with the engine off down to 50 (that's the glide). That's it. Rinse and repeat. And repeat. And repeat...

By doing this, you're still averaging 60 km/h, but it turns out that pulse and glide is significantly more efficient than driving along maintaining a steady 60 km/h.

If you're like me, it seems completely counter-intuitive. You're asking, "how can that possibly be more efficient than maintaining a steady speed in the highest possible gear?" After all, it violates one of the main commandments of efficient driving: conserving momentum.

Why it works

The secret is in the glide, and it is best illustrated by the extreme Prius demonstration.

The Prius is particularly excellent at gliding because under most conditions when the the accelerator is released below 40 mph, the gasoline engine shuts off completely and the transmission effectively freewheels in neutral (it's actually slightly more complicated than that, but stick with me). So, while gliding, it's effectively getting infinite mpg - it's using no gas at all.

For that reason, the marathon drivers picked 40 mph as the upper limit of their pulse & glide cycle (33 mph was the bottom). So in order to achieve 109.3 mpg, they just had to average 54.65 mpg while pulsing gently from 33 - 40 mph. And it turns out, in a Prius, you can. So, assuming equal length pulses & glides, they traveled half the total distance of their trip getting 54.65 mpg, and half the total distance using no fuel at all. It averages out to 109.3 mpg.

Pulse & glide in a Geo Metro

Still skeptical, I went out in my car with the ScanGauge. I really didn't believe it was going to work, but here are the numbers I saw. I went to my "test course" - a nearly perfectly level stretch of 2-lane highway about 6.5 km long - but these numbers aren't meant to be taken as experimentally valid. I only did one run, so consider yourself warned. It's just a snapshot:

* At a steady 80 km/h (about 50 mph) I was getting 59 mpg (US) (there was a tail wind)

* "gliding" down from 90 to 70 km/h took 16 seconds

pulse & glide results - Firefly

* "pulsing" back up from 70 to 90 km/h at a rate of acceleration that also took 16 seconds I was getting about 34 mpg (US)

* So my pulse and glide average would be 68 mpg, vs. 59 at the same average speed. That's a 15% increase over the steady state mpg - theoretically.

I say theoretically because the engine would have to be off in the glide to get that mileage. You could do it, but it adds another step in an already arguably impractical process (remember the engine shuts off automatically in the Prius when you lift off the accelerator).

So I took a couple more readings. With the engine idling, and the car in neutral, the average mpg shown on the ScanGauge in the glide down from 90-70 km/h was 550 mpg. When you average that against the 34 mpg of the pulse, it works out to an average of 64 mpg. Now we're at an 8% increase over the steady-state mpg.

pulse & glide chart - Prius

I would name the difference between the two techniques "full" pulse & glide (neutral, with engine off in the glide) vs. "mild" (neutral, with engine idling in the glide).

So, now you know the next time you find yourself cruising down a lonely road at a steady speed, you're not getting the best mileage you could. You could be pulsing & gliding to maintain the same average speed, and saving lots of fuel in the process.

To exceed your steady-state mpg (X), you just have to be able to "pulse" at a rate of fuel consumption that is greater than half of X (assuming equal length pulses & glides; you may be able to increase the proportion of glide to pulse - meaning faster acceleration in the pulse, or glides that are timed to take advantage of descending a grade - and still beat your steady-state mpg for that average speed). You can see how fuel economy instrumentation plays a critical role in determining the best rate of pulse to make this work.

The Pulse & Glide Workout!

But it's not really very practical, is it? When I said off the top that there's nothing special about hybrid technology that makes this work, that's only true in theory. In practical terms, the Prius enables this technique because all of its individual steps are performed through a single control - the throttle pedal.

Contrast that to my manual shift Firefly: in order to duplicate the behaviour of the Prius requires 6 discrete steps using 3 of my limbs... every 16 seconds. Glide: release accelerator, clutch in, key off, pause...key on. Pulse: pop clutch to restart engine, depress accelerator. That's quite a workout, compared to 2 steps in the Toyota accomplished entirely with the right foot: glide - release accelerator; pulse - depress accelerator.

Practical implications

What useful information comes from this for the non-hybrid driver?

* (Okay, the first one is hybrid related...) Toyota ultra-efficient cruise control! The Prius could potentially have a "pulse and glide" cruise control setting to completely automate the cycle. Set your target speed, and the car pulses & glides around it.

* For me, the technique simply underlines the importance of maximizing the amount of "glide" (whether engine on or off) in my driving. In other words, time spent in neutral, or with the clutch depressed. For example, when approaching a stop or a forced speed reduction, rather than maintaining a constant speed as I approach, I now try to execute the optimal pulse that permits me to coast half the distance (or more) with as little braking as possible.

* It causes you to carefully consider the comparitive efficiencies of different ways of accelerating or decelerating. E.G. deceleration efficiency, from best to worst in a non-hybrid (standard liability statement applies - don't do this if it puts you or others at risk): (1) engine off, in neutral (or clutch in); (2) engine idling, in neutral; (3) engine running, in gear (it's true that some cars' fuel injectors shut off when decelerating in gear above a certain engine RPM threshold, but the savings in fuel is cancelled by the faster rate of deceleration from engine braking. Relative to coasting in neutral, it's less efficient.); (4) braking (assumes engine also running, in gear).

* The pulse & glide downside: it stands to reason that the technique is somewhat harder on the machinery (in terms of wear) than simply maintaining a steady speed. This is even more true in "full" pulse & glide mode, if you are repeatedly using the starter to re-start the engine. For that reason alone I'd be reluctant to use it to boost "steady state" (e.g. hwy) mileage. Its benefits are more practically realized in situations where you have to accelerate and decelerate on a regular basis anyway (e.g. sub/urban driving).

[TinTin]

How do you get around the regen braking when "gliding" in the CRZ? is it like the civic hybrid where if you are smooth enough it will just not regen?

[Scotty001]

Whew, that was a post or 2 full. Good stuff though... Thanks.

[Ludercrz]

Originally Posted by TinTin

How do you get around the regen braking when "gliding" in the CRZ? is it like the civic hybrid where if you are smooth enough it will just not regen?

what they are referring to is pressing the brake to regen. using the engine to regen while gliding is different.

at least that's how i see it.

[TinTin]

Originally Posted by Ludercrz

what they are referring to is pressing the brake to regen. using the engine to regen while gliding is different.

at least that's how i see it.

I saw a video with a civic hybrid anf there were no regen bars at all when he was gliding.

[Scotty001]

Originally Posted by TinTin

I saw a video with a civic hybrid anf there were no regen bars at all when he was gliding.

I traded in my 07 Civic Hybrid. Although not always, there were times when I would get a bar or two of regen when gliding... Especially when going down a grade (downhill) where I could pretty much let it roll and maintain speed.

[wicked1]

Hey, I made a post about doing almost exactly the pulse-glide thing this morning...
So, I pulse up to speed, then just barely press the accelerator in enough so that it's not charging the battery, but not really giving it fuel either, for the glide phase.. There's a very fine line there.. but you can find it.
At that point, it's almost like it's in neutral. *(when in 6th gear in the MT)

-w/out pushing the accelerator in partially like that, the car seemed to slow down too quickly for the glide

[Vash337]

im curious to see how this stuff works for you guys. after seeing some of your gas milages *example: ludercrz's 27.6* it made me second think getting one. i get that kind of mileage in my rsx, except it's also quick when i want it to be *and paid off * so i started contemplating other kseries hondas like 4door civic si's and tsx 6speeds.

if i get this car i want to half drive green, and half drive "red" while getting better mpg than a much faster kseries can do (26-31mpg real world)

[wicked1]

I got a tsx about the same time as the crz. TSX is girlfriends car.
For driving off the highway my crz seems quicker, and blows away the tsx gas mileage. My average 5 mile no highway, tons of stops and hills commute gives me ~33 in the crz and the couple of times I drove her car, I got about 14mpg for that route!
Now get up over 80 on the highway and the tsx has more power to spare and has better gas mileage than the crz.

If I were making the choice between the two cars I guess it would depend if I were going to be doing a lot of long road trips (tsx wins) or mostly urban or country roads (crz wins).