Pulse and Glide (Hypermiling trick)

[unicycle]

I drove my usual route into Manhattan today, but this time I tried the pulse & glide technique I'd just figured out from a hypermiling website. It seems to have worked.

P&G
Basically this technique calls for choosing some optimum speed, say 65, and gently pulsing up to about 5 mph above that before gliding back to a speed about 5 mph below it. In this case, a person would be ranging from 60-70.

P&G + Coasting
Since our smarties are so quick to decelerate via the engine, you can extend the glide by shifting into neutral as soon as you hit your optimum+5 speed. This simply prolongs the glide and forces you to pulse (accelerate ) less often.

Anyway, I didn't make any other adjustments to the car before the trip (more on that soon), and I found by the end of the ride that, according to my SG, I'd avg'ed over 55 mph for the trip and had used only 1.45 gallons for about 80 miles (normally the trip uses up a bit more like 1.7-1.75 gallons).

My next step is to inflate the tires to 43 psi in order to see if there is yet another gain in mpg's.

[NCC1701]

It seems counterintuitive. To change speed or direction takes energy. If you're doing 70 and take your foot off the gas, friction will slow you down. To overcome this and speed up takes more gas than driving a constant speed. Just, as you know, accelerating from stop is energy intensive, speeding up from 60 to 70 is also. I just can't see how this could improve your MPG.

I smell snake oil.

[MENSA42]

Originally Posted by NCC1701

I smell snake oil.

i agree that it makes no sense. after all, i get MUCH better mileage in my Toyota when i use the cruise control on the interstates than when i don't.

and to put 43LBS in your tires? you must live on some great streets, because around here, they would EXPLODE after hitting one chuckhole...

[WickedMessenger]

No, it doesn't make sense that this works. But you do have data to back it up. It would be interesting to see if you can duplicate this several times. I wonder if this is also confusing and hard on the transmission. Not to mention disruptive to traffic as a 10 mph delta is much more than the normal variation in a traffic flow. If the people following you are putting on the brakes, your gain is their loss. You might be hypermiling but the net effect to the planet is to use more energy and create more greenhouse gases. But it's all about saving 10 cents, not the big picture, isn't it?

[smart'n aint easy]

If I was driving with someone who was doing this, I would be tempted to jump out the window. That sounds like it would make you sick with all that accelerating and coasting.

[unicycle]

Originally Posted by WickedMessenger

No, it doesn't make sense that this works. But you do have data to back it up. It would be interesting to see if you can duplicate this several times. I wonder if this is also confusing and hard on the transmission. Not to mention disruptive to traffic as a 10 mph delta is much more than the normal variation in a traffic flow. If the people following you are putting on the brakes, your gain is their loss. You might be hypermiling but the net effect to the planet is to use more energy and create more greenhouse gases. But it's all about saving 10 cents, not the big picture, isn't it?

Your last point is WELL taken, and I completely agree. In fact, I have a whole blog dedicated to your notion of the greater good and for ppl speaking up for it (Voice of Society Man)

But I only do this when there are no drivers anywhere near me, which is most of the time bc my commute is at weird hours.

As for the transmission, there are some who worry that this is more taxing on the tranny. We'll see. I plan to get a lot of miles out of my car, so I'd def'ly be worried if I heard that this technique hurt the car.

And regarding my data (to back things up), well, this was only one test. So you're right to ask for follow-up data -- one trip certainly doesn't prove anything.

Originally Posted by ncc1701

Just, as you know, accelerating from stop is energy intensive, speeding up from 60 to 70 is also. I just can't see how this could improve your MPG.

Actually, my target is 60, so my P&G speeds were 55-65. That's a lower point in the 5th gear, so it's not stressing the engine much -- certainly a LOT less than 0-10 mph. And since I'm only giving it gas when I'm speeding up (the other times, the car is in neutral!), I'm using a lot less fuel than if I were holding steady. Hypermilers have been able to squeeze incredible mpgs out of hybrids with this technique -- over 100 mpg is quite common for them. By shifting my smart into N, I'm basically restricting fuel flow to a low (but safe) level but still gliding enough (rather than leaving the car in D) to get somewhere before having to pulse again. Check out my other posts for links to hypermiling techniques -- they explain things better than I do, or at least differently than I do.

Originally Posted by jeepster55

and to put 43LBS in your tires? you must live on some great streets, because around here, they would EXPLODE after hitting one chuckhole...

Oh, good point. I do have some bumps along the highway that need consideration. I'll try, say, 38 or 39 psi first. Thanks.

[Smart Enuf]

I'd be concerned about how much concentration it takes to keep up this technique, concentration which should be focused on the road and other cars around you. It would seem to take as much or even more brain processing than talking on a cell phone (look at speedo, accelerate, look at speedo, shift to neutral, look at speedo, shift to drive, accelerate, look at speedo, etc.). You said you only do it when there are no cars around, so it may not be as much an issue for you. But when others are doing it on a busy freeway, that could be problematic.

[stevenvillatoro]

Pulse/glide DOES work... at least with hybrid cars. As for the PSIs in the tires, the hybrid owner websites (greenhybrid.com, for example) have concluded time-and-time-again that safety, handling, braking, and tire life generally improve with higher pressures. Conversations about this topic should be based on fact only, because many of the actual benefits are counter-intuitive and unexpected. I found a huge benefit with my Insight, which I ran at 45-50 PSI, but almost no gain by overinflation with my Camry Hybrid. Low roll-resistance tires are worthwhile for good MPGs. I tried raising PSIs in my smart, and the ride with more than 36 PSI in the rear was unacceptably harsh. I now have my fronts at 31 (versus standard 29) and have noticed no deterioration in ride quality. The lower the tire series (height), the greater the risk of impact damage by potholes, etc. due to overinflation. My conclusion is that the smart's recommended pressures are pretty close to optimal already, except for a small bump in PSI up front. Would be interested in more pulse/glide discussion and testing. I believe the jury is still out on coasting in neutral... safety, legality, potential damage to transmission, etc.

[WhiteNBlack08]

Originally Posted by smart'n aint easy

If I was driving with someone who was doing this, I would be tempted to jump out the window. That sounds like it would make you sick with all that accelerating and coasting.

If I was driving near someone who was doing this, I'd probably run them off the road. Talk about inducing road rage, that would do it in a hurry.

[unicycle]

Originally Posted by Smart Enuf

I'd be concerned about how much concentration it takes to keep up this technique, concentration which should be focused on the road and other cars around you. It would seem to take as much or even more brain processing than talking on a cell phone (look at speedo, accelerate, look at speedo, shift to neutral, look at speedo, shift to drive, accelerate, look at speedo, etc.). You said you only do it when there are no cars around, so it may not be as much an issue for you. But when others are doing it on a busy freeway, that could be problematic.

Right, and that sort of issue is addressed at the HM sites -- you can't do these sorts of things with drivers all around you and only two lanes, for example, if only because it causes them frustration, wastes (their) gas, etc. The conditions need to be ok.

But as for the concentration, that's not a good point, really, unless the driver is mentally impaired. You don't need to be looking at the speedo, really, in order to have a good sense of how fast you're going. In fact, most of us (since we don't have cruise control) would have to gauge our speed by listening to the motor, or looking at other cars, or checking out the speedo. Shifting into N and back to D takes little thought -- tho you have to be careful not to try to shift into N when you're already there -- then you'd be pushing towards R (tho the car shouldn't allow that to happen). So as a precaution, I leave my right hand on the gear shifter. I can't imagine it takes my mind off driving too much. On the contrary, I've found that the extra concentration causes me to be much more alert, and that makes me a much safer (and more awake!) driver. Sometimes on my long drive I get tired, and this keeps me focused and makes the miles drip away so that I seem to be getting home faster (that is to say: time flies). So I advocate this technique for most ppl.