Pulsing On Flats

[2TonJellyBean]

If I'm driving along in an automatic transmission equipped vehicle that cannot do engine off coasting at a very steady 55mph on a perfectly flat section of road using cruise control, would using a P&G technique increase mileage significantly while maintaining the same average speed?

With a heavier vehicle, adding to the mass needing to be accelerated each pulse cycle, what kind of MPG increase should one expect is see if a steady cruise control speed returned 30mpg?

[omgwtfbyobbq]

Ideally, I would guess something like 35-40mpg, but we need the OD gear ratio/tire size to get a good idea. It's more wear on the transmission clutch packs, but if the mileage increase is large enough it may be worthwhile.

[GeekGuyAndy]

I did a test on this. Driving cruise at 40mph I got 29.4mpg. Drivingpulse and glide (accelerate to 45 with rpm no higher than 2200 then coast to 35; average was 36mph) yielded 34.8mpg. So a 5.4mpg increase on my car, which is 18.3% higher than keeping a steady speed. That test was a month ago, and now with better technique I can get 40mpg on the same route.

[2TonJellyBean]

Andy, one issue with your test is that while you observed an 18.3% improvement, you were also reducing your average speed by 10% which in and of itself could be a significant portion of those savings.

[GasSavers_StanleyD]

Originally Posted by 2TonJellyBean

Andy, one issue with your test is that while you observed an 18.3% improvement, you were also reducing your average speed by 10% which in and of itself could be a significant portion of those savings.

Andy went from straight 45 to a pulse and glide from 35 to 45. If his acceleration (during pulse) and deceleration (during glide) were constant and smooth, then I dont see how his average speed was below 40mph. With constant acceleration from 35 to 45 your average speed will be smack in the middle at 40mph. Thats math.

If Andy pulse and glided from 35 to 40, THEN he would have experienced about a 6.5% decrease in speed. Please explain your 10% decrease in speed theory. Maybe Im missing something. But for now Id have to disagree witht he 10% decrease in speed. Has anyone tried to see the difference from a constant 55mpg to P&G from 50-60 on level ground. Id like to know as I currently only P&G on hills taking advantage of sweet downhill coasts where I actually gain speed.

[GasSavers_StanleyD]

Originally Posted by 2TonJellyBean

Andy, one issue with your test is that while you observed an 18.3% improvement, you were also reducing your average speed by 10% which in and of itself could be a significant portion of those savings.

OOPS, my bad. Just noticed that his avg speed was 36mph. I dont understand how his average speed was only 36 when he was pulsing from 35 to 45. His car must have been decelerating real fast or he spent a LOT of time coasting at low end of speed due to car not slowing down much near the end. Andy please explain.

Andy, maybe you should compare this P&G run to a straight constant speed of 36 mph. This way you are comparing two runs of the same length and same average speed. 2TonJellyBean does make a good point.

Sorry JellyBean for earlier post.

[cfg83]

StanleyD -

Originally Posted by StanleyD

OOPS, my bad. Just noticed that his avg speed was 36mph. I dont understand how his average speed was only 36 when he was pulsing from 35 to 45. His car must have been decelerating real fast or he spent a LOT of time coasting at low end of speed due to car not slowing down much near the end. Andy please explain.

Andy, maybe you should compare this P&G run to a straight constant speed of 36 mph. This way you are comparing two runs of the same length and same average speed. 2TonJellyBean does make a good point.

Sorry JellyBean for earlier post.

I can theorize a response to this. It may be that his route brought him to full stops and/or traffic slow downs. On the freeways in LA, even though my overall strategy is to P&G between 50 and 65, my best runs show an average speed of only around 50 MPH because the flow of traffic allowed me to extend my glides below 50 MPH.

There are your "strategies" and the compromises you choose to make in real time.

CarloSW2

[Zvolen]

I took it as he slowed down, glided to an average of 36MPH but I could be wrong or reading it wrong.

[trebuchet03]

Originally Posted by cfg83

StanleyD -



I can theorize a response to this. It may be that his route brought him to full stops and/or traffic slow downs.

Or disproportionate pulse and glide time. It makes sense that the rate of deceleration would slow down as your vehicle speed slows down. Purely from aero resistance.

From a math standpoint, ideal situations (for calculation) is pulse time=glide time (I don't think I have to tell you that though ). But the ideal economy situation is pulse time << glide time. And the real world situation is pulse time < glide time and glide time above mean pulse/glide speeds is less than glide time below the mean pulse/glide speeds (the mean in this case being 40).

Then again - there could have been a woman with a walker crossing the street, halting traffic

[GeekGuyAndy]

Hello again,
The route had only one stop, but was on 3.8 miles total so even one stop on that would bring me down to 0mph, which would decrease the overall average speed. Especially since I likely didn't accelerate to 45 right before the stop, so even the last quarter mile on both ends is dropping the average. These runs incuded from a stop in the beginning to a stop in the end also, so I wouldn't expect 40mph even on a average moving speed of 40mph if you know what I mean.