Driving 55mph? (Is it the most efficient speed?)

[PeteHalo]

Last night I drove 3 miles across the town and according the onboard computer managed to do 61mpg. On the way I had to stop 4 times at the traffic lights and max speed was 30mph. Using engine braking wherever possible really helps to keep the consumption of a feather weight car like my smart Roadster (round 1700 pounds) very low even at urban speeds but once you raise the speed from 30mph the mpg will drop quite drastically. This morning I cruised 50 miles down the motorway at 65mph and managed to do 39mpg.

[Sandy]

On the last few trips I've been setting the cruise at 58 or so,
just to see how it compares to the modified P&G I do in the commute to and from work.
I' going to do a table or graphic once I get a few more runs,
but the slower cruise has so far yielded about the same or better mpg than the P&G of speeding up down hill and then holding a contact throttle position going up and trying to keep the mpg's up while not holding up traffic.
This sometimes is not wise as the traffic gets upset as I speed up down hill then slow up hills.
The 58 or so cruise had much less cars 'getting around' me while going slow uphill,
and held a good mpg.
The cruise is a lot less tiring driving too.

[MetroMPG]

I think calling that a "modified P&G" may be confusing - a glide, by definition, is "power off" (whether engine of, or just idling in neutral).

Regardless of terminology, it'll be interesting to see your comparison of the 2 techniques. You should start up a new thread on it.

[s2man]

Isn't speeding up going downhill and slowing down going uphill DWL?

[DifferentPointofView]

yea, I'm pretty sure, but I'm also pretty sure that the order goes in reverse, slow down going up and speed up going down

[brucepick]

I listen for the sound of air rushing past the car. On a no-wind day there's a distinct increase in sound between about 60-63 mph. Of course it gets gradually louder as speed increases but there's a major increase in the low '60's. Of course every car will be different but you can listen for the sound of rushing air. More sound = more turbulence = reduced FE.

I take this as an indicator of what speed to target. Wind speed affects the sound level. With a strong headwind the sound increases happen at lower road speeds, and the opposite for tailwinds. So since I have to drive the actual current conditions I now go mostly by the sound of airflow - plus of course whatever urgency I have in getting to my destination or dealing with traffic.

I commute 60 mi. each way. Partly state roads at 40-55 mph with several miles between lights, and partly open highway posted at 55-65 mph. Also some city roads at one end of the drive with frequent lights. No FE instrumentation in my '89 car.

[Sandy]

'You're are Correct Sir'

It is more like DWL,
I've tried the P&G but with an automatic,
going to neutral or powering the engine off isn't easy,
nor feasible or safe in commute traffic.
So my modified P&G naming isn't truly accurate and the DWL is.

I've gotten tremendous improvement by doing the DWL,
and very close to it using the slow-cruise at parts of the highway where it seems to make sense.

[DifferentPointofView]

I listen for the sound of air rushing past the car. On a no-wind day there's a distinct increase in sound between about 60-63 mph. Of course it gets gradually louder as speed increases but there's a major increase in the low '60's. Of course every car will be different but you can listen for the sound of rushing air. More sound = more turbulence = reduced FE.

It's really helpful when you have a leaky door and you hear wind noise

No FE instrumentation in my '89 car.

Mine is my leaky door

[Chris D.]

my trucks engine seems to relax a bit easier with the vacuum guage right around 60mph and at 55 it strugles just a little bit.. (less vacuum)

I have a 2.4 dohc 16v engine thats built for torque.. (long intake runners)

[s2man]

Originally Posted by DifferentPointofView

It's really helpful when you have a leaky door and you hear wind noise

Hey, I've got one of those instruments too!