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

[PA32R]

I've extensively tested my LR3, the post in my blog is at:

http://hamiltonianfunction.blogspot....l-economy.html

It turns out that 43.4 m.p.h. is my best estimate of most fuel efficient speed.

[DifferentPointofView]

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)

It really depends. the vacuum probably goes up because of reduced pumping losses, because the throttle plate is more open. It doesn't necessarily mean it's more stressed at 55, it just means your throttle plate is more closed.

Or is it the other way around? I can't remember. someone know?

[Chris D.]

more vac = less throttle position..

but the thing is to stay at a consistant 55mph on a flat stretch on a windless day requires about 14 vacuum where as on the same stretch the truck is willed to right around 60 and the vacuum is at 17..

the higher the number, the less throttle position your using..

anything 20 or higher is decelleration..

[atpcliff]

Hi!

Nixon proposed a 45 mph National Speed Limit as the most efficient. Congress wanted 65 mph, so they compromised.

I WOULD like a new National Speed Limit at whatever the most efficient speed would be for America. I would like to know how many barrels of oil we could save per day, and wonder if it would be enough to stablize the price, and for what period of time?

I believe that enforcing more standardization in the manufacturing of drive-trains could increase a National Speed Limit even further, as more vehicles would be able to be more efficient closer to the National Speed Limit.

I am tired of Americans sending our money over to Saudis who are funding Muslim terrorists who want to kill us.

cliff
YIP

[ebacherville]

any one drive a motor cycle, the difference between 45 and 65 is HUGE.. if you don't have a cycle just use your had out the window..

Even the difference between 50 and 60 is pretty big.. someone used the term exponential.. not exponential.. but gets the point across.

Now if you do full aero mods like the aerocivic, there can be far less disturbance of the air and get far less resistance at those upper speeds.

This proves that the cars are very poorly aerodynamically designed.. even if they look slick there usually not very slick to the wind.. its kind of shocking how some cars look very correct but are so far off..

[i_am_socket]

P&G in an automatic (mine at least) isn't too tough going to neutral. Engine Off would be deadly dangerous though.

Geo-political opinions aside: people don't follow the speed limit now, what makes you think people would follow a more specifically efficiency guided one?

The sweet-spot for my corolla (sans instrumentation) seems to be between 50 and 60. My Focus would do better at 60-65. At some point I had a hypothesis that whatever speed was top dead center of the speedometer was most efficient, but I never had the chance to test the theory.

[Chris D.]

sweet spot for my tacoma truck seems right in the area of 40-43mph.. 5th gear..

[Frankenstipe]

The point at which my auto shifts into 4th gear, accelerating as slowly as possible (usually right around 2,000 RPM), my speed is just about 43 MPH I think. It's between 40 and 45, but I'm definitely not going to be doing that speed on any highway near here, when I get a Scangauge I'll test it out on some back roads but that won't be for another month or two maybe.

Right now I'm cruising at 55 MPH (2,000 RPM), and trying not to accelerate past that RPM. Probably won't know for sure what MPG is until the tank is done next week some time.

[JohnnyGrey]

# Gau Mar 11, 2008 3:16 PM GMT Actually no, 55 isn't the most efficient speed The best ratio for gas is just above minimum rpm in your highest gear. RPMs is what eats gas, not speed... t Generally older cars run from 45-60 depending on gears and ratio. However on a lot of newer higher end cars with 5 and 6 speed gears, those number goes up...

Both RPM and speed eat gas, and by that logic alone, the most efficient speed is 1mph. However, the BSFC map changes all this. The most efficient speed is where you can go fast enough to get into a good spot on the BSFC map, but not high enough that drag eats up all your efficiency. If you drive looking only at the BSFC map, you'll be getting the most crank power from your gas, but you'll be literally throwing it to the wind in the form of air resistance. We're going for MPG, not HP/G, so the only way to really find out is to test it out. My automatic 2.2L Cavalier peaks at 42mpg @ 53mph. There's another member on here with that powertrain who might find that info useful. For other powertrains, it will differ.

On the slow end, gearing limitations and the low end of the BSFC eat your MPG. On the fast end, wind drag does.

[DifferentPointofView]

Mine is actually at about 46, when the torque converter locks up. at 45 it slips out of locked mode and the rpm's go up to about 1500 at 45.