[PSimpso]

The highway speed limits are mostly 70 MPH here in Michigan. I'm wondering if I'd get better gas mileage on the highway at a slightly lower speed. Does anyone know what the most efficient speed/RPM combination is on the highway - or is it not that simple? I'm driving a V6 sedan.

 

[jimijam]

Try it. It's your car, your gas, your roads, your environmental conditions, your tires, your engine, your body weight ...... go try it.

 

[chris918]

The closer you stay to TQ lock up, 50 mph, the better mileage you will get.

 

[WDHewson]

The closer you stay to TQ lock up, 50 mph, the better mileage you will get.

Good response. Get to lock up and don't go much faster.

Maybe the same speed would be near the optimum for an MT.

 

[VFR4Lee]

Some years back the government said it was 55 mph.
Do you trust them? They are here to help you! :joker:

 

[sonicc]

And here I was thinking I was pushing it with averaging 25mpg lol

My 5.0 gets 19-20 with morning trafficl

 

[desertrat]

An engineer friend and I did some experiments to determine this using 3 different makes of vehicle, Honda, Toyota, and a Dodge diesel pickup. We found basically the same thing applied to all three. The slowest you could go and still stay in the highest gear without lugging the engine provided the best mileage. On flat level roads with no traffic this ended up being between 30 and 40 mph for all three vehicles. Obviously too slow for the highway.

 

[salcuta]

Every car is different. When I used to have my Cadillac CTS, it seemed that 35-45 roads were giving me the best mpgs. For highway, I'd say around 60 is where you'll get the best mpg.

 

[visionguru]

While each car is different, the optimal MPG speed should be close to 55 mph. Older Honda, such as 1989 Accord, 55 mph was specially marked on the dial. Don't know when Honda stopped doing that.

I once observed 2005 Accord Hybrid on many occasions:
@55~60, I got 42 mpg
@60~70, 35 mpg
@75+, 32mpg
Regular city stop-n-go driving, I got less than 20mpg. In winter, on mostly short trips, I got 8mpg!

 

[easymike]

As stated above and elsewhere, the lowest speed after TQ lockup in an auto, typically between 45-55mph. Even in an MT, if you lug it too low, it'll struggle, any faster than 55 and you're getting into wind drag issues

 

[BenzAccord]

What has been said already (Top gear, torque converter locked (where applicable)) + the RPMs around 2k in an I4 and about 1.5k RPM in a V6 on a flat road.

 

[I am Confused]

I get best mileage out of my '04 cruising at 55

 

[ChrisQ80]

In my personal experience when I went from NY to FL at the end of June, I was driving 70-80mph no A/C with the moonroof open, me, the g/f and some luggage achieved 34.5mpg in my modified 6-6 with Michelin Pilot Super sports. I think my new tune, and the lightweight rims/tires helped.

 

[stiller fan]

While each car is different, the optimal MPG speed should be close to 55 mph. Older Honda, such as 1989 Accord, 55 mph was specially marked on the dial. Don't know when Honda stopped doing that.

I once observed 2005 Accord Hybrid on many occasions:
@55~60, I got 42 mpg
@60~70, 35 mpg
@75+, 32mpg
Regular city stop-n-go driving, I got less than 20mpg. In winter, on mostly short trips, I got 8mpg!

They stopped doing that cause eventually, the feds lifted the national speed limit, which was 55mph for almost 20 years.

Sent from my SPH-L720T using Tapatalk

 

[jimijam]

I drove 54 mph average on the last tank of gas and 55 mph on the tank prior to that and I dint notice a change in MPG.

 

[Baldeagle]

I’m pretty sure 50 to 55 mph is the speed for max fuel economy. Aerodynamic drag has an exponential relationship with a speed. The curve for most cars starts to go ballistic around 60 mph. Below that speed drag is pretty much the same. If it takes 5 hp to maintain 40 mph it might require only 6 hp to maintain 55 mph - not much more.

But here's the point. 6 hp might require only 20% more fuel than 5 hp. But 55 mph is 36% more than 40 mph. For a little more fuel you travel a much greater distance. If burning 20% more fuel nets you 36% greater distance, it implies you get ABOUT 16% better fuel economy at 55 mph than at 40 mph.

It’s not just about being in top gear. It’s about the best ratio of fuel consumed for distance travelled. And that is more a function of drag and not rpm.

 

[jimijam]

Ima try to hit 56 mph average on this tank to see if my MPG goes up or down.

 

[Bondo-matic]

Older Honda, such as 1989 Accord, 55 mph was specially marked on the dial. Don't know when Honda stopped doing that.

From 1975 to 1994 the "National Speed Limit" was 55, as in the song "I CAN'T DRIVE 55" by Sammy Hagar.
98% of cars later in that era had the {55} highlight on the speedometer, not just Honda.

 

[AccordinGB2]

At 2k RPM my V6 is right at 65 MPH. Exactly 2k, exactly 65 on cruise - kind of a ying and yang thing. Yes, I am slower than others on the slab, and the left laners fly by - but that's just me.......

I get 30 to 31 at that speed.

Tires are at 34 PSI.

 

[KW2004Accord]

For the best mpg on the 160hp (my 04) it was stated in one of the ancient threads that 63mph was the ideal speed.