What speed yields the best MPG?

I have noticed that I tend to get better mileage between 65-70 mph than lower 60 and high 50's, I was curious to see what others have noticed. Of course the old myth is 55 mph will yield the best, but with newer cars being built cruise at speeds of at least 60 -70 mph, I would think they are tuned to yield better mileage at a higher speed than 55.

 

What's that... you want a poll???

Ditto on the 65-70 range. I have a theory I'd get better mileage off of cruise, but have yet to test it.

 

Cruise control seems heavy on tip in at the first site of an incline. Again, haven't tested the theory, but curious to see if anyone has given it a shot.

 

Got 23mpg on the last tank - the best in just over 18 months of ownership.

Cruise does in fact give you worse MPG's due to the many inclines that are on a road. However, if you were on a perfectly flat highway, you'd probably get better MPG's due to the consistency. Oh and I voted that >70 is best mileage because I usually average 27-28 mpg doing that lol. 460 estimated miles per tank ftw.

Hmmm.... I'll have to take a check, but for me it seems like running on 6th gear at around 1200 rpm is the best.

117.6 mph

Got around 62mpg when I was doing 45mph in 6th gear.

I vote <55mph. Lower engine speed, less wind resistance, better mileage.

 

Too bad I'd NEVER drive that slow!

I set the cruise at 65 and got 27...stg2 5eat...

also, if other post their transmission... might help/add to what people are getting

I seem to get the best mpg between 70 and 75. All you guys that claim to get better mileage at less than 55 in top gear, that has to be instantaneous mpg, not average. But it must be hard to maintain a steady pace at that low of rpm. As soon as you step on the gas to get back up to the speed you want it is extremely inefficient. Try going a whole 10 miles at that speed and then 10 miles at a faster speed. You will see better average at higher rpm. The most efficient engine output that I have found is somewhere in the beginning stages of the turbo kicking in at just under 3000 rpm.

Most I've had was 30 after about an hour of 60-65... I don't usually do that since there's either too much traffic to go that fast or if it's open I go up to the speed limit. This is on a 5eat too.

All you guys that claim to get better mileage at less than 55 in top gear, that has to be instantaneous mpg, not average. But it must be hard to maintain a steady pace at that low of rpm. As soon as you step on the gas to get back up to the speed you want it is extremely inefficient. Try going a whole 10 miles at that speed and then 10 miles at a faster speed. You will see better average at higher rpm.

 

Not all of us have 6mt transmissions.

117.6 mph

 

 

This from an insurance agent...he's my kind of guy.

 

I'm sure rao will say you get the best mpg with the car in the driveway.

Not all of us have 6mt transmissions.

I thought the 6mt final drive was the same as the 5mt? It was that they had a shorter ratio...

i got 29 mpg averaging 80 on the way back from charlotte.

I normally average 27.6 traveling to and from school. 5EAT for reference, and I don't use cruise anymore. I normally drive 80-85mph..... This time, I slowed the pace down to about 75 while on the highway and I got exactly 30mpg.

I find that I get ~24mpg cruising at 65 with cruise control set.

 

You'll never be able to get as much AVCS advance with your foot, than you will with cruise control. Even in hilly situations, most of the time CC will net you better results.

 

I always mean to try and cruise a tank at 55mph, but inevitably get frustrated or late and have to speed up.

 

I've gotten 400 miles to the tank only 2 times, IIRC. I've had the car for 118 fill ups.

IMO highest gear + lowest rpm = best MPG

 

but that is just my theory

I would have to disagree with cc being more fuel efficient. I am almost certain most would agree with me. I used to use cc on the highway, but tried not to and saw better results. I get mad if I don't average 400+ per tank. It's just a personal thing...

^ I have to disagree with you on that. You can't possible do better then the computer. CC will always get better MPG.

 

I can may be agree that CC will not as good mpg with a under powered car with a automatic tranny on hilly highway.

 

 

There are a lot of factures that contribute to good or bad mpg.

Best I've gotten on the highway at 65-70 was 24mpg.

Stg 2+ with a 5eat.

^ I have to disagree with you on that. You can't possible do better then the computer. CC will always get better MPG.

 

I can may be agree that CC will not as good mpg with a under powered car with a automatic tranny on hilly highway.

 

 

There are a lot of factures that contribute to good or bad mpg.

 

Yep.

 

You can disagree all you want. But until you sit in a car and watch AVCS action while on CC and off, you can only speculate. Throttle becomes a control function of the system, and the ECU can fuel based on intended throttle position rather than being reactionary.

 

Two identical modern cars, going exactly the same speed, on exactly the same highway side-by-side, and the CC car will get better fuel economy.

There really isn't an ideal speed or a sweet spot to get the best economy, there are way too many factors...

 

-Altitude

-Temperature

-Transmission (for gearing)

-Weather (like wind)

-Terrain

-Tires (proper inflation, rolling resistance)

 

When I go between my two places in Orlando and Savannah, I go the flow of traffic, typically between 75 and 80 mph (it is I-95 after all, where Floridians think the limit is 95)... and I average still around 25 mpg. Even slowing down to 70.. still 25 mpg.. that's with the 5eat. I don't know what the RPM is, and I don't know what the gearing is.. but my point is, what works for me may not work for others. If you're getting only 15 mpg then there is something wrong, but I think most people here get between 22-27 mpg.. and we only have what, 13 gallon fuel tanks? You're only talking about a 65 mile range difference..

16.1 gallons, IIRC.

 

I've DEFINITELY put 15.7 in mine, which is terrifying.

I have to agree with teh CC yields better mileage theory. You simply can't anticipate where to hold your foot. Especially given a MT, you are going to downshift if the hill is so steep your gear can't hold it, not many hills at highway speeds.

 

For reference I drive a 5MT, 40mi commute, moderate hills, CC 98% last tank yielded 25.1mpg (calculated), current comp readout says 27mpg (summer gas FTW) we'll see what that calculates to when I top her off today, but I have yet to have a greater than 1mpg difference.

 

I have only been able to try 55 in back roads that 55 would be safe to drive at, of course I don't "cruise" on those, the twisties are way too fun

 

In my daily commute I feel I would be a hazard to other drivers going under the speed limit. However to those arguing 55 would net better due to lower rpms and less resistance, how is it that many people (myself included) have seen an increase in MPG from low 60mph to high 60's? That is an increase in both, but a decrease in mpg....

 

Unfortunately my daily commute speed limit is 60mph, I have slowly been getting closer to 70 as I learn where the police sit, and I am continually seeing my mpg go up.

^ I have to disagree with you on that. You can't possible do better then the computer. CC will always get better MPG.

 

I can may be agree that CC will not as good mpg with a under powered car with a automatic tranny on hilly highway.

 

 

There are a lot of factures that contribute to good or bad mpg.

 

^^Agreed as well... but I wanted to add an exception to it.. and it only applies to hills or mountains..

 

If for some unknown reason (could be altitude, like climbing over I-70 up to Aspen or Viel) and the car slows down because of the altitude, once the car begins to descend down the mountain, cruise control will still add throttle to accelerate.. but without cruise, you can take your foot off the gas and let gravity do it for you.. it's slower, but it uses less fuel.. that's the only exception I can think of, but I would imagine even if you lived in that area you'd still get around 20 mpg..