On my highway trip I noticed that the mileage was much better between 50-55 mph (40-45 mpg) than between 60-65 mph (35-40 mpg)...

Anyone know for sure what speed keeps the car in top gear and nets the most mileage?

I have an Automatic...

 

No scientific proof behind this claim but I would venture to say the lower you are in rpm the less gas you consume. Having a manual I dread highways because going 70 means I must keep rpms @3k. I do better on the streets... You do 55 in Miami's highways you will get murdered, unless it's rush hour which would mean your pretty much screwed

 

With the engine off, rolling down a hill...a tail wind would help too.

 

(from the EPA)


From Wikipedia

The original data is located here:
http://cta.ornl.gov/data/tedb29/Edition29_Chapter04.pdf

For each of the vehicles tested, most efficient speed was:
Corsica: 50 mph
Legacy: 30 (smaller peak at 55)
Olds Eighty-Eight: 55
Cutlass: 55
Chevy Pickup: 45
Jeep Grand Cherokee: 40
Mercury Villager: 25 (smaller peak at 55)
Prism (rebadged Corolla): 25 (smaller peak at 45)
Celica: 25 (w/ smaller peak at 60)

Interesting observations:
1. In a car, the larger bore engines are most efficient at higher speeds, ostensibly with very tall overdrive gears. The Prism/Corolla was, at that time, available with a 3-speed automatic, no O/D. I don't know if this is the powertrain they were using. Still, even a large engine car can be fairly economical at highway speeds, chugging along at 1500 RPM, as long as the vehicle is reasonably low-drag.

2. The high-drag Pickup and Grand Cherokee do poorly over 45. I had an Element, so this is no surprise to me; mine could get close to 30 tooling around in the mountains at 40-45. Put it on the highway, and 22-23 was a best case scenario.

3. On average, the cars showed:
10.1% drop in fuel economy when driving at 65 vs 55
26.8% drop in fuel economy at 75 vs 55.

There's a reason 55 was chosen as the national speed limit during the Nixon administration, when the first fuel shock was giving the 10 mpg beasts of the day an unappreciated crash diet.

 

^^ good to know!

 

Most highways have a minimum speed limit and although its legal to do 45-50 on most freeways, do you really wanna do that, its not going to be very safe and your going to get alot of dirty looks, even by Prius owners

I've gotten 43 mpg in my Fit going 70 mph with the cruize/A/C on, so you don't need to go that slow to get great mileage

 

I've only seen minimum speed limits in a few states (much like the seperate speed limit for trucks is only seen in a few states), but in most states, you're going to get ticketed if you're intentionally driving slowly and holding up traffic.

 

iirc, the minimum speed on any road is 20mph less than the speed limit...

 

And it pretty much shows what I have observed in my car-that higher highway speeds get worse gas mileage. I am wondering what the graph of our cars looks like.

 

Each state sets it own speed limit laws. The federal government used to have a 55-mph mandate, and would withhold federal funding if they didn't comply, but that has been fully lifted for over a decade now.

From the Pennsylvania Code:
§ 601.4. Speed limits.

(a) A vehicle shall be limited to a maximum posted speed limit. The minimum speed for a vehicle on the Turnpike is 15 miles per hour below the posted speed limit, except as noted otherwise.

I don't know how that would apply to Interstate highways and state highways within Pennsylvania. Is the "Turnpike" a specific highway (like the Florida Turnpike) or a generic term for freeways/limited-access highways.

 

I drove between Baltimore and Philadephia, round trip ~500 miles. I got 56 MPG at avgeage speed of 55 mph.

 

iv got 37mpg crusing doing 70, ac on packed car with camping gear

 

Both cases I got the Fit up to speed then cleared the trip odometer and set the cruise control. This is on my commute home where I use 495, and there are some hills. I coast to a stop at my exit, park and take pictures of the trip odometer and mpg.

At 55 mph on the beltway with two runs averaging 7.25 miles, the average mpg is 52 mpg.

At 60 mph on the beltway with two runs averaging 7.05 miles, the average mpg is 48.5 mpg.

 

yo i noticed the same thing, i don't have THAT high of gas milesages tho, geez.. but i do generally 65 milers per hour and i get around like 41-42MPG, when iam doing like 80 milers per hour i get like 34 lol

manual here, not an automatic

 

Yesterday I wasn't able to complete the first run at 65mph...but for 4.4 miles I got 38.5 mpg on the gauge.

On a different road with a shorter run...
At 35 mph with two runs averaging 0.6 miles, the average mpg is 82.8 mpg.

At 40 mph with two runs averaging 1.2 miles, the average mpg is 54.5 mpg.

 

Went on a long trip this weekend for a soccer tournament with my daughter...did some readings...got to speed, set the cruise then reset the trip computer, then logged the miles and mileage.

Spd miles mpg description
50mph 5.0 38.8 Route 50-Many Hills
45 mph 7.2 63.1 Route 17-some Hills
70 mph 15.4 38.2 Route 66
63 mph 6.1 48.4 Route 66
60 mph 4.2 49.3 Route 66

 

interesting thanks for posting

 

My lifetime avg so far is 38mpg and my average speed is right around 45mph. (our altima had an avg speed display as well as avg mpg display & my driving hasn't changed in the last 5 years) I drive almost 0 highway but all country roads. some stop signs, a few weekly trips into the "City" (which means 20-30 Red Lights) but mostly my driving is 50mph roads with 25mph towns.

VT has minimum speeds often posted on the few highways it has. Rt 4 (where it's actual highway) has a minimum of 45 posted. When I do get on the highway, I usually average just over 70 and the mpg does suffer. usually around 38-39 in the summer (when I'm usually 40 or 41). In the winter, our highway trips usually involve the Ridgeline)

~SB

 

I do mostly Hwy driving so I got a manual shift since i won't be shifting much anyway. Looks like i made a big mistake. I just saw that the manual's 5 gear pretty much equals the auto's 4th.
Does anyone know how expensive or if it is even possible to put in more of an "overdrive" 5th gear to improve MPG and quiet the engine down??

 

Welcome to the freakworld - There's been threads on the forum talking about that. Here's a good one: https://www.fitfreak.net/forums/2nd-...stead-6-a.html

I would forget about the overdrive. The manual Fit actually has a good set up. It takes a bit to adjust to how the Fit likes to be driven. I thought the same thing when I first got mine.

I've come to enjoy the shifting character of my Fit. Owning a MT is all about the shifting. I don't think you made a mistake at all.

As far as speed, on the open road - 72 is a good compromise.