Best cruising speed for highest MPG.

[Miniata]

Not terribly scientific, but while I was out today, I spent some time with the cruise set to 50, 60, and 70 mph in 6th gear on a flat stretch of road. Thanks to traffic and a 55 mph speed limit I wasn't able to hold the lower and higher speeds as long as I'd have liked, but was able to do so for at least a mile. I used the average mpg instead of the instant mpg readout, since the instant readout bounced around too much, and reset the mpg display each time I changed speeds. In general, there was a 3-5 mpg drop in mpg each time I increased speed by 10 mph. 50 mph was the best of the speeds I tried.

[rice_classic]

Originally Posted by regal

This car is different, below 3k the direct Injection drops off like a rock and the port injection takes over. It may be interesting to find that the typical 55mph highway efficient mpg is burning more mpg than 65 mph in this car.

I don't think that's right. The DI never stops firing, you can hear it at idle. You might have it backwards... at high RPM, the port injectors stop firing.

Low RPMs: DI and Port simultaneously fire
Mid RPMs: DI and Port both fire but staggered
High RPMs: DI only

Fuel mileage is figured regarding gear, speed, powerband and duty cycle (throttle/Injectors).

I would imagine the best mileage is going to be in top gear (6th our case) so the most efficient speed would probably be at the slowest speed we can travel in 6th gear without bogging the engine or requiring an unnecessary depression of the throttle (bogging). I'm guessing this to be round 40-45 mph as this was about the lowest speed the car was comfortable with in 6th gear on a flat road.

[icemang17]

okay I didn't buy the FRS or hypermile it......but I did buy it because I figured it would get good real world mileage...and it does...

My typical 300 mile trip on the freeway averages 32.5mpg and I drive FAST...typically 75-85mph.....as traffic allows....

[eriktherod]

AT I assume? I'm currently at 27.9 avg. I drive mostly highway miles but I admit that my accel is not gradual and my shifts not at lower rpms.

[Minovsky]

i dont know why i only got 10.1 avg Is that the MPG reading? How come i see people with like 2XMPgs... .... =[ is it because i mostly drive in town and get a load of stop signs and intersections? How can i improve on the mpg.. i don floor my car either and i slowly build up speeds too... i always see the people infront of me get ahead at intersecions before i finally reach their speeds... i usually go on road from 40km/h - 80km/h... please help

[whaap]

Originally Posted by Vracer111

Cruising has a time factor involved... does no good getting better MPG at a much slower speed if you are going to be on the road for possibly DOUBLE the time compared to a faster speed that isn't as efficient - but not 1/2 as inefficient.

The question is gallons per MILE not gallons per HOUR.

[ArgentoAtl]

Originally Posted by FRiSson

...
You might want to dig up a test that Popular Mechanics performed measuring the most efficient way to accelerate a car to highway speed. They found that accelerating slowly is not the most efficient method. Instead, they recommend getting to your terminal speed at twice the maximum speed of the car. In other words, if your car goes from 0-60 in 7 seconds under maximum acceleration, you will get the most efficient performance by going 0-60 in 14 seconds. They found that the gains in getting to the highest gear quickly is more efficient than getting to it as slowly as possible.

I found a relevant article http://www.popularmechanics.com/cars...-this-weekend/.

Two questions grew from my reading of the article.

1) Your example of taking 7 seconds instead of 14 seconds makes some sense, but I did not see how to get that exact result from the link. Perhaps, you were just trying to give a rule of thumb you invented? The graphics in the article were a little hard to understand, imo, and they do not tell whether the tests were made with an automatic or a manual transmission, e.g., , but they do seem to suggest the general idea of your comment is correct.

2) The link article says that leaving the car in gear and descending a hill is more fuel efficient than putting the car in neutral and indicated that newer cars have a special fuel shutoff that works only when in gear and the accelerator is not engaged. First of all, do the twins have that feature? Also, one of the comments says that this turned out not to be true for the commenter who apparently experimented on a hill using the car's mpg sensor. Any comments?

Brian in Atlanta

[Tromatic]

You guys getting 30MPG need to start a newsletter or something. I'm thrilled when I get 25.

"Whenever possible, anticipate that a light will turn red and ease off the gas. Generally, the less you have to brake, the better your fuel economy."
The typical driver around here is either too stupid or too distracted to do that.

"But it turns out that nursing your speed up to the limit too slowly also lowers mpg."
Flooring it is always the answer. Not does it give you some space between you and the idiots, it saves gas!

[Tcoat]

Originally Posted by Tromatic

You guys getting 30MPG need to start a newsletter or something. I'm thrilled when I get 25.

"Whenever possible, anticipate that a light will turn red and ease off the gas. Generally, the less you have to brake, the better your fuel economy."
The typical driver around here is either too stupid or too distracted to do that.

"But it turns out that nursing your speed up to the limit too slowly also lowers mpg."
Flooring it is always the answer. Not does it give you some space between you and the idiots, it saves gas!

I get 32 on a regular basis. Dropped all the way down to 31 with the snows on and cold weather.
Mind you that is at 98% highway driving with cruise set at 75!
When I do drive city I do exactly like you said above with the addition that I actual row through all the gears down shifting with my foot off the gas. This keeps my revs up if I need to move quick but I am not using any gas just compression.

[Tcoat]

Originally Posted by ArgentoAtl

I found a relevant article http://www.popularmechanics.com/cars...-this-weekend/.


2) The link article says that leaving the car in gear and descending a hill is more fuel efficient than putting the car in neutral
Brian in Atlanta

Anybody that coasts down a hill in neutral is a tool anyway! You just turn your nice shiny sports car into a soapbox racer with no hope in hell of reacting fast enough if something goes wrong and you need to power out of it!

[Muaddib]

31.5mpg is my best record with PSS. I imagine the result would be closer to 35mpg if I had the primacy hp.

[phrosty]

If you granny drive, you can easily get 35. I got 36-38 during my break-in period, and that was about 50% city / 50% 75-85mph freeway. Helps to have an automatic.

[Dadhawk]

Originally Posted by phrosty

If you granny drive, you can easily get 35. I got 36-38 during my break-in period, and that was about 50% city / 50% 75-85mph freeway. Helps to have an automatic.

Over almost 60,000 miles I've averaged a little over 32MPG, and I never "granny drive" so that seems like a fair trade. I've been honestly surprised what great gas mileage I get given my less than hyper mileage driving habits.

For anyone that is interested I've documented every tank in my Owner's Journal first post (well its a couple months behind, I need to update it).

I've done a couple of timed tests when traveling (fill up, get on the Interstate, get off, calculate avg speed and mileage) and still get well over 30MPG averaging speeds higher than 70MPH.

I suspect when I buy new tires soon I'll end up losing some because I won't be buying low resistance summer tires.

[Vracer111]

I've gotten 31+mpg on stock sized sticky Extreme Performance tires averaging 70+ mph between every fuel stop on the interstate for several 1,400+ mile trips.... cruise speed in the car for me would be 80-85mph, that's where many things come together and you can easily maintain 30+ mpg... fall below 75mph at anytime and you have to use too much gas to maintain the speed, get closer to 90mph and then you are in a higher consumption rate and the MPG's really decreases. Keep it between 80-85mph with proper throttle control and don't use cruise control... see 30+ mpg all day long. You have to manage the throttle every single second you are on the road to get best fuel efficiency, can't do that with cruise control - it reacts too late and then with too much input.

Doesn't matter whether your path is flat or in mountainous terrain either... 30+ mpg with proper manual throttle control. Going up mountainous terrain is more critical in keeping excessive load off the motor resulting in excessive fuel consumption, but going down a mountain is where you will make the best fuel mileage EVER...and this is with the car spending most of the time in 4th and 3rd gear as well - so you will average better than flat interstate sections if you do it right.

The only time I ever get 30+mpg is on long highway trips though - for normal daily driving I average ~20 mpg. Mainly because the car is too fun to not be using the lower gears and taking it past 6krpm with every shift...along with accelerating into and through turns...and downshifting from 6th through 3rd when coming to almost every stop.