Ideal highway cruising speed?

[MikeDS]

Hey guys,

I was trying to glean this info from some of the tech threads, but didn't see if there was a consensus. What is the ideal cruising speed to maximize fuel efficiency and speed? Or in other words, at what speed does the MPG drop off quickly? I drive from LA to Phoenix sometimes and typically try to go as fast as possible (10 over the limit - 80 in Cali, 85 in AZ)...if I drove 70, 75, etc would I see a big change in gas used? Whats the optimimum over 65mph speed? Can I ask the same question 12 times? haha....

Thanks!

Mike

[djasonw]

I am pretty certain my experience with the Gen II holds true for the Gen III. The sweet spot for great highway mileage is 65MPH. Anything slower and you're impeding traffic flow but you will obviously get even better mileage. I usually average over 50 MPG when I set the cruise for that speed. The conditions have to be warm, mainly flat, light winds to achieve this type of mileage. I am sure others do better than I as I don't exercise some of the techniques used to raise MPG. Even when I'm going 75-80 I still manage over 45 MPG!! To this day, this car still amazes me.

[bwilson4web]

Originally Posted by MikeDS

. . .
I was trying to glean this info from some of the tech threads, but didn't see if there was a consensus. What is the ideal cruising speed to maximize fuel efficiency and speed? Or in other words, at what speed does the MPG drop off quickly?

My preliminary data:

Originally Posted by MikeDS

. . . I drive from LA to Phoenix sometimes and typically try to go as fast as possible (10 over the limit - 80 in Cali, 85 in AZ)...if I drove 70, 75, etc would I see a big change in gas used?

Perhaps it is time to begin making your own trip records and sharing it here?

• record start and stop locations - enough that we can find them on Google Earth to get altitude. Also wind direction and speed, temperature, tire pressure and use or non-use of air conditioner.
• reset trip meter once you reach cruising speed - this let's you record the distance, MPG and average speed w/o the acceleration overhead.
• [OPTIONAL] use a Garmin nuvi or equivalent GPS to record trip - this can provide a detailed speed and altitude record for analysis

Originally Posted by MikeDS

. . . Whats the optimimum over 65mph speed? Can I ask the same question 12 times? haha....
. . .

Well if you ask it '12 times,' the answer is 42, the Answer to the Ultimate Question of Life, the Universe, and Everything.

Bob Wilson

[MikeDS]

42 is way too slow....haha. It must be how many roads must a man walk down...

[bwilson4web]

Originally Posted by MikeDS

42 is way too slow....haha. It must be how many roads must a man walk down...

This is what happens when driving too far on "flash" when ~4.2, half-gallons remain.

Bob Wilson

[MikeDS]

haha

[Felt]

My experience here is Northern Utah, where the freeway can be a series of gentle ups and downs, and reasonably light traffic, I find a perfectly acceptable economy at 70 mph. I monitor the HSI gauge, and can maintain a lit ECO indicator at that speed. After a number of miles, I find the average will be just above 51 mpg . The indicated efficiency will decrease going up hills, but increase going down, while still maintaining the ECO indicator. 70 mph enables me to not be hazard with other motorist becoming frustrated. I do not drive in the left lane, because there are drivers that exceed the speed limit by quite a bit. I just let them pass.

[JRitt]

I just took a 500mi round trip @ 70mph and returned to the same filling station and got 49.6mpg. I'm happy with that. Tires@42psi, AC on max and drivers window open 1/2in

[ALS]

Your trip is 370 miles which I would call a medium distance trip.
Lets run the numbers and you decide.

Fuel at $3.00 a gallon.

At 75 miles per hour it will cost you $22.25
On average your trip should run a with stop about 5 hours 15 minutes.

At 70 miles per hour it will cost you $21.00 in gas.
On average your trip should run with a stop 5 hours and 36 minutes.

At 65 miles per hour it will cost you $20.20 in gas.
On average your trip should run with a stop 6 hours and 4 minutes.

At 60 miles per hour it will cost you $17.92 in gas.
On average your trip should run with a stop 6 hours and 36 minutes.

I do long distance driving between Pittsburgh and Naples Fl. which is 1170 miles. There are things that go on at higher speeds with your mind. The faster you go over 60 miles per hour the more your mind has to concentrate on the road due to the increased speeds. It also puts you reflexes on a hair trigger also. The average person can not stay at that level for more than a few hours with out problems. This is what makes you so metally tired on road trips.

Second you are also putting much more stress on the suspension and drive line components when your traveling over 60 mph. Parts wear out sooner than need be.

At 70-75 mph my range in a car is about 15 hours before I have to pull over and sleep for a few hours. At a maximum speed of 65 mph my range goes up to 21-22 hours.

Now my recommendation is to set the cruise control at 65 mph, put on some of you favorite Cd's and lean back and enjoy the ride.

[Felt]

Originally Posted by ALS

Now my recommendation is to set the cruise control at 65 mph, put on some of you favorite Cd's and lean back and enjoy the ride.

You make an excellent point. I would submit, however, at least from the mental fatigue standoint, geography can make a difference. I have lived in the East ... along I-95, and the traffic is unbearable .... and mentally tiring. I now live in the West, and the speed limit is generally 75 or more. Utah is experimenting with section where the speed limit is 80 mph. In Wyoming, 7o mph is very comfortable .... except when it is snowing.