Cruising at 100mph

[forrester123]

I will be using the German autobahns to get to the Czech republic when I go on holiday this April.
I have a low mileage E320 petrol & will need to get a move on to reach my destination on time.
Anybody know what mpg to expect when cruising at 80, 90, 100, 110?
Last year in France I got around 30mpg cruising at 80 mph on M/Ways.

 

[stwat]

Which model and year car?

 

[Scott_F]

You could just set off earlier.

 

[merc85]

You could just set off earlier.

Or buy a e55k and cruise faster lol

 

[moonloops]

Or by a 4WD merc and get there sideways

 

[st13phil]

At high speeds aero drag is the primary power consumer and it increases with the square of the speed, so you could take a simplistic approach and say that you'll need (100 x 100) / (80 x 80) = 1.56 times as much power to travel at 100mph as you would 80 mph. To produce more power you'll need more fuel in a similar proportion, so expect low-mid 20's mpg at 100mph cruise.

 

[shadenfroh]

My CLK 320 was happy with 8.9l/100km when I travelled back from Germany doing 140-150 km/h. Carried 4x wheels with tires and 1x girlfriend too. I had perfect conditions though, nice april weather, quality european fuel, clear highways.

I was never able to reach that figure again. Around here I normally do around 9.5-10l/100km doing about 160km/h.

 

[Charles Morgan]

The east west autobahns to the Czech border are pretty crowded and numerous are restricted to 130kmh, and there are considerable roadworks. In order to average 100mph you are going to need to hit a lot higher speed on the sections that are unrestricted. I would bet on it being high teens, low 20s.

 

[CabrioDave]

At high speeds aero drag is the primary power consumer and it increases with the square of the speed, so you could take a simplistic approach and say that you'll need (100 x 100) / (80 x 80) = 1.56 times as much power to travel at 100mph as you would 80 mph. To produce more power you'll need more fuel in a similar proportion, so expect low-mid 20's mpg at 100mph cruise.

That's how I'd estimate it.

(Technically, though, it's the work done that increases with the square of the speed - which is fine, because that's what you're spending the fuel on - and the power increases with the cube of the speed, because that indicates how fast you are doing that work. If you were measuring gallons per hour, that would matter )

 

[V8AMG]

Enjoy the drive, get there on time and don't worry about the mpg

 

[c955]

Also, do you know the capacity of your fuel tank? Having to make fewer refills will save a bit of time too

My W124 had the 90L tank specc'd instead of the standard 70L.

 

[BTB 500]

Also, do you know the capacity of your fuel tank? Having to make fewer refills will save a bit of time too

Yes, driving slower and making less stops will generally be quicker. But of course you may want to stop to stretch your legs etc. anyway.

In the Vito we can make it from Calais to Leonberg (450 miles) non-stop if I brim the tank before arriving at the Eurotunnel in Dover. But driving 6-7 hours without a break is tough, so we normally do top up somewhere in the middle now

It's actually quite hard work keeping track of the current speed limit on European motorways ... it varies from one country to the next, and in Germany goes up and down like a yo-yo. 120 or 130 kph is very common but some sections are lower e.g. 110, and even less through roadworks and (less obviously) over bridges. We normally set the cruise control to 125 kph.