The 56 mph myth
Discussion
Forgive me if this has been mentioned before but I keep coming across non motoring folk saying that 56mph is the scientifically proven most economical speed at which to drive. Whilst it certainly explains how many A Road queues are heade by a Micra, an old Mondeo and a Rover 25 maintaining 56mph , with the cars often optimising their economy by running in a tight packed bunch 10 ft or less apart, I doubt the 'science'.I think it is founded solely on the fact that the EU economy figures used to quote consumption at 90km /h and 120 km/h- respectively 56mph and 75 mph.Am I right?
dcb said:
Really ?
Thousands and thousands of different cars currently on sale and
previously on sale, everything from the four cylinder Nissan Micra to
the mighty BMW 760Li and you're sure of your claim ?
Brave chap.
My previous chariot, an E39 BMW 530, averaged over a mere 85,000 miles
and nine years of ownership, would do 30 mpg at 70 mph, 27 mpg at 90 mph
and 25 mpg cruising at anything up to 154 mph, but mostly 120 ish mph
default autobahn cruise speed.
So there's a real world example of a 3 mpg drop from 70 mph to 90 mph
and a 2 mpg drop from 90 mph to let's say conservatively about 120 mph.
Your claim doesn't look quite so strong now.
Indeed, I checked the numbers from a recent Austrian trip in my
current BMW 325 and got the following
31.3 mpg, max about 100 mph
29.4 mpg, max 155 mph
36 mpg, max 89 mph
28.2 mpg, max 142 mph
28.5 mpg, max 145 mph
Ok row 3 is extreme because I was tailgating Italian lorries,
but the rest of the time, petrol consumption hardly varied from
28.2 mpg to 31.3 mpg. Just look at those maximums, though.
The car got some right treatment.
Cruising at 120 ish mph, with some faster runs up past 140 mph, doesn't
cost a lot of petrol, in a suitable car. I think high gearing counts
for a lot.
Sorry but I find it extraordinarily difficult - no ,impossible, to believe that a 1500kg ish big car like a 5 series will do 25mpg at 154mph. But only 30 mpg at 70 mph ..Come on, common sense tells me this just cannot be right!Thousands and thousands of different cars currently on sale and
previously on sale, everything from the four cylinder Nissan Micra to
the mighty BMW 760Li and you're sure of your claim ?
Brave chap.
My previous chariot, an E39 BMW 530, averaged over a mere 85,000 miles
and nine years of ownership, would do 30 mpg at 70 mph, 27 mpg at 90 mph
and 25 mpg cruising at anything up to 154 mph, but mostly 120 ish mph
default autobahn cruise speed.
So there's a real world example of a 3 mpg drop from 70 mph to 90 mph
and a 2 mpg drop from 90 mph to let's say conservatively about 120 mph.
Your claim doesn't look quite so strong now.
Indeed, I checked the numbers from a recent Austrian trip in my
current BMW 325 and got the following
31.3 mpg, max about 100 mph
29.4 mpg, max 155 mph
36 mpg, max 89 mph
28.2 mpg, max 142 mph
28.5 mpg, max 145 mph
Ok row 3 is extreme because I was tailgating Italian lorries,
but the rest of the time, petrol consumption hardly varied from
28.2 mpg to 31.3 mpg. Just look at those maximums, though.
The car got some right treatment.
Cruising at 120 ish mph, with some faster runs up past 140 mph, doesn't
cost a lot of petrol, in a suitable car. I think high gearing counts
for a lot.
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