Quote:
Originally Posted by AP
car manufacturers should publish this most economical speed (all things being equal).
I think it would be a great benefit to owners. A lot of variables involved here including the engine, gearbox , temperature and loads on the negine from gadgets such as a/c, heated seats etc.
Aircraft have V speeds which define the speed thigs occur or limitations and perhaps cars should have something similar?
I've a 530d and for me it this best economical speed seems to be around 50mph but is difficult to measure.
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WhatCar with fuel economy guru Peter de Nayer did tests across a wide range of cars, to see how and when modern engines give the best mpg. The conclusion surprised many, it is still the lowest speed you can drive in top gear. That means less than 40mph for many cars. Certainly not much higher than 40mph in any car they tested.
They tested the cars at constant speeds and at 10mph increments. There is not one car in the test that improves fuel efficiency with speed over 40mph, all the graphs show increased consumption as speed increases.
If anyone has a controlled test where the 80mph figure is better than the 70mph figure, I'd love to see the data. I'm sure Peter De Nayer would appreciate seeing it as well.
I have a graph of a 535i test, (N54 engine) which clearly follows an almost straight line increase of fuel consumption as speed increases, consumption drops about 9mpg (US) between 50 - 80mph.
Just driving at different speeds and reading the OBC is not a sound test. It has to be controlled, or something as small as a 2mph wind speed, head or tail, will completely skew the result.
HighlandPete