Driving Economically - 56mph Myth??

jase1

jonny19719 wrote: »

The lowest engine revs in top gear without labouring the engine.

Not always true (although it tends to work as a rule of thumb).

Some lean-burn engines give their best fuel economy at high revs with narrow throttle opening. Toyota Carina E was a prime example. The Mitsubishi GDI was another.

I was under the impression that the best economy occurs at top gear where the car is at its peak torque -- which is low down on a diesel but not necessarily the case for a petrol engine.

Farzackerly

jase1 wrote: »

I was under the impression that the best economy occurs at top gear where the car is at its peak torque -- which is low down on a diesel but not necessarily the case for a petrol engine.

I've usually found that to be the case.

highshorting

It's a myth - sort of.

Wireless_2

Its not a myth, its simple physics, rolling road resistance can be regarded as a constant, up to approximately 56 mph it is the greater force of resistance when compared to aerodynamic resistance, but at approximately 56 mph the forces are equal.

Beyond 56 mph the graph of aerodynamic drag rises exponentially, and it is this that causes increased fuel consumption at speeds beyond approximately 56 mph.

A better drag coefficient improves fuel economy, which is why the shape of all modern cars are so similar, the same simple physics apply to all vehicles.

The suggestion that approximately 56 mph is a result of someone, or some organisation, deciding to choose approximately 90 kph because it looked a neat figure on paper is wrong.

The fact is that the magical velocity is not exactly 90 kph, but 90 kph is a good approximation, just like we use an approximation when considering the force of gravity.

forgotmyname

2008 then 03/2011 and now?


Or maybe its just a figure that most cars at that time could reach?? Getting to 70 required something sporty.

If forces are equal at 56mph then why can i get better fuel consumption at 80mph in 6th than 56mph in 6th?

70 - 80mph = similar consumption but below 60mph is worse.