Engaging 5Th Gear

[Bazile]

When is it most economical to engage 5th gear for best mpg

Is it over a certain speed or revs ?

[Toureman]

depends what vehicle you have, there's a big difference between petrol and diesel what engine power, etc.

[Teddio]

It depends whether or not you're going uphill. If your car is struggling in 5th gear it is both bad for the engine and uneconomical. Of course it depends on the car but for a typical diesel engine, which develops maximum torque between 1500 and 2500 rpm, I'd change from 4th to 5th at around 1500rpm. For a typical petrol engine change to 5th at 2000rpm.

[tonyav]

When ever the car feels comfortable with it, ie not juddering and can still accelerate ok.

[aelmpvw]

5th?

[Hymie]

When I am descending a hill, I regularly slip the car into 5th gear at less than 30mph – with the resultant engine revs well under 1,000 – coasting down the hill. But climbing the same hill I might not engage 5th gear until at least 50mph or more.

[Hymie]

Just thought I’d add that when I learnt to drive, cars only had 4 forward gears. About a year ago, while driving a hire car on a motorway at 70mph in 5th gear, I noticed that the engine revs were at around 4,000. I thought to myself that the vehicle had a high revving engine by design – I then looked down at the gear-knob to see that it had a six speed box.