When do you use 5th gear

My Impreza won't pull 5th much below 45mph (any slight acceleration is accompanied by nasty vibration levels), our A3 1.9TDI tells me to switch to 5th above 45mph, and down to 4th below this, and the average fuel consumption is better when I only use 5th above that speed.

It totally depends on the car, but a lot of very modern cars don't achieve better fuel consumption in top gear at low rpm as they require more fuel to achieve the same torque at the wheels (wheel torque is the key to maintaining speed and lower gears have greater torque multiplication).
 
I'm usually in 5th under 25mph. My car has simulated 7 speed flappy paddle sequential cvt thing though.

But yeah, for optimum fuel economy you want to be in a high enough gear to avoid engine braking when you lift off the throttle. On the flat in 5 speed manual, that's 4th or 5th depending on car.
 
It really depends on the car. My mum's Swift has an instaneous MPG readout on it, and I've tried 30 in both 4th and 5th, because I always do 4th and she always does 5th and was nagging me for "wasting fuel". 4th gear gave much more MPG than 5th, not sure why. The engine was labouring pretty badly in 5th though.

On my car... you can't do 30 in 5th, end of. The engine will pull you up to 35 on a flat surface with no gas whatsoever.
 
mpg wise, being a geek, i found mpg was better if you kept the revs closer to 2k rather than really low like 1k when using 5th
 
Usually at just under 40MPH and upwards. Any lower than about 35MPH in 5th and my 306 starts to struggle a bit. It might pull from 30MPH, but it'd probably take an age to pick up any speed and it wouldn't sound very nice.

Oddly enough my step-dads MK3 Golf GTI 8v will go just about anywhere at any speed in 5th with no complaints.
 
If I'm sitting at 30 then I'll go into 5th, however I'll move down if I have to accelerate/go up a hill.
 
Cruising above the legal limit. Top gear on my car is so high, and boost late enough, that it will barely pull at all in top (sixth) at sixty-five. If traffic conditions keep me near the limit I have to stay in fifth.


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My 1.25 Fiesta use to happily sit at 30 in 5th.

I put it into the highest gear where I deem it suitable. If there's uneven terrain, hills, lots of traffic I don't bother with 5th and 30. Otherwise, it's in 5th.
 
The gearbox in my IS220d has the dodgiest ratio's ever 1st gear is good for around 10mph till its screaming its knackers off, 2nd gear will get you to around 20mph and 3rd gear wont red line till 100mph-110mph. Really bad ratio's, cant pull off for toffee in 2nd. 4th gear normally happens at around 45mph-50mph.
 
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