At 80 there's a better chance of you being in a fatal accident and never needing fuel again.

Depends on the drag coefficient, also wrong board.

>>6001
>also wrong board.

The majority of people on this site are poofs who drive hairdresser's cars. Right board.

>>6002
It's all old Jags and Volvos.

Depends on the car.

My fabia does over 50mpg at 50mph on the motorway.
At 70 it's more like 40-45mpg.

With a 6-speed gearbox it wouldn't drop as quickly when you get above 50.

>>5999
Why did you post this in /poof/, you berk?

>>5999

The question is utterly meaningless without knowing what you are driving. Different engines have different levels where they are most efficient in outputs, different shape vehicles have different wind resistance.

It would be like asking 'at what temperature and how long should I cook?' without mentioning the food.

>>6006

This.

In my current car, there's only about 100rpm difference between 70 and 80 in 6th gear. In my last one it was close to 1000, so significantly different results.

Drive your car in top gear at 70 and 80 then get back to us. Or just post your make, model and year here.