Gear ratios are chosen bearing in mind torque v rpm and top speed/max power.

102Nm at 2500 rpm, 60bhp at 5000 rpm, Top speed 96 mph, Aerodynamics brick

Re fuel consumption, what is important is not how much revs it is doing but how far down you are pressing the throttle. Your sister's Panda has 60bhp and 102NM of torque @ 3000rpm, coupled with a tall boxy (i.e, not very aerodynamic) shape. And in the words of Scotty, "Ye canna change the laws of physics"!. In other words, you need a lot of torque at low revs to do what you expect of it (you know, like you get in a turbo diesel).

Another day, I had a party, and I was to wait for a bus it did not turn up, so I had to call my sister to get me home! Her car is cute Fiat Panda 1.2 8v 2007 which never been in before, but when she cruises the speed at 70mph (she did at 80mph sometimes) I was look at the rev counter it meet at 3,800 rpm for 80mph, I was wonder if she drove for a very long would not do any good to the engine? I have a diesel which do 2,300rpm at 70mph in fifth gear. I can't believe the rev on petrol, it seems far too much! Why are they doing that low gear ratio instead of high ratio, it would be save a lot on fuel.

Actually, 3.8k revs at 80mph is quite reasonable - my old (90s) Micra would happily sit at 70 in 5th with 4k revs, if a little bit noisy, whereas my current 15yo Mazda3 1.6 petrol will do the same at about 3.5k revs.

The engine suns just as sweetly as it did when I first bought it back in early 2006, and still gets the same average 40ish mpg. The Micra averaged around 53 - not bad for a car designed nearly 30s years ago!

I have a diesel which do 2,300rpm at 70mph in fifth gear. I can't believe the rev on petrol, it seems far too much!

It depends on the petrol engine/gearbox design. My 2014 Superb 1.4tsi 125ps does just under 2400 rpm at 70mph in sixth gear - about the same as my previous 2003 1.9pd diesel in top gear. The turbo tsi has good torque at lower revs so pulls the overdrive 6th gear surprisingly well. The sixth gear must be a tall overdrive as at 6000rpm you'd be doing about 180mph which obviously the 1.4 can't do (official top speed is 127mph).

Mrs BJ has a 1.2 Panda that is a bit of a screamer at 70mph. Actually I hate it on a motorway as well as high engine revs, wind noise is bad and it's really thrown around by winds especially when passing lorries. Saying that it's a great car around town especially when parking.

Edited by Big John on 29/06/2021 at 19:46

Does driving with high revs on small petrol units wear the engine more quickly? Knew a bloke who ran 2cvs for years and revved them to the limit most of the time and he reckoned they were unburstable... and he didn't burst one either.