Manuel conversion and MPG??

[Doggo]

I have said it before, but over 350 miles from a 'lude must involve witchcraft.

You have to turn the aircon off:

I don't use the aircon!

[RattyMcClelland]

There is a reason trucks are restricted to 57 mph init. 55-57 is the 'sweet spot' apparently

Or it could be that 56mph is 90kph (give or take rounding), which is the European speed limit for HGV's and was imposed purely for safety reasons, nothing else...


That's not to dispute the general argument about lower speeds giving better fuel economy (in general) etc. But there is no 'one speed' that is best for fuel economy on all cars. It's dependent on a massive range of things (as many others on here have said) so is very different for every car.
As an example, in CX petrol Turbo's, if you sit on the motorway at anywhere between around 55-70mph, it sits 'on boost', guzzling fuel (you'd be looking at something between 18-25mpg). Cruise at <something quite a bit more than 70> and it sits nicely off boost and you can get over 35mpg.

This. 56mph is just the standard now. It used to be the sweet spot on trucks due to gearing, engine speed and aerodynamics.

Nowadays engine efficiency has changed along with aerodynamics ands it's different. 56mph is just a good all round balance of speed, cruising gear ratio, safety for large heavy hgv and fuel efficiency.


There is a generics efficiency curve which is fuel efficiency vs air speed which is completely different for electric cars.

[lewd lude lover]

56mph is just a good all round balance of speed, cruising gear ratio, safety for large heavy hgv and fuel efficiency.

A good all round balance. Taking into account all of the little differences this is the reality for most vehicles. Turbo/nonturbo Brick shaped/bullet shaped. Makes no matter to the average.

The 'well my car does this' argument is as hollow as the 'my religious book says that' one.

[wurlycorner]

Errr.... Right. Factual examples in a discussion are hollow. Ok. We'd best leave that one there then.




One thing I did mean to add earlier though was that knowing that lorries will be spending most of their time at 56mph (due to the road speed limit), manufacturers probably have deliberately engineered them (as best they can with the things that are in their control e.g. gear ratios, engine management etc.) so that they achieve better fuel economy at that speed, rather than at speeds fairly closely either side of it.
However, that is deliberate reverse engineering to achieve it, rather than what occurs just as a natural result of driving at 56mph. You would always achieve a far better fuel economy with the same shaped/mass/powered vehicle at 40mph for example, having followed the same process, because the rolling and drag restistance is so, so much lower at those speeds...