Cars MPG (or L/KM) is an inverted bell shape vs speed
The same as aircraft drag or fuel burn per NM: fly slow eats lot of MPG, fly fast eats lot of MPG
Physics are different but conclusions are the same, so not sure what are we comparing 
I wonder how these curves work out with an electric car? I would imagine the bottom of the curve will be to the left of where it is for a car powered by an ICE.
alioth wrote:
I wonder how these curves work out with an electric car?
An electric car use 0 L/km, so it should be easy to draw 
An electric car still uses joules/km (and L/km can be converted to joules per km) so you can still make the comparason :-)
Those fuel economy figures I assume are for steady state speeds. There can be a big hit to economy if you have a lot of braking and accelerating. much as start stop traffic can really hit economy with a decent sized engine
Of course, electric cars gain advantage here: they will at least get some of the energy back from regenerative braking, instead of throwing all the energy away as heat in the brake discs.
On the other hand, the Tesla Model S that I was following a few weeks ago is so wide, the driver couldn’t keep it completely within his side of the road and had to pull in and slow right down every time a car came the other way (partly, this was a driver competence issue, it will (just) fit within the lane on a typical Manx road). The Tesla Model S is almost as wide as a Transit van! (only 9cm narrower than a full-size Transit) — which is getting a bit absurd. I also noticed some sports cars are absurdly wide, e.g. Lambos and Ferraris, which means practically in the Isle of Man they’ll do well to do more than 50 mph due to their bloated width making it hard to overtake anything (I bet a Mazda MX5 would practically be faster, and a motorcycle would leave them all in the dust).
Off_Field wrote:
Those fuel economy figures I assume are for steady state speeds. There can be a big hit to economy if you have a lot of braking and accelerating. much as start stop traffic can really hit economy with a decent sized engine
Indeed, average of fuel MPG consumption should be above fuel MPG consumption at average steady speed, this may explain why the actual consumption is way higher in lower speeds…
alioth wrote:
so you can still make the comparason
It’s the same curve, only scaled by 1/4 Every electric car has a velocity where it will go the farthest. Usually around 40-60 km/h. I think Tesla even has a sort of race on this, on the track.
At my engineering school when we participated at Shell EcoMarathon the constraint was to make 20km and maintain 25kmh average speed, now get max MPG
6000mpg average was not unusual for the prototypes although some years people reached 10000mpg or even 12000mpg
Besides aerodynamic design and ground friction to maximise MPG lot of play was about engine & fuel management techniques: to account for winds, accelerate/stop/restart engine while keeping average speed in check
For vehicles in that race category (about 150hp engine & 150kg weight) my understanding low consumption speed was indeed about 25kmph
alioth wrote:
I bet a Mazda MX5 would practically be faster, and a motorcycle would leave them all in the dust
Which may account for one of the former and nine of the latter at our house.
Ibra wrote:
Besides aerodynamic design and ground friction to maximise MPG lot of play was about engine & fuel management techniques: to account for winds, accelerate/stop/restart engine while keeping average speed in check
Most of which can be captured in a simple mantra… don’t use the brakes.
