RE: New BMW iX3 gets 286hp and 285-mile range
Discussion
Numeric said:
I would really like this explained further if you would be so kind - really interested but a bit poor at things like this so be great to learn.
For any car, the amount of energy lost to aerodynamic drag increases with the square of speed, so any car needs twice as much power to overcome drag at 85 than at 60 (because 85 squared is pretty much twice 60 squared). Also regardless of drivetrain type, once you get up to that sort of speed the huge majority of energy being lost is to aerodynamic drag (as opposed to tyre deformation, etc). The difference between EVs and ICE powered cars comes in the drivetrains themselves. An EV will typically be something like 90% efficient at all loads and all speeds. However an internal combustion engine gets more efficient as the load on it rises. A typical diesel engine might be 20% efficient at 60mph but 30% efficient at 85mph. That means where an EV is using twice as much energy to travel at 85 as 60, an internal combustion engine will be using 2*(20/30) times as much energy, which is only 1.5 times as much energy. Thus the difference in economy is lower for the ICE.
Of course the ICE is using far more total energy at either speed, but oil contains an enormous amount of energy.
I wonder what the range would be if it was an estate instead of an SUV. Wouldn't it be nice if a manufacturer said, "We could put this drivetrain into an SUV, but they are inherently poor when compared to normal cars in both performance and efficiency. As we actually want to make the world a better place, we are going to focus on cars."
I can dream
I can dream
BigChiefmuffinAgain said:
This is distinctly... average.
LimaDelta said:
Sigh. Oh BMW, you were looking so promising with the i3 and i8, and now this. Same boring stuff as before.
Isn't that a good thing? Not everyone wants a car that looks like a demented pram, or a spaceship. They just want a normal car, that happens to be electric. That's one thing that Tesla have, largely, got right. It's this sort of thing that's going to help EVs to become mainstream, not over-styled, overly complex, vanity projects like the i3 and i8.Jon_S_Rally said:
I wonder what the range would be if it was an estate instead of an SUV. Wouldn't it be nice if a manufacturer said, "We could put this drivetrain into an SUV, but they are inherently poor when compared to normal cars in both performance and efficiency. As we actually want to make the world a better place, we are going to focus on cars."
Exactly this. I get that the fact you are sitting on top of the batteries can mean a certain increase in ride height is necessary, but Tesla have shown that it is perfectly possible to make a "normal" car - and it turns out that if you make something that isn't about as aerodynamic as a pile of bricks you can get better range out of it too.kambites said:
For any car, the amount of energy lost to aerodynamic drag increases with the square of speed, so any car needs twice as much power to overcome drag at 85 than at 60 (because 85 squared is pretty much twice 60 squared). Also regardless of drivetrain type, once you get up to that sort of speed the huge majority of energy being lost is to aerodynamic drag (as opposed to tyre deformation, etc).
The difference between EVs and ICE powered cars comes in the drivetrains themselves. An EV will typically be something like 90% efficient at all loads and all speeds. However an internal combustion engine gets more efficient as the load on it rises. A typical diesel engine might be 20% efficient at 60mph but 30% efficient at 85mph. That means where an EV is using twice as much energy to travel at 85 as 60, an internal combustion engine will be using 2*(20/30) times as much energy, which is only 1.5 times as much energy. Thus the difference in economy is lower for the ICE.
Of course the ICE is using far more total energy at either speed, but oil contains an enormous amount of energy.
Just a note to say thank you for an interesting, informative post!The difference between EVs and ICE powered cars comes in the drivetrains themselves. An EV will typically be something like 90% efficient at all loads and all speeds. However an internal combustion engine gets more efficient as the load on it rises. A typical diesel engine might be 20% efficient at 60mph but 30% efficient at 85mph. That means where an EV is using twice as much energy to travel at 85 as 60, an internal combustion engine will be using 2*(20/30) times as much energy, which is only 1.5 times as much energy. Thus the difference in economy is lower for the ICE.
Of course the ICE is using far more total energy at either speed, but oil contains an enormous amount of energy.
It also shows why Tesla styling is a bit marmite - they have gone all-out on aerodynamic efficiency to try and minimise the impact of high speed cruising, which has a knock-on impact on styling. I think they've done a good job, but I do get the "squashed frog" jibes too.
Wills2 said:
I think that very much depends on the driving usage and it appears to be the reverse of ICE cars, shorter low speed runs give a better range whilst cruising down the motorway at 70 mph hurts the potential range.
Harry's garage did a good review on the Ipace and discovered that as he only managed a real world range (leaving a sensible 30 mile reserve) of around 150 miles on a round to London and it was the motorway sections that did the damage.
The motorway cruise is definitely one of the issues, with 'fuel' so cheap it is going to be tempting to cruise or try to at least at well north of 70mph. Having to calculate whether you are better going slower and reducing the recharge time/cost as well as planning what fast charger to use given factoring in if there will be one available at that site when you arrive will be a pita.Harry's garage did a good review on the Ipace and discovered that as he only managed a real world range (leaving a sensible 30 mile reserve) of around 150 miles on a round to London and it was the motorway sections that did the damage.
I remember what it was like going on holiday in the early 00's with a car that liked super-unleaded, the Isle of White had a single station that sold it, very few stations at the northern end of the A1 did either. Charging faciliies will gradually improve in the way s-u availability did, eventually.
kambites said:
For any car, the amount of energy lost to aerodynamic drag increases with the square of speed, so any car needs twice as much power to overcome drag at 85 than at 60 (because 85 squared is pretty much twice 60 squared). Also regardless of drivetrain type, once you get up to that sort of speed the huge majority of energy being lost is to aerodynamic drag (as opposed to tyre deformation, etc).
The difference between EVs and ICE powered cars comes in the drivetrains themselves. An EV will typically be something like 90% efficient at all loads and all speeds. However an internal combustion engine gets more efficient as the load on it rises. A typical diesel engine might be 20% efficient at 60mph but 30% efficient at 85mph. That means where an EV is using twice as much energy to travel at 85 as 60, an internal combustion engine will be using 2*(20/30) times as much energy, which is only 1.5 times as much energy. Thus the difference in economy is lower for the ICE.
Of course the ICE is using far more total energy at either speed, but oil contains an enormous amount of energy.
I made a heavy-footed run over 200 miles in an e-tron at 85 ish a few days ago and lost about 25% of range over a steady 60.The difference between EVs and ICE powered cars comes in the drivetrains themselves. An EV will typically be something like 90% efficient at all loads and all speeds. However an internal combustion engine gets more efficient as the load on it rises. A typical diesel engine might be 20% efficient at 60mph but 30% efficient at 85mph. That means where an EV is using twice as much energy to travel at 85 as 60, an internal combustion engine will be using 2*(20/30) times as much energy, which is only 1.5 times as much energy. Thus the difference in economy is lower for the ICE.
Of course the ICE is using far more total energy at either speed, but oil contains an enormous amount of energy.
You’re absolutely right with the maths but drag as a proportion of total energy loss at these speeds must be less than assumed.
Other than buyer resistance which informs car manufacturers commercially, this use of an existing ICE bodyshell and chassis with batteries thrown in is an evolutionary dead end. It's like the first cars which looked like a carriage had been decoupled from its horses, with an engine thrown in somewhere. Absolute dead end design. They didn't last long.
If you're going to do an EV, don't build in all of the packaging disadvantages of an ICE designed car. Design it from the ground up as an EV. Form follows function. It will have to be aerodynamic. Its packaging will be way better for a given footprint. It need not be so wide due to a lower CoG. That will also help minimise frontal area (CdA).
It's therefore going to lose the three box look of a standard car. It won't look like an SUV, because that is not aerodynamic enough. It's going to look like something from this century, not the last. The car should look like it's a BEV, not some warmed over domestic appliance like this BMW, coloured appropriately in Hoover White.
The conservative sheeple will wail at the "radical" shape of cars like Tesla, iPace and such like. But when the designed advantages of a ground-up BEV wipe the floor with a conservatively repurposed ICE designed car, it won't be long before opinions change.
An ICE SUV with batteries instead? No thanks. I'd rather have a horse drawn carriage. I'll buy a BEV that was designed to reflect its powertrain, not work around it.
If you're going to do an EV, don't build in all of the packaging disadvantages of an ICE designed car. Design it from the ground up as an EV. Form follows function. It will have to be aerodynamic. Its packaging will be way better for a given footprint. It need not be so wide due to a lower CoG. That will also help minimise frontal area (CdA).
It's therefore going to lose the three box look of a standard car. It won't look like an SUV, because that is not aerodynamic enough. It's going to look like something from this century, not the last. The car should look like it's a BEV, not some warmed over domestic appliance like this BMW, coloured appropriately in Hoover White.
The conservative sheeple will wail at the "radical" shape of cars like Tesla, iPace and such like. But when the designed advantages of a ground-up BEV wipe the floor with a conservatively repurposed ICE designed car, it won't be long before opinions change.
An ICE SUV with batteries instead? No thanks. I'd rather have a horse drawn carriage. I'll buy a BEV that was designed to reflect its powertrain, not work around it.
theboss said:
I made a heavy-footed run over 200 miles in an e-tron at 85 ish a few days ago and lost about 25% of range over a steady 60.
You’re absolutely right with the maths but drag as a proportion of total energy loss at these speeds must be less than assumed.
You’re absolutely right with the maths but drag as a proportion of total energy loss at these speeds must be less than assumed.
It is of course a simplication. Coefficient of drag isn't actually a constant over all speeds because as the speed of air over a complex body rises, the air-flow can detach at different points which can effectively lower or raise the CD as speed rises. Then you have to take into account how the airflow interacts with other objects/surfaces near the car, especially the road itself - harmonics in the turbulance underneath a car can produce some particularly odd variations in drag as speed changes. I assume the Etron is also on air suspension, in which case it probably adjusts its ride height depending on speed?
Edited by kambites on Tuesday 14th July 14:53
theboss said:
I made a heavy-footed run over 200 miles in an e-tron at 85 ish a few days ago and lost about 25% of range over a steady 60.
You’re absolutely right with the maths but drag as a proportion of total energy loss at these speeds must be less than assumed.
Some losses don't scale by the square and may be a relatively larger proportion at lower speeds, averages are also not the same as integrating over the journey. For example a steady 60mph could be 10% less than an average 60mph with half at 40mph and half at 80mph. Road surface, weather and wind are also going to change consumption along with the efficiency of the motor and power circuits at different loads, and parasitic loads like air con and lights. You’re absolutely right with the maths but drag as a proportion of total energy loss at these speeds must be less than assumed.
I guess that if you had a device measure your driving style over a few thousand miles it would be possible to model the expected range you might get in an EV using that data. Look a business opportunity for someone...
kambites said:
It is of course a simplication. Coefficient of drag isn't actually a constant over all speeds because as the speed of air over a complex body rises, the air-flow can detach at different points which can effectively lower or raise the CD as speed rises. Then you have to take into account how the airflow interacts with other objects/surfaces near the car, especially the road itself - harmonics in the turbulance underneath a car can produce some particularly odd variations in drag as speed changes. I assume the Etron is also on air suspension, in which case it probably adjusts its ride height depending on speed?
Edited by kambites on Tuesday 14th July 14:53
Yes the e-tron is on air suspension, it has various driving modes which vary the height and I believe it also varies it’s height automatically with speed. The max efficiency mode lowers the height as well as blunting throttle response, putting the AC in eco mode etc.
I had been wondering how this iX3 would compare and if it would be worth waiting for but having read this I’m glad I’ve done what I’ve done
Genuine question, has everyone commenting actually driven an electric car? I never have so I have no point of comparison. They just have no interest to me and my only other experience of them is in Ubers. So I judge them as boring from slight ignorance.
One thing I have in my head is still the charging infrastructure. I know that in a petrol car I'm always going to be able to find fuel at any time of the day. It would really worry me buying one of these. Forget to plug it in when I get home (not unrealistic after unloading kids, shopping etc) and I would be screwed.
One thing I have in my head is still the charging infrastructure. I know that in a petrol car I'm always going to be able to find fuel at any time of the day. It would really worry me buying one of these. Forget to plug it in when I get home (not unrealistic after unloading kids, shopping etc) and I would be screwed.
EyeHeartSpellin said:
One thing I have in my head is still the charging infrastructure. I know that in a petrol car I'm always going to be able to find fuel at any time of the day. It would really worry me buying one of these. Forget to plug it in when I get home (not unrealistic after unloading kids, shopping etc) and I would be screwed.
If you have somewhere convenient to charge, I think it quickly becomes as much part of your "getting home" routine as locking the car. Public charging (for everything except Teslas) is a bit hit and miss at the moment but is improving rapidly. Personally I wouldn't buy an EV intending to regularly charge it anywhere except at home or at work yet, although people do. If your usecase actually involves driving hundreds of miles a day so it would be the end of the world if you forgot to charge it occasionally when you got home, an EV probably isn't the right vehicle for you yet anyway. Personally if I'm going to drive 200+ miles the next day I always check things like tyre pressures, oil level, etc. the previous evening anyway so checking the car is fully charged would just become part of that routine.
Edited by kambites on Tuesday 14th July 16:00
RumbleOfThunder said:
Still not good enough as it's still a compromise. The chassis wasn't designed or packaged as an EV from the outset, so it's always going to offer less than ideal range and power.
This!Skoda Enyaq looks vastly superior from what I've read so far. It can tow and a AWD version to follow.
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