MG4: Drag, Various Conditions

The point is that you contradicted my post by saying that the figure should have been 5.98 kWh. Which was INCORRECT - hence my response.

You then admitted your mistake, so I repeated the the figure of 1.5kWh as being the correct one, and not 5.98kWh.
It was supposed to be 5.98 kJ which was mistakenly typed as 5.98 kWh.

Immediately after I hit "Post Reply" button I realised the error and corrected it. I already said that. But the one person in the world who saw that error was you.

Perhaps to make that clearer I should have just changed the mistaken kWh to kJ and left the 5.98, but instead I changed the 5.98 to 1.66 and left the units as they were.

Meh - teacup, meet storm. Of the 3.5 people reading this thread, I doubt anyone was confused.
 
I see the Mods have been at work - Edits now seem to be flagged (though not retrospectively), also a couple of posts seem to have been merged.

Actually, they'd do well to delete all posts after #14. Do a Patrick Duffy, as it were...

Hmm - but not that last post, which was edited, but not flagged..
 
Anyway, this thread caught my eye as up until relatively recently (in career terms) I spent quite some time working on aerodynamics optimisation. Difference being it was for high performance cycling, not motor vehicles. The physics/maths is the same.

Aside from aerodynamics testing using novel techniques and technology I was involved in the development of, I wrote a bunch of online tools solving the power / speed equations, based on the Martin et al model:

Screen Shot 2023-12-07 at 9.00.34 pm.png

Screen Shot 2023-12-07 at 9.00.57 pm.png

Power from speed is relatively trivial but solving speed from power requires solving a cubic equation, which does not always have a closed form solution.

Some screenshots of the tools:

Screen Shot 2023-12-07 at 9.08.10 pm.png


Screen Shot 2023-12-07 at 9.09.45 pm.png

Screen Shot 2023-12-07 at 9.11.46 pm.png

I have since retired that work and website.

The business lives on in the UK (AeroCoach - cycling aerodynamics experts and wind tunnel/aero testing).
 
Very nice - would be good to use this for the MG4 if we could get some info on things like rolling resistance, drivetrain efficiency etc. Some of these could be estimated if someone could perform some rather tedious tests, I suppose.

At motorway speeds, aero drag probably dominates by some reasonable margin, I would think.
 
But does not an increased weight also affect the profile of the car (also depending on the loading dispertion e.g., it could lower the bottom or raise the front.... or vice vesa :eek: ) Have you factored this into your calculation?. It would also be handy to know the affects that temperature has on the air density affecting factors... ;)
 
Very nice - would be good to use this for the MG4 if we could get some info on things like rolling resistance, drivetrain efficiency etc. Some of these could be estimated if someone could perform some rather tedious tests, I suppose.
Tedious is the right word.

Roll down tests (i.e. at zero power) could be done, just need a good data logger for speed readings. With enough variance in starting speeds it is possible to tease out CdA and Crr with some regression analysis.

Alternatively it's also possible to do independent testing of Crr, and then assume it is a fixed value (which if using the same test venue is not unreasonable), and assign all other energy consumption to the remaining factors. It's just balance sheet accounting for energy.

The hard part is accounting for uncontrolled variables (wind being the obvious one). With the right venue that can be minimised, or measured with suitable data loggers.

Best however is to eliminate/minimise/control or tightly manage such variables.

There is a long (formerly abandoned) tunnel in the UK set up for just this sort of thing:

Alternatively, if there was a way with OBD to capture/log the car's power and speed data at high frequency, then testing on a circuit (e.g. with lap times order of magnitude 1-minute) by performing multiple laps enables use of a really neat visual diagnostic technique (originally described by Prof. Robert Chung) as virtual elevation testing.

The circuit needs to be "not twisty" like a race track - more like a smooth oval - to reduce variance with tyre scrub (edit: and avoid the need for any braking*). Some elevation change on the circuit can be advantageous but it doesn't need much - it's pretty interesting how good of a diagnostic tool this is. I used it a lot with cycling, eventually morphing into a real time data capture/modelling system at the velodrome giving CdA outcomes instantly (rather than doing post-hoc processing of logged data).
At motorway speeds, aero drag probably dominates by some reasonable margin, I would think.

90+% I would expect when on flat road. Once you add in a gradient though then increasing gravitational potential energy can become the dominant factor.

* this could be problematic with no way to turn off regen braking
 
Last edited:

Are you enjoying your MG4?

  • Yes

    Votes: 911 77.7%
  • I'm in the middle

    Votes: 171 14.6%
  • No

    Votes: 90 7.7%
Support us by becoming a Premium Member

Latest MG EVs video

MG Hybrid+ EVs OVER-REVVING & more owner feedback
Subscribe to our YouTube channel
Back
Top Bottom