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Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 12:48 pm
by KolorMeCarbon
Has anyone made any bodywork mods that have improved the i3's aerodynamics enough to show a noticeable improvement on efficiency?

I looked around the car for any obvious air dams or restrictions to good air-flow.

I noticed the rear bumper under-tray doesn't fit together very closely.

The rear tray and bumper overlap by about 50mm but the lowest part of the bumper is about 25-30mm lower than the undertray. This creates a 4ft wide scoop which collects the air that's passed under the otherwise quite smooth and aerodynamic, battery cover.

Before I go wild with the plastic-rivets and duct-tape, does anyone know if sketchy looking panel gap is actually an airscoop for cooling the rear motor or the battery?
My car is the BEV, so it doesn't have a ReX system to keep cooled.

Also, there's a shallow front louvred grille at the bottom of the front bumper- I'm guessing this is used for ReX cooling (do BMW fit both models with same bumper?).

If that front grill is redundant on the BEV I'd like to move the license-plate down there, in keeping with the car's other bad-ass mods.

Re: Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 1:49 pm
by Bawareca
Front grill is functional-BEV and REX have the low temp coolant system radiator there and the condenser for the AC. It is really small and the exiting air is ducted to exit under the car, so not much of a drag there. There are actually models with shutters on the lower grill.

Re: Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 2:57 pm
by KolorMeCarbon
That's useful to know, I'll take a closer look at the ducting before 'improving' the aerodynamics and wrecking the thermodynamics.

Re: Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 4:01 pm
by jadnashuanh
The car sat in a wind tunnel for a long time fine tuning things before the final car was released. I'd be surprised if you can make any simple changes that would affect range. Any weight you add with a mod may not produce a positive benefit from a small improvement in cd.

Re: Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 5:07 pm
by KolorMeCarbon
I'll post a photo of the rear bumper panel gap tomorrow if it's not raining.

It doesn't look like wind-tunnel design under there, more like lazily refitted rear bumper.
At least with a pic, other i3 owners can compare it to how theirs looks.

It also looks like some sound deadening fibres are stuck in adhesive residue. Maybe a panel got damaged by previous owner.

Re: Improve aerodynamics for better mpK

Posted: Sat Sep 30, 2017 7:05 pm
by alohart
KolorMeCarbon wrote:I'll post a photo of the rear bumper panel gap tomorrow if it's not raining.
Is the triangular hole in the photo below the gap that you are referring to?

Image

Re: Improve aerodynamics for better mpK

Posted: Mon Oct 02, 2017 7:54 am
by KolorMeCarbon
I wasn't able to photograph the undertray/ bumper interface, but it does look like the bumper has been refitted after the car had its wrap done, without most of it's fixing clips.

I've used Zip-tie and duct-tape for a secure, aerodynamic fix.


The wheel wells are the worst offenders for drag, any other minor mods I do won't really make up for the turbulance problems there.

'Law of diminishing returns' in effect.

Re: Improve aerodynamics for better mpK

Posted: Sat Oct 07, 2017 12:30 pm
by ecoangel
Lower it and fit 155 tyres all round - lower fontal area has big effect over 40 mph.

Re: Improve aerodynamics for better mpK

Posted: Tue Oct 31, 2017 9:43 am
by Blacky
Actually all of those sound like great ideas. I could try them out sometimes

Re: Improve aerodynamics for better mpK

Posted: Tue Oct 31, 2017 10:55 am
by jadnashuanh
ecoangel wrote:Lower it and fit 155 tyres all round - lower fontal area has big effect over 40 mph.
Some of that depends on how the air underneath is ducted. THe bottom of the i3 is fairly smooth to minimize drag. THey purposely chose narrow/tall tires to minimize their affect on drag while maintaining a decent tire patch.

Without an air tunnel to test things, it's a lot of expensive trial and error to try to improve on this. The i3 was designed from the ground up to be both functional and efficient with EV power in mind. Obviously, some things were overcome by cost, but the difference may not be worthwhile in actual efficiency and economics. Maybe aesthetics, but that's a personal viewpoint. If there were some easy improvements, they would have been done during vehicle development given the goal for the car. The thing was not rushed into production and started with a clean slate.