Improve aerodynamics for better mpK

[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.

 

[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.

 

[KolorMeCarbon]

That's useful to know, I'll take a closer look at the ducting before 'improving' the aerodynamics and wrecking the thermodynamics.

 

[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.

 

[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.

 

[alohart]

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?

 

[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.

 

[ecoangel]

Lower it and fit 155 tyres all round - lower fontal area has big effect over 40 mph.

 

[Blacky]

Actually all of those sound like great ideas. I could try them out sometimes

 

[jadnashuanh]

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.

 

[imolazhp]

Lower and add rear wheel skirts, might not be pretty (the wheel skirts) but would help with drag.

 

[ecoangel]

It was built to a price. CdA is actually no better than a 1990s Toyota Camry.

Lowering any car reduces effective frontal area no matter how badly designed the undertray is.

For down-force without a drag penalty then yes a flat bottom with proper diffuser is the way forward for race cars.

 

[ecoangel]

Nice pics Art,

Any more developments?

 

[electronchaser]

It was built to a price. CdA is actually no better than a 1990s Toyota Camry.

Lowering any car reduces effective frontal area no matter how badly designed the undertray is.

For down-force without a drag penalty then yes a flat bottom with proper diffuser is the way forward for race cars.

Hi ecoangel, sorry for bringing up an older thread, but I've been thinking about lowering the car on a new set of sports springs, which give about a 2cm drop up front. How much would a 20mm lowering reduce the frontal area, and thus drag. ( have one of the redesigned i3's with the new front end, 120ah ).

Many Thanks!

 

[Bertone]

Re-opening this topic...

I believe the front of the i3 could have been made more aerodynamic by the BMW engineers.

If you look at the area between the front headlights and "kidneys", it is not a very smooth surface...in fact air will flow between the headlight and kidney and be trapped under the frunk area producing drag.

Perhaps those "holes" could be "filled" with, for instance, polystyrene to form a smooth surface. Also the kidneys can be made more smooth "filling them up"..

The difficulty is to make a perfect fit...but polystyrene is a light and easy-to-work with-material so perhaps it is doable.

What do you think? Just a crazy idea....??

 

[Boxbrownie]

Re-opening this topic...

I believe the front of the i3 could have been made more aerodynamic by the BMW engineers.

If you look at the area between the front headlights and "kidneys", it is not a very smooth surface...in fact air will flow between the headlight and kidney and be trapped under the frunk area producing drag.

Perhaps those "holes" could be "filled" with, for instance, polystyrene to form a smooth surface. Also the kidneys can be made more smooth "filling them up"..

The difficulty is to make a perfect fit...but polystyrene is a light and easy-to-work with-material so perhaps it is doable.

What do you think? Just a crazy idea....??

Don’t forget to tape over all the shut lines also :lol:

 

[eNate]

I believe the front of the i3 could have been made more aerodynamic by the BMW engineers.

...

What do you think? Just a crazy idea....??

Careful there, or we'll be all driving Honda Insight look-alikes!

 

[alohart]

Careful there, or we'll be all driving Honda Insight look-alikes!

Having owned a 2000 Honda Insight for 15 wonderful years, I resemble that comment :lol:

 

[robthebold]

Re-opening this topic...

I believe the front of the i3 could have been made more aerodynamic by the BMW engineers.

If you look at the area between the front headlights and "kidneys", it is not a very smooth surface...in fact air will flow between the headlight and kidney and be trapped under the frunk area producing drag.

Perhaps those "holes" could be "filled" with, for instance, polystyrene to form a smooth surface. Also the kidneys can be made more smooth "filling them up"..

The difficulty is to make a perfect fit...but polystyrene is a light and easy-to-work with-material so perhaps it is doable.

What do you think? Just a crazy idea....??

Don’t forget to tape over all the shut lines also :lol:

I think caulk would be even better, combined with taking a green sharpie to the edges of the windows.

 

[PVEVman]

Just rip off the side mirrors and use cameras. Put the screens in the corners of your dashboard and you should have better rear view vision too, without dead zones!