BMW i3 - Low Hanging Fruit (improving aerodynamics)

[Vman455]

I would hesitate to go any lower than you have already; generally, there's a "sweet spot" where CD goes down as the body is lowered, but rises again with more lowering. According to the aerodynamics textbooks I've read, this is somewhere around 0.75 body cover:1 wheel diameter.

Mirrors will be your best bet. That underside looks very good for a production car already, but you may be able to cover the opening at the front subframe and behind the motor at the rear (or is yours a REx?).

Good luck! There are a couple of these running around my town, and I love seeing them--especially since the carbon fiber used in the body was manufactured in my hometown of Moses Lake.

[Snax]

Originally Posted by Vman455

I would hesitate to go any lower than you have already; generally, there's a "sweet spot" where CD goes down as the body is lowered, but rises again with more lowering. According to the aerodynamics textbooks I've read, this is somewhere around 0.75 body cover:1 wheel diameter.

Agreed. I don't think there is much to be gained there, although I am also looking at adding a front splitter. The front bumper profile rounds under relatively smoothly, but that would reduce some of the pressure and lift I get under the front end at higher speeds - and hopefully clean up aero overall.

Mirrors will be your best bet. That underside looks very good for a production car already, but you may be able to cover the opening at the front subframe and behind the motor at the rear (or is yours a REx?).

It is a REx, so it does need to breathe a bit, but I wonder if just adding an exhaust louver over that rear most opening flat with the rest of the covering would help. Supposedly the REx version has a 0.01 cd penalty, and I can't figure any other place that could be coming from aside from that opening.

[mpg_numbers_guy]

Mirror delete and wheel skirts, as noted before. Filling in any part of the underbody that isn't completely smooth, covering up that opening in the front of the car beneath the "grille", for aero. Maybe a kammback if not a full boat tail.

I wouldn't go extreme and do something like shave the door handles on a car that expensive just for another 0.01 MPG, but YMMV.

Tire pressure and slow speeds are probably your best bet for improving range with that car.

[California98Civic]

Originally Posted by redpoint5

My money would be on mirror delete, but what do I know. Rear wheel covers could be it.

I don't disagree that the mirrors are a good mod to attempt. But in thinking about the lowest fruit, I include complexity and reversibility and possible police hazzards. One can experiment with wheel well covers almost for free, using cardboard, then build with materials much cheaper than cameras and much less likely to get a cop on you. That's all... the A2 windtunnel experience & results are relevant here, probably.

[Snax]

Originally Posted by mpg_numbers_guy

Mirror delete and wheel skirts, as noted before. Filling in any part of the underbody that isn't completely smooth, covering up that opening in the front of the car beneath the "grille", for aero. Maybe a kammback if not a full boat tail.

Unfortunately, I don't believe any kind of a block of that front opening is a good idea except for perhaps during winter, as the car actively cools the battery during driving and charging from the heat pump radiator up front. While that kind of thing is relatively easy to monitor with an ICE motor, battery temperature is a black hole of information for owners and constant overheating would most definitely shorten the life.

[mpg_numbers_guy]

Originally Posted by Snax

Unfortunately, I don't believe any kind of a block of that front opening is a good idea except for perhaps during winter, as the car actively cools the battery during driving and charging from the heat pump radiator up front. While that kind of thing is relatively easy to monitor with an ICE motor, battery temperature is a black hole of information for owners and constant overheating would most definitely shorten the life.

Is the battery in the front of the car then? If it's for battery cooling then definitely leave it open; maybe duct it a little better since most factory ducting is subpar at best. Usually the batteries are underneath the car or more toward the rear.

[Snax]

Originally Posted by California98Civic

I don't disagree that the mirrors are a good mod to attempt. But in thinking about the lowest fruit, I include complexity and reversibility and possible police hazzards. One can experiment with wheel well covers almost for free, using cardboard, then build with materials much cheaper than cameras and much less likely to get a cop on you. That's all... the A2 windtunnel experience & results are relevant here, probably.

I had not seen that chart yet. Great info.

Fortunately I don't have to worry about legalities with the mirrors, as Oregon law is fairly arbitrary requiring only a "clear view" of the rear, and no specifics as to the number or placement of them.

I'm definitely going to delete them, as they are a noticeable source of noise at highway speeds. I think I have decent cameras and a monitor picked out to take up the slack - and hopefully actually expand my field of view at the same time.

Wheel covers are the likely to be my first step nonetheless, since it costs next to nothing to try.

[Snax]

Originally Posted by mpg_numbers_guy

Is the battery in the front of the car then? If it's for battery cooling then definitely leave it open; maybe duct it a little better since most factory ducting is subpar at best. Usually the batteries are underneath the car or more toward the rear.

It is underneath, but uses a heat pump to circulate coolant through the system.

[Tahoe_Hybrid]

Originally Posted by Snax

Ha ha, yeah . . no . .

I was just looking under the rear area ahead of the bumper, and it looks like they did wrap everything up like a diffuser, but it lacks side dams. I might try hot gluing something on down there to test out as that seems like one of those things they would likely have compromised out of the design for durability considerations.

All else on the car is otherwise so clean that substantial gains seem most likely to be with either my driving or the boat-tail I am so against.

Anyway, unless people have other suggestions, I will probably stick to this thread for whatever mods and testing I do.

well you could not drive at all and take the bus to get more mileage

[Snax]

Originally Posted by California98Civic

Found the pdf for this study BTW.