BMW i3 - Low Hanging Fruit (improving aerodynamics)

[mpg_numbers_guy]

Originally Posted by Snax

Anyway, on another note, it looks like the Torque app has had something potentially useful added to it with fuel consumption reporting. The value reported is completely wrong, but it does accumulate a long term average which settled at 17.8 for the recent test. Given the 40.8 MPG actual measured fill, I can probably safely change the displacement in the settings for a more accurate idea of the extended consumption for each trip as quick way to compare without stopping to fuel up.

I found that the Torque app doesn't seem to count any mileage over 100 MPG in their long term trip average. For example, suppose you were going downhill and the readout said 99 MPG instantaneous, Torque would factor that into the trip log, while if you got over 100 MPG going downhill, it would not factor that in.

The long term average is very inaccurate too. You'd probably have to do an even 50% city 50% highway split to get it even, since it overestimates city FE and underestimates highway FE.

In my Civic, Torque said my best city FE trip was 71 MPG when it was really upper 50s, and said my best highway trip was 49.1 when it really was 60 - calculated over 300 miles.

[Snax]

Originally Posted by euromodder

Those massive wheels are also costing range
If you ever have one off the car, please weigh it, I fear it's gonna be pretty heavy even if it looks airy.

The large diameter / small width helps, but the weight works against you

They are actually remarkably light weight. BMW made the profile of the spokes surprisingly thin and very flat on the back side. I wouldn't guess the wheel and tire combo is much over 35 lbs. total. I don't believe I am likely to gain much with wheel discs, but obviously I am going to try. Fairing the rear wheels however is another story. Probably lots of cleanup possible there.

I'll be removing them again soon and will check.

[Snax]

Originally Posted by mpg_numbers_guy

I found that the Torque app doesn't seem to count any mileage over 100 MPG in their long term trip average. For example, suppose you were going downhill and the readout said 99 MPG instantaneous, Torque would factor that into the trip log, while if you got over 100 MPG going downhill, it would not factor that in.

The long term average is very inaccurate too. You'd probably have to do an even 50% city 50% highway split to get it even, since it overestimates city FE and underestimates highway FE.

In my Civic, Torque said my best city FE trip was 71 MPG when it was really upper 50s, and said my best highway trip was 49.1 when it really was 60 - calculated over 300 miles.

Definitely going to take it with a grain of salt. I did notice yesterday that with the range extender totally off, the app was reporting 255 MPG without the correction for displacement while moving, and it dropped to 0 MPG while stopped. Whether that counts toward the average or not I did not notice. I haven't driven with it corrected yet, but that shouldn't skew things too badly overall for collecting data in motion anyway.

I have to wonder if the accuracy of it is more dependent on the individual vehicle ECU.

[mpg_numbers_guy]

Originally Posted by Snax

Definitely going to take it with a grain of salt. I did notice yesterday that with the range extender totally off, the app was reporting 255 MPG without the correction for displacement while moving, and it dropped to 0 MPG while stopped. Whether that counts toward the average or not I did not notice. I haven't driven with it corrected yet, but that shouldn't skew things too badly overall for collecting data in motion anyway.

I have to wonder if the accuracy of it is more dependent on the individual vehicle ECU.

IIRC 255 is the highest that the instantaneous readout will display. As far as I know it won't be consistently factored in on the average due to being over 100 MPG. It may work differently on different ECUs; I haven't been able to verify that.

Maybe I missed it earlier, but doesn't your car have built in efficiency instrumentation? If so, those are typically much more accurate, and if not, a Scangauge is much more accurate and doesn't cost all that much when you think of it long term.

[Vman455]

Originally Posted by Snax

They are actually remarkably light weight. BMW made the profile of the spokes surprisingly thin and very flat on the back side. I wouldn't guess the wheel and tire combo is much over 35 lbs. total. I don't believe I am likely to gain much with wheel discs, but obviously I am going to try. Fairing the rear wheels however is another story. Probably lots of cleanup possible there.

I'll be removing them again soon and will check.

I can't find data for the 20", but this Jalopnik article reports BMW said the 19" would be 15 lbs before production started. With the tire weights listed at tirerack.com, that would make 31 lbs front/33 lbs rear.

[Snax]

Mirror delete mostly complete! (I just need to fine tune the trim a bit.)

[Snax]

Thoughts on how to finish the rear of the skirt?

I haven't tuft tested anything for lack of a camera or other easy means, but I am confident of 100% separation behind the rear wheels. Assuming no boat tail, would it be best to leave it open like that and just brace it?

[mpg_numbers_guy]

Images don't display on my end.

[Snax]

Originally Posted by mpg_numbers_guy

Images don't display on my end.

Okay, fixed I think.

[California98Civic]

That angle is too sharp to taper effectively, and you don't want to be building some sort of boat tail extension I've heard you say. Seems like your best option is to taper the trailing Edge of the wheel well skirt a little and create a box cavity like separation point at the tail end of the car.