Center of gravity

[GeorgeJ]

Hi all, I am very impressed by the technology that has been incorporated in the i3 and the result is a vehicle with impressive driving dynamics. With all the experts on this forum I am wondering if any have center of gravity data in the i3 and perhaps how that stacks up with a 3 series BMW or some other benchmark? Thanks for in insights.

 

[ultraturtle]

I'm pretty much the opposite of an expert. I'm only an observer, so take this for what it's worth:

The i3 has 50/50 weight distribution (like every other well handling BMW I'm familiar with), so you can plot COG halfway between the front and rear axles.

See the note roughly 1/4 of the way down this page: https://www.press.bmwgroup.com/usa/...=9&id=T0149790EN_US&left_menu_item=node__8601 stating:

BMW’s signature, near-perfect 50-50 weight distribution.

 

[WoodlandHills]

The CG is very low due to the weight of the batteries being below the floor and the lightness of the tall looking body.

 

[HomelessDude]

The subject came up at a BMW i3 event I attended a number of months ago, if my memory isn't faulty I believe the rep quoted the CG at 18.5 inches. He also was very specific that it was the lowest CG of any production vehicle over 60 inches in height.

 

[ultraturtle]

WoodlandHills and HomelessDude make a good point regarding low CG. It enhances cornering tremendously, helping to offset loss of sideload performance of the i3's impossibly skinny tires.

Consider these sets of performance data from Edmund's, of both the i3 and 328i with traction control enabled:

http://www.edmunds.com/car-reviews/track-tests/track-tested-bmw-328i-six-vs-four.html

http://www.edmunds.com/bmw/i3/2014/road-test-specs.html

Traction control cannot be disengaged on the i3 for good reason. Unlike internal combustion engines (ICEs), maximum torque from the electric motor is available from essentially zero RPM. Without traction control, a quick stomp on the accelerator could easily result in burning pretty much all of the rubber off of your rear tires in a matter of seconds. Sadly, BMW mapped the power available from the electric motor at low speeds to values far below potential wheel spin in most conditions, so off-the-light performance suffers somewhat, but it's still pretty sweet.

Aside from zero to 30 acceleration, skid pad results are the only metric where the i3 lags behind the 328i, and only by 9% (.78 vs .86 g). Considering that the i3 out accelerates the 328i up to 60mph, gets 350% greater efficiency (MPGe) operating on battery power, and 50% greater efficiency (MPG) operating on gasoline, I'm very pleased with all of the design tradeoffs the BMW engineers made - to include those impossibly skinny tires.

 

[GeorgeJ]

This copied from a post on Bimmerpost:

The center of gravity figures are public, published in official BMW press releases. So:

i3: 18.5"
3-series sedan: 20.0"
4-series coupe: 19.6"


Other cars:

Toyota FT-86 / Subaru BRZ / Scion FR-S: 18.1"
Tesla S: 17.5"
Lexus LFA: 17.7"
Porsche 911 GT3: 17.9"