Thread: BMW i8 vs M4
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      08-07-2013, 03:57 PM   #3
swamp2
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Drives: E92 M3
Join Date: Sep 2006
Location: San Diego, CA USA

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The comparison/analogy breaks down because like the i3 the i8 also has a complete carbon fiber unibody or "life module"/passenger cell in BMW speak (1st image below).

The existing BIW (body in white - basically the complete unibody) for the regular 3er or 4er probably weighs right around 1000 lb (see 2nd attachment below). I think we can all agree that this BIW will carry over from the base 4er to the M4 (and similarly with the 3er/M3). With the rough but decent approximation that carbon fiber can save about 50% of the weight compared to a regular steel construction, that is 500 lb saved in the i8 that won't be saved in the M4! It MUST be saved in the i8 to make up for all of the extra weight of electric motors and batteries!

Thus in short I see this as no good evidence that the M4 will weigh as little as 3300 lb.
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