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      08-07-2013, 02:14 PM   #1
caneaddict
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BMW i8 vs M4

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Here's the latest review of the i8 with plenty of good info on the cars stats:

http://www.autocar.co.uk/car-review/...t-drive-review

What I find interesting is how close the i8 and M4 are in stats.

i8 wheelbase is 0.4" shorter than M4
i8 length is 2" longer than M4
i8 width is 4.6" wider than M4
i8 height is probably 2.5" lower than M4
i8 weight probably within 50 lbs of M4
i8 power 357hp 420 lb/ft vs M4 probably 450hp 415 lb/ft

First, I think this strongly supports the notion that the M4 weight will be close to 3300 lbs. According to the article above, the i8 achieves most of its weight savings from the same things Dr. Nitschke mentioned the M4 will utilize:

"The outer body is a combination of carbonfibre (roof), aluminium (bonnet and outer door panels) and composite plastic (bumpers, fenders)"

The i8 is a slightly larger car to the M4 overall and must support significantly more weight in the added complex componentry used for electrification including batteries and yet it still comes in at 3278 lbs.

The article indicates that BMW sees the Porsche 991 Carrera 4S as the direct conventional competition. However, the C4S is a significantly smaller car. I really think as far as conventional engined sports cars, the M4 appears to be the most direct competition to the i8. And unless green credentials are very important to the Buyer, a direct car to car comparison - i think the M4 has the advantage - with a bonus 40% discount.

Last edited by caneaddict; 08-07-2013 at 03:24 PM.
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      08-07-2013, 03:45 PM   #2
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Interesting. Nice find and thank you for sharing.
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      08-07-2013, 03:57 PM   #3
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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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      08-07-2013, 04:42 PM   #4
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Thanks swamp2,

The article didn't mention the CFRP monocoque so i wasn't aware of that. Too bad BMW didn't decide to blow everyone away by doing the same for the M cars. I would pay $90k for a 2900 lb M4!
Given the equal size of both cars, more hp in the M4 as well as probably at most 150 lbs weight difference (i still think the M4 will come in under 3400lbs), it still appears the M4 will be faster around any track.
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      08-07-2013, 05:34 PM   #5
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I think the i8 is going to cost over $120K though.
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      08-07-2013, 11:18 PM   #6
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Quote:
Originally Posted by caneaddict View Post
...it still appears the M4 will be faster around any track.
Yes. The i8 will have a power to weight ratio very close to the current M3. Even with fairly conservative predictions of 3500 lb and 430 hp the new M4 will have a substantially better power to weight ratio than either and thus will be faster, straight line or track.
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      08-11-2013, 07:17 PM   #7
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