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      12-15-2018, 06:05 AM   #1
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Request - Carbon Fiber roof Option in X3M/X4M

Aside from the aesthetic advantages Carbon Fiber offers those who prefer its patterned appearance, significant weight savings and lowered centers-of gravity can be seen when it is used for large areal components such as the roof and hood. These advantages would seem even more relevant for SUV/SAV platforms which, by definition, have elevated heights c/w coupes and sedans. Although I’ve had trouble locating component weights for the G01’s solid roof and moonroof options, it has been suggested in other Forums that moonroof deletions in some models may save 40-50lbs (with CF subtracting another 15lbs over an OEM solid aluminum roof). If these estimations are accurate, that’s roughly 50-65lbs off the highest section of the X3 which seemingly must yield at least some degree of lowered CG. https://www.2addicts.com/forums/show....php?t=1495538 , https://www.m3post.com/forums/showthread.php?t=301171

As it appears the G01’s moonroof mechanism requires ~ 1-1/2” space, if this option is deleted it could also allow for a more aerodynamic roof design without affecting headroom. Using a screen capture of our G01 from the BMW Connected app I made a rudimentary photo-edit to conceptualize. Although it would interesting to see how this design might alter wind tunnel profiles c/w the OEM solid aluminum roof, intuitively it seems Cd x A should improve as well? As I have no background in Fluid Dynamics my theory could be way off base, but this design must have some aero benefits for BMW's Design team to offer such for the M5. For those interested in some background, here is a link to a Ford Motor Co presentation on vehicle aerodynamics from 2005: http://www.saea.com.au/resources/Doc...-A-Seminar.pdf

And here’s a video showing the manufacture of a CF roof for the M3:
.

So would a CF roof and hood significantly alter the X3M’s performance and handling in daily use? Perhaps not, but it might be a reasonable consideration for those awaiting the X3M w/ ZCP.
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Last edited by Max Well; 02-28-2019 at 10:56 AM.. Reason: Adjusted title
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      12-15-2018, 07:13 AM   #2
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Agree. I'd like to see a CFRP roof standard on the X3 M and then the sunroof as an option. Plus when others compared weight savings on the M3 F80 the glass panel is much smaller on the cars versus SAVs so perhaps a few more pounds and even structural improvement gains. Next, I think if they want to net the weight gain from increased cooling from a stats perspective it's an easy place to go. And then it's just a personal preference in me liking the look even on my black car.
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      12-15-2018, 10:04 AM   #3
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Good points, ando.

Having seven years of X3 ownership spanning five vehicles (three F25 X3 35i and two G01 X3 M40i), we’ve never used the moonroof. But we always ordered with that option thinking it might improve trade-in value. Same thing with the roof rails.

But not this time – we’d like to order exactly as we want and let the chips fall as they may at trade-in. It would be helpful to understand the weight and aerodynamic consequences of options before ordering, but realize that probably won’t happen. And doubt BMW will share wind-tunnel results of their roof designs, or with and w/o roof rails. Slides 38 & 39 in the Ford presentation suggest rails might induce some drag, but those aren’t as sleek as BMW’s design so who knows.

Maybe they can at least provide ‘Cd x A’ values for the different editions (ZCP vs non-ZCP).
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      12-21-2018, 01:23 PM   #4
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Here is a rough idea with a CF aero roof and no rails (how we will option if they give us the chance).
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      12-22-2018, 01:35 AM   #5
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The weight was one of the reasons why I didn't order the moon roof for my m40i. Other reasons were the fact that I don't care much for them, cost and safety.

CF roof would make sense for the X3M
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      12-31-2018, 07:27 AM   #6
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While researching CF roof items I came across this image and description at BMW's F90 M5 Competition web page this morning. This raises the possibility that it may be a standard item in the X3M Comp as well?
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      12-31-2018, 07:44 AM   #7
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Quote:
Originally Posted by Max Well View Post
While researching CF roof items I came across this image and description at BMW's F90 M5 Competition web page this morning. This raises the possibility that it may be a standard item in the X3M Comp as well?
For the US market a CF roof is standard on all M5 models.
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      01-01-2019, 11:04 PM   #8
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I don't see BMW putting the CF roof on the X3M unless they flip the script on what we've seen so far. The official camo reveal and different photo leaks show the X3M with a watered down appearance.
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      01-02-2019, 08:06 AM   #9
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Quote:
Originally Posted by Transfer View Post
I don't see BMW putting the CF roof on the X3M unless they flip the script on what we've seen so far. The official camo reveal and different photo leaks show the X3M with a watered down appearance.
You may be right, Transfer - but I hope not.

Performance SUV sales remain important profit centers for Mnfrs and this segment is already intensely competitive. With the F-Pace SVR, MB's AMG series, AR's Stelvio, L's Urus, and Porsche's offerings, the stakes are high for the X3M's release. Unless they plan on upping the HP to SVR range (no indications of that so far), weight savings will be key to hitting competitive parameters it seems. And what better way to accomplish that goal - lessen the roof's weight where it will have the most effect in lowering the CG. If CF was shown to improve the M5's performance and handling, then it should have an even more profound effect on the 8" taller X3. CF technology is now commonplace and can take advantage of the headroom available in the G01 for an aero design to mesh with the current rear roof segment.

As the G01 X3 leads all BMW's offerings YTD in North American sales, it doesn't seem too far-fetched to suggest the X3M may have a similar impact on M sales, if they only give it a chance to have a fair fight in the segment.
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      01-02-2019, 10:33 PM   #10
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Oh don't get me wrong, I think there are great benefits to CF roof on X3M/X4M but I also think BMW will be making this car as a money grab from the casual driver with too much money in their pockets who wants the best smallish SUV and has no idea about performance specifics other than "well it's an M" and "Jeepers it's fast!". If they do that, we will all be disappointed so I sincerely hope I'm incorrect and they do put effort into appearance and driving dynamics beyond just power. I mean if we're realistic, wouldn't like 90% of X3M buyers opt for a no cost sunroof over a CF roof? I doubt BMW will give the option outside of a huge fee if at all.
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      01-03-2019, 06:08 AM   #11
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Quote:
Originally Posted by Transfer View Post
Oh don't get me wrong, I think there are great benefits to CF roof on X3M/X4M but I also think BMW will be making this car as a money grab from the casual driver with too much money in their pockets who wants the best smallish SUV and has no idea about performance specifics other than "well it's an M" and "Jeepers it's fast!". If they do that, we will all be disappointed so I sincerely hope I'm incorrect and they do put effort into appearance and driving dynamics beyond just power...
I'm hoping the G01 M40i catches the category of buyers you describe - even without a tune it can satisfy the vast majority of 'casual drivers'. And I doubt BMW would be so near-sighted as to have that objective in mind during the X3M's design given the competition (and profitability) in this segment. This could be a huge success for them if they keep M's heritage in all aspects (including appearance and driving dynamics as you suggest).
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      01-23-2019, 11:39 AM   #12
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Read through the 3er's CF thread mentioned in OP again, and noted IND gave weight of E90 OEM non-sunroof at 24lbs, and CF mod for the E90 at 9.8 lbs [ https://ind-distribution.com/product?sku=E90CFROOF ]. If someone has access to an E90 and could measure roof length and width we can then estimate wt/unit surface area of each and extrapolate potential weight savings a CFRP would allow the X3M (if BMW allows us to option a basic version) based on our G01's measurements.
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      01-24-2019, 04:44 PM   #13
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My kid measured the roof on my E-90; 49 inches in width, 58 inches in length.
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      01-24-2019, 06:10 PM   #14
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Quote:
Originally Posted by AUS1969 View Post
My kid measured the roof on my E-90; 49 inches in width, 58 inches in length.
Great, thanks for sharing, AUS1969.

Some quick calculations based on your E90 data suggests OEM Al X3M roof (without panoramic moon roof) would weigh about 27.9 lbs (12.6 kg), and a CFRP based on IND's 2008 data would come in at 11.4 lbs (5.2 kg). Surely the large moon roof would add a substantial amt to the OEM Al.

Will re-check calculations in the AM as I'm heading out after dinner, but many thanks to you and your son for providing us some real data. Hopefully BMW will surprise us and offer a CFRP for at least the Comp.
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      01-27-2019, 10:11 AM   #15
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Quote:
Originally Posted by Max Well View Post
... will re-check calculations in the AM...
Looked at the data again and realized our G01 roof is actually tapered width-wise front to back. So with these more accurate numbers - weight savings of CFRP vs OEM aluminum roof is reasonably estimated at 18 lbs (30.3 vs 12.4). Still unable to find a weight for the panoramic moon roof.
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      01-27-2019, 02:59 PM   #16
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I'd be satisfied with just a sunroof delete option, but the masochist in me would enjoy seeing the forums blow up if the carbon roof was a dealer-installed option like the M2.
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      02-02-2019, 07:06 PM   #17
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Quote:
Originally Posted by glennQNYC View Post
I'd be satisfied with just a sunroof delete option, but the masochist in me would enjoy seeing the forums blow up if the carbon roof was a dealer-installed option like the M2.
Today I finally got around to trying to find the thread(s) you implied in your post, glennQNYC. I'm assuming it was the Performance Parts thread ( https://f87.bimmerpost.com/forums/sh....php?t=1492934 )? I spend some time loitering around the M5 Forum but have never been to the M2 series. It would have been nice to have had the CliffsNotes version, as I still don't know what the answer was/is for the M2C and the CF roof, despite reading through 32 pages.

What was the end result - does the M2C get it from the factory, from the VDC, from the Dealer, or ?

Not that it has a definitive bearing on what we'll see, but it might help to anticipate and understand Corporate's (CFO's) directive on how this might play out.
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      02-02-2019, 08:42 PM   #18
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Thanks for the weight analysis. CFRP roof weight saving for performance gain may not be as noticeable as offering CFRP drive shaft. Let's see if BMW offers those in X3M ZCP.
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      02-03-2019, 10:36 AM   #19
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Quote:
Originally Posted by Mii View Post
Thanks for the weight analysis. CFRP roof weight saving for performance gain may not be as noticeable as offering CFRP drive shaft. Let's see if BMW offers those in X3M ZCP.
Thanks, Mii. I've come to look at weight savings in SUV/SAVs from two different angles. First, from just a pure performance standpoint (as in acceleration and braking), there is no doubt less weight should yield improvement in that area. I hadn't thought about the drive shaft in particular, but assuming CF has the same strength and longevity in that environment as opposed to just skin and structural applications, weight savings there would also be good. I tried to check ETK for weights of non-CF BMW shafts but was unsuccessful - if you have reference weights for the standard OEM and potential CF shafts that would be interesting data if you can share.

Secondly, and perhaps far more important from a 'handling' perspective in taller SAV designs, intuitively it seems lowering the CG (especially from the top) should allow improved cornering stability. In watching videos of performance SAVs on the Ring, it appears they have more tendency to lean during high speed turns c/w their coupe/sedan siblings.

If one removes weight from lower regions without addressing the top, an argument could be made (theoretically at least) that the CG would actually be raised - so in essence improving acceleration/braking but at the sacrifice of stability and handling?

It's a fascinating field, but as I am by no means an Engineer or Physicist I may be way off in my logic. However, as BMW is manufacturing many of their high-performance vehicles with CF aero roofs there must be something to this idea. And for them to do so for even the 53" high M850i, I can only imagine the beneficial effects it might have on the 66" tall X3M. Frankly, other than cost, I cannot envision any argument for at least the X3M Comp to not have such as standard as ando suggested previously. If BMW wishes their M Division to remain relevant in this rapidly expanding field of high-end bespoke manufacturing, it would appear a missed opportunity if financial restrictions limit design and engineering who can make the Comp run with the best in this group.

I'm including some images of the M850i CF roof (almost a work of art), pjdizzle94's M5C roof which he kindly shared in December ( https://x3.xbimmers.com/forums/showp...2&postcount=40 ), and a size chart comparing the three models. If anyone out there is a Physicist or Engineer and can suggest the potential improved 'moment of inertia' on the X3M framework with the removal of 18 lbs off the top, would be interested in reading.
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      02-03-2019, 11:49 AM   #20
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Without a doubt that CF roof on F92 8-Series among others like F80/82/90 achieved both weight saving and aesthetic pleasing in the eyes.

Without derailing CF roof thread too much (if you prefer to start analysis on a separate thread, please feel free), here are other threads with carbon shaft, weight discussion for reference. General consensus is that it may not reduced a whole lot of weight (steel vs carbon shaft), though gives additive advantage of responsiveness and power transfer.

https://f80.bimmerpost.com/forums/sh...d.php?t=921523
https://f80.bimmerpost.com/forums/sh...php?p=22692129

This is the official quote from BMW (could be marketing BS, though sounds compelling):
Carbon Drive Shaft One-Piece:
- 40% weight saving from predecessor (this maybe where we can derive the approximate weight)
- Helps to reduce rotating mass
- Increased stiffness
- Better acceleration and responsiveness

Believe or not before BMW switched later production F80/F82 to steel shaft, BMW used to publish regular M3 (not CS) official 0-60 in 3.8s, now updated to 3.9s, go figure.
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      02-03-2019, 03:53 PM   #21
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Quote:
Originally Posted by Mii View Post
Without a doubt that CF roof on F92 8-Series among others like F80/82/90 achieved both weight saving and aesthetic pleasing in the eyes.

Without derailing CF roof thread too much (if you prefer to start analysis on a separate thread, please feel free), here are other threads with carbon shaft, weight discussion for reference. General consensus is that it may not reduce a whole lot of weight (steel vs carbon shaft), though gives additive advantage of responsiveness and power transfer. ...

This is the official quote from BMW (could be marketing BS, though sounds compelling):
Carbon Drive Shaft One-Piece:
1). - 40% weight saving from predecessor (this maybe where we can derive the approximate weight)
2). - Helps to reduce rotating mass
3). - Increased stiffness
4). - Better acceleration and responsiveness

Believe or not before BMW switched later production F80/F82 to steel shaft, BMW used to publish regular M3 (not CS) official 0-60 in 3.8s, now updated to 3.9s, go figure.
Thanks for the links and input, Mii, and I'll take some time to digest those threads. No worries on derailing the thread, as I'm all for trying to maintain continuity on the theme of a thread, and those CF discussions should mesh nicely. My immediate thought, before having even looked at those (commenting only on BMW's suggestions as to what the CF drive shaft might bring):

1). - if 40%, any weight savings is a good thing, and hopefully we can identify # of lbs to provide a reference to curb weight
2). - no doubt if the weight reduction is accurate
3). - seems a given
4). - having trouble blindly accepting that one. Theoretically, yes, but one still has to look to the weakest link in that chain of processes controlling the downstream result, so considering turbo responses, ..., seems that contribution will be much less significant in a combustion system.

Which brings me to another concern regarding lack of data for some key elements when Performance Enthusiasts are researching options. Specifically to #2 as an example. What about wheel weights? When deciding on a wheel - aesthetic is no doubt an important component for many, but from a personal standpoint, I will always opt for the lighter weight wheel when possible. Unfortunately even at ETK those weights are often not provided. At this level (M), that data should be available IMHO.

Thanks again for sharing your ideas.
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      02-04-2019, 06:32 PM   #22
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I think there is a very low chance there will be a carbon roof for 2 reasons
1. Functional: The cf roof functional purpose is to grab an extra couple tenths on the racetrack by slightly reducing center of gravity ... the only place the minor weight savings will really matter. But i think bmw would say those who really crave those extra few tenths will just get the lighter lower sedan
2. Aesthetic: probably the #1 reason for most M buyers, carbon roof brings the boy racer swagger and style.... let's be honest the roof on the x3 is too high for most people to notice it
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