02-05-2019, 10:27 AM | #23 | ||||||
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From 16 Aug 2017 0820PM, post #336, CanAutM3: Quote:
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So, Mii, certainly an interesting topic which was thoroughly discussed in that second thread. My take - like many of our Forum discussions which involve unknowns in data, it's difficult to arrive at firm conclusions as to actual significance (realized benefits) of CFRP in the drive shaft setting, although the theoretical advantages are at least compelling. I'm still trying to make a case for the CFRP roof, however. |
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02-05-2019, 11:47 AM | #24 |
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If I'm not mistaken, wasn't the drive shaft on F80/F82 M3/M4 changed from CF to steel? Why would they include them in the X3M/X4M if they were removed from the M3/M4?
https://f80.bimmerpost.com/forums/sh....php?t=1411862 https://www.autoblog.com/2017/08/11/...r-driveshafts/
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02-05-2019, 12:14 PM | #25 |
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That's my understanding as well, kozzi. I don't think it will happen for the X3M and X4M, but I had never even heard of CFRP's application in a drive shaft so was an interesting topic to read. On the other hand, apparently other Mnfrs have been and are currently using so there must be something to it. Whether reason for discontinuation was related to early wear or other failure issues, or it was cost, or ... is unclear to me, but I would rather see that CFRP used in the roof if I have to make a choice as to where to spend extra money to make the X3M and X4M stand out in their class (still making a case for it)!
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02-05-2019, 02:48 PM | #26 | ||
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Historically the majority interested in performance vehicles have focused on coupes and sedans. Rightly so, as it has only been the past 5-10 years Mnfrs began designing high-performance SUV/SAVs. So it seems a natural progression of thinking that reduction of roof weight on SAVs might have similar minimal effects as it has on those cars (with relatively small roof surface areas and short heights). But I would respectfully suggest placing CFRP on the higher and more expansive roof areas inherent to SAVs provides a far greater benefit over coupes and sedans than you and others may indicate. The problem is that analyses to prove such have been hard to find. I’ve tried to put some of the pieces together - we already know the fore-aft CG of the X3 and can compare to the M550i and M850i. I’ve reasonably estimated the weight of the X3’s CFRP roof by extrapolating known weight/surface area of the E90 OEM solid aluminum and CFRP mod (30.3 lbs minus 12.4 lbs = 18 lbs. savings). Although ETK and RealOEM do not list all weights for the G01’s moon roof components, they do record the weights of the F49 X1 and F15 X5 moon roofs (56 lbs. and 103.4 lbs., respectively). Until we can find out the exact weight this is all we have to go on, so using a value between those yields an X3 moon roof estimate of ~79 lbs. So conservatively it seems a CFRP would yield a savings of 66.6 lbs over the moon roof option, and at the highest point of the 66” high X3. If we could then figure out the height of the CG (a really important variable in calculating Roll reactions), then one could at least run numerical estimates to quantitate and compare possible beneficial effects. Two articles from Car and Driver helped make clear not only the critical importance of the CG in its relation to performance and handling but also how to calculate CG’s height for a vehicle. https://www.caranddriver.com/news/a1...ravity-height/ https://www.caranddriver.com/feature...tests-feature/ An excerpt from the second link - “CG height will help you grasp why one supercar is able to trounce a similarly powerful and lightweight rival. Dynamically speaking, it is one of the most important differences between a svelte sports sedan and a hulking sport-utility. Total weight, CG height, and its fore-and-aft location are the Matthew, Mark, and Luke of handling-performance secrets.” I would expand your thought that the purpose of CFRP ‘is to grab an extra couple tenths on the racetrack by slightly reducing center of gravity’ further. Hard to see how removing 66 lbs. from the roof shouldn’t also lead to noticeable improvement even in daily driving involving higher speed maneuvers on highways and their curving and high angle on-off ramps, for example. Not in inner city traffic jams, no doubt, but intuitively, it remains difficult for me to believe that a finely tuned X3M Comp wouldn’t notice a difference in handling with 66 lbs. removed from the roof. Quote:
Once the X3M and X4M are released, hopefully Car and Driver (or someone) can calculate the CG height of both moonroof- and CFRP- (if we’re given the chance) optioned models. Or at least run the slalom and skidpad tests – hard to imagine the CFRP won’t have significantly improved performance in those areas (time will tell, but hope BMW at least offers the option). Last edited by Max Well; 02-05-2019 at 05:19 PM.. Reason: Removed extraneous [/quote] found in paragraph |
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02-06-2019, 09:25 AM | #27 | |
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However when it comes to "is it worth the engineering and marketing investment for the majority of consumers purchasing this product" I think my points still hold. Say a carbon roof gives 10% improvement in in handling for an X3 but only 5% for the M3, the M3 will still be the better handling track car in absolute terms. So in my opinion (and i would suspect BMWs product management) if you are the type of person willing to sacrifice the sunroof for performance on a premium vehicle, you are very likely (but not always) the same person who wants maximum performance overall and would choose the sedan (or coupe). We also know that there is another group who are "casual" M buyers, purchasing for the badge and style, who would go for the carbon roof purely "cuz it looks awesome" and that use case is negated by the SUVs height.. I think you can add on the market expectation for premium SUVs that they not have a sunroof but instead a giant glass roof, it would seem even more out of character to the average X3M buyer to have the solid carbon roof. like I noted above would love for BMW to thumb their noses at the above logic and offer it as an option for enthusiats who also want the suv |
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02-06-2019, 12:59 PM | #28 | |
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It seems the old-school homogeneity of Performance Enthusiasts as only coupe and sedan Drivers has evolved as high-performance SUVs have been refined and competition expands. Suspect a fair number of us have had our time in coupes and sedans but now appreciate the practicality this design provides, but we don’t want to lose the performance aspect. Manufacturers understand this as they race to capture a piece of this growing profitable pie - with the introduction of a number of elite high-performance SUV/SAV offerings (Lamborghini Urus, Jaguar F-Pace SVR, Maserati Levante Trofeo, Alfa Romeo Stelvio Quad, upcoming Aston Martin Varekai and Ferrari Purosangue …). While I would agree with much of your discussion in regards to ‘premium vehicles’ (which in my mind is just the more mainstream Acura, Lexus, Infiniti, BMW, Jaguar, MB, Porsche… models), I can’t agree that it characterizes those interested in the world of bespoke high-performance (>170mph) vehicles as seen with SVR, AMG, M (esp Comp and above), Porsche’s upper range, and those Mnfrs listed above. Hopefully in that rarefied air the ‘casual’ buyers you describe are few and far between. Perhaps not. As I’ve not seen studies analyzing the ‘average’ or ‘casual’ M buying population you describe, I don’t know the percentage they represent. Maybe you are right - perhaps company Marketing has shown it represents a sizeable portion which they feel the need to address. I tend to think not (and hope not), but we’ll see how BMW positions the X3M and X4M – we’ll know soon enough. |
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02-06-2019, 09:34 PM | #29 | |
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https://www.bmw-m.com/en/all-models/...w-x3m-x4m.html "FINAL STAGE OF DEVELOPMENT. Before the new BMW X3 M and the BMW X4 M are unleashed on the market to set new standards for Sports Activity Vehicles (SAV) and Sports Activity Coupés (SAC), both high-performance models will reach the final stage in their maturity at the Nürburgring. The legendary race track is the perfect venue for BMW M's ultimate testing and tuning programme." Does the X3M need a CF roof? IMO, I think BMW (CP version) should give its customers the option. Nothing wrong with an "all of the above" approach if you are going to claim setting "new standards" in class. BMW also has no problem stating the new 3 series is a "game changer" that will obviously roll forward into the new M3/M4. BMW marketing at its best or BMW positioning to be the best? We'll know soon enough indeed.
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02-09-2019, 04:13 PM | #30 | |
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I’ve spent time researching CG height and ‘Static Stability Factor’ (SSF) - lots online about these and how important they are for determining vehicle dynamics (including Roll Resistance). Rather than listing a number of links, just searching those terms yields plenty for those interested. And although I have no background in Mechanical Engineering, I’ve tried to quantify the beneficial effect on these variables if one options a CFRP Roof rather than the Moon Roof. Considering my superficial knowledge of the subject, I would appreciate input from those familiar with the science as to whether my assumptions and conclusions appear reasonable. I’ve attached jpegs showing my thought process in case I am way off base. As CG heights for BMW’s vehicles are not readily available online, I estimated baseline CG height for the X3M (25”) (and for reference M850i (20”) and M550i (21”)) based on information found here: http://www.accidentreconstruction.co...ers%5b1%5d.pdf, Physics of Automobile Rollovers, by L. David Roper, page 6. To summarize my results, it seems if one could option the CFRP roof, CG height should lower 1”, and the SSF would improve from 1.264 to 1.318 (approaching car values). If accurate, this could potentially allow for significant improvement in handling, especially with cornering and skid pad dynamics. |
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02-20-2019, 03:15 PM | #31 |
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Have adjusted the CG and SSF calculations based on the more reasoned estimate of the X3M's moon roof of 126.6 lbs. vs an OEM Aluminum section in it's place of 15 lbs. Because of the slightly wider track and lower height of the X3M, it starts with an SSF of 1.29 (with an assumption the CG with moon roof comes in around 24.7"). BMW doesn't share that data so estimation is all we have to go on.
As expected, replacing the 126.6 lbs. moon roof with a 15 lbs. Aluminum section suggests the CG could decrease by 1.5", with an increase in the SSF to sedan-range values of 1.38. If these estimations and calculations are reasonably accurate, one should expect improved handling. As previously noted, disclaimer - my background is not in Mechanical Engineering or Physics, so would defer to those experienced in these areas as to whether this methodology is sound. I'm just a lay person trying to understand how options can affect aerodynamics and handling. And CFRP would remove an additional ~18 lbs. from the base Aluminum roof as well. If anyone can share the measurements of the X4's moon roof and actual roof I can run similar estimations for the X4M as well. Last edited by Max Well; 02-21-2019 at 06:04 AM.. Reason: Corrected yet another 'CFRP' reference to 'OEM Al' on 2nd image... |
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02-28-2019, 02:33 PM | #35 | |
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I doubt they will make CS versions of the X3M/X4M but you never know. Maybe an X4MCS? Will certainly be overkill for my needs. X3MC looks to be the sweet spot so I'm looking forward to real world reviews.
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03-20-2019, 02:18 PM | #36 | ||||
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1-CFRP standard (no rails, no moon roof) 2-ID7 3-535HP +/- 10HP 4-Laser lights 5 +/- adjustable air suspension (? weight difference – if adds ‘significant’ weight, is that offset by improved performance and handling from a lower CG and better SSF?) 6 +/- Bowers & Wilkins Diamond Surround Sound (? weight difference c/w HK – would keep HK if ‘significant’?) 7-With lower CG and improved SSF (if #’s 1 & 5 produce such) can wider wheels be optioned? 8-If #7 is true, wheel wells would be flared more (as a number have already requested) A rough idea of how that might appear, c/w the original - |
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03-20-2019, 04:34 PM | #37 | |
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Just to clarify - the CFRP is desired for it's weight reduction at the top of the vehicle where it makes the most difference in CG and SSF (not because it can be seen); and air suspension has been touted by Mnfrs for years as a way in which to improve aerodynamics at speed by it's ability to improve Cd (which is why I mentioned it - not in reference to comfort as you mention, at least for the intent of my discussion). Unfortunately it becomes a self-fulfilling prophecy if there isn't an upper echelon version one can option into... Wouldn't be cost-effective for them to have fabrication for a small number of parts, I get that. And BMW has obviously assembled market research to know what their demographic is willing to spend. But I suspect there is a subset out there, especially in the M world, who'd be willing to ante up for a refined X3M. In the end it does come down to economics, though, and you may be right - perhaps they don't see a profit in marketing top-of-the-line components to the demographic they're trying to reach for the X3 and X4. For the minority who desire more 'fit and finish', even if BMW is preferred, the boutique Mnfrs are there. |
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03-27-2019, 12:42 PM | #38 | ||
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10-05-2021, 10:44 PM | #40 |
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@Max Well - I'm going to submit a request too!
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