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      12-16-2013, 08:27 PM   #23
gee-m-w
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The e90 was 22,000 Nm/deg without folding rear seats. The F30 is allegedly 30% higher, which gets you to 28,000 Nm/deg. The point of my post is that if you take an F30, do everything you can save weight, and make it so different that you need to call that unibody the F80, did you weaken it over the F30?

Does the F80 change any major parts of the unibody from steel to aluminum, like the front clip?
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      12-16-2013, 08:53 PM   #24
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Quote:
Originally Posted by GregW / Oregon View Post
I thought the general feeling was the Cayman was actually better than the 911 as far as handling?
By and large I would say with the exception of the GT2/3 variants, the cayman and boxster were better handling than the 911. The GT cars were so balanced and planted and were beyond sublime to drive.
Under 100k nothing could touch the boxster/cayman and you'd have to move to a GT car or something of the likes to match it.
In addition, the cayman/boxster were much more accessible than a 997 911. That is all changed now since the 991. Honestly, when they say the 911 is the best suspension and damped car in the world, that's not any exaggeration. It's truly just astounding...i have yet to drive a car so dialed in and easy to push. The 991 handles more like a cayman/boxster now so I don't think saying they're better platforms is valid anymore.
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      12-16-2013, 10:47 PM   #25
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Originally Posted by GregW / Oregon View Post
I thought the general feeling was the Cayman was actually better than the 911 as far as handling?
981BS with the optional Sports Suspension (not the PASM option) is quite a thing to behold. I've never driven a 991, so I can't compare it, but god damn is the 981BS/SS combo something.

Very interested to see what Porsche does with the upcoming 981 GTS and/or the R.
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      12-16-2013, 11:11 PM   #26
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Quote:
Originally Posted by Wolfinwolfsclothing View Post
BThe 991 handles more like a cayman/boxster now so I don't think saying they're better platforms is valid anymore.
Very much the case having tracked and raced these cars. The 991 (and some 997s for that matter) is actually easier to drive at the limit, mid-engine cars are quite challenging at 10/10th but easily accessible and rewarding at 8/10th.

The 991 GT3 is being compared to cars punching above it's weight...458,MP4-12C. With rear wheel steer the car has nullified it's ass-engined handicap, but retained it's traction and braking advantage.

I have a hard time believing the new M3/4 will challenge a 991S even though the Porsche is getting softer. They start life with such different genetics.
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      12-17-2013, 02:58 AM   #27
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Quote:
Originally Posted by consolidated View Post
I have a hard time believing the new M3/4 will challenge a 991S even though the Porsche is getting softer. They start life with such different genetics.
They will very likely deliver a drivers race at the strip and very close best reported magazine times. However, the M4's lap times will probably typically fall short of the 991S. It will best the base 991 (3.4l) though.
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      12-17-2013, 04:20 AM   #28
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Quote:
Originally Posted by gee-m-w View Post
The e90 was 22,000 Nm/deg without folding rear seats. The F30 is allegedly 30% higher, which gets you to 28,000 Nm/deg. The point of my post is that if you take an F30, do everything you can save weight, and make it so different that you need to call that unibody the F80, did you weaken it over the F30?

Does the F80 change any major parts of the unibody from steel to aluminum, like the front clip?
The official threads have discussed the differences between a F3x and F8x chassis. Do you really believe they would weaken the chassis on their M model?

None of the lightweight components weaken the chassis, instead the CFRP strut brace increase stiffness as well as do the solidly mounted rear subframe.
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      12-17-2013, 08:50 AM   #29
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I'm just saying there is no alchemy. The lightest wheels are not the strongest wheels. In the default case a 20 pound forged wheel has a higher static load rating than a 16 pound forged wheel.

Is there a difference between the F30 unibody and the F80 unibody other than the roof? Or are those the same exact unibody, and the F80 weighs exactly 11 pounds less for the roof only? Did they use aluminum in the front clip?

Just so I'm being abundantly clear, I mean this diagram in its entirety (colored and silver parts) and nothing else:

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      12-17-2013, 10:34 AM   #30
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Read the official threads, it lists the weight savings. If it's not listed there, it isn't on the car (would you expect BMW to not "brag" about all the weight savings they have made, but just choose a few of those?). And a aluminium structure can be just as strong, just more expensive to manufacture.

Again, do you believe that BMW deliberately have chosen to compromise the integrity of the chassis on their Halo car?
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      12-17-2013, 10:55 AM   #31
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Compromised is a strong word. Even if it was only as strong as the E90 that would be more than adequate. The emphasis on efficiency, which is being achieved through lighter weight. This isn't about making the strongest M3 in the world. If they did, it would be 3800 pounds.

They built a fast attack boat, not a tank.
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      12-17-2013, 12:26 PM   #32
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Quote:
Originally Posted by gee-m-w View Post
Compromised is a strong word. Even if it was only as strong as the E90 that would be more than adequate. The emphasis on efficiency, which is being achieved through lighter weight. This isn't about making the strongest M3 in the world. If they did, it would be 3800 pounds.

They built a fast attack boat, not a tank.
Compromised is defined as:

"To reduce the quality, value, or degree of something"

If BMW has weakened the chassis of the F8x over the F3x, then that would mean that they had compromised the structural stiffness of the chassis, right?


Some quotes/info taken from the official threads, since it seems you haven't taken the time to read them

Quote:
An aluminum stiffening plate, CFRP front strut brace and additional bolted joints between the axle subframe and the body structure all help to increase the rigidity of the front end.
Quote:
The rigid connection between the rear axle subframe and the body – without the use of elastic rubber elements – is borrowed from motor sport and serves to further improve wheel location and therefore directional stability. “The double-elastic mounting for the rear differential within the rear axle subframe – which is bolted to the body structure – has allowed us to achieve a new level of driving precision, but without neglecting comfort,” says Albert Biermann, citing another example of the perfect symbiosis of pure-bred motor sport technology and excellent everyday usability.
Quote:
“Together, the rigid front and rear structures, precise axle kinematics and an impressively responsive electromechanical power steering system help to deliver the outstanding steering and handling characteristics of the BMW M3 Sedan and BMW M4 Coupe,” sums up Biermann.
Quote:
On the outgoing models, the CFRP roof was confined to the Coupe version. Now, for the first time, the four-door BMW M3 will get this striking design and functional feature as well. The CFRP roof brings weight savings of five kilograms (11 lbs) in the case of the BMW M3 Sedan and more than six kilograms (> 13 lbs) in the case of the BMW M4 Coupe. It also lowers the vehicle’s center of gravity, which has a positive impact on driving dynamics.

Made from aluminum rather than conventional steel, the front side walls and the hood (with power dome) make an important contribution to the models’ lightweight design concept, while at the same time improving axle load distribution.

On the BMW M4 Coupe, the contoured roofline with central channel continues into the trunk lid, emphasizing the even sportier personality of the new model. The newly developed trunk lid not only provides extremely effective tail end styling, its geometry is at the same time precisely tailored for optimized aerodynamics, while the use of carbon fiber and plastics makes for additional weight savings.

The new BMW M3 Sedan and new BMW M4 Coupe also feature a CFRP propeller shaft. The high rigidity and low weight of the CFRP tube mean that the propeller shaft can be produced as a single-piece component, without a center bearing. This achieves weight savings of 40 percent over the previous model and a reduction in rotating masses, which in turn results in more dynamic powertrain response.

The CFRP strut brace in the engine compartment is a further example of how all weight-saving measures on these vehicles have also been tailored to the improvement of driving dynamics. Weighing only 1.5 kilograms (3.3 lbs), the strut brace offers superior rigidity to a comparable aluminum component and at the same time plays a key part in the excellent steering response and precision of both vehicles.
The use of carbon in these models is a reminder that BMW is a global leader in high-strength, lightweight CFRP construction, and that it was BMW who brought out the first mass-production vehicle with a body consisting entirely of this material – the innovative BMW i3.
When I read the above, plus all of the other info available, there is NOTHING that indicates a less torsionally rigid version than the F3x. Quite contrary, everything points to added stiffness from strut brace, solid mounting of rear subframe etc.

Not sure I understand where your concern for the torsional rigidity of the F8x comes from
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      12-17-2013, 01:14 PM   #33
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Quote:
Originally Posted by Boss330 View Post
Compromised is defined as:

"To reduce the quality, value, or degree of something"

If BMW has weakened the chassis of the F8x over the F3x, then that would mean that they had compromised the structural stiffness of the chassis, right?


Some quotes/info taken from the official threads, since it seems you haven't taken the time to read them









When I read the above, plus all of the other info available, there is NOTHING that indicates a less torsionally rigid version than the F3x. Quite contrary, everything points to added stiffness from strut brace, solid mounting of rear subframe etc.

Not sure I understand where your concern for the torsional rigidity of the F8x comes from
I agree and furthermore the car seems to have gotten a lot of ring time from an early stage. I'm pretty sure that any concerning chassi flex has been addressed. Not a worry of mine.
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      12-17-2013, 02:53 PM   #34
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Quote:
Originally Posted by Boss330 View Post
Some quotes/info taken from the official threads, since it seems you haven't taken the time to read them
You guys (you and gee-m-w) need to take care with the language. Are you disusing a stiffer chassis, a stronger chassis or a more crashworthy chassis? There is often correlation but they are not the same thing. Then as far as each category goes there are subcategories, for stiffness, for example there is lengthwise bending, torsional, lateral bending, etc.

Also as far as BMWs quotes go the superlatives are always left without a direct comparison as to what (to the base model, to the prior generation M car, to a competitor). I think it is abundantly clear the M4 will have greater torsional rigidity than the 435, but one is still making some assumptions about BMWs carefully chosen words.
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      12-17-2013, 04:07 PM   #35
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I could see someone hitting a pothole on the Cross Bronx Expressway and having a $19,000 repair to replace some aluminum bit on the front 1/4.
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      12-17-2013, 05:14 PM   #36
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Quote:
Originally Posted by swamp2 View Post
You guys (you and gee-m-w) need to take care with the language. Are you disusing a stiffer chassis, a stronger chassis or a more crashworthy chassis? There is often correlation but they are not the same thing. Then as far as each category goes there are subcategories, for stiffness, for example there is lengthwise bending, torsional, lateral bending, etc.

Also as far as BMWs quotes go the superlatives are always left without a direct comparison as to what (to the base model, to the prior generation M car, to a competitor). I think it is abundantly clear the M4 will have greater torsional rigidity than the 435, but one is still making some assumptions about BMWs carefully chosen words.
We are discussing torsional rigidity as per topic. Not sure what you mean by "take care with the language"

Crashworthiness has neven been mentioned by anyone, it's the rigidity of the chassis as pointed out in my previous post and which also was the concern of the OP (i.e have BMW decreased torsional rigidity on the F8x vs the F3x in their quest for less weight).

And since no one of us has access to BMW internal documents, all of the subcategories you mention will not be possible for us to go in detail on... The topic here is whether there has been any weakening of the F8x chassis over the F3x chassis due to use of lightweight materials. My point being that it instead seems the base chassis ("body in white") is the same, but that the F8x has some added braces and rigid mounting of subframes that increase rigidity over the F3x.

Excuse me if I haven't been clear about that, but since no one has mentioned crashworthiness before I thought it wasn't necessary to make a point of explaining explicitly that we weren't debating crash worthiness... Also the topic of the thread was kind of hinting at what the discussion was about...
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      12-17-2013, 05:16 PM   #37
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Quote:
Originally Posted by gee-m-w View Post
I could see someone hitting a pothole on the Cross Bronx Expressway and having a $19,000 repair to replace some aluminum bit on the front 1/4.
Kind of like on the E60 5-series then, which had a aluminium front structure
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      12-17-2013, 11:26 PM   #38
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Quote:
Originally Posted by Boss330 View Post
We are discussing torsional rigidity as per topic. Not sure what you mean by "take care with the language"
gee-m-w said "if it was only as strong as the E90" whereas you reply when on and on about stiffness. Again, yes, it's pretty clear that with the add on bracing parts that Ms are always stiffer than the base car. I only brought up strength and crashworthiness as general strength related concepts since gee-m-w brought up strength.
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      12-17-2013, 11:30 PM   #39
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Quote:
Originally Posted by gee-m-w View Post
I could see someone hitting a pothole on the Cross Bronx Expressway and having a $19,000 repair to replace some aluminum bit on the front 1/4.
You seem to imply that BMW doesn't even test their cars... Although M cars surely place higher loads on various components things are still tested. Most cars including BMWs will also enjoy nice progressive failures with larger and larger loads (larger and larger potholes). First a tire or wheel will go, then a suspension member will go, then a mounting point might yield, finally a major subframe or frame component will actually fail. No guarantees that this is true for every BMW, every M or every car, but generally this is the way cars are designed to deal with large wheel impact loads such as potholes.
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      12-18-2013, 01:28 AM   #40
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I don't know of any BMW model that hasn't improved in rigidity from generation to generation so I am sure it has. Maybe not by a big enough margin to brag about though.
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      12-18-2013, 10:58 AM   #41
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Quote:
Originally Posted by pruettfan View Post
I don't know of any BMW model that hasn't improved in rigidity from generation to generation so I am sure it has. Maybe not by a big enough margin to brag about though.
At least we know that BMW claims a 30% more torsionally rigid unibody for the F30 vs E90:

http://www.autozine.org/Archive/BMW/new/3er_F30.html

http://www.f30post.com/forums/showthread.php?t=612668

Last edited by Boss330; 12-18-2013 at 03:06 PM..
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