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      06-25-2010, 10:39 AM   #1
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SCOTT, could you get this info for me?

Could you ask the engineers who design the chassis of the E82 (1 coupe), what is the torsional rigidity number of this platform? And also, will they increase the M version of the 1 series' rigidity?
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      06-29-2010, 10:38 AM   #2
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OK, 4 days without an answer is what I'm worrying about the 1M: the platform.

Yes within the same platform, you can always put in a larger hp engine, a better suspenssion, better wheels & tires etc. to make a 'motorsport' version of a car model. This is not only applied to M cars, it also applies to any car models in the world. But one thing can not be changed: the structure of the platform. You can not change the platform, or else it is exactly like designing a whole new car.

The E8x platform was developed long time ago (back to 2003), and I am sure the structural torsional rigidity requirement at that time is not up to the level like what is now (compared within BMW). I am worrying about whether it will make sense to sell a M car with a structural stiffness which is already outdated...
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      06-29-2010, 11:19 AM   #3
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Just an FYI i don't have any numbers...but the guys that autox their verts don't have any issues.

I only mention this because the verts have the lowest structural rigidity of all the E8xs and we do just fine
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      06-29-2010, 12:20 PM   #4
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They can add bracing and suspension components that increase this. With that said, I agree it needs to be done to this chassis and a new suspension is GREATLY needed. I don't doubt that ///M will put a lot of energy into this.
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      06-29-2010, 01:18 PM   #5
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Quote:
Originally Posted by BrokenVert View Post
Just an FYI i don't have any numbers...but the guys that autox their verts don't have any issues.

I only mention this because the verts have the lowest structural rigidity of all the E8xs and we do just fine
I totally agree the stiffness of the structure will not seriously affect autox performance, for cars within this price level.

But racing performance is not the only aim of stiffness (or torsional rigidity), IMO its most important role is to improve the driving experience and the ride quality.

As a reference BMW E90 has 22,500 Nm/deg of torsional regidity; compared to Audi A8's 25,000 Nm/deg, VW Phaeton's 37,000 Nm/degree, and Rolls-Royce Phantom's 40,500 Nm/degree. Nobody will take a A8, Phaeton or Rolls Royce to autox or racing, but the engineer still need to make the frame of such cars as stiff as possible, to enhance the ride quality.
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      06-29-2010, 01:29 PM   #6
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Quote:
Originally Posted by felixcat View Post
I totally agree the stiffness of the structure will not seriously affect autox performance, for cars within this price level.

But racing performance is not the only aim of stiffness (or torsional rigidity), IMO its most important role is to improve the driving experience and the ride quality.

As a reference BMW E90 has 22,500 Nm/deg of torsional regidity; compared to Audi A8's 25,000 Nm/deg, VW Phaeton's 37,000 Nm/degree, and Rolls-Royce Phantom's 40,500 Nm/degree. Nobody will take a A8, Phaeton or Rolls Royce to autox or racing, but the engineer still need to make the frame of such cars as stiff as possible, to enhance the ride quality.
You just compared the E90 to full size vehicles that don't even compete in the same classand I believe the Audi has a aluminum spaceframe---for lightness. I really think that for those cars it's the ride quality the reason why they are so stiff---it's the fact they are large luxury cars with a lot of "extras" attached, plus safety. These cars are known for their "waftibility" and "solidity". And the more options you put on a car plus unsprung weight puts stress on the chassis. Especially since LWD cars might get bendy. I mean the RR is a HUGE car, and with everything jammed into such a small space a car, that is one dense car...and yes the handling factors cone into play...but at that price no one wants a bendy chassis...Just my guess.
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      06-29-2010, 02:35 PM   #7
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Quote:
Originally Posted by IS3andME View Post
You just compared the E90 to full size vehicles that don't even compete in the same classand I believe the Audi has a aluminum spaceframe---for lightness. I really think that for those cars it's the ride quality the reason why they are so stiff---it's the fact they are large luxury cars with a lot of "extras" attached, plus safety. These cars are known for their "waftibility" and "solidity". And the more options you put on a car plus unsprung weight puts stress on the chassis. Especially since LWD cars might get bendy. I mean the RR is a HUGE car, and with everything jammed into such a small space a car, that is one dense car...and yes the handling factors cone into play...but at that price no one wants a bendy chassis...Just my guess.
Torsional rigidity does not measure how the chassis bend vertically, it measures the degree that the chassis twisted transversely...But yes lwb will partially contribute to this. Anyway, torsional rigidity can tell you how good is your car's chassis dynamics.

Now this is interesting: the BMW E46 Coupe has 12,500 Nm/deg of torsional rigidity, while E90 has 22,500 Nm/deg. Speaking of time, E8x is born between them, I really want to know how BMW set the strength requirement for this platform around year 2003...
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      06-29-2010, 04:05 PM   #8
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Quote:
Originally Posted by felixcat View Post
Torsional rigidity does not measure how the chassis bend vertically, it measures the degree that the chassis twisted transversely...But yes lwb will partially contribute to this. Anyway, torsional rigidity can tell you how good is your car's chassis dynamics.

Now this is interesting: the BMW E46 Coupe has 12,500 Nm/deg of torsional rigidity, while E90 has 22,500 Nm/deg. Speaking of time, E8x is born between them, I really want to know how BMW set the strength requirement for this platform around year 2003...
Thanks for correcting me I forgot about what torsion means---twist, transverse...

Imagine what the numbers are for the C4 Vette which was known as Lacking in rigidity. Or those cars with hydrolicz, all that twisting and bouncing with all that weight on those huge LWB 60s era cars has to really weaken the chassis.
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      11-12-2011, 12:33 AM   #9
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Thread bump!

Anyone managed to come across this number? If not for the 1M, what about the 135i?
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      11-12-2011, 03:45 AM   #10
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talking about thread revival...
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      11-12-2011, 06:48 AM   #11
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talking about thread revival...
ehh ive seen worse
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      11-12-2011, 08:16 AM   #12
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Quote:
Originally Posted by sparoz View Post
talking about thread revival...
wow! i had to look at the date, because the topic really threw me off!
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      11-12-2011, 03:55 PM   #13
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Quote:
Originally Posted by alphagamma View Post
Thread bump!

Anyone managed to come across this number? If not for the 1M, what about the 135i?
I did a little searching and I can't find one. Just using a crystal ball, however, I'd guess between 20,000 and 25,000 Nm/deg. The majority of the chassis is the same as the E90 though probably not quite as beefy in some areas. This is offset by the shorter wheelbase, only 3-4% but all else being equal it makes the car that much stiffer.

What are you using the numbers for, if I may ask?
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      11-12-2011, 11:07 PM   #14
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I want my 2 minutes back.
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      11-13-2011, 02:36 AM   #15
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Originally Posted by robertm View Post
I want my 2 minutes back.
It took you 2 minutes to go through all the post??!
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