M3/M4 to Get Steel Driveshafts Beginning Nov. 2017. Sales top 68,000 to date.

[domino_z]

Fk 30 pages, can anyone give this homeboy the cliffs on the expected real world physical impacts of this change from behind the wheel

Thinking about doing another build order in 3 pedal form

[Absurdium]

Originally Posted by domino_z

Fk 30 pages, can anyone give this homeboy the cliffs on the expected real world physical impacts of this change from behind the wheel

Thinking about doing another build order in 3 pedal form

The real world difference will be comparable or less than the difference between real butter and I-can't-believe-it's-not-butter.

Jokes aside, most of the issue is only in principle. If you drove two back to back, one with CF and one with steel, would you be able to tell the difference: not likely, but maybe ever so slightly. Is this going to impact the drivability and performance of the car? Not really. If you can post a best lap of 1:35.xx on a specific track with the CF shaft, expect to post a best lap of 1:35.xx with the steel shaft, maybe a tenth off.

Please don't let this stop you from ordering one of the last cars in production available with 3 pedals!

[aerostar]

Originally Posted by Absurdium

The real world difference will be comparable or less than the difference between real butter and I-can't-believe-it's-not-butter.

Jokes aside, most of the issue is only in principle. If you drove two back to back, one with CF and one with steel, would you be able to tell the difference: not likely, but maybe ever so slightly. Is this going to impact the drivability and performance of the car? Not really. If you can post a best lap of 1:35.xx on a specific track with the CF shaft, expect to post a best lap of 1:35.xx with the steel shaft, maybe a tenth off.

Please don't let this stop you from ordering one of the last cars in production available with 3 pedals!

But they're also much better for people who mod their cars for power. The CF shafts are much more stable and can handle a lot more force without warping.

There was a video posted earlier in the thread comparing tensile strengths. Check it out.

[Absurdium]

Originally Posted by aerostar

But they're also much better for people who mod their cars for power. The CF shafts are much more stable and can handle a lot more force without warping.

There was a video posted earlier in the thread comparing tensile strengths. Check it out.

Yup I've seen that video before this thread even came up actually. I definitely appreciate the engineering that goes towards building the CF shaft.

You're also right in saying that the CF shaft will be able to handle a lot more power and the stability benefit is true as it's a one piece construction. However unless BMW puts in a very poorly made steel shaft, I don't think the shaft will be the limiting factor for adding power or be much less stable than the CF shaft for people to notice. Factors like stock turbo limitations, DCT torque limitations, and maybe cooling (though S55 has great cooling) would come before the integrity of the steel shaft becomes a risk. However since no specs have been released for the new shaft, I'll admit a lot of this is my own speculation

[domino_z]

Considering I did my current zcp build with a sunroof and will again, track racing in a near 1500kg sedan ain't my bag

I was more so thinking the added weight of the steel shaft might slow the rev up akin to a heavier flywheel - which would be more noticeable on a manual bw shifts

[Absurdium]

Originally Posted by domino_z

Considering I did my current zcp build with a sunroof and will again, track racing in a near 1500kg sedan ain't my bag

I was more so thinking the added weight of the steel shaft might slow the rev up akin to a heavier flywheel - which would be more noticeable on a manual bw shifts

I'm not sure what your timeline is but you could always try to get one right now. It seems from using my car and several other members' cars as evidence that BMW is still putting in CF shaft as of now.

[EstrlM3]

Originally Posted by Absurdium

I'm not sure what your timeline is but you could always try to get one right now. It seems from using my car and several other members' cars as evidence that BMW is still putting in CF shaft as of now.

This is what I’m hoping for as well... car is in status 112 just hoping mine makes the cut with the cf shaft.

[HPIA4v2]

If you are talking about 2018 M3 at the dealer right now, they should still have the CF drive. Those are most likely built up to Nov 2017. Dec built have not arrived in States yet due to prod halt in Dec. So no guarantee cars built in Dec or even Jan will have CF drive shaft.

[drexplode]

I was told by my dealer STBMW that steel shafts will be introduced in March 2018.

[Parabolica]

Originally Posted by PichaDis11

The Law does not give a shit about production dates. Lol

Then how was BMW able to extend this to 1Q? I am sure the law doesn't give a shit that they may have a bunch of extra CF shafts left over.

[HPIA4v2]

All mfg reserve the right to use replacement parts that deem similar in function, BMW AG doesn't violate any law. Unless someone can prove steel shaft is not safe at certain speed, for example.
It happens more often than not, many mfg actually has provision not to use a single supplier; for example, aux fans on older BMW were both made by BOSCH and Phillips so if BOSCH had issue producing fans BMW would not halt production.

The way BMW AG runs the assembly floor is rather amazing, shown by how the LED icon headlamps were put on for cars without exec package at the beginning of the 2018 run. Now you can't get LED icon headlamp unless you order exc package.
So looks like from the outside, the foreman at assembly line would do anything to keep the assembly line moving
Though in case of CF shaft it's announced ahead of time so it's planned

[sleeprequired]

Originally Posted by HPIA4v2

All mfg reserve the right to use replacement parts that deem similar in function, BMW AG doesn't violate any law. Unless someone can prove steel shaft is not safe at certain speed, for example.
It happens more often than not, many mfg actually has provision not to use a single supplier; for example, aux fans on older BMW were both made by BOSCH and Phillips so if BOSCH had issue producing fans BMW would not halt production.

The way BMW AG runs the assembly floor is rather amazing, shown by how the LED icon headlamps were put on for cars without exec package at the beginning of the 2018 run. Now you can't get LED icon headlamp unless you order exc package.
So looks like from the outside, the foreman at assembly line would do anything to keep the assembly line moving
Though in case of CF shaft it's announced ahead of time so it's planned

if they advertise a part or feature in a car and don't supply it they're absolutely open to litigation. period.

[PawnStar]

Originally Posted by PawnStar

M3/M4 will still be great, just won’t have the real masterpiece CFRP driveshaft, will not offer exceptional strength while reducing rotating mass, which will result in a not as tight a drive with more counteractive momentum.

will not be a FEATHERWEIGHT HEAVY-HITTER, maybe a middleweight heavy-breather

Reposting from Nov, when it was announced.

[kyrix1st]

Originally Posted by domino_z

Fk 30 pages, can anyone give this homeboy the cliffs on the expected real world physical impacts of this change from behind the wheel

Thinking about doing another build order in 3 pedal form

If you have ever tried LTW flywheel on your cars, you will see that throttle response is vastly different just by shaving off 3-6kg. CFRP probably loses around 10kg.

[F80Moe]

Originally Posted by PawnStar

Reposting from Nov, when it was announced.

The way it has been marketed and hyped..

All of a sudden replaced by regular M perf steel

[CanAutM3]

Originally Posted by kyrix1st

If you have ever tried LTW flywheel on your cars, you will see that throttle response is vastly different just by shaving off 3-6kg. CFRP probably loses around 10kg.

The flywheel is a much larger diameter than the driveshaft, hence any weight reduction has a greater effect on rotational inertia. Further, the flywheel is coupled directly to the engines whereas the driveshaft's speed is reduced by the transmission gear ratios in the lower gears, where throttle response matters most.

[kyrix1st]

Originally Posted by CanAutM3

The flywheel is a much larger diameter than the driveshaft, hence any weight reduction has a greater effect on rotational inertia. Further, the flywheel is coupled directly to the engines whereas the driveshaft's speed is reduced by the transmission gear ratios in the lower gears, where throttle response matters most.

If I recall correctly, flywheel diameter is around twice that of driveshaft. Assuming constant change in angular velocity(or tangential speed v, whichever you prefer) for both in the event of car's acceleration where engine and drivetrain are connected, for the weight increase of driveshaft at 12kg (I set it for the sake of calculation convenience), the driveshaft's rotational acceleration (i.e. centrifugal force) would have the same affect as gaining 6kg in flywheel weight. Deceleration due to gear (if any) would have little effect since engine power overwhelms any deceleration from the drivetrain. (give it 3x in diameter then the impact would be equivalent to 4kg increase)

[adc]

Originally Posted by kyrix1st

If I recall correctly, flywheel diameter is around twice that of driveshaft. Assuming constant change in angular velocity(or tangential speed v, whichever you prefer) for both in the event of car's acceleration where engine and drivetrain are connected, for the weight increase of driveshaft at 12kg (I set it for the sake of calculation convenience), the driveshaft's rotational acceleration (i.e. centrifugal force) would have the same affect as gaining 6kg in flywheel weight. Deceleration due to gear (if any) would have little effect since engine power overwhelms any deceleration from the drivetrain. (give it 3x in diameter then the impact would be equivalent to 4kg increase)

You are assuming the driveshaft diameter is the same between CF and steel, which I’m pretty sure is wrong. The steel item should be at least 1” smaller in diameter, which will reduce the rotational inertia a bit (meaning it will probably still be bigger than for a CF item but not as big as you all think). What’s more, a CF shaft has all the mass at the outside being hollow, worse for rotational inertia.

I can’t help but think of my previous E90 M3, which had one of the best throttle response I ever experienced in a car, certainly better than the F80, and all engineered with a common steel driveshaft. So we should be ok...

[kyrix1st]

Originally Posted by adc

I can’t help but think of my previous E90 M3, which had one of the best throttle response I ever experienced in a car, certainly better than the F80, and all engineered with a common steel driveshaft. So we should be ok...

Different engine. Subjectivity. Turbo lag. Too many variables in this case.
High compression NA V8 >> turbo I6

What's clear is that you will feel the difference if there is indeed 10kg driveshaft difference. You won't know sht if it's your first M. Nice job BMW!

"Numbers (and physics) don't lie, Penny."

[HPIA4v2]

BMW is just doing what Apple did, slow done old iPhones to make iPX faster.
Cause the CF still goes to CS M3/M4

[CanAutM3]

Originally Posted by adc

You are assuming the driveshaft diameter is the same between CF and steel, which I’m pretty sure is wrong. The steel item should be at least 1” smaller in diameter, which will reduce the rotational inertia a bit (meaning it will probably still be bigger than for a CF item but not as big as you all think). What’s more, a CF shaft has all the mass at the outside being hollow, worse for rotational inertia.

I can’t help but think of my previous E90 M3, which had one of the best throttle response I ever experienced in a car, certainly better than the F80, and all engineered with a common steel driveshaft. So we should be ok...

It is a fair bit more complex than this. Have a read of post #553

Ultimately, the effect of drivetrain rotational mass is not about throttle response but rather about total acceleration. But as a mentioned earlier, the effect of the CF vs steel driveshaft is rather negligible. For me, the main difference lies in the stiffness of the shafts that will make the drivetrain more elastic (less sharp and responsive in transitions) with a steel driveshaft.

[CanAutM3]

Originally Posted by kyrix1st

If I recall correctly, flywheel diameter is around twice that of driveshaft. Assuming constant change in angular velocity(or tangential speed v, whichever you prefer) for both in the event of car's acceleration where engine and drivetrain are connected, for the weight increase of driveshaft at 12kg (I set it for the sake of calculation convenience), the driveshaft's rotational acceleration (i.e. centrifugal force) would have the same affect as gaining 6kg in flywheel weight. Deceleration due to gear (if any) would have little effect since engine power overwhelms any deceleration from the drivetrain. (give it 3x in diameter then the impact would be equivalent to 4kg increase)

According the various articles and data in in RealOem.com tend to indicate that the steel driveshaft will be about 2.5kg (5.5lb) heavier than the CF one). Further, a flywheel diameter is much more than twice the diameter of a driveshaft. The whole purpose of a flywheel is ADD inertia, it therefore design in that respect. A driveshaft is usually designed to minimize inertia as much as possible. It is a better approximation to say that a flywheel is BOUT 4 times the diameter of a driveshaft.

You also need to recheck your physics text books. As a general rule of thumb, inertia increases with the square of the radius, hence an object that has 4 times the diameter of another will have 16 times the rotational inertia.

Further, all this discussion about mass is not about throttle response but rather about effective mass and it's effect on the car's acceleration. The rotational component of effective mass is proportional the cube of the gear ratio. Meaning a change of inertia on the flywheel has ~111 times the effect that the same change in inertia on the driveshaft has in 1st gear (4.806^3).