Carbon fiber driveshafts

[discoboy1]

seeing the benefits on the new M3/M4 of these driveshafts, anyone thought of
having one made for 1M?
These guys seem to do custom jobs

http://www.bactechnologies.com/high-...50-driveshafts
Thanks for feedback!

[eeghie]

Originally Posted by discoboy1

seeing the benefits on the new M3/M4 of these driveshafts, anyone thought of
having one made for 1M?
These guys seem to do custom jobs

http://www.bactechnologies.com/high-...50-driveshafts
Thanks for feedback!

- Hesitantly interested in the costs. Yet if anyone was saving money for a 1M CSL, it's a no-brainer.

- For any volume buy, it's too bad that the 1M drive shaft is exclusively for our model.

- Perhaps related to their usual customers but what I believe is a big benefit to most 1M owners, is not even mentioned: due to the lower rotational mass, centrifugal forces and subsequently over-steer is reduced.

[Pete_vB]

Originally Posted by eeghie

- Perhaps related to their usual customers but what I believe is a big benefit to most 1M owners, is not even mentioned: due to the lower rotational mass, centrifugal forces and subsequently over-steer is reduced.

I don't follow. What mechanism are you suggesting that will reduce oversteer?

[eeghie]

Originally Posted by Pete_vB

... What mechanism are you suggesting that will reduce oversteer?

Our relatively heavy OEM drive shaft (as compared to the aftermarket carbon fiber driveshaft), when rotating at the same speed (~same cornering speed) will require more momentum to pull through a corner. This momentum created by the centrifugal forces of the rotating drive shaft will resist any cornering and will always be opposite the momentum that eventual drives the car through the corner. This momentum that resists cornering, is part of the normal effect of oversteer (~the resistance of mass going through a corner). It would however be reduced when using a lighter driveshaft.

In other words our heavier OEM drive shaft acts as a larger flywheel as any lighter (CF) drive shaft.

Once the moment of inertia [kgm^2] (=shaft parameter that quantifies how far away the mass is located related to its axis of rotation) of both shafts is known, the difference can be quantified. At this point I'm not sure whether it will be a significant reduction or not, hopefully we'll get some sense of this either by experience of a pilot buyer or possibly by calculations ...

[Pete_vB]

Originally Posted by eeghie

Our relatively heavy OEM drive shaft (as compared to the aftermarket carbon fiber driveshaft), when rotating at the same speed (~same cornering speed) will require more momentum to pull through a corner. This momentum created by the centrifugal forces of the rotating drive shaft will resist any cornering and will always be opposite the momentum that eventual drives the car through the corner. This momentum that resists cornering, is part of the normal effect of oversteer (~the resistance of mass going through a corner). It would however be reduced when using a lighter driveshaft.

In other words our heavier OEM drive shaft acts as a larger flywheel as any lighter (CF) drive shaft.

Once the moment of inertia [kgm^2] (=shaft parameter that quantifies how far away the mass is located related to its axis of rotation) of both shafts is known, the difference can be quantified. At this point I'm not sure whether it will be a significant reduction or not, hopefully we'll get some sense of this either by experience of a pilot buyer or possibly by calculations ...

Did someone claim "reduced oversteer" someplace, or is this something you're coming up with yourself?

I don't believe a change would have any noticeable effect on handling balance, and I can probably do some math to prove that. First consider that inertia goes to the square of the radius, so a 2" diameter driveshaft is going to have ~1% of the inertial effect of a 20" diameter flywheel of the same weight. And you don't hear about lighter flywheels making cars oversteer less.

Second I'm not convinced that even if it was much heavier it would increase oversteer. Yes it will increase tire loading when the car tries to change direction, but it will apply that loading to both the front and rear equally, meaning the car would be slower to turn in rather than prone to oversteer.

When the flywheel effect gets big you do start to see handling issues stemming from the fact that a right turn loads the tires differently than a left turn. This is seen in Hybrid race cars, such as Audi's Le Mans racer, that use flywheels to store electric energy. However they are likely using something on the order of a ~20 kg, ~10" flywheel spinning at ~50,000 rpm, and with the weight concentrated on the perimeter. Something like this would probably have something approaching 5000 times the rotational inertia of our driveshafts, at which point in their much lighter cars they do begin to see effects on handling.

I'll also mention that the driveshaft mass is located low and in the center of the car, one of the last places you want to lose weight. I'd do a lightweight flywheel/ clutch or wheels before I did a carbon driveshaft from a performance perspective.

[eeghie]

Originally Posted by Pete_vB

Did someone claim "reduced oversteer" someplace, or is this something you're coming up with yourself?

I don't believe a change would have any noticeable effect on handling balance, and I can probably do some math to prove that. First consider that inertia goes to the square of the radius, so a 2" diameter driveshaft is going to have ~1% of the inertial effect of a 20" diameter flywheel of the same weight. And you don't hear about lighter flywheels making cars oversteer less.

Second I'm not convinced that even if it was much heavier it would increase oversteer. Yes it will increase tire loading when the car tries to change direction, but it will apply that loading to both the front and rear equally, meaning the car would be slower to turn in rather than prone to oversteer.

When the flywheel effect gets big you do start to see handling issues stemming from the fact that a right turn loads the tires differently than a left turn. This is seen in Hybrid race cars, such as Audi's Le Mans racer, that use flywheels to store electric energy. However they are likely using something on the order of a ~20 kg, ~10" flywheel spinning at ~50,000 rpm, and with the weight concentrated on the perimeter. Something like this would probably have something approaching 5000 times the rotational inertia of our driveshafts, at which point in their much lighter cars they do begin to see effects on handling.

I'll also mention that the driveshaft mass is located low and in the center of the car, one of the last places you want to lose weight. I'd do a lightweight flywheel/ clutch or wheels before I did a carbon driveshaft from a performance perspective.

Your arguments for no expectations of significant handling improvements seem logic to me! Cost aside lighter wheels would be my priority too.

[Dackelone]

Originally Posted by eeghie

Your arguments for no expectations of significant handling improvements seem logic to me! Cost aside lighter wheels would be my priority too.

I really do not see how a cf drive shaft could make a car oversteer(or even understeer)less. Yes, much less rotational mass. But less oversteer - Noop.


Since the F8x uses a heavily mod'd N55 engine... I wonder IF the factory cf driveshaft could be a direct bolt in. ? I wonder who will be the first to find out.

[Pete_vB]

Originally Posted by Dackelone

Since the F8x uses a heavily mod'd N55 engine... I wonder IF the factory cf driveshaft could be a direct bolt in. ? I wonder who will be the first to find out.

The 6" difference in wheelbase makes that very unlikely IMHO.

[discoboy1]

Originally Posted by Dackelone

I really do not see how a cf drive shaft could make a car oversteer(or even understeer)less. Yes, much less rotational mass. But less oversteer - Noop.


Since the F8x uses a heavily mod'd N55 engine... I wonder IF the factory cf driveshaft could be a direct bolt in. ? I wonder who will be the first to find out.

The F8x has a longer wheel base, so most likely the driveshaft would be too long.
On a side note, on one of my previous cars, I replaced the driveshaft from the steel version to aluminium, and could definitely feel the difference on acceleration.

[Dackelone]

Originally Posted by discoboy1

The F8x has a longer wheel base, so most likely the driveshaft would be too long.
On a side note, on one of my previous cars, I replaced the driveshaft from the steel version to aluminium, and could definitely feel the difference on acceleration.

Yes, I know the wheel base is longer. What I meant was that the ends might be the same. I was wondering if one could cut the "difference" out of the M4/M3 part and somehow glue it back together. ? Or have a new customer cf tube made up. Just thinking out loud.

[Pete_vB]

Originally Posted by Dackelone

Yes, I know the wheel base is longer. What I meant was that the ends might be the same. I was wondering if one could cut the "difference" out of the M4/M3 part and somehow glue it back together. ? Or have a new customer cf tube made up. Just thinking out loud.

That sounds far more likely. Ideally you'd just water jet cut the CF tube shorter, blast off the end, surface prep and then high strength epoxy. You'd drop the center support bearings in the process. Unfortunately it may not be quite so straightforward- in some pictures the tube tapers toward the end attachment? And the outside of the tube is captured in metal as well, perhaps replaceable with a machined piece, as you're surely destroy it while shortening the tube...

The whole thing might save what, 10 lbs? Easily over $100 per pound. Fitting those new carbon brakes might be a better option.

[Jay-K]

i'm in.