Group Buy: YFCM Carbon Driveshafts

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Last 2 days to get in on this

Let me know if you have any questions.

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We have hit 30x + paid orders on this. The GB is a GO! You can still join until March 31st.

[Epoustouflant]

How do I access group buy pricing? I only see full retail on your site.

I created a specific Group Buy listing that combines all BMW M applications. It's here.

[Acetech]

How do I access group buy pricing? I only see full retail on your site.

[Epoustouflant]

Anything for a 5 speed conversion?

I'm talking about it with Steven. I added Z4M and E39 M5 since.

We've gone past the 30x thresholds. This is a go and I will start invoicing this weekend. The GB will stay open until March 31st.

[bigjae46]

Anything for a 5 speed conversion?

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Currently at 24/30.

I'll be adding Z4M and E39 M5 applications tomorrow most likely.

[simonnim]

Thank you for the information!

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Is it because the SMG shift unit connected to the tranny would get in the way of the flanges or something?

That's right.

See below. The SMG has the actuators with shifter linkage just above the flange.

[simonnim]

Yes! You'd opt for the 6MT version.

Is it because the SMG shift unit connected to the tranny would get in the way of the flanges or something?

[Bry5on]

Hmm, I thought area moment was mostly relevant to quantify torsion and the mass moment tells you how resistant a body is to changes in rotational velocity. Might need to brush up on things.

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.

Darn, you’re right, thank you for the correction! Here I am in stress analysis world trying to type between meetings. My mistake. I’ll edit the above!

If OEM 19lb is 3” then an 11lb carbon shaft would need to be under 4” - sounds more like it

[Epoustouflant]

Does this bolt up to a SMG -> manual conversion? They're the same tranny aren't they?

Yes! You'd opt for the 6MT version.

[Epoustouflant]

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.

It's common misconception. I've talked about this in my E9x M3 review here.

We conflate weight reduction with rotational inertia.

Many often misunderstand carbon driveshafts: I did too!

We expect them to feel like lightweight flywheels: we are used to these drastically improving low to mid range engine response.

While the driveshaft does lose 10+ lbs over stock, it does so on a much smaller radius compared to the flywheel.

The carbon driveshaft is all about tightening up the drivetrain - throttle response improvements are overwhelmingly the result of less flex in the driveshaft over stock.

Carbon is herein used to create a stiffer, more shock absorbing driveshaft that allows to connect the transmission to the differential in a single, stiff piece.

Moment of inertia is addressed with a lighter flywheel.

I have LFW fitted to my S65 DCT and S85 SMG3. I lost 14 lbs off my S85 crank with this. The changes to low to mid range pick up were immense. The carbon driveshaft had no where near the effect these had on that aspect of the driving experience.

[simonnim]

Does this bolt up to a SMG -> manual conversion? They're the same tranny aren't they?

[heinzboehmer]

Area moment is actually to the 4th power of diameter/radius. If the OEM driveshaft is 19lb at 3” OD, an 11lb driveshaft must be <3.4” OD to have a reduction in area moment (the thing that lets it spin up/down faster). Some assumptions here obviously, which would generally favor the OEM setup at these weights.

Area moment is not the only benefit (overall 8lb savings, plus some torsional stiffness increase, presumably) but I’d have thought that to be a primary motivator for a carbon driveshaft.

edit: still think this is a cool product, to be clear! 8lb of mass is still 8lb, even if there isn’t a rotating weight/inertial benefit.

Hmm, I thought area moment was mostly relevant to quantify torsion and the mass moment tells you how resistant a body is to changes in rotational velocity. Might need to brush up on things.

Anyway, I also assumed this was the primary motivator for this driveshaft, which is why I asked. Agreed though, this seems like a cool product.