[AxM2CS]

11/30/2020 Production Date.

[ZL9M2]

I used to think the carbon roof was really cool. Now I worry it will be the greatest liability on this car.

[SilverM2_CS]

Environmental pollution maybe?

[AxM2CS]

Very unlikely. The clear coat is hermetically sealing the CF. There might be a plausible argument for UV and other solar radiation, but I'd bet the paycheck on temperature cycling. There is a CTE (Coefficient of Thermal Expansion) mismatch between clear coat and CF. The thickness and mass of the clear coat is large relative to that of the CF, so when each expands and contracts at different rates due to the CTE mismatch the CF is going to tend to get pulled and squeezed by the clear coat. This would be less of an issue if the the clear coat wasn't as thick as grandma's reading glasses.

[sdhotwn]

Originally Posted by AxM2CS

Very unlikely. The clear coat is hermetically sealing the CF. There might be a plausible argument for UV and other solar radiation, but I'd bet the paycheck on temperature cycling. There is a CTE (Coefficient of Thermal Expansion) mismatch between clear coat and CF. The thickness and mass of the clear coat is large relative to that of the CF, so when each expands and contracts at different rates due to the CTE mismatch the CF is going to tend to get pulled and squeezed by the clear coat. This would be less of an issue if the the clear coat wasn't as thick as grandma's reading glasses.

And it's interesting that it seems to be at/near edges and corners in both cases where the bottom layer is likely glued in place which would increase shear in the body of the material as well for a big temp differential.

[AxM2CS]

That - and, in my experience (mainly with hybrid semiconductor devices), CTE-induced delamination tends to propagate from the edges. The very center of mass stays put, and the two materials progressively expand & contract more at increasing distances from the center. I'll be inspecting and imaging the roof every few days, so this theory may become apparent sooner rather than later, I'm afraid. Especially with volatile temperatures as winter subsides. I'm more or less reconciled to needing a new roof in the car's future.

[sdhotwn]

Originally Posted by AxM2CS

That - and, in my experience (mainly with hybrid semiconductor devices), CTE-induced delamination tends to propagate from the edges. The very center of mass stays put, and the two materials progressively expand & contract more at increasing distances from the center. I'll be inspecting and imaging the roof every few days, so this theory may become apparent sooner rather than later, I'm afraid. Especially with volatile temperatures as winter subsides. I'm more or less reconciled to needing a new roof in the car's future.

I wonder if those of us that store for winter will be less susceptible, or hotter climates will see it etc... be interesting if this is a major issue and if any trends occur. If it's high enough rate, hopefully we can push on BMW to resolve. We'll see!

[AxM2CS]

Misery loves company. Will try not to root for failing roof postings here.

[Wah]

Originally Posted by AxM2CS

That - and, in my experience (mainly with hybrid semiconductor devices), CTE-induced delamination tends to propagate from the edges. The very center of mass stays put, and the two materials progressively expand & contract more at increasing distances from the center. I'll be inspecting and imaging the roof every few days, so this theory may become apparent sooner rather than later, I'm afraid. Especially with volatile temperatures as winter subsides. I'm more or less reconciled to needing a new roof in the car's future.

Out of curiosity... does your car sit in the sun a lot? Also do you have PPF?

[AxM2CS]

Yes and yes.

[Hedoniste]

I occasionally drive mine during winter so I will occasionally inspect the roof.
I hope that they will be able to fix this problem for each owner concerned.

[ZL9M2]

Originally Posted by AxM2CS

That - and, in my experience (mainly with hybrid semiconductor devices), CTE-induced delamination tends to propagate from the edges. The very center of mass stays put, and the two materials progressively expand & contract more at increasing distances from the center. I'll be inspecting and imaging the roof every few days, so this theory may become apparent sooner rather than later, I'm afraid. Especially with volatile temperatures as winter subsides. I'm more or less reconciled to needing a new roof in the car's future.

Could you maybe get in touch with BMW and explain this to their engineering dept? Seems as if they missed that email!!!!!!!!!!

[medphysdave]

Originally Posted by ZL9M2

I used to think the carbon roof was really cool. Now I worry it will be the greatest liability on this car.

This thought has crossed my mind.

[AxM2CS]

Had my 10K mile service Monday. Dealer took photos and referred it to BMW. Will keep you all posted. I'm not in a hurry to do anything .. want to monitor it for awhile. Not looking forward to a new roof every 12 months. Glad I extended the warranty 3 years when I bought though.

[medphysdave]

I pointed out the roof flex at my 10k as well. They documented the flex they saw. We both agreed that we didn't think it was a design flaw, but good to get it on record well within the warranty period.

[tjlazer]

Right well, washing my car today I found a few similar issues to those reported here. It is under an extended warranty so I will see what BMW say about it…to me it’s not a big issue right now but I don’t want it getting worse. Yes this is a DD machine, regularly outside in all weather.

[Philly_sweden]

Originally Posted by tjlazer

Right well, washing my car today I found a few similar issues to those reported here. It is under an extended warranty so I will see what BMW say about it…to me it’s not a big issue right now but I don’t want it getting worse. Yes this is a DD machine, regularly outside in all weather.

I love it! CS or not. The car should be able to be used as a DD! Keep it up!

[tjlazer]

Originally Posted by Philly_sweden

I love it! CS or not. The car should be able to be used as a DD! Keep it up!

That’s my thinking, it’s a car and i’ll use it! I have michelin pilot alpin on, it goes anywhere -15c…no problem!

[chris719]

Before my M2C got totaled, I noticed the same kind of defect starting in my M Perf CF spoiler. Obviously a completely different construction, but I think temperature cycling may be contributing it because it didn't happen until I started using it in the winter.

[Artemis]

Cross-referencing:

• "BMW M2 CS CFRP roof weave issues: "Garching, we have a problem" ?"
  https://f87.bimmerpost.com/forums/sh....php?t=1765570
• "CFRP roof of my M2 CS features a deformity - Replacement proposed"
  https://f87.bimmerpost.com/forums/sh....php?t=1819852
• "M2 CS roof defect"
  https://f87.bimmerpost.com/forums/sh....php?t=1898496

[m2ss]

Originally Posted by chris719

Before my M2C got totaled, I noticed the same kind of defect starting in my M Perf CF spoiler. Obviously a completely different construction, but I think temperature cycling may be contributing it because it didn't happen until I started using it in the winter.

Hopefully my M Perf carbon fiber diffuser won't be affected, been driving year round, will keep an eye out...