The carbon slicktop thread

[SQ13]

Forgive the denseness but I'm still a bit confused. You're basically saying because of the lack of angle cut on the front of the karb roof, the panel does not sit as flush as it would if there was an angle cut like on the OEM panel, and thus might have adherence/gluing issues? Also the roof is an extra 7mm forwards because of it?

Yes, installing as is would cause the roof to sit on top of the nub, which would cause a large gap between the roof and flat portion of the body. This would most likely cause issues with windshield install.

You must do one of the following to prevent this:
1. Grind down the nubs
2. Cut roof corners at an angle like OE to clear the nubs

No, the overhang is not due to the above..it’s a separate thing I noticed. The front lip just happens to be larger on the Karb roof. You can either leave it or cut the excess lip off. Only one person has documented cutting off the excess; after watching some vids and talking to some people who have installed the Karb roof, I’m pretty sure most people just leave it.

The fitment of the roof is perfectly fine. The alignment of the exposed/raised portion of the roof lines up perfectly with the roof rails and pillars.

[CrisSilberGrau]

FYI for those who are installing a Karb roof… The corners on Karb roof are not cut at an angle like the OE and other aftermarket roofs. The angled cut allows the roof to clear a welded nub on each corner, and I believe it avoids contact with a layer of sheet metal for the A and C pillars (will confirm this tomorrow since apparently none of the pics I took contain fully exposed corners). If the second point is true, that means the roof will sit more flush with the body/bows. Additionally, there is 6-7 mm of overhang on the front edge of the roof.

It’s kinda surprising that after looking thru this thread, other online posts, and in the vids I’ve seen for the Karb roof install, only one person mentioned the overhang and no one talked about the nubs. I think they ended up grinding down the nubs and leaving the overhang as is (except for the one forum member here), which I’m sure is fine. I’ve been tempted to do this as well to avoid the extra work of cutting carbon fiber lol.

Anyways, the point of this post is to let future Karb roof installers know that Karb recommends cutting both the angles on the corners and the overhang. And to clamp the front and rear edges every 10-15 cm, especially if the roof is slightly raised at one corner. BMW’s official install instructions calls for five clamps each on front and rear edge….as long as you’re not using two clamps like I’ve seen some people do, you’ll probably be fine. Just follow either Karb’s or BMW’s instructions. And wear proper PPE if you end up cutting the roof—you do not want to inhale the CF dust and have fibrosed lungs.

Forgive the denseness but I'm still a bit confused. You're basically saying because of the lack of angle cut on the front of the karb roof, the panel does not sit as flush as it would if there was an angle cut like on the OEM panel, and thus might have adherence/gluing issues? Also the roof is an extra 7mm forwards because of it?

[CrisSilberGrau]

Part of me wants to try having the roof painted in a sort of "fade" silver grey. From a distance it would seem to be paint matched to the car, but up-close, the weave shows through.

How dare you...

[Cronenberged]

Not sure I understand?

If any of the details from the OEM panel are imprinted in the CF panel. It looks like it, but the limited quality on the forum doesn’t show it. Mostly looking at the edges that will be in contact with the frame when adhering it.

[bigjae46]

bigjae46 can you show depiction of how similar your CF roof is to the OEM panel.

Not sure I understand?

[Cronenberged]

bigjae46 can you show depiction of how similar your CF roof is to the OEM panel.

[Sid_E46]

For those that used 3M Panel Bond...how many 200ml cartridges did you need?

1 was more than enough.

[bigjae46]

For those that used 3M Panel Bond...how many 200ml cartridges did you need?

[Nate047]

Nooooooo leave it

[Sid_E46]

Part of me wants to try having the roof painted in a sort of "fade" silver grey. From a distance it would seem to be paint matched to the car, but up-close, the weave shows through.

[0-60motorsports]

1x1 spread tow roof completed! 5.6lbs. Straight out of the mold, no clear coat. Weighed a slick top roof panel - 18.4 lbs.

It feels a little stiffer than the OE roof when trying to twist the roof diagonally.

That weave looks so sexy! Nice work brother.

[bigjae46]

1x1 spread tow roof completed! 5.6lbs. Straight out of the mold, no clear coat. Weighed a slick top roof panel - 18.4 lbs.

It feels a little stiffer than the OE roof when trying to twist the roof diagonally.

[SQ13]

Lol I did all of the above and still struggled with it. Def not a quick job for me 🙃 i followed the instructions but my technique was probably poor. Glad it’s over now

[heinzboehmer]

1) the bit walking off

Did you center punch the spot welds? I bet that helps a lot with the walking.

[Sid_E46]

Yeah I think it’s just for alignment purposes. With the Karb roof, I’m temporarily snapping in the original roof rails, as well as measuring the front and rear edges all the way across, to help make sure it stays square.



I did use the Blair bit with a Milwaukee drill and constantly struggled with 1) the bit walking off and 2) having to apply a ton of downward pressure to get it to cut. Maybe I wasn’t doing it right. Would like to hear how you did three sides in 30 mins lol.

Agreed. Belt sander with 3M 80 grit belt was very efficient for removing the protruding spot welds and cleaning up the surfaces, and I would highly recommend it. It would likely work well to grind down the spot welds if using the Blair spot weld drill bit isn’t desired…just need to be careful and not go too deep.

You need to use some cutting fluid and also use relatively light force initially so that the guide bit can have a divot to follow. One the divot is formed, you can press down harder so that the spot weld cutter can make contact with the metal.