CF Roof Decision — RKP vs Karb

[LSB4Me]

Hey Guys,

My spare oe slicktop headliner is looking at me funny all of a sudden, so it’s time to buy a roof and get the parts on the car.

RKP and Karb are similarly priced and, from research, seem to be of similar high quality. Points to note:

1. I have a set of CSL rails, so reusing the stock rails (with rack tabs) is moot for me.

2. I will be getting the RKP from IND, so it will be clear coated.

3. I will be PPFing whichever roof gets purchased.

Curious as to what the braintrust here thinks between the two and would appreciate any thoughts/comments.

Thanks in advance.

[9kracing]

Nowhere on the RKP page do I see the words "prepreg" or "autoclave"

I'd go with Karbonius

[Avedis]

From the homework I have done for my build:

RKP

1. Fit is perfect, requires no trimming
2. Made more for CSL rails. If using original roof rails, you will need to add CSL specific spacers (they call them fixing clamps 51137898131)
3. Purchase from IND, ships instantly with no import costs

Karbonius

1. Fit is too long in front, the expectation is that you trim to size (approx 7mm)
2. Fit in rear requires trimming corners at an angle to clear factory roof guides (or cutoff the factory roof guides and leave roof as is)
3. Can reuse original roof rails since it comes with clips just like factory roof.
4. Can purchase from IND directly or from Karbonius with delay and import costs.

Quality wise, they both seem really well made. If you search around in the slicktop thread and member’s build journals, you can see that people have installed both with good results. Since you already have the CSL roof rails, I’d probably go with RKP. Just throw it on with no fitment type modifications then add the rails.

[x Spades x]

I would 100% get the RKP roof


I bought the Challenge roof back in 2014 abd did the conversion. PPF'd the roof right after and 11 years later it still looks BRAND new (with 100k miles sunce the conversion). Quality is second to none.

[bigjae46]

Nowhere on the RKP page do I see the words "prepreg" or "autoclave"

I'd go with Karbonius

Why does that make a difference? Prepreg makes it harder to screw up but a post cured infused part is just as strong as part cured in an autoclave. The properties are in how the part is post cured according to the specific resin matrix formulation.

[bigjae46]

Hey Guys,

My spare oe slicktop headliner is looking at me funny all of a sudden, so it’s time to buy a roof and get the parts on the car.

RKP and Karb are similarly priced and, from research, seem to be of similar high quality. Points to note:

1. I have a set of CSL rails, so reusing the stock rails (with rack tabs) is moot for me.

2. I will be getting the RKP from IND, so it will be clear coated.

3. I will be PPFing whichever roof gets purchased.

Curious as to what the braintrust here thinks between the two and would appreciate any thoughts/comments.

Thanks in advance.

I don't think there is much of a difference or no way to tell unless someone has bought a recently produced part. The issue is whoever makes the part will typically use a composite mold - fiberglass and polyester resin. Even if the mold is heavily reinforced, the mold will eventually wear out. Heat cycling can cause the mold to slightly change shape over time. So the 1st part is perfect, 10th part is ok, 20th part is a challenge, and the 25th part fits like trash. There are many, many other variables. How are the mold stored? Climate controlled? How well was it taken care of? For example, a shop may build to a thickness 3x the part it will produce. Me, I only care about making 3-4 parts in most cases so I make mine about 1.5x the thickness.

The shop could make their molds with epoxy and fiberglass or carbon cloth but epoxy is about 3x more expensive than polyester and the mold construction is much more complex. Not to mention that epoxy does not play well with gel coats and other chemicals - which is why you have the issue with epoxy yellowing and clear coats flaking off. It is possible that Karbonius uses an epoxy mold.

I would not PPF a carbon part. And I would especially not PPF a clear coated carbon part. Fact is you're going to have to re-clear the roof from time to time. Urethane clears do not chemically bond with epoxy. The clear relies on a mechanical bond which will eventually fail.

With that said, I would trust Karbonius more than RKP. I'm not sure I've seen either one.

[EthanolTurbo]

They're both great, buy what is cheapest/most convenient.

[LSB4Me]

Update: I bought the RKP. IND was top notch throughout, as they always are.

Reasoning: I didn’t like that the Karb roof required adjustments for the alignment nubs in the front. RKP is already angled to clear.

[Avedis]

Update: I bought the RKP. IND was top notch throughout, as they always are.

Reasoning: I didn’t like that the Karb roof required adjustments for the alignment nubs in the front. RKP is already angled to clear.

Nice. Who is doing the install?

[LSB4Me]

Nice. Who is doing the install?

ABS in South El Monte. This forum (and IND) recommend them.

Also, thanks for your response above. It was succinct and flagged the rail issue. I ordered the “clamps” and am going to retain my stock rails, rather than use the CSLs. For now, I think.

[Projecte46m3]

Good choice on the RKP! I got mine from IND as well which made for a great experience. The super sized box arrived in perfect condition and the roof was all prepped and ready for install.

RKP content below...I paired mine with the oem CSL roof rails and it was an easy install! I did add some soundproofing / insulation on the underskin of the panel to cut down on noise and temps.

[Epsilon]

ABS in South El Monte. This forum (and IND) recommend them.

Also, thanks for your response above. It was succinct and flagged the rail issue. I ordered the “clamps” and am going to retain my stock rails, rather than use the CSLs. For now, I think.

Also have RKP. Not sure if dealing with tariffs from Karb is worth the stress.

Indeed, good choice with ABS. If not ABS, people would have gone with Option 2 which would be a huge mistake.

Advice: Get this plug before the shop does the water test:

https://www.ecstuning.com/b-genuine-bmw-parts/plug/51718170298

My quick story: 2M called me and told me my speakers were making funny noises. I later found out the antennae plug that they removed was letting water into my trunk and the BM53 was soaked.

[bavarian3]

Good choice on the RKP! I got mine from IND as well which made for a great experience. The super sized box arrived in perfect condition and the roof was all prepped and ready for install.

RKP content below...I paired mine with the oem CSL roof rails and it was an easy install! I did add some soundproofing / insulation on the underskin of the panel to cut down on noise and temps.

Love this content.

bigjae46 or anyone else with knowledge: May be a dumb question but, why isn't anyone having the panel clear coated before install assuming this is just a gel coat.

Remembering back to my e36 m3 days I had a VIS carbon hood - it was clear coated(with some black paint to give a candy coat look) before installation. While others would see theirs yellow and crack over time mine was perfect for something like 12yrs until I sold it. This car sat out for quite some time too.

[bigjae46]

Love this content.

bigjae46 or anyone else with knowledge: May be a dumb question but, why isn't anyone having the panel clear coated before install assuming this is just a gel coat.

Remembering back to my e36 m3 days I had a VIS carbon hood - it was clear coated(with some black paint to give a candy coat look) before installation. While others would see theirs yellow and crack over time mine was perfect for something like 12yrs until I sold it. This car sat out for quite some time too.

Composite parts will use either polyester resin or epoxy. The VIS hood was likely polyester resin...all of the mass produced parts from China are polyester. If the underside of the hood is solid black - it is gel coat over fiberglass chop mat. Then it must be polyester resin because the binders in chop mat is not compatible with epoxy.

Polyester is chemically compatible with automotive clear coat which explains why the clear coat held up for so long.

Clear coat does not chemically bond with epoxy. There are cases where you can remove the clear coat in chunks on an E9X M3 roof with a finish that is failing. So for an optimized CF/epoxy part, the clear will need to eventually be re-done. There are things that can extend it's life but the clear will eventually start to fail. Some will use Duratec sunshield which is an in-mold clear gel coat which provides UV protection - this is the most durable option and I think (theory here, no long-term experience) the best option. Duratec also creates a surface that is compatible with clear coat.

The downside to Duratec is it won't produce the undistorted glossy finish that everyone wants. If anything it has a slightly distorted satin sheen to it.

Still, you can spray an epoxy part with clear, just needs to be sanded differently, I think you need to leave a 320 grit scratch for a mechanical bond. I'm not a painter so definitely not an expert. It will look better but comes at the cost of durability.

Maybe the best option is a thin layer of duratec sprayed in mold and then an automotive 2k clear.

I'm not up to date on this because I don't spray clear...I suck at painting...so I'm sure things will change if it hasn't already.