worf928

That link indicates that the (list?) price will be $17,970. Or is it the option price? Won't know for a while.

That might be affordable to some, or all, of the folks in this thread with TTs/TTSs, but in no world in this universe is it very cheap.

Are the wheels in the parts DB yet? Or was this an over-the-phone kinda thing? I suspect that the number you got was in the wrong currency units given the PR from Porsche.

I agree. The wheels are awesome. I'm just disappointed that they seem to be more expensive and heavier than the wheels Carbon Revolution has been selling for a couple of years.

The CR wheels (at least in 19" sizes which is better IMO anyway) are <$14k for a set. (Vivid Racing's website; maybe those are fake prices...)

And the CR wheels are 40-50% lighter.

I would actually pay $14k for wheels that were ~1/2 the weight of OE. But, I see no reason to pay $18k for wheels that are only ~20% lighter. I'll wait for the tech to develop further.

Thanks for the link and vid. I'm not an expert either but, if the woven-before-baking CF is so awesome why aren't the wheels mo'lighter?

Why is Porsche's CF wheel better? It's more expensive. It's heavier. What does it do that's better than CR's?

Maybe CR's wheel explodes after 5k miles? Or maybe it's weaker than a similar alloy wheel and cracks at the mere sight of a small pothole.

More likely is Porsche milking the audience that wants cutting-edge tech at any price, like they did with HIDs in the late 90s and LEDs until last year.

I know: All non-answerable questions for now.

oceancarrera

If the price could come down to a reasonable high end wheel price, the weight savings,
un-sprung weight performance gains, can be a great reason to buy them. plus they look cool
if you can get matching CF pattern bits everywhere else on the car.

ace37

3D woven can be much better if they could get enough plastic in the fibers. Typically you want 65-70% fiber by volume for the best standard engineering properties. Sometimes you want more plastic in there with modifiers to help the impact strength. That reduces the standard structural properties but might improve the overall design and even make for a lighter weight product.

A few things are going on with carbon wheels. If well designed they will be excellent under fatigue, a little better than aluminum for strength and stiffness to weight, and significantly inferior in regard to impact damage. Also depending on the plastic used you can have concerns with moisture and UV damage. And when connected to steel the carbon will increase the corrosion potential in the steel (in terms of the electrochemistry of corrosion). So in the end you will get better traditional structural properties along with some new deficiencies that may or may not matter. Often with carbon different failure modes govern your design. In aircraft generally we concern ourselves greatly with strength and fatigue properties of metals and hot wet open hole compression strength of composites. In some cases you almost don't even have to assess the strength - the other failure modes govern the design and so it ends up way stronger than it needs to be.

In the case of a composite wheel, Porsche's centerlock wheels may actually be a benefit. Carbon fiber reinforced plastics aren't very good at bearing loads from bolts. The centerlock design may diminish that weakness.

Right now the international standards for auto wheels are pretty weak. For instance several years back (haven't checked recently), the only standard including fatigue testing did not require any lateral loading at all - so no cornering at any speed. But since nobody has to certify wheels in the first place it was a start. Maybe it's gotten better, I hope so. If the testing requirements are too extensive though nobody bothers to certify their wheels.



What I think is going on with the weight of these wheels is Porsche might just want all of their wheels to survive a nuclear holocaust. I can't think of any Porsche wheels that are incredibly light for the material and manufacturing technique. And their engineering is great, so I have to assume they just design them to be quite durable and that means they have to use more material and therefore the weight isn't as light as you'd like to see. This looks to be a tech demonstration and development effort and for that reason it needs to look sexy to many and sell enough volume to fund further research. And in the long run this type of development is very important as it helps Porsche develop new skills and processes that might (through innovation) find great applications in other areas.

oceancarrera

Well the Ford Gt won Lemans on CF wheels. They hadn't mentioned UV or moisture fears but as you say above it must have been a huge concern.
Bare in mind Ford only had racing and or research/development testing not Ace37's unique unverifiable knowledge/speculation/theories etc...

ace37

Thats not what I said at all, and just as a street car is not a LeMans race car, Porsche's street wheels are not going to be the designed like those used for a LeMans race. I've done research, development, analysis, and testing on these materials and I work for one of the big aerospace/defense OEMs. The comment on the fatigue testing was from a graduate course in fatigue years back. The comments on unique failure modes are common knowledge to design and analysis engineers that work with these materials, are news to most people, and are readily verifiable through the academic literature. The ASM handbook on composites is a good reference. Some find these technical details interesting but reading about it from a source like that is a bit too much for their interest level and/or background.

If you care to understand or challenge what I am saying, by all means ask about or politely challenge it, but don't blindly dismiss it with veiled ad hominem jabs and examples that don't address my points. Be a better quality of disagreeable and we'll get along just fine. Maybe I'll learn a few things from you - it happens all the time when the discussions are constructive.

Also, rereading my post I see I used a fair bit of technical terminology that is not familiar to most. I apologize for that. If anyone is interested I can rewrite it.

worf928

@ace37: thanks for the technical prose!

oceancarrera

I can't see how you would know how Porsche is building these rims. With all that you have researched don't you think that there may be a newer development in this technology? Why would Porsche even publish anything they come up with? How can Ford put them on their GT350R and warranty 16 to 20 grand in wheel options (not sure on pricing, lazy)? I think you have great research but the World is much faster these days. Thanks for sharing.

worf928

As I understand it, 'typical' non-decorative CF strength properties are a function of how the various layers of fiber are aligned with each other. You can produce a CF item with one or two optimized strength properties (e.g. compression, but not flexure) that would be lighter, smaller, than one optimized for all possible properties. Yes?

If so, then, I take what you right above "3D woven can be much better" in that context: That the goal of the 3D woven approach is to produce a weave that isn't just strong in tensile (for example) but also strong in flexure, shear, etc? The result though, will be a heavier, bigger product that might have some 'useless' strength properties for the intended application?

Adding plastic to help impact strength makes sense. I would assume that any reduction in structural properties could be made-up with additional material. It's not at all clear how adding plastic might result in a lighter product assuming the structural properties are a fixed constraint.

So, no matter how much plastic you add (non-absurd proportions of course) impact resistance of CF will always be inferior?

This is because the compression force is distributed over a larger total area?

worf928

The design lifetime of race car components is expressed in units of hours. The design lifetime for consumer auto components must be expressed in units of years. If the CF wheels used on the Ford GT Le Mans racer car have the same designed lifetime of wheels in F1 then they were thrown away after Le Mans.

Your sentence makes as much sense in context as "it smells blue."

Hours vs. Years. Yellowing of exposed CF due to weeks and months of exposure to UV light IS a concern for consumer-grade CF. Otherwise GM would not have wasted significant CapEx on developing a special clear coat for CF for the C6 Z06.

If you took the time to actually process what ace37 wrote you might have clued-in on the notion that he is involved in CF materials for aircraft. For aircraft, the lifetime of structural components is expressed in units of decades.

What experience do you have in this subject? What expert knowledge of CF materials do you have that justifies disparagement of someone who writes about the subject? Be specific.

He didn't write that he did. What confusion of thoughts in your head convolved to produce the conclusion that he did?

What is this in response to? It's totally out of context.

ace37 actually did share. He shed some light on the topic that could have resulted in readers of this thread learning something from a back-and-forth discussion. You, however, obviously sneer at anyone with actual knowledge of a subject.

ace37

Super super long post warning...


Yeah, that's pretty much true. Some of the properties will coalign though - for instance the longitudinal tension and bending flexure strenghts and stiffnesses along the longitudinal axis will typically go hand in hand. So this is a long answer but it should give you some good conceptual understanding...

An easy way to understand how carbon fiber reinforced plastics work is this: the carbon fibers themselves are little ceramic fibers. Think about them like very long glass filaments but stronger and more stiff. These ceramic fibers are very strong and reasonably lightweight but are also brittle and easy to break to pieces. But we like strength, so we get creative and figure out how to make it less brittle. Initially to get fibers to be useful in large scales we just use bundles of loose fibers to make ropelike products. That way if one brittle fiber breaks, no big deal, you have thousands more, and while over time it will fray it will carry a lot of load and no longer be delicate. The problem is, with loose bundles of fibers you have essentially no shear or compressive strength, so the applications are limited to the kinds of things you can do with ropes. This is where we got really creative and came up with composites materials.

The idea is simple: take that rope. All the areas in the rope that have air in them - replace that air with a structural plastic like epoxy. Glue everything together. Now when you need to move it sideways, the plastic transfers loads from one fiber to another and the reinforced rope remains stiff. Not super duper stiff but a lot better than a dry rope. And if you push on it, that same plastic causes the fibers to resist the compressive loads. Now we're getting somewhere. instead of rope, use a sheet of woven glass fabric. Impregnate it with plastic. Now you have a panel that is reasonably strong and light and can carry shear and bending loads, not just tension only. A much more versatile thing.

Carbon fiber works like that. Now thinking again about the fibers, your intuition will work to figure out how the properties go.

1D:
If you pretty much line all of the fibers up in one primary direction and only have a few cross stitches to keep the bundles together, you have what we call unidirectional fiber. Like you'd expect, that is very strong and stiff in one direction - whichever direction the fibers will be pulling or pushing in. If the carbon fiber product is a square and flat plate made of unidirectionally arranged fibers, you can readily understand that if you hold the plate one way it will bend and flex much more easily than if you rotate it 90 degrees. The strength of this plate is due to the fibers that can resist loads, so the stiffness and the strength of this plate pretty well go hand in hand. If instead of a plate you have a 3D block, the same concept holds true - it's very strong in one orientation and much less so in the other orientations. (Typically unidirectional fibers are put together in thin sheets that can be glued together. They can be and often are rotated relative to one another so they aren't all quite aligned in the primary direction. That helps out if you have a little load in a secondary direction.)

2D:
Now let's assume that instead of all the fibers being in one direction, say you weave the fibers into a flat square plate like you'd weave any ordinary fabric. Like a shirt or a pair of jeans but made of carbon fabric. Assume you have about as many fibers along one edge as the other, so a 1:1 ratio in the primary and secondary directions. (And you don't have to - you can do this 2:1 or at any ratio you like.) Now with the 1:1 ratio you can imagine if you were to squish the edges of the plate, the plate will be as strong and stiff on one edge as on the other. And yet if you glued a pile of these plates together to make a 3D block, the third dimension would still be weak - the block would behave like a cube made of plywood - it's just held together by a weak glue (the reinforcement plastic). Also, because not all of your fibers are oriented in the primary direction, compared to the unidirectional fibers, for the same total mass of material you'll have less of it resisting loads in that primary direction. So your peak strength (normalized to a given area or volume or weight) in the primary direction will drop when you add reinforcements in a dimension - it has to.

Aerospace often uses these composite materials to tailor structural properties by need. Make it thicker or thinner in places, glue together fabrics or unidirectional fibers, rotate them at different angles, etc. Typically you'll need to carry more load in a primary direction than in a secondary one, so why not tailor your material to have more strength in one direction than the other - then you can carry all of your loads using less total material. This reduces the weight, and in aerospace lower weight usually further reduces the loading so you get compounding benefits.

3D:
There has always been interest in developing 3D composites. This means like when you go from unidirectional (1D) fibers to plane fibers (2D), now you throw fibers perpendicular to reinforce the plywoodlike plate structure into a full 3D mesh or network of fibers. Now that sounds grand in some ways - no more weak glued-together-plates type behavior. It also is a bit complicated to make and that means it's expensive. The big functional problem is, just like when we go from 1D to 2D, going up to 3D we again have less of the total material resisting loads in the primary or even secondary directions. So your strength and strength to weight ratios drop again. And if you don't care to bias and scale your strengths preferentially into a primary, secondary, and tertiary dimension, you quickly start to find that metal alloys that are basically equally strong in all directions are really hard to beat. So a better metal alloy is often used instead of a 3D composite.

Actually it's less about that. Usually braiding is to help the impact resistance and help it handle pin loads. And yes it's heavier and bigger. I'll try to explain:

Pin loads: Think about a screw going through fabric. Pull that nail sideways. It really messes up the fabric, right? Well, if you put plastic in the fabric guess what, the screw is still problematic! Metal does really well at restraining screws and pins and rivets though. So Boeing sometimes laminates thin carbon fiber sheets to titanium sheets so the titanium can carry the fastener loads an the carbon can be strong and stiff. Yeah, that's complex and has some minor issues, but overall it works well enough that they are happy to do it. When on a car wheel you have five lug nuts, they are big, but overall they behave somewhat like the screw in raw fabric. Which is why I was saying the centerlock design might actually be beneficial.

Impact resistance: So one of the most common glues or plastics used in carbon fiber reinforced plastics is epoxy. Think JB Weld. It chips and cracks, right? And the carbon is ceramic... which is even worse for chipping and cracking. So yeah, put those together and you can see why impact might be a problem. When you have a bunch of glued together plates of unidirectional or woven fabric, again thinking like plywood, hit them with a hammer and they delaminate and the panel is ruined. (By the way, when a mechanic accidentally drops a steel wrench onto a composite airplane wing it's a very big deal.) The idea behind 3D braiding (and quite a few other 3D technologies) is that you put carbon wires in there to hold that plywood together and help restrain it in an impact or overload event. And braiding really works quite well for impact loads - one of the biggest benefits is in braided composites, the impact damage usually stays very small in size and location. So that's typically what they're after - better impact resistance. Not always, but typically.

Research on braided composites has been popular since the 1980s. 3D braided composites are generally used to make what we call preforms - the idea is you make something to essentially the final shape out of fabric (a "preform"), then you figure out how you want to get the plastic in and the air out to make the final part.

While that first answer describes how this works, one of the more interesting things that works really well is you can take that epoxy or whatever plastic you're using and throw things like tiny rubber clumps into it. Then in an impact event, the local pockets of rubber can displace and the energy is dissipated without shattering the epoxy and separating it from the carbon tubes. However, it takes up volume, adds mass to your product, and it's one more thing to buy and do so you have to consider how much benefit you'll get.

If a flammable plastic was used, sometimes a fire retardant to the plastic to help mitigate that. Dirt is actually a common one. Literally they just throw it in. And if you want it a certain color you can throw in pigment. Often UV protecting substances are mixed in. The carbon is perfectly fine with UV but the plastic might not be. It can break the intermolecular bonds and over time cause local delaminations.

You might initially think you want the plastic to perfectly glue to the fibers. Actually, that makes the whole thing quite brittle and it behaves a lot like a ceramic! So typically the best structural properties are achieved with a "good" bond. "Good" in this context is usually defined by a bunch of chemists or chemical engineers who try a bunch of things and see what combination of chemicals makes the final product perform the best in whatever controlled test they decided was the most appropriate. What they do is they apply chemicals (termed "sizing") to the carbon fibers which is a treatment to make the expected type of plastic bond "optimally" for the "best" material properties. I use quotes there because those things really depend on the application. These sizings are usually proprietary to the carbon fiber seller right now. Maybe that will change in time.

You might be able to find a few examples to counter, but generally yeah. Plastic isn't great at impact, and as a ceramic, carbon fibers are worse. So compared to metals which are really good at impact, it's not going to perform as well. The engineering question becomes this: does that even matter. Often the answer is no, so the composite may be a better choice.

Now if that plastic were rubber, yeah it might do better in impact than a good metal product. But rubber won't give you CFRP with decent structural properties. So it's all a set of trade-offs - what do you really care to have and how much money/effort can you spend to get it.

Answered above after the second quote.

Detailed Designs

I won't pretend to have the answers. But even for me in my industry, not all things called by the same name have the same cost, quality or require the same experience to create. What I have seen is that just because a part is "carbon fiber" doesn't mean it's even worth while to consider. There are countless versions of hoods that are carbon fiber, have terrible fit, a pathetic resin/clear coat that fail(turn yellow, starts flaking, etc.) or are much heavier than a well engineered piece.

When I/my shop performs paint correction, installs a paint protection film wrap or coats a car one could make an argument that we are priced too high. If one merely uses the names of the services performed as the guide for hitting the mark, they'd be right. But the devil's in the details and the difference in doing something pretty good or doing something to an OCD level is great. While it's not for everyone, for some, saying X-service was performed is not enough....they want something as close to perfection as they can get. For others, good enough is suitable(no hate intended...just making an example of it). Pushing the limits of what's possible requires someone with the pursuit of the opulent and a wallet to match.

My guess is that Porsche understands all of this better than anyone else at their level. They would not make CF wheels that have any realistic probability of failing like so many other mass produced CF parts do.

It's all speculation on my behalf. I perceive these things and I could be completely wrong. But, hey, this thread is pretty awesome and there's some awesome content being shared so why not share my .02?

My thoughts but way better articulated by someone who appears to actually know what's up.

oceancarrera

Well I was about to spring on a set from Carbon Revolution for my R8. They make them for Ford on their GT350r's. It was easier to understand the weight savings because they discussed the savings compared to their stock rims on Mustang forums and others too. Now I'm not so sure on buying them. I guess I didn't want to here Ace37's conclusions....Oh well

ace37

If you're being serious here, it doesn't matter how the sausage is made. Find out if owners that use them the way you would like them, if you care do check if they weigh what is claimed (my OMP seats are 15% heavier than claimed, and with non-prepreg composites this isn't unheard of), and then decide if it's worth the money to you. If you like them for the aesthetic and uniqueness, that's perfectly fine - it's a luxury good for you. I think they look great and it's fun and cool to have the latest thing. I'll give you a big thumbs up if you post a picture of a sweet R8 on carbon wheels! And being an early adopter your purchase will help development of the technology. More sales justifies more R&D for future tech and over time it will get better and better.

oceancarrera

I like them because I thought there would be a noticeable performance (handling) gain. There are too many variables when it comes to rims to compare. Two pounds a corner or so doesn't cut it. I thought it was larger. (not sure on that, I don't know what mine weigh) I don't care for the look of what I have now but they are OK. Thanks