A pretty geeked out one today, thanks to Australian Colin M (as opposed to formerly RI and now VT Colin M). But it's got "versus" in the title so as we've learned it will be highly read for years and years.
Coming specifically asks whether there is any benefit to the automated "filament winding" method of making carbon rims. Before we get too much into that, we need to first show the "normal" carbon rim making process, and then explain just WTF filament winding is. And that's best done with an assist by some videos (sorry Catherine, video is better for this).
In "traditional" carbon rim manufacture, the tech puts a bunch of pieces of pre-cut carbon sheet into or onto a mold.
This photo is from a Corima MCC wheel's hub being molded, so it's not technically a rim part but it's a cool and illustrative shot. This is a "female" mold, because the mold is on the outside and the parts being molded are on the inside. We mentioned the Corima MCC wheels in the "Past and Future of Spokes" post last week. My most trusted carbon expert would have a conniption that the hands in this photo are not gloved - bare hands transfer skin oils that can compromise bonds and dirt that can contaminate bonds. His operation (they make boats and boat parts) is basically full clean room. But I digress.
Here is the sort of seminal video on how traditional carbon rims are made. While each factory/manufacturer will have different takes on this, this expresses the basic "how it's done" of the normal process. With minor differences, this is how our Cafe Racer, RCG, GOAT, HotFoot, GX24, and All-Road rims are made.
First and foremost, what we call "carbon fiber" is actually a mix of carbon fibers and resin. The resin is the plastic goo that, once catalyzed (a thermic reaction), hardens and holds the fibers in place. Both parts depend on the other, and you want to correlate their properties to get the most out of the system. The carbon sheet pieces you see being put into/onto the molds already have the resin "pre-impregnated" (called pre-preg) into them. Basically, the raw carbon sheets (think of a big piece of cloth) are laid out onto a table, and a measured amount of resin is poured onto the sheet, and then spread out onto the sheet, saturating that sheet. "Saturating" is actually tightly defined, with a normal ratio of carbon to resin somewhere in the 63% carbon to 37% resin range. This matters - problems happen on either side of a pretty tight band, and that band depends on a lot of different variables that are part of the system design. Once the carbon is "pre-pregged" it is refrigerated to prevent the thermic reaction that catalyzes the resin. Pre-pregged material can only be stored for so long before it goes bad.
There are other ways to "join" the carbon fibers and resin. Wet layup is what old school surfboard shapers use, as in this video. Funny note - the mixing pot that the guy in this video uses is from the company that one of my best friends runs - Jamestown Distributors.
Bike parts shouldn't be made using wet layup, it's pretty crude.
Another way to do it is by resin infusion, which is where you load the mold with all of the fiber sheets, and then "pull" the resin into the fiber using vacuum suction. Some bike parts are made this way, it's not crude at all. The challenge with infusion is that it can be problematic to get the resin into tight corners and complex curves, leaving dry spots. Dry spots ruin the whole part, so you want to limit infusion to relatively "plain" parts.
In filament winding, the mold is replaced by a mandrel. The mandrel is just a form over which you lay the fibers. The fibers are wetted out (the resin is put into them) as they come off the spool, which is where that action takes place.
Here's one video of filament winding:
And the second filament winding one is here:
So with all of that out of the way, are filament wound rims better? To the best of my knowledge, despite a lot of claims out there, there is only one company that really makes true filament wound rims, and that is Venn. Making a VERY long story short, I believe Venn's story that they're the only ones really doing this. There are some (primarily German, I think) companies that are making braided rims, which is essentially making a sock out of carbon and resin, and then molding that into a rim, and that deserves consideration too. I've never held a Venn rim in my hand, never seen one in person. I know that they had some teething problems initially but I think they're getting sorted or have gotten sorted. And I don't know how they go from a filament wound "thing" to rim - understandably they don't post videos about that.
Are filament wound and/or braided rims, where the layup process is done by machine automation, better than hand-laid rims? Boy isn't that a big question. Ultimately, I believe that these processes offer a lot. The process controls are pretty great, as you tightly control the resin ratio, the tension under which the fibers are loaded onto the mandrel, you don't have human hands contaminating things, etc. Obviously from the videos, people and machines are part of both processes, so neither is all one way or the other. But the more process control the better.
Maybe we'll all just wind up 3D printing rims in the future and be done with it?
So what's my personal verdict? I think that both ways, engineered and executed correctly, make great products. To me, it's more a case of "are we doing what we're doing well" than "is the process that we use an iron-clad better way?" I don't think either has made that claim on any metric yet. If filament winding or another process is able to yield rims that are as good, but cost much less, then that's great. If one can prove to make a much better product at equivalent cost, that's also great. But neither of those has happened yet. Believe it or not, there is so much going on with composites and molding even still. I lucked into a conversation in February with a guy who's leading some crazy innovations in this, and though we haven't figure out a way to have it impact us (significantly because we can't/won't commit to the investment necessary to kick it off - and that's another post entirely), it's wildly interesting and may happen for us sometime in the future.
This one will either spark crazy amounts of discussion or cause everyone to flip the channel. If the former, we're of course happy to answer any questions you might have.
I don't think there are any slam dunks out there. If you're still alive, our pre-order closes tomorrow. Getcha some awesome wheels at $100 off the regular price.