Before the start of stage 15, VN spotted a 3D-printed chain catcher tucked behind Froome's notable (non-sponsor) Osyemmetric chainrings.

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SAPPADA, Italy (VN) — Less than 24 hours after Chris Froome made his presence known in a big way on Monte Zoncolan, he was back at the starting line on his Pinarello F10 XLight. Before the start of stage 15, I got a closer look at his bike. Tucked behind his notable (non-sponsor) Osyemetric chainrings was what appeared to be a 3D-printed chunk of plastic, just underneath the bottom bracket. There’s another, flatter piece mounted near the top of the bottom bracket shell/bottom of the seat stay.

The bottom piece is secured to the bottom bracket shell and chainstay with what appears to be epoxy. This inelegant hunk of plastic and its mate higher up on the bb shell presumably serves as a chain keeper, in an effort to keep his chain in check should it hop off his notably oblong chainrings.

While it’s become commonplace for manufacturers to create prototypes via 3D printing, few, if any, other teams use actual parts in competition that have been 3D-printed. Team Sky has certainly led the way with such unique components: At the 2017 Tour de France, for example, some Team Sky riders (most notably Geraint Thomas) used 3D-printed titanium handlebars during the opening time trial in Dusseldorf. Now we can add Froome’s unique chain catcher to the list of 3D-printed parts used in competition.

While it’s cheap and easy to create 3D-printed plastic parts, uses on race bikes are limited because such parts usually aren’t durable enough for regular use. (And how many of us truly need custom plastic parts?) Conversely, the titanium 3D-printed bars Team Sky used at the Tour de France last year were plenty durable, but the price of constructing such components from titanium raises the cost significantly. It makes sense for pro teams looking to create precision custom parts for its riders, but for the rest of us, such an astronomical price tag is likely to keep 3D-printed titanium components, especially sizable ones like handlebars, out of our hands and off our bikes.

But Froome’s chain keeper doesn’t need to be particularly durable since it will rarely see any actual use. And judging by the photos, it’s not exactly an elegant part. Because of its location on the bike, it doesn’t need to be particularly attractive since it won’t be seen. And aerodynamic losses are likely to be minimal. Even if Froome loses a fraction of a watt from the piece, it’s certainly better than dropping a chain at an inopportune time and getting the chain lodged in the tight spaces between the chainrings and the frame.

Team Sky representatives wouldn’t say why Froome needs a custom 3D-printed chain keeper, but given the unique shape of his chainrings, it wouldn’t be surprising to learn his drivetrain requires a unique shape and positioning for such a part. Because his chainrings are oblong, Froome’s shifting performance suffers. If he shifts when the chainring isn’t in an optimal position, the likelihood of dropping his chain increases significantly.

Of course, since it’s a custom part, the 3D-printed chain keeper technically shouldn’t be considered legal under UCI rules. Bikes and components need to be available for purchase to consumers — in other words, it needs to be available to everyone. Don’t rush off to your local bike shop just yet, though. It’s likely Team Sky applied for an exemption to this rule, so unless you’ve got big bucks to spend, you’ll probably never be able to acquire such parts for yourself. (This is also probably how Team Sky’s 3D-printed titanium handlebars at the 2017 Tour de France were usable in competition.) That is unless you have access to a 3D printing machine and a lot of time on your hands.