Wireless shifting eliminated the Di2 junction box and the wires running to it, but the frame ports designed for those wires still exist. The E-Wire Closed Grommet from Cervelo plugs the top tube port on frames originally designed for wired electronic routing, sealing the opening when you're running SRAM eTap or any other wireless drivetrain that doesn't need access to the frame interior at that location. Without the grommet, you have an open hole collecting road spray, grit, and moisture that accumulates inside the frame over time.

The rubber construction provides a tight press-fit seal against the port walls. Unlike rigid plastic grommets that can crack or work loose from vibration, the rubber material conforms to the frame opening and stays put through repeated wet rides and temperature swings. The closed design means there's no slot or pass-through for wires, just a solid plug that sits flush with the top tube surface. It's a small detail, but a frame with properly sealed ports looks finished rather than cobbled together, and sealed ports stay cleaner inside than open ones.

Cervelo designed this grommet specifically for the top tube port geometry on their S5 from 2011-2014, S2 and S3 from 2014-2018, S3 Disc from 2016-2018, and the P5X. If you've converted one of these frames from Di2 to wireless, or bought a used frame that was missing this piece, the closed grommet finishes the job properly. The rubber eventually degrades from UV exposure and repeated cleaning chemical contact, so even frames that have had the grommet installed from day one may need a replacement after several seasons. Check that yours still seals tight and sits flush before the wet season arrives. A fresh grommet costs almost nothing compared to dealing with corrosion or contamination inside your frame.