This project was an early exploration into combining carbon composite tubing with machined aluminum hardware to create a lightweight, modular bike rack for an E34 wagon. The system is built around two roll-wrapped carbon fiber tubes with bonded aluminum end inserts that provide strong, threaded attachment points.
Construction
The tubes are 1 inch OD carbon with approximately 0.065 inch wall thickness. Each end is reinforced using turned aluminum hex stock, bonded in place with structural epoxy. A thin 0.125 inch layer of 75D urethane isolates the carbon from the clamping hardware and prevents point loading.
Mounting System
The rack attaches to the factory roof cleats using simple, serviceable hardware. Stainless U bolts secure the rear tube. At the front, a bent 6061 aluminum bracket clamps around the tube and bolts to the wheel tray. Standard angle brackets adapt the tubes to the OEM cleats without modifying the car.
Bike Interface
The front of the bike mounts to an over-the-counter fork mount fastened directly to the bonded aluminum insert inside the front tube. The rear wheel sits in an inverted 2 by 4 handrail section, which naturally forms a pocket that holds the tire. A small U bolt secures the tray to the carbon tube.
Design Intent
The goal was to create a lightweight, low-profile rack using accessible materials while testing tube bonding, composite isolation, and simple mechanical interfaces.