RAD

RESEARCH AND DESIGN

Tandem Project (2026)

THE PROJECT

The tandem we built for the 2026 season. Pilot: Will Seitz. This page covers how it was designed and built.

Finished black carbon tandem bicycle lying on grass, built from two Cervelo P-series frames — The finished 2026 tandem.

THE BUILD

The 2026 tandem was built from Cervelo P-series framesets, modified with the help of 64Cycles, a composites manufacturer. The work took about three months. The frame uses a double down tube layout.

Two Cervelo frames sitting on a plywood build table with a jig — Frames on the build table.

Frame sections aligned along a straightedge with blue marking lines drawn on the tubes — Marking and aligning the frame sections.

Tandem frame joined together with visible filler and unfinished joints, standing against a garage door — Frame joined, joints not yet finished.

Close-up of a bonded carbon joint at the lower end of a down tube on the build table — Close-up of a bonded joint.

ECCENTRIC BOTTOM BRACKET

The bottom bracket shells were modified to take an eccentric bottom bracket. Unfinished shell first, finished install second.

Bottom bracket shell cut open and prepared, unfinished — Eccentric BB shell, unfinished.

Underside of the frame at the bottom bracket, sanded to bare carbon weave before finishing — Eccentric BB shell, unfinished, from below.

Finished bottom bracket shell with eccentric insert and glossy black paint — Eccentric BB installed, finished.

Second view of the finished, painted bottom bracket shell — Eccentric BB installed, second view.

THE FINISHED FRAME

Finished black tandem frame on a stand in front of a wooden fence, one side — Finished frame, one side.

Finished black tandem frame on a stand in front of a wooden fence, other side — Finished frame, other side.

AERODYNAMICS AND STIFFNESS

The frame shapes were modelled in ANSYS Fluent with the aerodynamics department at UAB, using 72 Nvidia P100 GPUs. In the simulations the double down tube layout added no additional drag and made the frame much stiffer.

STRUCTURAL TESTING

There is no ISO standard for tandem bicycles, and finite element analysis was not practical for this build.
We built the tandem and load tested it. In use it feels stiff and handles well.
It raced two World Cups and a World Championship in 2026 without problems.
64Cycles has developed an ISO test rig, which we will use going forward.

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+1 [205] 902-5236
will@rdand.net

Cervelo is a trademark of its owner. This tandem is an independent modification and is not a Cervelo product.