Thorn Mercury 40

A Modern Classic for Versatile Riders

When it comes to building a bike that can truly do it all — from smooth sportives to rugged trekking — the Thorn Mercury 40 stands out as a modern masterpiece of design and engineering. Taking cues from the robust Thorn Nomad MK3,  the Mercury offers a lighter, more responsive frame with the same dedication to versatility, durability, and comfort.

Built for Modern Performance

At its heart, the Mercury 40 is a 700c / 650B steel frame with tight, modern geometry. Whether you prefer a Rohloff hub or a derailleur drivetrain, this frame accommodates both — and goes a step further by integrating a Gates belt-drive compatible split, giving you the option of a traditional chain or low-maintenance belt setup.

The frame is designed for either disc or rim brakes, and tyre clearance is generous:

• 700c wheels fit up to 40mm tyres (35mm with mudguards)

• 650B wheels allow for up to 50mm tyres, with or without guards

Tailored Fit Across the Range

Fit is crucial for comfort and performance, and the Mercury 40 doesn’t cut corners. With eight frame sizes available, it caters to a wide range of rider heights and riding styles:

• Five sizes with longer top tubes are ideal for use with flat bars

• Three sizes with shorter top tubes are designed for drop bars or riders wanting a more upright position with flats

This approach makes it easier to build a bike that fits both your body and your riding goals.

Premium Steel, Perfected Geometry

Constructed from Thorn 858 heat-treated steel, the Mercury 40 is crafted with tubing specifically designed for each part of the frame — not just off-the-shelf options. This attention to detail results in a ride that’s responsive yet comfortable, offering the classic feel of steel with modern stiffness and confident handling.

Versatility at its Core

The Mercury 40 can be built up to suit your needs:

• As a lightweight, drop-bar "sportive" bike for fast road rides when paired with a carbon disc fork

• As a fully-loaded trekking rig, using Thorn’s 700c Super Tourist forks and front & rear carriers to carry up to 25kg of luggage with ease
• Or 650B rim brake option with a steel fork for a superb bike for brisk riding and light weight touring.

There’s even a disc-brake trekking fork available for riders venturing into rougher terrain.

Built to Last

Every detail has been considered for durability and longevity:

• Stainless steel dropouts (Rohloff EX / derailleur ISO disc) resist corrosion
• A stainless steel eccentric bottom bracket shell provides easy chain tensioning when using hub gears
• The frame comes complete with a sealed FSA Orbit XLII headset, 27.2mm alloy Thorn seat post, eccentric insert, and tool

What's Not Included?

To give you the flexibility to build your bike your way, the Mercury 40 frame does not include fixing screws or a bottom bracket.

Final Thoughts

The Thorn Mercury 40 is more than just a bike frame — it’s a platform for adventure, endurance, and everyday utility. Whether you’re dreaming of long-distance tours, daily commuting, or a fast weekend escape, the Mercury 40 is ready to be the heart of your next build.