A Lightweight Aluminium Frame Built for Confident Trail Riding

The Trek Marlin Gen 3 Frameset is the foundation for a purpose-built trail mountain bike at an accessible price - an all-new generation Alpha Silver Aluminum frame with trail-focused geometry and a specification that makes it upgrade-ready from the day it is built. The Marlin Gen 3 represents a significant capability step up from previous generations, bringing bigger tyre clearance, internal dropper post routing, a ThruSkew rear axle, and longer slacker geometry that delivers more stability on steeper trails and at higher speeds.

This is a frameset only - the frame and headset are included but no other components. Fork, wheels, drivetrain, cockpit, seatpost, and all other components must be sourced separately as part of a custom build. The Marlin Frameset suits riders who want to specify their own component build - starting with the proven Marlin Gen 3 trail geometry and aluminium construction as the foundation.

The Marlin Gen 3 frame is available in 8 sizes with smart wheel sizing - XXS and XS frames use 26-inch wheels, with wheel sizes increasing proportionally along with frame sizes so every rider gets an appropriately proportioned bike. The XXS and XS sizes use a curved top tube and lower standover height for easier mounting and dismounting for smaller riders.

• Marlin Gen 3 gives you serious trail capability with bigger tire clearance, internal dropper post routing, ThruSkew rear axle, and longer, slacker geometry that gives you more stability on steeper trails and at higher speeds
• You'll get a lightweight aluminum frame that's robust enough for the ride without weighing you down
• Fender mounts make it easy to accessorize, so your mountain bike can double as a rugged commuter
• Marlin models in XXS and XS frame sizes have a curved top tube and a lower standover height that makes it easier for smaller riders to mount and dismount
• Internal routing looks sleek and makes adding a dropper post easy

Expanded size range

With 8 different sizes, Marlin has a bike made to fit every rider. Each frame is equipped with smart wheel sizing, with XXS frames rolling on 26" wheels, and wheel sizes increasing proportionally along with frame sizes, so every rider gets the fit they need.

ThruSkew Rear Axle, Slacker Geometry, and Larger Tyre Clearance

The ThruSkew is Trek's rear wheel retention system that provides the alignment and security benefits of a full thru-axle while retaining the standard 135x5mm rear hub spacing of a quick release system - allowing compatibility with the wide range of standard rear hubs without requiring a dedicated thru-axle hub. Compared to a standard quick release open dropout, the ThruSkew provides more precise and secure rear wheel alignment, reducing wheel movement and flex under hard trail riding loads.

The all-new Gen 3 geometry is longer and slacker than the previous Marlin - extending the reach for improved stability at speed and on steeper descents, and lowering the head tube angle for a more confident front-end feel on technical terrain. This geometry makes the Marlin Gen 3 a more capable trail bike than its predecessor without sacrificing the approachable character that makes the Marlin range popular with riders building confidence on singletrack.

The frame accommodates larger tyres than the previous generation - providing clearance for the wider, higher-volume tyres that modern trail riding benefits from for improved traction and compliance on rough terrain.

Internal Routing, Fender Mounts, and Upgrade Compatibility

Internal derailleur and dropper post routing is integrated into the frame - making the installation of a dropper post clean and straightforward without external cable routing that adds visual complexity and vulnerability to trail debris damage. For riders who plan to add a dropper post as an upgrade after the initial build, the Marlin Gen 3's internal routing makes this a simple future addition rather than a complex retrofit.

Rack and kickstand mounts allow the Marlin frameset to be built as a dual-purpose trail and commuter bike - a practical option for riders who want one bike that handles both weekend trail rides and daily commuting without requiring a dedicated second bike. The fender mounts allow fenders to be added for wet weather commuting use.

The frame uses a semi-integrated 1-1/8-inch headset, 36.4mm bolt-on seat collar, and 135x5mm ThruSkew rear axle. The rear skewer is a 173x5mm QR.

FAQs

What is included with the Marlin Gen 3 Frameset?

The frameset includes the Alpha Silver Aluminum frame and headset only. All other components - fork, wheels, drivetrain, cockpit, seatpost, saddle, and brakes - must be sourced separately as part of a custom build.

What is the ThruSkew rear axle and how does it differ from a standard quick release?

The ThruSkew provides more precise and secure rear wheel alignment than a standard open quick release dropout while retaining the standard 135x5mm rear hub spacing for compatibility with the widest range of rear hubs. It eliminates the wheel movement and flex that open dropouts can allow under hard trail riding loads.

Does the Marlin Gen 3 frameset have internal dropper post routing?

Yes. Internal routing for both the derailleur cable and a dropper post is integrated into the frame, making a dropper post installation clean and straightforward as an initial build component or future upgrade.

What size range is the Marlin Gen 3 available in?

The Marlin Gen 3 is available in 8 sizes. XXS and XS sizes roll on 26-inch wheels with a curved top tube and lower standover height for smaller riders. Wheel size increases proportionally with frame size across the full range.

Can the Marlin Gen 3 frameset be used as a commuter as well as a trail bike?

Yes. Rack, kickstand, and fender mounts are integrated into the frame, allowing accessories to be added for commuting use. The Marlin Gen 3 is specifically noted as suitable for building into a dual-purpose trail and commuter bike.

Specs:

Geometry Chart