A venerable of Trek’s mountain bike line-up, the new Top Fuel adds more travel and geometry adjustment while enhancing the utility of its downtube in-frame storage. Despite being engineered for longer forks and deeper travel shocks, the Gen 4 Top Fuel frame is lighter by 220g, in carbon and aluminium, compared to Gen 3.  

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The core numbers are a 120mm frame and 130mm fork, positioning the Top Fuel Gen 4 as an XC or trail bike, depending on build options. Could it be classified as downcountry? Probably. 

Mino-link geometry

Trek says you can run your Top Fuel Gen 4 with a 130mm shock and 140mm fork if most of your riding is on more demanding trails. Enabling the suspension increase and geometry changes is the four-position Mino-link. Think of it as a dual-slot flip-chip, which also serves as the shock mount. 

Running a 130mm fork, the Top Fuel Gen 4 sits at a 65.9-degree head angle in the Mino-High setting and 65.5 degrees in the ‘Low’ position. If your Top Fuel Gen 4 has a 140mm fork up front, the Mino-High position will have it at a 65.5-degree head angle, which slackens to 65.1 degrees in the ‘Low’ configuration. 

2024 trek top fuel shock.jpg, by Liam Mercer

Compared to the Gen 3, the new Top Fuel is about half a degree slacker throughout the sizes and has a slightly longer reach. The size medium Top Fuel Gen 4 has 447mm of reach, compared to the Gen 3’s 445mm. 

Although two positions account for the geometry adjustment, the other two provide something rather interesting - leverage rate adjustment. In it's forward position, Mino-Link shifts the frame to a 14 per cent leverage rate which is its less progressive setting. In its rear position, it then gets more progressive, sat at 19 per cent. This neat little adjustment provides riders with the option to achieve a more poppy and playful feel, or one that's better suited to navigating chunky terrain with composure.

Redesigned chainstays and frame storage

The other significant design upgrades for the new Top Fuel are size-specific chainstay lengths. The Gen 3 had 435mm chainstays throughout its sizing, while the new bike keeps that size for the Gen 4 small and medium frames, while the medium-large and larger versions have 440mm chainstays, which grow to 445mm on the extra-large. 

2024 trek top fuel dt store.jpg, by Liam Mercer

More compact riders should benefit from agility with the chainstay-specific sizing, while taller riders should feel more centred when leaning into- and through tight switchbacks. 
Cockpit geometries vary between the aluminium and carbon bikes. The aluminium frame Top Fuel Gen 4s are built with a 35mm stem clamping 780mm width alloy handlebars. Carbon frame Top Fuel Gen 4s feature a Bontrager monocoque carbon RSL integrated handlebar/stem, with 820mm handlebar width and 45mm stem length. 

Frame storage is a valuable feature for riders, but poor weather sealing and noise suppression can create a very annoying riding experience on the trail. Especially when loose tools and spares start rattling away in the frame during a descent. 
Trek’s engineers have enhanced the Gen 4 Top Fuel’s downtube storage with a larger door opening and better sealing. Inside, there’s a new two-bag system for carbon frames, with a padded bag for tools and a minimalist bag for your spare tube. 

Prices, spec and weights

The Gen 4 range starts with an aluminium frame Top Fuel build at 15.9kg/35.05lbs, priced at £2,500. It features a RockShox Recon Silver RL fork, X-Fusion Pro 2 shock and Shimano Deore drivetrain, rolling on Bontrager Gunnison Elite XR 29x2.4in tyres. 

Spend £3,500 for the Top Fuel 8, and the weight drops to 14.58kg/32.15lbs, while suspension components upgrade to a Fox Rhythm 34 fork and Performance Float DPS shock. With the Top Fuel 8, you also get Shimano XT drivetrain bits. Trek’s premium aluminium offering is the £4500 Top Fuel 9, which adds SRAM AXS GX Eagle drivetrain, dropping weight to 14.38 kg/31.71lbs

2024 trek top fuel riding.jpg, by Liam Mercer

The Gen 4 Top Fuel carbon range starts at £6,000, with the 13.45kg/29.66lbs 9.8 XT. Suspension specification is a RockShox Pike Select+ fork and Deluxe Ultimate RCT shock, while the components are true to its naming convention: with a Shimano XT drivetrain. Carbon meets wireless shifting with the Top Fuel 9.8 GX AXS, at £6,500 and a weight of 13.20kg/29.11lbs. 

Bontrager Line Pro 30 carbon wheels become part of the new Gen 4 range with the Top Fuel 9.9 X0 AXS. Priced at £8,500, the 9.9 X0 AXS weighs 13.10 kg/28.89lbs, and features a RockShox Pike Ultimate fork and Eagle XO rear derailleur. Topping the Gen 4 Trek Top Fuel range is the 9.9 XX AXS, with an upgraded SRAM XX SL Eagle AXS rear derailleur. Priced at £10,000, the 9.9 XX AXS weighs 12.85kg/28.33lbs.  

• www.trekbikes.com

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