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Trek Gen 4 Top Fuel is Faster and More Nimble With DownCountry Adjustability

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The Trek Top Fuel has seen a fair amount of change over the past few years. It’s morphed from a race-only cross-country steed, to a fun, fast trail monster in its fourth iteration. Trek is hitting its stride with the Trek Top Fuel Gen 4. The bike isn’t undergoing full-on changes, but refinement and maximizing the most usage out of a single design. 

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That maximization comes from suspension refinement, a 4-position monolink, small geometry improvement, and a lighter frame. The new Trek Gen 4 Top Fuel has a staggering eight different build options, starting at $2,700 and topping out at $10,500. 

Trek Gen 4 Top Fuel 9 XO hot

Trek Gen 4 Top Fuel – What’s New?

The Gen 4 Top Fuel boasts many changes from the previous version. Some are additions, like the 4-position Mino Link and size-specific chainstay length—other compatibility changes like the ability to take on MX wheels and longer-stroke shocks (130mm-140mm). 

Trek Gen 4 Top Fuel rider


Most of the improvements, though, are refinements to the previous design. Geometry-wise, the new Gen 4 Top Fuel moves from a 66-degree head tube angle to a 65.5-degree angle (size med) and a slightly longer reach, 445mm (Gen 3 – M) to a slightly longer 447mm (Gen 4 – M). 

Better Storage

The Internal frame storage gets an update. The update brings an improved storage door with a tighter seal and a bigger opening, and the cables are protected (bags won’t snag). Trek now offers a two-bag system on all bikes with storage doors: one padded for tools and one unpadded for tubes. Carbon bikes will arrive with both bags, while alloy bikes come with one padded tool bag. 

Those who were not Knock Block fans rejoice—Trek is eliminating the Knock Block for the Gen 4 Top Fuel. 

Also, for riders who struggled with longer dropper seat posts in the Gen 3 version of the Top Fuel, the new frame boasts an improved dropper insertion, allowing for longer droppers in smaller frames. 

Lighter Frame Both Alloy and Carbon

The frame (alloy and carbon) is now 220 g lighter than the previous generation, with the same travel and more features. 

Trek Gen 4 Top Fuel geo

Familiar and Similar Geo

The geometry on the new Trek Gen 4 Top Fuel is refined rather than revamped. The bike’s idea is fun and fast, with a bit of playfulness mixed in. The design team ticked the headtube back to 65.5 degrees (previously 66) and kept the effective seat tube angle at 76 degrees. 

Trek Gen 4 Top Fuel 8

Size Specific Chainstay Length

Something we’re seeing on bikes across the board is size-specific chainstay length. It gives the bike a balanced handling and ride experience across all frame sizes. For the new Top Fuel, this means keeping the rider’s weight centered between the wheels. Shorter riders will have better wheel maneuverability, and taller riders will get better front wheel control. The previous Gen 3 Top Fuel had a 435mm chainstay across all sizes. Now, the Gen 4 Top Fuel boasts 435mm (Small and Med), 440mm (Med/Lrg and Lrg), and 445mm (XL only).

More Versatile and Adaptable

The new Gen 4 Top Fuel is compatible with up to 140mm fork and a longer 185×55 shock, gifting riders 10mm more rear travel.

If you want to move to a 27.5 wheel, the stock shock is 185×50. It is compatible with a 27.5″ rear wheel but requires a 140mm fork and Mino High setting. Let’s talk more about the 4-position Mono Link. 

Trek Gen 4 Top Fuel mono link

This new 4-position Mino Link offers the same geometry adjustment as the previous Top Fuel but now with a leverage rate adjustment. Riders can adjust geometry and leverage rates independently to dial in their ride.

Trek Gen 4 Top Fuel leverage rate line

In a nutshell, the “stock geo” has low geometry and is less progressive, but riders can adjust to have more combinations easily.  Here’s a breakdown of all geometry and leverage combinations. 

Trek Gen 4 Top Fuel leverage difference
  • Lower position = low BB/slack HT(65.5–stock)
  • Upper position = high BB/steep HT(66)
  • Forward position = less progressive(14%-stock)
  • Rear position = more progressive(19%-stock)

Suspension Kinematics

Trek made slight refinements to the suspension kinematics. The anti-squat is slightly higher for better acceleration in and out of turns. The leverage rate is bumped up from 13.5% to around 14%.

Trek Gen 4 Top Fuel anti squat

The idea behind this adjustment was to make the bike even more trail-oriented, and more riders could adjust the leverage to a more progressive 19%.

Trek Gen 4 Top Fuel 9 XX hot

Trek Top Fuel Gen 4 Models

  • Top Fuel 5
  • Top Fuel 8
  • Top Fuel 9
  • Top Fuel 9.8 XT
  • Top Fuel 9.8 GX AXS
  • Top Fuel 9.9 X0
  • Top Fuel 9.9 XX
  • Top Fuel 9.9 XTR

Trek Top Fuel Gen 4 Line Pricing 

The new Trek Gen 4 Top Fuel Line is available now at your local Trek dealer or online at Trekbikes.com

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Marcellus | Bombtrack

Nice to see an anti-squat graph that includes the number of the cog height.

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