Short travel sender or comfy endurance rig? Both!

Recently revamped, Trek now has a deep lineup of their 120mm Top Fuel XC Bikes, with a commitment to two entry-level models. Coupled with that, the new (Gen 4) Top Fuel works well across a broad range of ‘cross-country’ rider styles. Here’s my take on the performance and capabilities of the all-alloy, Top Fuel 8.

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Video: The Tech, Features & Ride Impressions

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Features and Details

The Top Fuel 8 is a 120mm cross-country bike with no electronics or carbon to be seen. As with all models in Trek’s Top Fuel lineup, it is a 29er in sizes medium through to extra-large, with the size small built around 27.5″ wheels.

The frame and shock on this aluminium model weighs 3.7kg which is around 1.2kgs more than the carbon models of the Top Fuel. The complete weight of this model in size large is 14.4kgs, which is around 3kgs more than the World Cup winning, top-of-the-range models. The difference in pricing for those 3kgs will make your eyes water; put it this way: you could buy four Top Fuel 8’s for the same money you’d spend on the blingest build.

What you do need to know, is the geometry and kinematics, or if you like – the keys to the bike’s handling – runs consistent across all models of the Top Fuel, that’s for the carbon and alloy chassis models. So yes, with the Top Fuel 8, you are getting the same chassis and suspension layout as it’s richer siblings, like the Top Fuel 9.8 (we tested here) and the Top Fuel 9.9.

Another point worth mentioning is with the Gen 4 Top Fuel, Trek has added yet more dropper insertion, meaning 200mm dropper posts are a go. The 65.5-degree head angle and generous reach numbers throughout the size curves are, in my opinion, future-proofed and unlikely to go off trend soon, or ever!

The Top Fuel has 120mm of rear suspension travel which, with an aftermarket shock, can be tweaked to 130mm. Upfront, the bike runs a 130mm fork as stock, but Trek says 120mm or 140mm forks will do fine and won’t void any warranty claims. That’s a wide range of versatility, which is why this bike can be raced at a World Cup or rallied as a lightweight trail bike.

On our test bike, both the Fox fork and shock have manual lockout levers, with adjustable rebound. The drivetrain is a mix match from Shimano; it’s an XT rear derailleur and shifter, Deore cranks and SLX cassette and chain combination.

Continuing with the trail-ready build kit, the brakes are four-piston Shimano hydraulics with 180mm one-piece rotors, front and rear. At 170mm, the Bontrager Dropper is decent in length.

There’s a key feature in the Top Fuel’s single-pivot suspension layout that Trek runs on most of their bikes, the ABP. It stands for Active Brake Pivot, and is a concentric bearing locate on the rear axle that allows the chainstay and seatstay to rotate on the same point. In the process, it keeps the suspension fully functional when the bike is under braking.

Trek has dropped the steering limiter (aka Knock Block) as the frame has sufficient crown clearance. This means riders can run any length (or brand) stem. The frame storage has a pretty big door with a tight seal and the internal cabling inside the downtube is concealed so it shouldn’t rattle.

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Ride Impressions

Fit, sizing and comfort | I’m 1.74m tall and tested a size large. The cockpit is very broad and roomy and something I noticed immediately is the frame is nice and long. This means there’s more stability at speed plus room to move about (forward and aft) to shift body weight around. I appreciate the shorter (170mm) cranks Trek have specced on this bike. The Bontrager saddle never bothered me but the grips are not very forgiving and would be something I’d recommend changing out.

Performance of the build kit | Other than the grips there’s no other obvious weak points in the performance of the components. I set the bike up with 15% sag, 20/25 psi in the tyres and never needed to tweak anything. The Shimano drivetrain worked flawlessly, after the initial setup that is. The shock tune felt really good, – that’s soft and sensitive on smaller bumps with great support as the bike ran deeper into it’s travel.

On longer fire road climbs and tar sections, I’d recommend using the lockout on the shock (it’s very easy to reach down and flick it on, without stopping) thereby returning some efficiency the burly trail tyres pilfer. However, as soon as the trail turns techy the Bontrager Gunnison Tyres are pretty wicked. Climbing grip is insane and there’s plenty of bite on offer in corners or when speed must be cancelled. If you aren’t riding technical trails often or are using the bike for longer more marathon style riding, I’d recommend fitting a faster rolling tyre combination. Look for something that is both lighter and with a low-profile tread pattern – this single change will make a significant impact on rolling speed and fatigue on longer rides. [On that point, you might want to check out this explainer article: The New XC & Trail Tyres from Bontrager]

Overall ride feel | Replacing any lightweight carbon bits and pieces with a no-nonsense trail-ready build kit reduces the selling price and naturally adds some weight. This is not a ground-breaking discovery. What was surprising to me, is despite the extra couple of kg’s, the Top Fuel 8 isn’t a sack of potatoes on the trail. Yes it does require marginally more effort to crank up to speed and get jiggy on the trails, but it’s still a playful, fun, ride.

On the Top Fuel 8, I really enjoy being able to chuck the bike down technical lines and fast descents, without thoughts of preserving things like pricey carbon rims or insubstantial tyres. Whilst we are talking techy lines and downhills, I think the real secret to the Top Fuel’s confidence-inspiring ride quality is it’s geometry. I think Trek has hit a sweetspot of sorts with the BB height, reach, angles and of course, dropper insertion, making the Top Fuel an incredibly capable bike. So much so, on many of the flowing trails around Cape Town that I frequent, the Top Fuel is faster than longer travel Enduro sleds.

Bottom Line | The Top Fuel 8 is a short travel, wallet-friendly ride that is down for a broad spectrum of cross-country riding. Ride or race a marathon, rally your favorite singletrack or even take on a local Enduro. It’s a 120mm bike that can do it all. //

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