Think Top Fuel, and the image of a XC race bike instantly springs to mind. But like a faded polaroid tucked into the corner for a dusty picture frame, it’s not an accurate representation of the current design. With the Fuel EX increasing in travel, the Top Fuel has been swept along in its backdraft and seen in high definition, it’s now a capable 29er trail bike with modern sizing and 120mm travel and one of the best down-country bikes on sale. 

A dropper post and sorted cockpit complement the Top Fuel’s playful and poppy nature

Trek offers the new Top Fuel in carbon and alloy options, where the Top Fuel 8 tested here is the high-end alloy build. Regardless of frame material all Top Fuels come with integrated downtube storage. And while the quick release hatch under the bottle cage isn’t big enough to cram a three course lunch into the frame, there’s enough space for a tube, multi-tool, a few snacks and a lightweight jacket. 

Down tube storage is handy for those riders who are travelling light

Frame

Trek always offers a comprehensive size range; and with frame options from S to XXL, with a tweener M/L option too, the Top Fuel 8 is no exception. It also has geometry adjustment, but rather than having Trek’s signature Mino Link on the seat stay pivot, the Top Fuel has a flip chip at the lower shock mount. In the low setting this gives a relatively tall 340mm BB height for a 120mm bike, which is probably the only carryover from its race-bike roots – designed to let you keep the cranks spinning, and the speed high at all times.

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The rest of the Top Fuel’s vital stats are on the money though, where a slack 65.6º head angle and steep 77.2º effective seat tube angle make it easy to hammer up the climbs and shred the descents. 

Flip chip in the lower shock mount offers 0.5deg head angle and 8mm BB height adjustment

It’s built solid too, the complete bike tipping the scales at 14.89kg. It also comes with a combined rider and bike weight limit of 136kg (300lb) so it’s clearly no wet noodle. Yes, it’s not the lightest for a 120mm bike, and not far off what you’d expect for a 150mm bike, but that’s the price you pay for integrated storage, as the alloy down tube needs reinforcing when you cut a hole in it.

Thankfully, the Top Fuel 8 rides light, as there’s less travel to pull through to get the bike off the ground, so it offers a different ride experience to modern long-travel trail bikes which tend to have one eye on enduro racing. 

The stock RockShox Pike Rush RC fork dishes out 130mm of travel

Suspension

There are no sag gradients on the 130mm travel RockShox Pike fork, which we assume is down to cost saving, but set-up is still really straightforward with a tape measure to hand. And while the Pike has a reputation for having a sporty, firmer tune, the basic RC version on the Trek felt smooth and composed in all situations. Yes, the RC damper has a very wide range of rebound adjustment, but there’s only a small range that’s actually usable, but it is enough to get the rebound just so; and that’s all that really matters, right?

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You need to be equally attentive when setting up the rear suspension. Set to 30% sag, the top-end RockShox Deluxe Ultimate RCT shock bottoms relatively easily. So if you want to run the shock softer to achieve a lower dynamic BB height, you’re going to need to add volume spacers. As such, we increased the shock pressure and reduced the sag to 27.5%.

This small change alone was enough to prevent premature bottom out, but we could still use all of the available shock stroke when we really needed it. We also ran the low-speed compression setting in the minus position for maximum plushness. In the low geometry setting we measured rear wheel travel at 115mm, which is 5mm less than claimed. 

Components

One of the biggest differences in terms of ride feel between the Lapierre and the Trek, other than sizing, are the wheels. The Bontrager Line 30 rims have a 30mm internal rim width, 5mm more than the Mavic rims on the Lapierre XRM 6.9 we tested the Trek against. This adds to the overall volume of the tyres and the stiffness of the bike. It is also why we dropped the tyre pressures slightly on the Trek, even though we were running the exact same tyres on both bikes. 

Bolted on chainstay protection is a neat and considered touch

With 108 points of engagement the freehub on the Bontrager rear wheel offers rapid, secure engagement, with less chain slack and chain slap as a result. The bike is not totally silent though as there is a little bit of cable rattle, but it will probably disappear when you stuff the BITS storage box to the gills.

The contact points on the Top Fuel 8 are all sorted and while there’s a stack of stem height adjustment, the three 20mm spacers don’t offer any fine tuning of the handlebar height. So swapping one of the 20mm spacers of a 10mm, a 5mm and two 2.5mm spacers, would be our first move before leaving the store.

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Nothing else needs changing though. The mix of Shimano XT and SLX for the 12-speed drivetrain worked flawlessly in the dry, dusty test conditions, where the smaller 30t chainring is a real saviour on long draggy climbs or on days when your legs feel like lead. 

ABP suspension design transforms the seat stay assembly into a floating brake mount

Performance

The steep seat tube angle on the Trek Top Fuel 8 really helps with the pedalling dynamics on steeper climbs and the cockpit is long enough that even with the shorter 45mm stem, you never feel cramped or uncomfortable when climbing. It’s not so steep though, that it feels like the pedals are behind you when sitting down spinning across flatter, rolling singletrack.

Stand up to sprint and the rear suspension on the Trek clearly gets animated, the rocker link flapping around like the tail on an overly excited puppy. So the best approach is to sit and spin up the climbs, as the shock remains remarkably still and lifeless until you encounter a bump. Also if you really want to go for it on smoother climbs, the rear shock has a firmer pedal threshold setting. In short then, gaining elevation on the Top Fuel 8 is relatively straightforward and painless.

Knock Block 2.0 steering lock with 72º steering angle, protects the frame without limiting steering

So, it’s somewhat surprising just how rapidly you can throw those gains away. This bike simply rips the descents. Given the limited travel it still seems to carry speed everywhere, and while bumps that would normally chip away at your momentum are still felt though the chassis, they do not perturb the Trek one bit. It rails corners too. Simply load up the suspension mid-turn, and the Top Fuel has just the right amount of support and extension to keep the front end loaded, before slingshotting you out of the turn faster than you entered it. Combine the raw speed with the balanced weight distribution, and the Top Fuel 8 is a really fun, exciting ride and blisteringly fast too.

Would the Trek Top Fuel 8 be even faster with a genuinely low geometry setting? You bet it would. But we’d settle for a bigger rotor on the SRAM DB8 rear brake, as this bike is so fast in fact, that the 160mm rotor feels wholly inadequate and it looked like it had been tempered after just a couple of rides. 

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The Top Fuel 8 is at home on fast sweeping singletrack