Although raced by Evie Richards on the elite-level cross-country circuit, Trek’s latest Top Fuel 8 Gen 4 is a bike that’ll cater to a raft of tastes thanks to its impressive adaptability. Despite the meagre suspension travel, it dishes out stellar trail manners up and downhill and is primed for UK trails.
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Trek Top Fuel 8 Gen 4 mountain bike – Technical details
Down-country, cross-country, small-travel trail, whatever you want to call it, the Trek Top Fuel covers the lot. That’s because, out of the box, it boasts 120mm of travel at the rear paired with 130mm at the front, which can be boosted to 140mm and 130mm, respectively. It’s not as straightforward as flipping a chip, however, as you will need a longer stroke shock and a new fork but the opportunity to boost its versatility is there.
And speaking of flip chips, Trek’s famous Mino-Link is present, but it does more than tweak geometry. It also provides two suspension adjustment options, allowing the rider to pick from a more linear or a more progressive suspension kinematic. It can be done by unthreading a bolt, turning a couple of metal chips and reassembling. Additionally, the Gen 4 Top Fuel can be run with mixed, or 29-inch wheels.
Also found on the Alpha Platinum Aluminium frame is Trek’s internal frame storage with a redesigned BITS bag. The door to the downtube storage acts as a spot for a bottle cage and there’s an accessory mount found in the usual spot under the downtube.
Other features include ISCG mounts, a fat 34.9mm seat post diameter, and a threaded bottom bracket. Cables are routed internally too with the brand opting for the traditional form of routing, so all the good stuff is present.
The geometry looks rather well-rounded. Up front is a 65.5-degree head tube angle and the effective seat tube sits at a steep, but not too steep 75.9 degrees. On this large frame, the reach measures 477mm and there’s a 440mm chainstay. The wheelbase comes in at 1,270mm.
Trek Top Fuel 8 Gen 4 mountain bike – Componentry
At £3,500, the Top Fuel 8 Gen 4 sits at a point that balances performance with value. That’s made clear through the specification of the Fox 34 Rhythm fork which isn’t the most sophisticated, or light fork around but its damping isn’t too shabby, to say the least. The rear 120mm of travel is controlled thanks to a Fox Float DPS Performance shock.
With a mix of Shimano’s Deore, XT, and SLX kit making up the drivetrain, braking is also controlled by Shimano kit but present is a set of the brand’s four-piston Deore brakes. These are paired with 180mm rotors at both ends and work incredibly well for the price point. They feel great, and provide more than enough power for the bike’s intentions. Adding to the bike’s adaptability, it can rock a 200mm brake rotor.
As expected of a Trek bike, Bontrager handles most of the finishing kit with a set of Line Comp 30 wheels with Gunnison Pro XR tyres. I had my reservations about the latter, but I was quickly impressed with the lack of rolling resistance and abundance of grip.
The dropper, saddle, stem and grips also come from Bontrager, as does the handlebar. And while there’s nothing wrong with the build kit, it’s ripe for upgrades.
Trek Top Fuel 8 Gen 4 mountain bike – Performance
After swinging a leg over the Top Fuel Gen 4, it’s clear that there’s a cross-country twinkle forged within its alloy tubes. Its front end is low and the seat tube isn’t so steep that I’ve been bolt upright over the bike. With that, weight spread a little further over each wheel than steeper and slacker trail bikes that are typically more aggressively shaped and sprung.
The result is a bike that pulls no punches. It’s a keen climber that balances rider weight well while keeping handling lively and sharp. Its personality under pedalling is eager too, where it’s encouraged me to push equally as hard as racier XC bikes while providing a more comfortable and welcoming platform to pedal. Granted, if you’re looking for an out-and-out cross-country bike, the pedalling performance could be better but the Top Fuel isn’t a full-on XC bike.
When descending, the Top Fuel feels rather muted. For a short-travel bike, I certainly expected it to give more feedback and, generally, be more lively. But on the other hand, it’s supremely predictable. Nearly every time I’ve ridden the bike with my reviewing hat on, I’ve loaded it back into the van with the impression that it’s a sensible option, and in the grand scheme of things, that’s not a bad trait. It gives a bike with comparatively little travel figures and quite a lot of headroom in the capability department.
That all comes from a well-developed suspension kinematic and the option to pick from a more linear character to something more progressive is a powerful tool. It allows the rider to choose from a more forgiving rear end that’s happier to chew through its travel, which is ideal for those who like to blast through chunkier terrain. For anyone who would rather pop over that section of trail, the progressive setting makes a real difference as it boosts mid-stroke support for a firmer platform when pushing through heavier compressions. For the most part, I ran the bike in its progressive setting as I prefer a progressive feel but I’m a big fan of having the option.
Active Braking Pivot is a long-standing feature on nearly all of Trek’s full-suspension mountain bikes, and with good reason – it works. Found on this iteration of the Top Fuel, it’s clear that the suspension works independently of braking input. As such, there’s little brake jack, and grip is abundant when slowing, boosting traction and braking stability.
Despite the suspension kinematic not delivering the level of feedback I would expect of a bike like this, the Top Fuel claws back vital agility points through its geometry. The head angle sits towards the slacker end of the scale for a bike of this type, which opens up stability when the going gets quick but it’s not so slack that it sacrifices responsive handling. The geometry is very well balanced but because there’s a real hint of response, especially in the front end, the bike’s a party in the corners. The geometry can be raised and made steeper thanks to the Mino-Link, if that’s more your jam.
Although a 170mm travel dropper is rather generous, there’s plenty of space for even more travel and, on such a surprisingly capable bike, it’s a shame not to see Trek capitalise on that. While I understand it’s a down-country bike, it’s not as stiff-collared as race-ready XC rigs, so a longer post should be included out of the box. And to note, I sit at the lowest end of this large frame’s size recommendations at 5’10”. I have an inseam of 77cm and there’s plenty of room available.
The Rhythm-level fork is neither perfect nor the lightest. It works well and provides good damping, but it takes more attention to get it working at its best. Set up as usual, it tends to blow through its travel, which can get fairly unnerving on such a forward-weighted bike. Upping the sag to around 25 per cent improved the fork’s support, as did adding more volume spacers than usual. If I were to buy this bike for myself, the fork is the first and maybe the only thing I would upgrade, save for the dropper.
Trek Top Fuel 8 Gen 4 mountain bike – Verdict
Purpose-built down-country bikes with alloy frames from big brands are fairly few and far between. Specialized does it with the Epic 8 EVO bikes, but they share the same carbon frame as the XC thoroughbred but boast slightly burlier componentry. The Epic 8 EVO Comp will set you back £4,250 but that extra money gets you a carbon frame, a Fox 34 Performance fork and SRAM’s GX drivetrain. However, it doesn’t have the level of adjustability as the Top Fuel Gen 4.
Scott’s Spark 950 is fairly similar at £3,800. It’s a little fancier for the extra £300 with its cool integrated shock technology. It gets a SRAM GX drivetrain with an NX shifter and a RockShox Pike RL3 fork with 130mm of travel paired with a RockShox Deluxe Select shock that damps 120mm. It gets Shimano MT501 two-piston brakes, which don’t quite have the grunt that the Top Fuel 8’s does. The geometry is slightly more conservative, too, with a 65.8-degree head tube, a 76.4-degree effective seat tube, and a 470mm reach. It’s certainly a case of horses for courses, but my money would go on the Trek.
Unsurprisingly, Canyon’s Lux Trail CF 7 is a rather good package for the cash (here’s our review of the Lux Trail CFR). It has a carbon frame and posher components but leans heavier into the XC and marathon discipline. Notably, it doesn’t get the adjustability found on the Top Fuel, and, because of that, it stands alone in a space that many brands are attempting to fill.
The Trek Top Fuel 8 Gen 4 is one bike for many people. It might not be as engaging as other bikes in its category, and it would be good to see a slightly fancier fork but it excels in the versatility stakes. It packs predictability, so while it might not be particularly hair-raising, it begs to be pushed harder than its travel figures suggest.
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About the bike
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Alloy frame, Fox 34 Rhythm fork, Fox DPS Performance shock, Shimano SLX/XT drivetrain, Bontrager everything else.
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