Wil reviews the 2025 Trek Top Fuel in XC mode

For the past six months I’ve been riding the absolute pants off a 2025 Trek Top Fuel 9.8 GX AXS test bike. Many of you will have already read that review and will know how impressed I’ve been with the on-trail performance of the latest 4th generation Top Fuel and its shape-shifting versatility. It was a real highlight of the year, and it’s up there as one of the best mountain bikes I’ve personally ridden.

While the Top Fuel started out in its stock configuration with 130/120mm of travel, it wasn’t long before I had it in the workshop so I could mess around with the in-built suspension and geometry adjustments. Thanks to the nifty 4-position Mino Link and stroke-adaptable shock, I was able to add 10mm of Trek-approved travel at each end. Along with a few other spec changes, the Top Fuel morphed into an awesomely capable but still light and sporty 140/130mm travel trail bike. In fact, it rode so well that I genuinely think Trek should offer that setup as a stock bike.

More recently I’ve veered in the other direction. This has involved reducing the travel to 120mm front and rear while fitting a lighter build kit to tune it up for racing duties. The Trek Factory Race team utilised a similar setup at the Mont-Sainte-Anne round of the World Cup series last year, and since then I’ve had a lot of folks ask me to test it out.

Well wonder no more, because here I’ll be diving into the details behind the current build and discussing what the Top Fuel is like to ride in XC mode as well as how it compares to the short travel Supercaliber.

Stripping and rebuilding the Trek Top Fuel

Before building up the Trek Top Fuel as an XC race bike I decided to strip it down to the bare frame. This was done for a couple of reasons. I was keen to get a closer inspection of all the small parts, pivot bearings and cable routing to see how everything was travelling after six months of solid riding. I was also curious to see what the frame weighed.

Hitched up to the Flow Scales Of Broken Dreams™, our Medium size Trek Top Fuel C frame clocks in at 2.6kg including the RockShox Deluxe RCT shock. That’s exactly as Trek claims, which is nice to see.

As I’ve discussed previously, it’s not the lightest option in this travel bracket, but it’s also not the heaviest. To put things into perspective a Pivot Mach 4 SL frame and shock is claimed to weigh 2.08kg, the Specialized Epic 8 EVO is 2.21kg, a Santa Cruz Tallboy is 2.83kg, and a Yeti SB120 is 3.02kg.

120mm travel RockShox SID

Out of the box the Trek Top Fuel 9.8 GX AXS comes fitted with a 130mm travel RockShox Pike. The frame is rated for use with 120-140mm of travel however, and fitting a different air spring is all that’s required to shorten or lengthen the Pike as needed.

Conveniently for me, I already had a 120mm travel RockShox SID on hand that I’ll be pitching against the latest Fox 34 Step-Cast as part of an upcoming head-to-head review. The XC-ified Top Fuel would be an ideal test platform, so on went the SID.

While the SID also uses 35mm upper tubes like the Pike, it is a significantly lighter fork thanks to its pared-back chassis and Charger Race Day 2 damper. The result is a hefty weight reduction of almost 400g compared to the Pike (1,516g vs 1,908g). That’s a lot!

How does that impact the geometry?

The shorter 120mm travel SID drops down the front end, steepening the angles and lowering the BB. However, where the geometry ends up depends on whether you run the Mino Link in the High or Low position. Initially I started out in Low but found the Top Fuel to be a little lazy on tighter and flatter XC trails. Flipping the chip into the High position lifted the BB back up and sharpened the steering nicely, providing a handling package that felt more appropriate for the intended application.

With the 120mm travel fork and the Mino Link in the High position, the Top Fuel’s BB sits at 339mm off the floor and the head angle clocks in at 66.1° according to my measurements in the workshop. The seat angle comes in at around 78.3° for my saddle height, which is very steep for an XC bike. In fact, it’ll potentially be too steep for those who ride both XC and road and are looking to mirror the saddle position between their race bikes. You’d need to push the saddle all the way back on the rails to slacken it out, or you could look at getting an offset clamp adapter like those from Swiss brand FAIR Bicycle. Personally, I haven’t had any such issues and have found the seated position easy to adapt to.

It’s worth noting that shortening the fork travel also has the effect of extending the reach a smidge, which combined with the lower stack height results in a more aggressive and forward-biased riding position. Thanks to the short head tube you can get the bars down quite low, as exhibited by the TFR athletes during the Mont-Sainte-Anne World Cup.

What about suspension setup?

In preparation for the rebuild I had attempted to seek out a SIDLuxe shock to match the fork, partly for weight savings but also to try and emulate the setup of the TFR race bikes. Unfortunately it was going to be difficult to source a SIDLuxe in the relatively long 185x50mm size required for the Top Fuel, since it’s not a stock item in Australia. I decided to stick with the Deluxe shock instead, but had the 55mm stroke reduced to 50mm in order to bring rear travel back down to 120mm.

The first couple of rides were spent messing around with shock pressures as well as the Mino Link’s fore/aft position. This adjustment tweaks the leverage rate between 14% and 19% progression, which has a pretty big impact on the suspension behaviour. With a stronger preference for efficiency I settled on the more linear setting with 27% shock sag. I also adjusted the low-speed compression dial from the softer ‘-‘ setting to the neutral position.

The cumulative effect of all these changes is considerably greater pedalling stability overall as well as more support through the mid-stroke. Pedalling efficiency can be elevated further by switching the low-speed compression dial into the ‘+’ setting, which is something I would do for racing on smoother courses.

Any other spec changes?

Alongside the suspension and geometry changes, I’ve made a few component upgrades to help round out the Top Fuel’s XC vibe.

That includes the incredibly light and smooth-riding Zipp 1Zero HiTop wheelset that is currently adorned with 2.4in wide Maxxis Rekon Race tyres. I also fitted my SRAM XX SL Transmission, which was dead easy thanks to the wireless shifting and threaded BB.

Level Ultimate brakes provide the stopping power, and I’ve elected to run the lighter Centerline X rotors along with organic pads to suit the dry and dusty summer conditions. Prior to hitting the trails I spent some time lubricating and massaging the calliper pistons, as I did with the Level Bronze brakes that originally came on the Top Fuel. This improves the sharpness of the bite point and I find it helps with overall power too.

I refitted the lightweight Bontrager RSL one-piece carbon cockpit, though this time around I slipped on a set of Ergon GA3 grips. These feature a mini-wing profile that disperses your weight over a broader surface area and provides greater vibration damping, making for a very comfortable grip. To match, I bolted on an Ergon SR Pro Carbon saddle, partly for comfort but also to help shed a few more grams.

Trek Top Fuel weight

Confirmed weight for the custom-built Trek Top Fuel in this 120mm travel XC configuration is 11.27kg without pedals. That’s nearly a kilo lighter than the stock build, with much of the reduction due to the wheels, tyres and fork.

Real weight weenies will spot opportunities for further savings. You could drop close to 100g with a Fox 34 Step-Cast, and Shimano’s XTR groupset is a bit lighter than the SRAM XX SL Transmission.

Silicone foam grips would shave a few more grams and so too would a shorter travel dropper post. It’s worth pointing out that the 170mm travel Bontrager Line Dropper is actually pretty light at 603g given its girthy 34.9mm diameter. An equivalent 180mm travel OneUp V3 Dropper is lighter at a claimed 535g, but a RockShox Reverb AXS is way heavier at 792g. Alternatively, you could fit a shim and a slimmer diameter post such as the Fox Transfer SL for the lightest possible setup.

On the trail

With all of the changes to the Trek Top Fuel, the change in its riding persona has been considerable. The lighter wheels and semi-slick tyres make a huge difference to the overall rolling speed, and these would be my first recommended upgrade for anyone who’s looking to add a bit of pep to their Top Fuel.

The more aggressive riding position delivers a renewed sense of urgency, and the firmer shock setup encourages you to push just that bit harder on the pedals. Rapid acceleration is your reward, something that is particularly invigorating when heading uphill. The Top Fuel was already an amazing technical climber in its stock configuration, but the reduced weight and lower front end of the XC setup only accentuates its abilities on the ups. It’s more responsive at the pedals and less effort is required to maintain your momentum when negotiating chunky steps.

I continue to be impressed at how neutral the Top Fuel is to chain torque. The back end does well to resist bobbing unless you’re particularly messy with your pedal stroke. The shock only moves when you need it to, and that helps to deliver bags of usable traction on scrabbly trails. There’s excellent sensitivity from the ABP suspension design and trunnion bearing mount, keeping the rear tyre driving assertively into the dirt even when you’re hammering out of the saddle.

In the saddle, the steep seat angle provides a stable and centralised riding position. As mentioned earlier, some folks might find it to be a little too forward, but I’ve gotten along with it well even on longer 3+ hour rides.

It still rips, within reason

Compared to the heavier long travel setup, the handling isn’t as foolproof on the descents. Most of this is due to the shallow tread profile of the Rekon Race tyres, which as you’d expect don’t provide nearly as much grip in loose terrain. And while the SID is an excellent fork, it’s not quite as sure-footed as the Pike, especially when combined with the steeper head angle.

That being said, the XC-flavoured Top Fuel still feels beautifully smooth and grippy. It hugs the ground closely, with a compliant ride quality that helps to maintain contact between the tyres and trail. This differs to a lot of overly-stiff carbon XC race bikes that suffer from being pinged around on rocky terrain. In comparison the Top Fuel delivers a more refined ride feel thanks to its compliant chassis and active suspension. It’s neutral under braking and there is very little feedback through the drivetrain, allowing you to pedal through choppy sections without being jerked around. Indeed the rougher and more technical the traverse, the better the Top Fuel gets.

The RockShox suspension is also impressively plush on the descents, with great sensitivity and control front to back. It is easier to bottom out the Deluxe shock with the Mino Link in the linear setting, but that’s only the case if you’re riding heavy handed. On typical XC terrain where you’re managing lightweight race tyres, it feels spot on. And if you’re just trail riding for fun, you only need a 6mm hex key to adjust the Mino Link and a shock pump to reset sag if you’re looking for a plusher and more rampy feel from the back end.

Any compromises?

Although the Trek Top Fuel delivers good efficiency, it doesn’t have the sane throw-the-hammer-down response of some of the raciest XC bikes out there.

Part of this will boil down to your chosen chainring size. I’m currently using a 32T chainring, which suits me fine in terms of gearing while also offering a nice and neutral level of anti-squat. However, for big-legged riders putting down maximum watts, it’s worth noting that pedal efficiency will suffer if you decide to fit a larger 34T chainring. This will reduce the amount of anti-squat and lead to more pedal bob.

Flipping the shock’s low-speed compression adjuster into the firmer ‘+’ setting does help to stabilise the back end on smoother courses, but it’s not the sort of thing that you’d fiddle around with mid-race. There’s also no option to fit a remote lockout on the Top Fuel, and that will make it a non-starter for some. Of course you could get around that by fitting a RockShox Flight Attendant system like the TFR team, which for me would be the ultimate racing setup.

On the topic of XC race bikes, as mentioned earlier the Top Fuel isn’t the lightest option out there. For a point of reference, these are the four frames that I’ve been able to weigh myself in the workshop;

• Giant Anthem – 1,807g (w/Fox Float DPS)
• Canyon Lux World Cup CFR – 1,941g (w/Fox Float DPS)
• Specialized S-Works Epic 8 – 1,950g (w/RockShox SIDLuxe)
• Trek Top Fuel – 2,600g (w/RockShox Deluxe)

Of course the Top Fuel differs to the other three in that it features a proper multi-link suspension platform rather than a lighter single pivot flex-stay design. It also has the capability of being configured as a 140/130mm travel trail bike, which isn’t possible with the others. The in-frame storage, guided cable routing and Mino Link all add weight too.

Whether that versatility and everyday usability is worth the added heft is entirely up to you. Personally, I’m totally sold on the idea of owning a Top Fuel along with a race wheelset and a 120mm fork that would allow me to switch between setups and effectively have two-bikes-in-one.

Trek Top Fuel vs Supercaliber

With the Trek Top Fuel in this 120mm travel XC configuration, the current gap to the Supercaliber does narrow somewhat, and that may have a few prospective buyers weighing up which way they should go.

If you’re not familiar with it, the Supercaliber is Trek’s dedicated XC race bike that features a 100-110mm travel fork and 80mm of rear travel. Its unique carbon chassis is built around the IsoStrut suspension design with a one-piece swingarm and incredibly thin flex-stays. The integrated shock makes for an insanely clean profile that provides room for two bottles inside the front triangle, a feature that will be very appealing for long distance XC riding and marathon racing.

It also helps to get the weight down. Trek claims the Supercaliber SLR frame frame and shock weighs just 1,950g, which gives it a healthy 650g advantage over the Top Fuel.

Furthermore, serious racers will no doubt give a thumbs up to the dual remote lockout on the Supercaliber. It doesn’t really need it on the trail however, as the 80mm of travel and high anti-squat ensures the back end responds with furious efficiency under pedalling inputs. It makes the Supercaliber an incredibly fast race bike that rockets up very climb like its life depends on it.

The downside is that you will find yourself getting knocked around a lot more on rockier terrain. In fact, I’ve actually found the Top Fuel to be a superior technical climber as it delivers more usable grip for clearing tricky features. It’s better at maintaining momentum when pedalling through the chop, offering a smoother and calmer ride quality all-round. It’s also significantly more planted on the descents, which for a lot of folks will make it more fun to ride.

Ultimately it’ll be the terrain and application that dictates which of these two bikes is the most suitable for your needs.

Highly skilled XC racers who value efficiency and low weight above comfort are going to elect for the Supercaliber every day of the week. It’s light, efficient and incredibly quick to ride along flowy undulating singletrack. However, it’s focus is quite a bit narrower than the Top Fuel.

If you enjoy tackling rowdier terrain and you value the in-built geometry and suspension adaptability, the Top Fuel is easily the more versatile choice. As someone who isn’t a national-level XC racer, it’s the bike I’d go for, hands down.

Long-term durability

Following the past six months of testing, Trek Top Fuel has been holding up pretty well.

The downtube hatch remains snug and rattle-free and all the pivot bearings are still rolling smooth with no play or noise present. The same goes for the SRAM DUB BB. And while the Bontrager Line Dropper isn’t the slickest or fastest-returning post out there, it’s remained solid throughout testing with only a bit of Slickoleum required every now and then to keep it sliding smoothly.

Unfortunately the paint job on our test bike hasn’t been the most durable, with a number of chips having appeared around the seat and chainstays. Some of the paint has also flecked off around the lower shock mount, though having spoken with our contact at Trek US it sounds like this could be a defect from the factory, which if true would likely be covered under warranty for a consumer.

While we’re down at that part of the frame, weirdly there’s no drainage hole below the shock mount. This means that every time I wash the bike it leaves a pool of water and muck behind. It’s not a big deal for our dry climate, but those who frequently ride in muddy conditions will need to pay extra attention when cleaning.

The dusty summer conditions have led to some creaking from the headset, which was easy to resolve with a quick clean and re-grease. On that note, I’m thrilled that Trek decided to avoid sending the cables through the headset. This was especially welcome when I rebuilt the frame, with the internal guide tubes making it easy to route the rear brake hose and dropper post cable.

The moulded-in tubing does add some weight, and I’ve seen other brands quote 100g or more for the extra carbon and plastic required for those hidden tunnels. I for one would be happy to forgo the guided cabling and downtube storage if it meant Trek was able to get the Top Fuel frame weight closer to the 2kg mark, but I suspect I might be in the minority there.

One other downside of the internal guide tubes is the fact that the paths are predetermined. In the case of the Top Fuel it means you can only run the rear brake hose around the head tube if you’re connecting it to the right-hand lever. It’s a small quibble, but is still annoying for Aussies, Kiwis and Brits who prefer running their rear brake on the left.

Flow’s Verdict

As you can probably tell, my love affair with the Gen 4 Trek Top Fuel continues to grow. This is a fantastic bike in its stock configuration, though I’ve had even more fun testing it out at both ends of its travel spectrum.

The 4-position Mino Link is no gimmick, adding genuine versatility to this frame that allows it shape-shift to your preferences. It does a convincing job too, with few compromises when switching between the long and short travel setups.

In the 120mm XC mode, the Top Fuel offers a smooth and refined ride quality that stands apart from a lot of other carbon race bikes on the market. Those after the lightest and most efficient option will still want to look elsewhere. But if you don’t need to carry two bottles and you value the in-built adaptability of the Top Fuel chassis, this is for sure one of the best riding XC bikes out there.

Wil’s custom 2025 Trek Top Fuel

• Frame | OCLV Carbon, ABP Suspension Design, 120mm Travel
• Fork | RockShox SID Ultimate, Charger Race Day 2 Damper, 120mm Travel
• Shock | RockShox Deluxe Ultimate, RCT Damper, 185x50mm
• Wheels | Zipp 1Zero HiTop, Carbon Rims, 30mm Inner Width
• Tyres | Maxxis Rekon Race EXO MaxxSpeed 2.4in Front & Rear
• Drivetrain | SRAM XX SL Eagle AXS Transmission 1×12 w/32T Crankset & 10-52T Cassette
• Brakes | SRAM Level Ultimate 4-Piston w/180mm CenterLine X Rotors & Organic Pads
• Bar | Bontrager RSL Integrated, Carbon, 27.5mm Rise, 760mm Width
• Stem | Bontrager RSL Integrated, Carbon, 45mm Length
• Grips | Ergon GA3, Small Diameter
• Seatpost | Bontrager Line Dropper, 34.9mm Diameter, 170mm Travel
• Saddle | Ergon SR Pro Carbon Saddle, S/M Width
• Actual Weight | 11.27kg (Size M)

Watch our original review of the 2025 Trek Top Fuel here:

ABOUT THE REVIEWER - Wil Barrett

Hometown

Bendigo, Victoria

Height

175cm

Weight65kg