Trek Top Fuel 9.9 X01 2021 in review - From XC-racer to our trail bike group test

“The Top Fuel 9.9 flies through singletrack and rips descents, but it really shines when pushed to its full potential during gruelling endurance races.” That’s what Trek say about the Top Fuel 9.9 X01, but how did it fare against its bigger brother, the Fuel EX?

For an overview of the test fleet head to the group test: The best mountainbike of 2021 – 22 models in review

**Trek** Top Fuel 9.9 X01 | 120/115 mm (f/r)
11.54 kg (size L) | € 8,999 | Manufacturer-website

115 mm rear travel, 11.5 kg and a lightweight spec. At first glance, the specs of the Top Fuel 9.9 look impressive, but how much fun will you have onboard the carbon rocket from Wisconsin? Just like its bigger EX sibling, the Top Fuel features Trek’s ABP rear linkage, albeit with 15 mm less travel and a standard FOX DPS Factory shock without Trek’s proprietary Thru Shaft technology. On the handlebars, a dual remote lockout controls a 120 mm FOX 34 fork and, together with the brake levers, shifters and dropper remote, makes for a rather crowded and untidy cockpit. Trek include their proprietary Knock Block in the headset, which limits the steering angle and prevents the fork from damaging the frame and cables from ripping in the event of a crash. On the trail, the system doesn’t affect the handling in any way. A large TPU plate on the downtube protects the frame against stray rocks, while a reasonably sized and well-positioned chainstay protector prevents chain slap and paint chips. Unlike other Trek models, the Top Fuel doesn’t feature a storage compartment integrated into the down tube, forcing riders to carry their trail essentials in a backpack or hip pack instead.

The spec of the Trek Top Fuel 9.9 X01 – Lightweight components for a true high flyer

The € 8,999 Trek Top Fuel 9.9 X01 is specced to ensure a lightweight construction and top efficiency. At 11.5 kg, it’s the lightest bike in our big MTB group test. However, Trek couldn’t achieve this without compromising on trail performance. While the FOX 34 Factory Step-Cast fork, which with its lighter chassis is significantly lighter than a conventional 34, unfortunately, it’s only suitable for particularly light riders. Fast and heavy riders will notice considerable flex in hard corners and compressions, which affects the handling of the bike and dents your confidence. Moreover, hard consecutive hits push the FIT4 damper to its limit. For the tires, Trek spec their own super light Bontrager XR3 Team Issue tires with a puncture-prone casing and shallow tread. While this setup reduces weight and rolling resistance, it generates poor traction in corners and under braking and could potentially result in irreversible damage to the Bontrager Line Elite 30 carbon rims. We recommend upgrading the tires the moment you pick up your bike from the store.

The Trek Top Fuel 9.9 X01 is great fun on fast, sporty laps and very comfortable on long tours, where it convinces with a comfortable pedalling position.

For better downhill performance, you should run a robust but fast-rolling semi-slick tire at the rear, paired with a grippy front tire with a more aggressive profile. Braking is taken care of by SRAM G2 RSC brakes with tool-free lever reach and bite point adjustments. The brakes run on small 180/160 mm rotors and tend to overheat easily, requiring strong fingers on long descents. The drivetrain consists of a high-quality SRAM X01 12-speed rear derailleur with a matching shifter but a cheaper (and heavier) SRAM GX 10–52 t cassette. The rest of the spec is made up of Trek’s in-house components, including the 750 mm Bontrager Line Pro carbon handlebars and 170 mm Line dropper post. The remote is combined with the lockout for the fork and shock – if you’re not careful you’ll activate the wrong lever!

**Hot, hotter, 160 mm**
The rear brake rotor is far too small and tends to overheat quickly in combination with the weak SRAM G2 RSC brakes. Alternatively, you could fit a 180 mm rotor at the rear – a bigger one won’t even fit.

**Even Beethoven would have got lost**
There are more remotes and levers than keys on a piano. On the trail, this can quickly lead to mistakes and makes you feel like you’re playing the Fifth Symphony.

Trek Top Fuel 9.9 X01

€ 8,999

Specifications

Fork FOX 34 FIT 4 120 mm
Rear Shock FOX DPS Factory 115 mm
Seatpost Bontrager Line Elite 170 mm
Brakes SRAM G2 RSC 180/160 mm
Drivetrain SRAM XO1 Eagle 1x12
Stem Bontrager Kovee Pro (35) 70 mm
Handlebar Bontrager Line Pro OCVL 750 mm
Wheelset Bontrager Line Elite 30 29"
Tires Bontrager XR3 Team Issue 2.4

Technical Data

Size S M M/L L XL XXL
Weight 11.54 kg

**Error 404 – Grip not found**
The Bontrager XR3 Team Issue tires lack grip and puncture protection. Ironically, the “Issue” suffix is quite fitting.

**Control tower**
Unlike GRAN FONDO editor-in-chief Ben, who rode the bike in this setup, we recommend installing the many factory-supplied spacers under the stem for a more comfortable riding position and more control downhill.

**Lightweight construction**
While the lightweight chassis of the standard FOX 34 FIT4 Step-Cast fork helps save weight, the lack of lateral stiffness and inferior FIT4 damper makes for poor trail performance.

The geometry of the Trek Top Fuel 9.9 X01

The Trek Top Fuel is available in six sizes, from S to XXL, which caters to riders between 153 cm to 203 cm tall. Typical for Trek, there’s also an intermediate ML size, which allows many riders to choose between at least two suitable frame sizes. The smallest S size has a modified frame shape with a slight kink in the top tube. A flip-chip in the seat stay allows you to switch between the high and low settings and adapt the geometry of the bike to your needs and preferences. Needless to say, we rode the bike mostly in the low setting, which drops the bottom bracket by 7 mm, slackens the head angle by 0.5 ° and shortens the reach by 5 mm. The size L in the low setting has a reach and seat tube of 470 mm. The reach is in the midfield of our test fleet while the seat tube is on the long side. Despite the low top tube, this restricts the insertion depth of the dropper and thus your freedom of movement, as well as making it hard to upsize if you’re between sizes – what a shame! At 603 mm, the stack height is the lowest in the entire test field. Trek compensate for this by stacking an odd-looking spacer tower under the stem and increasing the handlebar height.

Size	S	M	M/L	L	XL	XXL
Seat tube	394 mm	419 mm	445 mm	470 mm	521 mm	570 mm
Top tube	564 mm	599 mm	615 mm	632 mm	651 mm	677 mm
Head tube	90 mm	90 mm	90 mm	100 mm	110 mm	120 mm
Head angle	67.5°	67.5°	67.5°	67.5°	67.5°	67.5°
Seat angle	75.0°	75.0°	75.0°	75.0°	75.0°	75.0°
Chainstays	435 mm	435 mm	435 mm	435 mm	435 mm	435 mm
BB Drop	36 mm	36 mm	36 mm	36 mm	36 mm	36 mm
Wheelbase	1,117 mm	1,152 mm	1,168 mm	1,186 mm	1,207 mm	1,234mm
Reach	405 mm	440 mm	456 mm	470 mm	487 mm	510 mm
Stack	594 mm	594 mm	594 mm	603 mm	612 mm	622 mm

**Helmet** POC Kortal Race MIPS | **Glasses** POC Crave Clarity
**Jacket** GRAN FONDO Hemd | **Pants** GORE Vent

Can the Trek Top Fuel 9.9 X01 with its XC-racing DNA convince on the trail?

Uphill, the Top Fuel lives up to its name. The bike is damn fast and the neutral suspension makes it a great option for long rides too. On flat terrain, it convinces with a comfortable pedalling position, which is suitable for both fast, sporty laps and long rides. The Top Fuel accelerates fiercely and is extremely efficient even with the shock fully open. While you’d expect the active rear end to provide plenty of traction on technical uphills, the low-profile tread of the tire causes the rear wheel to spin out of control. On very steep climbs, the bike forces you to actively lean forward, while the slack seat tube angle positions you far back over the rear wheel, causing the front to lift off the ground. Nevertheless, the Top Fuel overtakes its direct competitor, the Merida NINETY-SIX 8000, without breaking a sweat – in all situations. On fire roads, the climb switch ensures extremely stiff suspension, ensuring excellent acceleration together with the lightweight wheelset. Even strong climbers like the YT Izzo and Yeti SB115 struggle to keep up with the American carbon rocket.

If you’re not too fussed about downhill performance, the Top Fuel is a great option for long rides and lots of fun on easy, flowing singletracks – provided you’re running the right set of tires. Nevertheless, its bigger brother, the Fuel EX, is the better all-rounder.

Tuning-tips: more robust tires with more aggressive tread | 180 mm brake rotor at the rear

Downhill, the Top Fuel loses its advantage over the competition, suffering from a significant lack of braking traction and cornering grip – not least because of its tires. As a result, it’s hard to unlock the full potential of the bike without pushing your own limits. While the tall and stiff cockpit conveys huge amounts of confidence, the stiff suspension passes on vibrations and hits to the rider almost unfiltered, making for vague and undefined handling and causing fatigue and arm pump. The Top Fuel shows its strengths on flowing singletracks with flat sections, where it’s intuitive and easy to ride. On faster and rougher trails with big steps, it quickly reaches its limits, falling behind bikes like the Yeti SB115. On very technical descents it also has to admit defeat to its bigger sibling, the Trek Fuel EX. On top of that, the Fuel EX is only slightly slower uphill but offers more reserves downhill and suits a wider range of applications.

Riding Characteristics

Uphill

sluggish
efficient

Agility

cumbersome
playful

Stability

nervous
confident

Handling

demanding
balanced

Suspension

harsh
plush

Fun Factor

planted
poppy

Value for money

terrible
very good

Intended Use

XC

Trail

Enduro

Downhill

Conclusion

In a direct comparison, the Top Fuel 9.9 X01 has to admit defeat to the Fuel EX. While it has a small advantage uphill, downhill it can’t keep up with the smooth handling and superb suspension performance of its bigger sibling. All in all, the Fuel EX suits a much wider range of application and delivers far more riding fun – even in the significantly cheaper 9.8 GX version we tested. If you’re not too fussed about downhill performance, the Top Fuel is a great option for long rides and still great fun on easy, flowing singletracks – provided you’re running the right set of tires.

Tops

accelerates willingly
easy, intuitive handling

Flops

Bontrager XR3 tires generate poor traction
remote cluster in the cockpit area is confusing
odd-looking spacer tower
no Trek storage compartment
very few advantages over the Fuel EX, which suits a much wider range of applications

Find more information here: trekbikes.com

The testfield

Get an overview of the grouptest here: The best mountainbike of 2021 – 22 models in review

This scale indicates how efficiently the bike climbs. It refers to both simple and technical climbs. Along with the suspension, the riding position and the weight of the bike all play a crucial role.↩
How does the bike ride and descend? How spritely is the bike, how agile is it through corners, how much fun is it in tight sections and how quickly can it change direction?↩
Is the bike stable at high speeds? Is it easy to stay in control in demanding terrain? How composed is it on rough trails? Stability is a combination of balanced geometry, good suspension and the right spec.↩
This is all about how balanced the bike is and particularly about how well it corners. Balanced bikes require little physical effort from the rider and are very predictable. If a bike is unbalanced, the rider has to work hard to weight the front wheel to generate enough grip. However, experienced riders can have a lot of fun even with unbalanced bikes.↩
How sensitive is the suspension over small bumps? Can it absorb hard impacts and does it soak up repeated hits? Plush suspension not only provides comfort and makes a bike more capable, but it also generates traction. The rating includes the fork and the rear suspension.↩
This aspect mainly comes down to the suspension. How much pop does it have, does it suck up the rider’s input or is it supportive, and how agile and direct is the bike?↩
We don’t calculate value for money in an excel spreadsheet or based on how high-end a bike is specced. We are more concerned with how a bike performs on the trail and how the bike benefits the rider. What good are the best components if the bike doesn’t perform well on the trail? Expensive bikes with a lower-end spec can offer very good value for money – provided they excel where it matters. Just as supposedly cheap bikes with good components can get a bad rating if they don’t deliver on the trail.↩
No, it’s not about racing, it’s about efficiency. Fast, fleet-footed and efficient – those who want to speed along flowy singletrack and gravel roads need a defined and spritely bike that accelerates with ease and efficiency. Nevertheless, reliable components are important too. We interpret XC more like the Americans do: big back-country rides instead of a marathon or XC World Cup with the ultimate in lightweight construction! Uphill-downhill ratio: 80:30 (not everything has to be 100%!)↩
...also known as mountain biking. Classic singletrack with roots, rocks and ledges – sometimes flowy, sometimes rough. For this, you need a bike with good all-round qualities, whether climbing or descending. Uphill-downhill ratio: 50:50↩
Even more extreme and challenging compared to Trail riding, riddled with every kind of obstacle: jumps, gaps, nasty rock gardens, ruts and roots. For this, you need (race)proven equipment that forgives mistakes and wouldn’t look out of place on a stage of the Enduro World Series. Climbing is just a means to an end. Uphill-downhill ratio: 30:70↩
Strictly speaking, a 200 mm travel downhill bike is the best choice for merciless tracks with big jumps, drops and the roughest terrain. Those would be the black or double-black-diamond tracks in a bike park. But as some of the EWS pros (including Sam Hill) have proven, it’s the riding skills and not the bike that define what you can ride with it. Climbing? On foot or with a shuttle, please! Uphill-downhill ratio: 10:90↩
You can find more info about our rating system in this article: Click here! ↩

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Words: Peter Walker Photos: various

Trek Top Fuel 9.9 X01 2021 in review – From XC-racer to our trail bike group test