Trek Top Fuel 9.9 XO AXS Gen 4 review
A versatile, light trail bike built for everyday speed
Words: James Rennie
Images: Justin Henehan
Let’s set the scene. I’ve been riding mountain bikes for the better part of 25 years and have taken the classic trajectory for someone of my age. I started out hucking jumps and then got into downhill racing before becoming old enough to realise that was all a bit scary. Then came enduro, which kept the racing dream alive. Now I’d firmly consider myself an “XC guy” and have to admit I own at least three sets of bib shorts (13-year-old me would not be pleased).
Why is this relevant? Well, the Trek Top Fuel has trod a similar path, albeit in reverse. Starting life in 2004, the Top Fuel spent its first 15 years as an all-out cross country race machine, plying its trade on the world cup circuit until 2019, when the Supercaliber broke cover beneath the Trek Factory racing team, basically making the Top Fuel redundant.
The Top Fuel, fresh out of a job, had to reinvent itself. So, in 2022, it was revised to be a 120mm short-travel trail bike (“downcountry” for those willing to use that term). Things got slacker, longer and more capable, and by all accounts this earlier edition was popular among those keen on a snappy allrounder.
This latest model follows in the footsteps of the previous Top Fuel and fits in nicely with my current phase in the bike-riding lifecycle.
Check out my First Look article for some early impressions.
Details
While the intent of the Top Fuel may have changed over the years, the silhouette hasn’t. I don’t know anyone who would say this isn’t a good-looking bike. The finish is high quality and its clean, straight lines and matte-black paint job with the blood-red decal make it an understated looker.
The Knockblock of the previous model is gone, and, while the spec is largely wireless, you can still run a mechanical drivetrain via internal tube routing.
Other features include internal frame storage which has room for a tube, tools, CO2 and maybe a small jacket if you press hard. It fits a 70cc OneUp pump also, just don’t expect to get it out in a hurry.
One feature that wasn’t on the last model is the four-way adjustable geometry thing which adjusts both geometry and progression and makes meaningful change between the modes.
At 176cm, I was at the top end of the sizing chart for the medium I tested, although I tend to prefer a smaller fit as a result of stretching myself onto bikes I couldn’t corner over the past few years.
Components
As far as build goes, the Top Fuel 9.9 X0 AXS Gen 4 leaves little to be desired. Starting with suspension, the RockShox Pike Ultimate with the latest Charger 3.1 damper provides a controlled feel up front. The small elastomer Buttercups make a noticeable difference, muting trail chatter nicely, really coming into their own on the 130mm travel fork, a travel bracket that requires a firmer set up.
Sram’s SRAM X0 Eagle AXS T-type Transmission handles shifting duties and lives up to the hype when it comes to shifting quality. You don’t realise how much of a difference it makes until you go back to regular drivetrain and clang your way through the gears.
The only annoyance I had with the derailleur was its lack of a hard B tension stop. There’s a lot going on around the axle pivot with Trek’s Active Braking Pivot (APV) design and I found that after a few rides the derailleur rotated forwards leading to some very annoying gear slippage. I torqued the derailleur bolt up with the long bar (real tight) and it thankfully didn’t slip again.
The Top Fuel is a full wireless affair, which I’m a fan of. I have regular Sram AXS on my personal XC rig and wouldn’t go back, especially for a bike that does a lot of shifting. I also really enjoyed the Reverb AXS seat post’s super easy activation and flawless return.
The Bontrager saddle was relatively comfortable, and its shorter nose stayed out of the way. There are more comfortable saddles out there but its more than passable for a stock item.
The only part I really didn’t like were Sram’s Level Silver Stealth brakes. It wasn’t that I wanted beefier brakes, although they wouldn’t have been out of place here. The lack of pad contact adjustment on the Level stoppers meant I just couldn’t get the throw short enough at my preferred lever reach.
Climbing
The Top Fuel’s climbing position was comfortable straight away, with no particular angle or measurement giving the sensation of being out of the ordinary.
I was immediately surprised at how efficient the bike was under power. Having predominantly ridden a cross-country race bike for the past couple of years, I expected the Top Fuel to be a little docile, but it transferred pedal input to the ground well. I very rarely used the rear shock lockout, even on the road.
The Top Fuel may not have been as snappy up the hills as a full-on race bike, but it certainly wasn’t far off. On my first ride I cleaned a very steep, loose climb that was right on the limit of my abilities. I think the Trek’s surefootedness is partly down to the seat angle and grippy Bontrager tyres, but also a product of the bike standing tall under power.
I also set climbing personal bests aboard the Top Fuel on a couple of my local singletrack climbs, a testament to its climbing abilities.
Descending
Descending performance is what sets bikes like the Top Fuel apart from the pure XC race weapons. Downhill is all about confidence—you want the bike to do what’s asked, rather than having to think about what it wants.
The Top Fuel didn’t have to be asked twice and provided a very predictable platform allowing the rider to push. The APV suspension stayed high in its travel which led to a very fast-feeling bike. It especially excelled on lower-grade technical trails, where it chattered nicely over the terrain. It was composed under braking too, the rear suspension remaining active, allowing the rider to put the wheels where needed while providing plenty of grip.
The frame felt laterally stiff and responded well to rider input when asking it to change direction. This was especially noticeable when holding off-camber sections where the bike stayed planted.
The majority of the tracks I rode on the Top Fuel were largely flowing singletrack with a few jumps or technical sections. I did venture down some harder, steeper trails and the Top Fuel performed admirably. It’s no enduro bike, but it holds its own, albeit at a slower pace.
There’s scope to fit a longer-travel fork and beefier tyres to make the Top Fuel a more capable descender. You could do a lot worse than the Top Fuel when lining up for your local enduro, especially in the North Island.
“You could do a lot worse than the Top Fuel when lining up for your local enduro.”
Who’s it for?
My kids have a book where the protagonist, George, builds a makeshift house out of a cardboard box. George then goes about keeping the other kids out for a range of reasons until, eventually, he finds himself outside, where he realises things are more fun when we share things with others. It ends with the punch line “this house is for everyone”. The Top Fuel, just like that cardboard box, is a bike for everyone.
In my first look, I described the Top Fuel as a versatile bike built for everyday speed and a nimble trail bike that wants to go fast without compromising on descending ability or comfort. The past weeks of rides have only confirmed this.
Whether you’re up for a couple of quick-fire laps and your local, an all-day exploration of a new trail network, or a marathon XC race like the Whaka100, this bike has you covered. Sure, it may swing closer to the XC crowd than the enduro “winch-and-plummet” crew, but it can still hold its own when things get steep.
Trek Top Fuel 9.9 XO AXS Gen 4 RRP NZ$16,499