Trek Top Fuel 9.8 GX Review | Lightweight and Cable Trail Bike

With the guesswork that befits a global bike brand, Trek have been adjusting their bikes on a regular basis. 2022 saw the new Fuel EX succeed the Fuel EX-e, and the Supercaliber was recently updated ahead of the Paris Olympics. In July, Trek released the fourth generation of the current Top Fuel. The Top Fuel returned in 2015 as a 100mm XC 29er, and that's the last iteration of the Top Fuel I rode. Recent additions have seen the bike enter the light trail category, but some riders feel it was lost with the last generation Fuel EX. The new 2025 Top Fuel looks very similar on paper and in silhouette, and some have suggested that maybe the Top Fuel is now what Trek said would be coming back in 2019. I was sent the 9.8 GX AXS ($8999.99) model for this review. winter. After testing both the new Norco Optic and the Specialized Epic EVO this year, the 130/120mm 29er Trek seems to sit somewhere between the two: indifferent and vanilla, like most Treks. But the question was – will this bike be as polarizing and mysteriously popular as vanilla Coke, or everyone's favorite like vanilla ice cream?

Original Impressions

The big Top Fuel 9.8 GX AXS I was sent sits in the middle of the range. In Australia, the range starts with the alloy Top Fuel 8 at $5499.99, and extends to the 9.9 XX AXS model at a staggering $18499.99. The carbon frame on the 9.8 model I'm testing is full carbon, and saves about 220g over the previous Top Fuel, which many thought was pork for purpose. Many of the usual Trek features remain, such as Active Braking Pivot (ABP) where the rear pivot is on the axle, and MinoLink, which is an option for central geometry adjustment built into the lower part of the shock mount. Trek has added an over/under advancement option to this mount to make it four positions in total, 14% or 19% further. So yes, it may be compatible with a coil shock – but if that's what you're thinking then you're probably looking at the wrong bike. It will lend itself to customization, especially considering the bike can be equipped with a 140mm travel fork and 185x55mm long shock with 130mm of rear travel if desired. And you can use it as a mullet if you're into that.

The Trek has a few notable standouts – such as a threaded bottom bracket for pain-free service, and a headset that functions only as a headset, not as a drain port or brake hose. There's tube frame storage with refined opening and closing, a top tube undermount accessory, a single bottle cage and short seat tubes and long head tubes in all five sizes. Interestingly, Trek has also introduced size-specific chainstays to ensure that the flexibility and fit of the bike remains the same across all sizes.

The geometry is world-class, with a 65.5 degree head tube angle and a hair less than 76 degrees for the seat tube. The reach is 477mm in size – all this in low condition. With a 440mm chainstay it's about what you'd expect from a bike like this. Trek says they've added some antisquat for better pedal response, and the shock progression is very similar to the previous model, with the option to increase it for faster flow paths and bigger hit support.

It's a really neat looking bike, and I think the lighter graphics really help with that, as does the one piece RSL carbon riser cockpit. I have used this one before and I love it. It's strong, light, and really wide at 820mm. With a GX AXS T groupset and Level Bronze 4-piston brakes it's a great build – functional and modern. Bontrager Line Comp alloy wheels have a 30mm internal rim and 108-point engagement hubs, wrapped in 120tpi Bontrager Gunnison and Montrose tires, for quick rolling and grip. You can really change the character of the bike with a little rubber – or by sliding the lighter carbon wheels in, depending on your preference.

Out of the box I added the supplied sealant, used Trek's website to find the basic settings for the Pike Select+ and Deluxe Ultimate RCT and threw it on the scale – it came in at 13.31kg before I added my pedals. Everything looked good – but it didn't give me the energy to go and ride it. I added more pressure on the fork to what was suggested as it felt softer, and headed for the trails.

On the road

I should probably be more excited to get into the new Trek Top Fuel. I hold the 2015 era bike in high regard, and watched the latest editions with interest, while feeling the chasm between Supercaliber and Top Fuel may be too wide. Having ridden many size Trek bikes over the past few years the fit was spot on – I'd downgrade if this bike wasn't mine, but I'm not sure Trek Australia would treat me well doing that to their $600. bars on this test bike. You should though, if you're making your own.

Going up the line I wasn't sure what to expect. It's not an XC rocket like my bike, but the Top Fuel rolls better than the Norco Optic and Specialized Epic EVO I've ridden a lot this year. The tires will play a big role, but the suspension is very balanced, with very little mushroom even when out of the saddle. That's a big plus for me. That's very different from the front, and the Pike delivers the dialogue in a way that a 120mm XC fork aspires to have. The Pike is a good indicator that the Top Fuel isn't a long-legged XC bike but something that can perform very well when you need it to.

On my local test tracks I certainly felt comfortable pushing the Top Fuel quickly, getting good support from the rear suspension, and great grip from the new Bontrager tires on the hero dirt that day. On the few other trails I used to test the bike I was happy to hit some small gaps, but I was more careful than I would have been if the bike had less rubber on the gravel sections. What I found when I compared it to how the Epic Evo, which I really liked, was how well it tracked in rockier conditions, which I think has a lot to do with the overall purpose. I know Ben Morrison said the ultimate Top Fuel can be ridden as a short travel enduro bike because of the frame stiffness and performance. Despite the weight reduction, Trek has only improved the power of the new model – meaning more suspension options will be appreciated.

On the next ride I got more and more comfortable in Top Fuel. The shifting was as crisp as expected, and even though I thought the 30t ring was done, it worked very well for staying and going around even some of Brisbane's steeps. But where I enjoyed Top Fuel the most was on the downhills. Whether it was on a groomed trail with lots of smooth features to pump yourself through, or a rocky terrain – both were a joy. I was impressed that the Trek had a suspension setup that offered just the right amount of support when pushing the bike, otherwise you had to ride it hard to survive. I ended up using only the normal setting and not the continuous time trial option, as in Top Fuel it really suited me.

This doesn't mean it works as an XC bike and a trail bike. It's just not like that. It's a heavier upright bike than a pure XC bike, but out of the box I'd still be happy to take it to a local XC race or something like a Quad Crown weekend. There is no substitute for a long-distance bike. At high speeds when I'm trying to squeeze the lips or the hits can send me further than I'd like to go, the Top Fuel reminds you that it's a 120mm travel platform. It just means that you use more body language as you get older, and that's fine by me. I think you can really increase the power of aggressive trail riding with a longer stroke and fork, as well as tires and brakes. The brakes on the Level are good but not very powerful, despite being a 4-piston brake. I think they are fine for the bike as is, but a bigger rotor would go with the front end if Top Fuel is going to be an overbuild project.

If I'm going the other way, I can happily take out long rides on big hills in Top Fuel, but you might want to take a backpack even if you know you're staying in cities. With just one bottle cage you're limited to liquids – in this case the Epic EVO will come out on top.

Our Take

Go back nine years and I was seriously considering Top Fuel as my personal bike. They really ticked a lot of boxes. Since then Trek drove a wedge in their XC and trail bikes, with the Supercaliber becoming the XC World Cup bike while the Top Fuel got longer legs and a lighter look. Many 2015 Top Fuel owners are wondering where to look for a replacement – and some are looking beyond the Trek. Times change, just like riding, and I think this fourth generation Top Fuel should better fill the gap between the updated Supercaliber and the new Fuel EX. In some ways it's the perfect bike for those who missed out on the last generation Fuel EX. And for others, it will work for riders who love the latest Top Fuel but want more power or less weight.

The new model is a better bike than the last Top Fuel in everything.

I was prepared to be overwhelmed by the fourth generation Trek Top Fuel. The documentation I was sent before the test bike arrived didn't make my heart skip a beat, and building the bike showed a common sense bike but nothing exciting. And you know what, vanilla is good. Because the new Trek Top Fuel 9.8 GX AXS has truly delivered on the road. It's a very efficient bike to ride and doesn't feel like much of a bike even on soft trails, while it's good for more. And most importantly, if one really misses the outgoing Fuel EX then Trek has brought you the perfect bike.