Trek’s ambition with the Top Fuel is to combine the best qualities of both cross-country and trail bikes. This genre-bending, 115mm-travel 29er is burlier than its XC thoroughbred, the Supercaliber, but lighter and more agile than the Fuel EX. It promises lightning-fast speeds, whether gravity is on your side or not.
Trek Top Fuel 9.8 frame
The Top Fuel’s full-carbon frame is obviously a Trek design, with that familiar twin-triangle shape and ABP (Active Braking Pivot) suspension design, where the rearmost pivot is concentric with the rear axle.
As on the rest of Trek’s full-sussers, the ‘Full Floater’ shock mounting of the old Top Fuel is gone. Instead, the Fox DPS air-can mounts directly to the frame at one end and to a magnesium rocker link at the other. Travel has been extended by 15mm for 2020.
In terms of geometry, the Top Fuel is now longer and slacker. Depending on which way you position the Mino Link flip-chip, the head angle can be set at either 67.5 or 68 degrees and the reach varied by 5mm, from 470 to 475mm on the large.
The effective seat-tube angle has been steepened to 75/75.5 degrees. With six sizes, it should be easy to achieve a perfect fit. The details of the frame have been well considered too, from its sleek, flowing lines to the fully-internal cable routing and integrated rubber protection finish.
Plus, Trek’s Knock Block steering-lock stops the fork crown fouling on the down tube.
In terms of geometry, the Top Fuel is now longer and slacker. Laurence Crossman-Emms
Trek Top Fuel 9.8 kit
That 115mm-travel, air-sprung rear end is matched to a 120mm Fox 34 Performance fork. A bar-mounted RockShox TwistLoc remote lets you lock out both ends simultaneously, providing a firm pedal platform that’s easy to toggle on or off.
Combine that with a Bontrager Line Elite dropper post, and the Top Fuel switches easily into downhill mode, although a 10mm-shorter stem and slightly wider bar would help the handling.
Shimano’s SLX brakes are good, but it doesn’t take much to find the limits of the 160mm rear rotor and the lever return was a little sluggish.
I found the Bontrager XR3 tyres slightly flimsy too. They’re efficient uphill but the low-profile tread isn’t great on unsurfaced trails and I sliced a hole in the thin casing on a fairly mellow descent.
The bike’s price tag isn’t insignificant either and, while the spec is solid, I’d happily lose the carbon wheelset and bar to save some money.
Trek Top Fuel 9.8 ride impressions
You have to bite your tongue before criticising a bike like this because by its versatile nature it’s never going to be the best of the best in any scenario. With this in mind, there’s very little to fault in the way the Top Fuel rides.
With a poised feeling on the pedals even in the lower/slacker setting, the bike blasts up hills with minimal effort and I rarely found I needed to use the lockout apart from on long fireroads.
As a trail bike, the Top Fuel puts on an impressive show and never faltered, even when hammered into turns or launched off drops. The suspension gives you a solid base to push into and I was surprised after the first ride to discover that it only has 115mm of travel.
The main limiting factor to this downhill prowess is the low front end. When things get steeper, you do notice you’re on a bike that’s also built for going fast up hills. The short head tube and low stack height are clear indicators of this, and while for general trail riding I found them a little low, this does allow the bar to be fully slammed for all-out XC attacks.
Even with the 13-degree-rise stem positioned as high as possible on the steerer, I wouldn’t have minded a little more height. But then, upping the fork travel would blur the lines between the Top Fuel and the longer-travel Fuel EX.
On a bike like this, there are always going to be trade-offs, and opinion is always going to be biased by riding style, but for rapid mile-munching that doesn’t get in the way of enjoyment on the descents, the Top Fuel is hard to beat.
As a trail bike, the Top Fuel puts on an impressive show. Laurence Crossman-Emms
Trek Top Fuel 9.8 geometry (based on high setting for size L)
Seat angle: 68.5 degrees
Head angle: 68 degrees
Chainstay: 43.3cm / 17.05in
Seat tube: 47cm / 18.5in
Top tube: 63cm / 24.8in
Head tube: 10cm / 3.94in
Fork offset: 4.4cm / 1.73in
Trail: 10.3cm / 4.06in
Bottom bracket drop: 2.9cm / 1.14in
Wheelbase: 1,185mm / 46.65in
Stack: 59.9cm / 23.58in
Reach: 47.5cm / 18.7in