Review: Trek Top Fuel, Gen 4 | The quiver killer

One frame, three bikes? You betchya!
| WORDS: Myles Kelsey | IMAGES: Max Sullivan |
In it’s stock setup, the new Top Fuel has 120mm rear and 130mm front travel, which is unchanged from the previous model. To improve ride quality, Trek says they took a few construction tricks from their latest Supercaliber (reviewed here) and tweaked the new Top Fuel’s tube shapes into smaller profiles. This saves weight and reduces chassis stiffness, making a bike that’s easy to ride. The aluminum and carbon frames are around 220grams lighter than the previous model.

However, the real story of the fourth generation Top Fuel is less about the diet it’s been on and more about the versatility Trek has knitted into the chassis. Trek sent us the Top Fuel 9.8 GX AXS model for review and we spiced things up by adding Dave George’s (The Gear Change) custom build, to the review.
Video: How did Trek make the Top Fuel so versatile?
Features and Details
Looking at the geometry, Trek hasn’t made any radical changes. The head angle is 65.5° which is only 0.5° slacker than the previous model. The seat tube angle is unchanged at 76°. However, the chainstays are now size-specific – so frame sizes S and M have a 435mm stay, frame sizes ML and L have a 440mm stay and the XL has a 445mm stay. The idea here is to position the rider in a slightly more central position, creating better weight distribution and handling, when climbing or descending. It’s something that a few other brands do, and it works well.

Details
FRAME | 120mm rear, downtube frame storage, ABP suspension layout (can be run as a 130mm rear) |
FORK | RockShox Pike Select+, 130mm |
SHOCK | RockShox Deluxe Ultimate RCT |
COCKPIT | Bontrager RSL Integrated Bar/stem |
SADDLE | Verse Short Comp |
DROPPER | Bontrager Line, 170mm |
WHEELS | Bontrager Line Comp 30 |
TYRES | 2.4″ Bontrager Gunnison / Montrose |
CASSETTE | SRAM T-Type, 10-52T |
MECH | SRAM T-Type GX AXS Wireless electronic |
CRANKS | 170mm SRAM GX Eagle, T-Type |
BRAKES | SRAM Level Bronze, 180mm rotors |
WEIGHT | 13.2kg (As tested, with sealant, bottle cage – no pedals) |
RRP | R125 000 |
A key to the expanded versatility of the Gen 4 Top Fuel, is the new 4-position flip chip at the lower shock mount. This ‘Mino Link’ as Trek calls it, enables riders to adjust geometry and the leverage rate of the suspension, independently.

The BB can be high or low and the head-angle can be steep or slack. It also gives riders the choice of running 14% or 19% progression setting on the shock. XC riders will likely be better off in the less progressive setting and trail chargers would probably be better off running more progression, ie: 19%.

There’s a couple more tricks up the Top Fuel’s sleeve. Whilst all models are sold with a 130mm fork, for those who want more ‘XC’ out of the bike it is compatible with a 120mm fork. Trek says this is an option their pro riders may explore for some of the gnarlier World Cup XC tracks.

Alternatively, riders who want more ‘shred-sled’ performance, can fit a 140mm fork. Mixed wheel-sizing can be done on all frame sizes, barring the size small. Incidentally, in a MX setup with a 140mm fork, the bike will have a very capable, 64.6° head angle. The bike also accommodates a longer stroke shock, so increasing rear travel to 130mm is a real option too.


There are two smaller changes that might interest you. Trek has dropped the steering limiter (aka Knock Block) as the new bike is designed with sufficient crown clearance. They’ve also redesigned the frame storage giving it a bigger door, tighter seal with concealed cabling.

The build kit on our test bike is a mix of SRAM, RockShox and Bontrager goodies. That’s Level Bronze brakes with 180mm rotors front and rear, RockShox suspenion front and rear, with the GX AXS T-Type wireless drivetrain.


A one-piece carbon bar/stem combo is a nice touch to drive weight down. Also worth mentioning is the new frame has yet better dropper insertion numbers – meaning 200mm plus droppers are an option on most frame sizes.



Tipping the scales at 13.2kg is understandable for a burly build. In fact, well over 1000grams could be trimmed simply by moving to a lighter wheelset and tyre combination. However, the no-nonsense alloy wheelset (and tyre combination) on this model is perhaps one of the main reasons the bike gets a 5-star rating when things get sendy. More on that in a bit.


This model Top Fuel is also available in a Lunar Silver colour. There are five frame sizes on offer, with generous reach numbers — starting from 417mm and rolling up to 512mm. Pricing wise, the base level build starts at R55k and the range tops out at a whopping R270k.

I also spent some time on Dave George’s personal bike that is setup with an Öhlins 120mm fork, a lightweight wheelset and SRAM XX1 drivetrain. It weighs 11.8kg.

Ride Impressions
The stock 130 front and 120 rear 9.8 GX AXS build
Initially, I was honestly perplexed when Trek launched the Gen 4 Top Fuel last year. At a glance it appeared to be strikingly similar to the Gen 3 model. Largely, the travel and geometry never changed. On closer inspection, the changes to the tube shapes, dropper insertion numbers and that new flip-chip began to make more and more sense. Yet, the burning question; is the Gen 4 that much better than the Gen 3? The answer; yes!

I can say that since I own a Gen 3 Top Fuel. Bought and paid for some two years ago, my personal Top Fuel is a bike I love. The favorite in my garage. My one bike that I can do a lot on. Simply put, my Gen 3 Top Fuel goes like the clappers. But, I will be selling it and upgrading to this Gen 4 model. Here’s why…

Generally, when the bike industry launches a new model of something, there are sometimes quirks. Sometimes the fit is off, the shock tune is poor or there’s something wacky in the geometry. Those oversights are usually quickly corrected. Then, as a model enters it’s second and third iteration, the better brands will have poured a lot of refinement into the product. Not that I’m saying the early generation Top Fuel was horrid – on the contrary, it was a great bike! For clarity, I’m pushing the point home that whilst newer versions of product X, may appear very similar to what it is replacing – sometimes the change in ride feel is far more substantial than one anticipates. This is the case with the Gen 4 Top Fuel. The ride feel is very different.


To get the bike setup, I used the suspension calculator on Trek’s website. The suggested settings were 100% spot on for me and felt good on the trail but I added 3-clicks of rebound damping to slow things down a little – an adjustment likely necessary to compensate for Cape Town’s high-summer temperatures.

The build kit on this bike is flawless — even the one-piece bar/stem combo that I usually mutter about – every time I look at one. Wait, I lie, the only thing I’d change on the bike is the grips – they don’t have enough damping in them, and maybe the bottle cage which regularly ejects bottles. The SRAM GX AXS T-Type drivetrain is solid and efficient. The saddle is shaped differently to what I use, but it is just as, if not more comfortable, than what I use on my bike. To those new Bontrager Tyres then — the compound is a lot softer than the XR4 Bontragers, resulting in more corner grip and climbing traction. Yet, they still roll quickly. Very nice! I’d like to spend more time on them but so far they feel grippy and robust enough for janky trails.

I ran the flip-chip in the low BB position and progressive suspension setting – because I like big hits. In this setting, the bike is very progressive and ramps up nicely from the mid-stroke, on big landings. The other bonus in this progressive setting is the extra ‘kick’ forward or extra drive on offer, when pumping terrain. The new Top Fuel feels a lot more like a Supercaliber, when climbing. There is definitely less wallowing about and the ride position feels a little more foward than on the Gen 3 Top Fuel.
I’ll sum up my ride impressions by saying this bike is predictable, comfortable and it’s easier to hit bigger stuff on than my Gen 3 Top Fuel. The bigger stanchion fork and alloy wheels combine well into the lightish overall package, delivering a ridiculously fun ride.
The custom build: 120 fork, 120 rear and lightweight wheels..
There’s a lot more flex and forgiveness in this setup so I can’t quite charge the bigger stuff, but at almost 1.5kgs lighter this bike is an absolute rocket ship. What’s more it carries speed very well. As an endurance racing machine, this bike feels a tad more efficient with the flip-chip in the less progressive setting and with the BB set in the high position. In this setting, there’s also better pedal clearance giving less chance of stalling, on techy climbs.

The most noticeable ride feel is the compliance in the wheels and fork. The steering is not vague, it’s just marginally less direct, with less deflections and more overall forgiveness. Which is exactly what you’ll want on long days out. I think this would make a great marathon race machine, especially for riders who ride rougher terrain and don’t enjoy the excessive and constant trail feedback that shorter travel race whips are known for.

For this review I didn’t get to try the bike as a MX wheelsize machine with 130 rear and a 140 fork but it is something I’d be very curious to try. I think that’d be an awesome shred-sled, capable enough for some local Enduro racing and flow line laps. If you own or are looking to buy a Top Fuel, drop a comment on our YouTube channel to let us know your setup and what you’ll use the bike for. // trekbikes.com