2021 Trek Session is a 200mm travel 29er downhill bike, with high pivot idler design, that can also be configured to run mullet or 27.5in wheels.
As downhill race bikes go, the Trek Session is easily one of the most decorated – racking up a whopping 38 world cup wins under the guidance of Aaron Gwin, Tracy Moseley and the Athertons. More recently Reece Wilson piloted the Session to its first male World Championship title at Leogang, Austria.
Trek Session need to know
- New high pivot ABP suspension layout with an idler gives a more rearward axle path and reduced pedal kickback
- Alloy only frame construction
- New shock Mino Link offers adjustable progression rate
- R sizing is based on reach, not seat tube – three sizes available 440/465/495mm
- Size specific chainstay lengths 439mm R1, 445mm R2 and 452mm R3
- Full length bolt on down tube protection
- External cable routing option for ease of maintenance
- Two bolt ISCG mount with 32-38t chainring compatibility
- Two models: Session 9 £6,300, Session 8 £4,500, frame only £2,750
With such an impressive list of palmares, Trek could easily be forgiven for taking the “if it ain’t broken, why fix it?” approach. But at the performance end of downhill racing time rests for no one, so instead of polishing the brass in its sizeable trophy cabinet Trek is going after more titles.
And to do that it’s actually looking backwards. Backwards to the rearward axle path and idler design of the original Session 10 and the Diesel before that. In fact, the new Session is a hybrid of old and new, combining the current ABP suspension layout with the higher pivot and idler of old to produce a 200mm travel 29er downhill race bike that can also be adapted for events like Red Bull Rampage with a few tweaks that we’ll get to in just a minute.
Why introduce the additional complexity of an idler? Well, the science behind the more rearward axle path clearly shows that it reduces the peak vertical velocity of the rear wheel, or to put it another way, it gives the wheel more time to climb the bump. And unlike some idler designs, the main pivot piston on the new Session is not so high as to give a completely rearward axle path.
The idler location plays a key part here too. It’s not concentric with the main pivot as Trek wanted to retain some chain tension, which in turn helps stabilize the suspension and make the bike pedal more efficiently for those all important finish line sprints. It’s a big departure though; compared to the old Session suspension design the new layout has a maximum pedal kickback of 8º vs 27º, which will allow the rear suspension to react more freely to impacts as it’s not fighting against the same degree of chain tension.
And unlike the single pivot idler designs used by the likes of Norco and Forbidden, Trek’s ABP design transforms the seat stays and rocker link into a floating brake mount which helps keep the anti-rise in check, so the rear suspension shouldn’t squat too much under heavy braking either. That’s the theory at least. We’ve not had the chance to ride the new Session yet, so it’s all we have to go on. Nonetheless, it’s interesting that it could be braking performance that really separates the raft of new idler designs.
New frame, new sizing
One criticism fairly leveled at the Session was that it was too short. Well, Trek has addressed that and gone a lot further with the latest design. It has now switched to what it’s calling R sizing. It’s based on the reach measurement rather than seat tube length and it’s a lot like Specialized’s S sizing. Trek offers the new Session in three frame sizes R1 (440mm), R2 (465mm) and R3 (493mm). It’s clear that reach measurements have been increased by about 30mm across the board, so there should be no need to upsize, even if Trek has actually made that easier thanks to the R2 and R3 sizes both sharing 450mm seat tubes. There’s currently no carbon frame option on the new Session and it’s hard to say if this is purely about economies of scale, but it certainly hasn’t stopped Commencal or Specialized racking up multiple world cup wins on aluminium bikes, so who knows.
Size specific chain stays
To balance weight distribution across all three frame sizes, Trek has also introduced size specific chainstay lengths. Taking design cues from Owen Pemberton, formerly of Norco and now Forbidden, the rear ends on the Session don’t actually change. Instead, it is where they attach to the front triangle that gives the dedicated chainstay lengths. By simply moving the main and rocker link pivots backwards relative to the BB as the frame sizes increase, the chainstay lengths, or more accurately, the rear centre measurements grow from 439mm on the R1, to 445mm on the R2, than max out at 452mm on the R3. It’s a neat, cost efficient way to offer size specific chainstay lengths as the same rear end can still be maintained across all frame sizes.
Trek’s trusty Mino Link offers two geometry settings on the Session. With the 29er configuration in the high position the claimed BB height is 358mm and the headangle is 63.6º. Dropping it into the low setting chips approximately 9mm off the BB height and slackens the head angle by 0.6º. But the Mino Link is not simply about offering two different ride charastices with one bike; combined with a headset extender cup, Trek can transform one frame from full 29in all the way to full 27.5in, for the likes of Brandon Semenuk, with the mullet setting slotting seamlessly in between. To correct the geometry Trek says the mullet configuration just requires a 27.5in rear wheel and the Mino Link in the high position, while the full 27.5in bike also needs the headset extender that’s supplied with the bike.
Coil or air shock? You choose.
Rather than striking a compromise between the most effective progression rate for either air or coil shocks, the new Trek Session has a second Mino Link in the lower shock mount that offers two distinct progression settings. In the forward position the Session has 20% total progression making it ideal for air-sprung shocks. Flip the shock Mino Link to the rearward setting and the total progression increases to 25% to better resist bottoming when used with a coil sprung shock.
So the new Trek Session is packed with innovative features and the alloy frame certainly keeps the pricing competitive with the top end Session 9 at £6,300 and the entry-level Session 8 at £4,500. If you want to go down the custom build route there’s also a frame only option for £2,750. The bike also appears to be every bit as customisable as it is capable and even though it looks very different to the previous Session it’s evident that it builds on the foundations laid down by over a decade of racing at the very highest level. All we need now is for the racing to start so we can see if Trek has maintained that winning pedigree.