Trek’s Procaliber hardtail with inbuilt seat tube flex (VIDEO)

Jamie Darlow

The hardtail that thinks it’s a full suspension bike, Trek’s Procaliber has a vertically flexy rear end for comfy riding

Key points

  • Seatstay and seat tube ‘decoupled’ to allow for flex in the seat tube, and connected only by two bearings and a bushing
  • Up to 11mm of vertical flex from the IsoSpeed decoupler system, Trek says, 71% more than a carbon hardtail
  • Designed for a more comfy ride when sat down pedalling, not stood up descending
trek proclaimer packshot

The top-end Procaliber 9.9 with RockShox RS1 fork and a £6,000 pricetag

Hot on the heels of the Stache 29+ bike, Trek has developed another innovative new hardtail, the Procaliber SL.

It might look like just another hardtail — 29in wheels, 1x drivetrain, 100mm fork travel — but Trek has built a load of vertical compliance to the seattube, letting the bike flex by over a centimetre as you ride.

The system is called IsoSpeed Decoupler and Trek developed the idea for its road bikes and cyclocross but for 2016 it’s brought the concept off-road.

How does it work?

The seat tube and downtube are ‘decoupled’ – they’re still connected by two bearings and a bushings but it allows for the seattube to flex under your weight.

Trek Procal

IsoSpeed decoupler lets the seat tube flex under your weight, but the tubes are still connected with bearings

What it doesn’t do is affect the way the bike pedals and it doesn’t give it any compliance when you’re standing on the pedals and descending. But it should make things more comfortable when you’re sat down pedalling.

Take a close look at the video and you’ll see a rubber seal at the join of the seat tube and seat stays. That’s not what does the flexing, it’s really just a dust cover to protect the connection, the seat tube is the part that moves.

So does it work?

IsoSpeed is definitely noticeable, more so than the usual bounce you’ll get from the tyres. Trek says it has 71% more vertical compliance than a carbon hardtail – in English that means it could flex by a not-negligable 11mm.

Our first impressions are it’ll be a welcome improvement on long climbs and might actually give more grip on the climbs.

Trek procal bike

Sat-down pedalling should prove more comfy, while out of the saddle descending will be unaffected

What else is new on the Procaliber?

Trek has brought it’s ultra-wide Boost back end with 148mm hub to the bike to make it stiff, and they also have boost on the 110mm fork hub to balance out some of that stiffness.

The wheels are now size specific too — ride 15.5in and you’ll get a 650b bike, up from there it’s 29in.

There’s also something called Control Freak Cable Management – basically a neat way to tidy up the bike and slot all the cables inside the frame. There are two big downtube entry ports, an exit down on the bottom of the downtube and a cinch point to stop it rattling.

Trek says there are now 54 different cable routing options on the market today, and the Control Freak can cope with it all. And that even UK brake options, which typically look scrappy with a left-rear brake: now entry ports on either side of the downtube clear that up.

Trek's Procaliber, the most comfortable hardtail in the world?

Trek Procaliber: the world’s comfiest hardtail?

The Procaliber range

  • 9.9 SL £6,000
  • 9.8 SL £3,400
  • 9.7 SL £2,250
  • SL frameset £1,800