New Trek Procaliber features a massive hole in the top tube to smooth your ride

IsoBow compliance system replaces IsoStrut on new Procaliber

Published: Thursday, 29 August 2024 at 15:00 PM

Trek’s latest Procaliber hardtail mountain bike has a new frame compliance system based around a large hole in the top tube.

Called IsoBow, the compliance system replaces Trek’s IsoStrut design and it’s said to be lighter and simpler than its predecessor.

Elsewhere, the new Procaliber keeps up with cross-country mountain bike trends, with fork travel increasing from 100mm to 120mm and a more aggressive frame geometry.

Trek says the bike has been designed with anyone in mind from rugged gravel riders to World Cup XC racers.

The Trek Procaliber starts at £1,200 for the base aluminium Procaliber 8 with the high-end, carbon-framed Procaliber 9.7 AXS topping the range at £4,250. A frameset is also available for £1,400.

International pricing is to be confirmed.

IsoBow frame compliance

The IsoBow does look simpler than the IsoStrut it replaces. – Trek

Trek says the new IsoBow frame compliance design is lighter and simpler than the IsoStrut system it replaces, and that its athletes can’t feel a difference in compliance between the two systems in a blind test.

The new design utilises flex in the rear triangle to smooth out trail imperfections.

The seat stays continue past the seat post allowing them to flex and dissipate vibrations.

Trek Procaliber 9.7 AXS with IsoBow — The new system leaves a large hole in the crossbar. – Trek

The Lapierre Prorace CF 9.9 has a similar system, which is a bit like GT’s Triple Triangle Design.

Only carbon Procaliber models feature IsoBow.

Trek Procaliber — Trek says reduced vibrations lead to less fatigue over time. – Trek

The new frame has a floating brake rotor mount similar to Trek’s full-suspenionSupercaliber XC bike. The mount is said to isolate braking forces from the seat stay flex to increase comfort and provide more consistent braking.

Trek says the new Procaliber frame is on average 150g lighter than the previous generation across the sizes.

Increased travel and clearance

Trek Procaliber on trail — Trek has designed the Procaliber for elite competition. – Trek

The new Procaliber now uses a 120mm suspension fork. This is in keeping with other cross-country hardtails which have increased suspension travel in recent years.

Also following a trend in XC mountain bikes, the new Procaliber can accommodate wider mountain bike tyres, measuring up to 2.4in.

Inside the front triangle is room for two water bottles, which should be enough to keep you hydrated on longer riders or in marathon races.

Trek hasn’t given the bike any frame storage, though there is a mount on the underside of the crossbar where you could mount a small pack.

Modern XC geometry

Trek Procaliber 9.7 AXS — The Procaliber has grown longer and has a slacker head angle. – Trek

Trek has also modernised the Procaliber’s geometry. It now features a slacker 67-degree head angle compared to the 68.8-degree angle of the previous Procaliber.

The effective seat tube angle has also steepened to 74.3 degrees from 73.8 degrees to maintain an efficient pedalling position.

Reach has increased, too, growing 10mm to 460mm in a size large.

Trek says all this has resulted in a bike with calmer handling and increased confidence which should lead to increased speed.