Ultra high-end shock brand, Extreme Shox, have released their first ever mountain bike fork. The EXT ERA fork uses an air/coil hybrid spring system, with a damper shaft offering external adjustments to High Speed Compression, Low Speed Compression and Rebound.

extreme shox add first ever mtb fork ext era hs3 air coil spring hybrid

Available in 140mm, 150mm, 160mm and 170mm travel options, the new EXT fork is now an upgrade option for trail, all-mountain and full-on enduro mountain bikes. Here, we give you EXT’s thoughts on the air/coil hybrid spring system, and explore why this fork uses not one but two positive air chambers, in addition to a negative air chamber.

EXT ERA Fork

ext enduro fork mtb 160mm 170mm travel 29" wheel
The largest recommended brake rotor size for the EXT ERA fork is just 203mm
  • Fork Travel: 140mm, 150mm, 160mm, 170mm
  • Wheel Size: 29″
  • Fork Offset: 44mm
  • Spring: Air/Coil Hybrid
  • Adjustments: High Speed Compression, Low Speed Compression and Rebound
  • Claimed weight: 2280g (29″ 170mm w/uncut steerer, axle and lube)
  • Price: € 1480 + VAT

EXT designed the new ERA HS3 fork with mid-stroke support at the top of the list of priorities. Support is arguably the most important ride quality we want out of our suspension forks. A “diving” fork can be a nightmare to ride because it can drastically compromise a bike’s geometry.

new ext era fork two positive air chambers for better mid stroke support

At full compression of your fork, whether you’re on an XC bike, a trail bike or a DH bike, several things happen: First up, the bike’s wheelbase shortens considerably. Secondly, the head angle steepens rapidly. Ultimately, all those lovely geometry figures you poured over while choosing your next bike – they go straight out of the window.

ext era mtb fork hs3
Despite the continuous teasing on social media, the EXT ERA actually has 36mm stanchions, not the rumored 38mm

Of course, it’s OK to use full travel of your fork. The reason you haul a 170mm travel fork up the hill is because you want 170mm of “give” when you’re slaying the day’s trails.

That said, you don’t want it diving into that travel for every compression, small or large. A fast bike is a stable bike, and that means having stable geometry. (Keep in mind, your rear is usually compressing nearly simultaneously, so it’s not like all of the compression is coming from the front, but the front needs to hold its own)

extreme shox explain fork mid stroke support dynamic sag
EXT reckon the ERA offers greater mid-stroke support on steep terrain as compared to a single chamber positive air spring

This is why EXT prioritized the mid-stroke support of their new ERA fork. More support means subtler changes to the bike’s geometry, and a more stable ride feel. So what have they done to achieve that?

HS3: Two positive air chambers

ext-era-fork-air-shaft-internals-integrated-coil-dual-positive-chamber-negative-spring
The two adjustable positive air chambers work with one high volume self activating negative air chamber

EXT are of the opinion that a single positive air chamber is insufficient to provide good mid-stroke support. You can improve it with the use of volume spacers up and to a point but, this comes with an increase in harshness from the end-stroke of the spring.

ext era offers better mid stroke support than standard single positive air spring forks
EXT say that the HS3 dual positive air chamber spring produces a dynamic sag position that is higher in the stroke than a that offered by a standard air spring

The HS3 air spring with its dual positive air chamber design is said to create a more linear spring rate that gives the rider more support around the dynamic sag region of the stroke.

Pressure of both air chambers is adjustable by the rider, and EXT provide a detailed chart to advise riders on how to set their pressures. The negative chamber is activated from the main, lower pressure positive air chamber that sits next to it in the shaft.

ext-era-hs3-positive-air-chamber-valves
Underneath the Air HS³ Cap are two air valves, + and ++ for the individual positive air chambers.

The air shaft also features an integrated coil spring which becomes active at the sag position. This is said to create a frictionless sliding movement resulting in a highly responsive fork. Speaking of friction…

Low friction… everything

EXT wanted to make their new ERA fork as frictionless as possible. Sadly, it’s not only the spring and damper that dictate the overall ride feel of your suspension fork, friction and stiction contribute significantly too.

Friction is especially apparent when the fork is experiencing high side loads. To minimize this augmented friction, EXT added a floating internal shaft guide in the damper cartridge. This shaft guide is made up of aeronautical carbon charged PEEK material, and it’s there to manage radial forces.

It allows the fork stanchions and lowers to undergo some degree of flex under side loads, while allowing the damper shaft to remain in its low-friction true configuration.

ext proprietary low friction materials damper shaft mtb fork

In further efforts to minimize friction, EXT developed a proprietary low-friction DU bushing guide material, damper cartridge coating and EXT SuperFinish shaft. The HS3 air spring also uses EXT’s dedicated grease, developed specifically to offer low friction for both low and high velocity movements.

That integrated coil spring we mentioned – that works with the air spring, and serves to completely eliminate stiction to give the rider more accurate feedback through the tire.

EXT ERA HDRV damper

The damper cartridge on the EXT ERA fork uses a new bump valve design called the High Dynamic Response Valve (HDRV). As we’ve seen on EXT shocks, the compression and rebound damping circuits are entirely separate entities.

ext fork damper external adjustment hsc lsc rebound

The ERA’s HDRV damper uses two separate shim stacks for mid and high speed compression damping, and an internal floating piston.

We asked the guys at EXT how exactly these two shim stacks work. They said that the main shim stack creates the pressure drop and deals with the main flow control. The secondary shim stack sits on top of the first stack via a dynamic cage.

extreme shox mtb fork damper shaft internals ifp hdrv valve compression rebound circuits separate
EXT claim their 22mm piston design eliminates the possibility of cavitation (oil-water mixing)

It acts as a preloading system and only affects the high speed part of the main valve flow and damping characteristic. This is similar to the design EXT use in some of their valves for motorbike suspension.

Ultimately, it means adjustment of high speed compression damping doesn’t interfere with the low speed compression and sensitivity. The damper offers 12 clicks of adjustment for both LSC and HSC.

15 clicks rebound adjustment
The EXT ERA fork offers 15 clicks of rebound adjustment

The internal floating piston in the damper of the EXT ERA fork is guided by a thrust bearing. This is a system EXT use to decouple the side load created during compression to recover shaft volume. It transforms these lateral forces into a rotary movement, thereby reducing friction during the sliding movement.

EXT say it delivers a very dynamic response that is super smooth due to a complete lack of stiction.

Stiff Chassis

The new EXT fork has a unique-looking steerer tube-crown interface. This shape was optimized by the EXT engineers for stiffness in all directions.

ext-fork-stiff-crown-steerer-tube-design
The EXT ERA crown was designed in collaboration with Mojo Rising

It is forged 7050 aluminium crown that is around 20% stiffer, frontally and laterally, compared to a “standard” fork crown.

ext era fork is 44mm offset only 29" 140mm 150mm 160mm 170mm travel options

The magnesium lowers on the EXT ERA fork are also optimized for stiffness with an asymmetrical wall thickness.

Pricing & Availability

extreme shox fork 1480 euro plus vat available now

The new EXT ERA fork retails at €1480 + VAT and is available direct from Extreme Shox now. Hold tight for a coil spring version; it’s on its way!

ExtremeShox.com

5 COMMENTS

  1. The fork is not as pretty bas as their Storia shock. Frankly, it looks a lot like a X-Fusion fork and no bolt on fender mount? But seriously, how easy is it to work on at home, with basic service or changing shim stack and will each fork be tuned to the rider as part the package like with their shocks? To bad they didn’t do something bc like Formula does with their CTS valves. Too bad nobody does.. Nice fork but not too impressed

    • The lowers look exactly like an X-Fusion Trace. Exactly. Like spot on exactly. What I’m saying here is they are using X-Fusion lowers in a $1700 fork. But that may not be a terrible thing, I think what you are paying for here is a very well executed and precisely assembled rehash of existing technology with what should be an excellent damper. And done right that could very well be an industry leading fork. But the press coverage of this thing is all the typical ridiculous hype. Everyone fails to mention the straight up copying of the Manitou IRT spring system, and the DT Swiss little coil assist spring, and the off-the-shelf lower casting. Because pretending it is something revolutionary and new sounds so much better.

        • Have you even looked? Do an image search for X-Fusion Trace 36 and see for yourself. Exactly the same. Every little detail, every contour. It’s the same casting. Do you think EXT wanted to pay for a unique casting for a low volume product? It’s by far the single most expensive part of a fork to put into production.

  2. nice fork. could be promising. it’s great to see options and hopefully a focus on quality damping. hopefully as their volume goes up, MSRP will come down some.

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