Fox’s new Podium fork eschews traditional design, using an inverted layout.
The novel upside-down (USD) design is claimed to boost plushness thanks to its increased bushing overlap.
A reworked air spring and fine-tuned GRIP X2 damper also increase performance, culminating in what Fox hopes is an “unfair advantage” over its rivals.
Retailing for a whopping £2,199 / $1,999.99 / €2,399 / CAD$2,679 / AU$3,349, those purported performance advantages don’t come cheap.
Let’s not forget the chequered history of USD forks. From Risse, Marzocchi and Manitou to RockShox, Push and Cannondale’s Lefty, it seems almost every minor and major suspension manufacturer has given the design a go.
But their popularity and mainstream availability indicate limited success, dictated by many factors including price and performance.
With the suspension know-how of Fox and technological advancements in the MTB industry over the last 20 years behind the new Podium, the chances of it being a flop seem slim.
Balancing weight, optimising stiffness and reducing friction were concepts at the heart of the Podium's development.
Fox claims it can unlock extra performance by mastering these three metrics, and the USD architecture is the best way to do it.
Fox Podium’s ultra high-tech 47mm-diameter chassis
Arguably, the Podium's performance hinges on its chunky 47mm-diameter upper legs that are bonded into the 'generatively-designed' crown.
Fox used AI models to help design the crown by optimising stiffness without adding excessive weight.
The aluminium alloy upper tubes – instead of the magnesium alloy that’s usually used for fork lowers – are the basis for the fork’s fore-aft stiffness, something Fox has worked hard to achieve.
Claimed to rival the rigidity of the dual-crown Fox 40, the Podium’s chassis should be marvellously precise regardless of the speed or terrain you’re riding.
Fox’s athletes and engineers blind-tested two different upper tubes and three crowns to help determine the best-feeling combination.
The aim was to increase the fork’s predictability and stability with fore-aft stiffness; a flexy fork in this plane is unpredictable and hard to tune.
36mm stanchions slide into the oversized uppers, which are the same diameter as Fox’s 36.
That means there’s wiper seal cross-compatibility between models, but only in one direction; Podium seals will fit a 36, but 36 seals won’t work on the Podium.
What is an upside-down fork?
Upside-down, or inverted, forks flip the components around.
A traditional fork's chassis has three main parts.
- The lowers: these are usually cast from magnesium and are the largest-diameter part of the fork. They have an arch and wheel dropouts, which clamp the wheel axle in place. Bushings are built into the lowers and lubricating oil circulates within them.
- The stanchions: usually bonded into the crown, these move in and out of the lowers as the fork cycles through its travel. The damper and spring are usually housed within the stanchions.
- The crown and steerer tube: the crown provides stiffness and an anchor point for the steerer tube that inserts a bike's frame.
Conversely, an inverted fork’s stanchions are at the bottom, with wheel dropouts attached directly to the stanchions. These are usually screwed and glued in place.
Like a regular fork, the stanchions still slide into wider-diameter tubes, but these are now called the 'uppers' and are bonded directly to the crown.
Finally, the crown and steerer architecture is identical to a traditional fork but, as mentioned, it’s attached to the uppers rather than the stanchions.
Because of their design, inverted forks lack the supporting arch or brace between the two fork legs, usually found on the fork’s lowers.
That means there are two, rather than three, cross-leg bracing points – the crown and axle – which give USD forks their distinct appearance.
20mm axle standard
That hefty upper’s fore-aft stiffness would be worthless if these forks lacked torsional or steering stiffness.
Upside-down forks lose one of the three bracing points (the lower’s arch) found on regular forks, so extra attention – needed to boost torsional stiffness – has to be paid to the axle and crown.
With the crown’s shape informed by AI, Fox went about blind testing multiple axles in different diameters, thicknesses and materials to determine the optimal design.
Testing revealed the 15x110 Boost axle wasn’t up to the job, so opting for the widely adopted 20x110 Boost standard was an obvious choice, albeit unusual for a single-crown fork.
Alloy and steel axles were also tried out, with the test team unequivocally preferring the feel of a steel axle. Different stiffnesses were also tested, in a bid to find the tipping point where “some of the [fork’s] magic goes away”.
The result is a 20mm steel axle – and a fork, according to Fox, that has torsional stiffness equivalent to a 160mm-travel Fox 36.
Increased bushing overlap equals friction reduction
The USD design has given Fox the freedom to increase fork bushing overlap.
According to the brand, traditional fork lowers create bushing limitations designers are always battling. Winning back precious millimetres of bushing overlap leads to compromises elsewhere (think axle-to-crown height increases), but this isn’t the case with inverted forks.
Bushing overlap is the distance between the upper and lower-most points of the upper and lower bushing.
According to Fox, this distance is 174mm in the Podium – 50mm more than the 38 and 11mm more than the 40.
This is important because as the fork is loaded and flexed fore and aft, the ‘bending’ force of the stanchions and uppers is passed through the bushings. The bigger the distance between the bushings, and the bigger the bushings are, the better these forces are managed.
Uncontrolled and peaking forces can lead to unpredictable behaviour during compression as the fork sticks and releases through its travel. This can override the consistency of the damper that many brands, including Fox, spend a lot of time perfecting.
Controlling these forces as the fork compresses leads to less friction and a smoother action, essentially mitigating unpredictable forces, resulting in a better-managed feel.
The bushing-to-axle distance also matters
Just as importantly, as the fork compresses, the distance between the axle (which is attached to the stanchions) and the bushes (which are fixed within the upper tubes) decreases.
In a regular fork, this distance remains the same; the axle and bushes are fixed on and in the lowers.
As the fork compresses, forces – bending and otherwise – put through it increase. Decreasing the distance between the end of the lever (the wheel axle) and the bushings is claimed to create a smoother-feeling fork.
With a USD fork, the relationship between forces and bushing load isn’t the same as a conventional one. According to Fox, the further into their travel they get, the smoother they feel.
A damper re-tune
Fitted with the impressive GRIP X2 damper with low- and high-speed compression and rebound-damping adjustment, the Podium’s extra smooth, bind-free chassis means Fox has had to re-work the damper's tune to compensate.
Compression damping has been increased thanks to a redesigned mid-valve, now with two ports instead of three.
During the fork’s development, different damper tunes were blind tested to discern which felt best, with the test team settling on the tune you can buy.
The rebound tune has also been adjusted compared to the standard GRIP X2, to accommodate for the lower unsprung mass of the USD design.
Like all Fox forks that precede the Podium, the compression damping is adjusted via two dials on the top of the fork leg and the rebound via two dials on the bottom, protected by a screw-on cap.
Air-spring refinement
Fox’s latest GlideCore air spring – found in the new 36 – is designed to insulate the spring from binding forces created by chassis flex.
The flex or bending forces the chassis deals with are passed into the fork’s internals, potentially creating ‘stickiness’ during compression and extension.
Decoupling nitrile butadiene rings (think thick rubber O-rings) between the air spring and stanchion enable the spring to ‘cant’ slightly within the stanchion as the bending forces are exerted.
The result is a fork that’s freer to compress with less binding, especially at higher loads caused by increased bike speeds.
According to Fox, the GlideCore rings can also compress slightly with vertical loading as the fork cycles into its travel before the spring is activated, resulting in a smoother ride.
The Podium’s air spring is filled from the bottom with auto-equalising positive and negative chambers.
Fox has redesigned the volume-reducer spacer for the Podium, cutting each spacer’s volume from 10cc to 5cc. This increases fine-tuning potential.
The spacers don’t clip together, either. Attached to the air spring’s cap – which is removed using a cassette tool – is a prong that the spacers slide over.
Finer details
Thanks to gravity, the lubricating oil in an upside-down fork sits against the seals which are at the base of the uppers. Compared to a regular fork – that relies on the oil being ‘splashed’ upwards towards the seals as its cycles through its travel – the Podium has the potential to feel plusher for longer.
Service intervals are said to be 150 hours of riding, which is slightly longer than the 38’s 125-hour figure.
Air bleeder valves sit on the top of the fork’s crown, integrated into the compression-adjustment dials and the spring top cap. But the inverted design means bypass channels – seen on the lowers of traditional Fox forks – aren’t needed.
The inverted design has the potential to reduce unsprung mass.
Everything on your bike that’s not suspended by a spring is classed as unsprung mass; for a traditional fork, this includes the front wheel and tyre, brake and fork lowers, plus the fork’s damper (or parts of it) depending on its configuration.
On an upside-down fork, the lowers are now the uppers, reducing the unsprung weight.
However, Fox was coy about the specifics of the Podium’s weight distribution – it’s entirely possible the unsprung mass is very close to a traditional mountain bike fork. Without disassembling the fork and weighing every component, it would be impossible to tell.
Carbon fibre stanchion guards bolt onto the dropouts, but these are optional. Cable-routing guides are also included, which clamp the fork’s uppers.
Fox has promised a mudguard will be available in time for autumn 2025. The brand says it mounts using two circular clamps on the uppers, just beneath the crown, and then has a locating wedge that slots inside the steerer tube.
Fox Podium Factory fork pricing details
The range-topping Podium Factory costs £2,199 / $1,999.99 / €2,399 / CAD$2,679 / AU$3,349.
Fox says more affordable Performance Elite or Performance models aren’t currently planned, but that may change if there is demand for them.
Fox Podium Factory fork specs
The Podium is available in 160mm and 170mm-travel options.
It’s officially only compatible with 29in wheels with a 44mm offset/rake figure, but there’s enough clearance to fit a 27.5in front wheel if you wish.
It uses a 200mm post-mount brake interface and is compatible with a maximum 230mm-diameter rotor.
There are two steerer types available, a 58mm model and a 68mm model designed specifically for electric mountain bikes. Both steerer types are eMTB-rated, however.
A 170mm-travel, 29in-wheel Fox Podium Factory fork with a 225mm-long steerer tube weighs 2,730g.
