Fox Factory Tuning programme makes your old suspension perform like new

It's easier (and cheaper) than ever to upgrade your Fox suspension

Every year suspension components get a little better; subtle refinements to damping tunes, and smoother, more supportive air spring designs add up to really noticeable improvements in performance.

So, if you want your top-end fork from a few years ago to match the performance of the latest and greatest model, you might think you’d need to fork out (pun fully intended) serious dough for the 2018 model.

Now, though, there is a better way. Fox will soon be rolling out a range of upgrades for its 32, 34 and 36 forks through its network of national service centres at relatively affordable prices. In fact, if you’re paying for a fork service anyway, you could upgrade to an EVOL air spring for an estimated €40 extra, and a choice of damping tunes (including the MY 2018 version) for as little as €25.

The shim stack assembly of the E16 damper laid out. If your fork is being serviced anyway, the shim stack can be swapped for as little as €25 extra
The shim stack assembly of the E16 damper laid out. If your fork is being serviced anyway, the shim stack can be swapped for as little as €25 extra

In other words, it’s now possible to upgrade the internals of an older fork to 2018 spec for just €65 more than the cost of a routing service (prices are yet to be confirmed and will vary by country and fork model).

So how will that affect how your fork rides? Well, before we get into what upgrade options Fox is offering, it’s worth explaining just what’s going on inside the damper of your fork.

A brief explanation of compression damping

The compression damping in your fork is controlled by a shim stack. Basically, this is an assembly of flexible metal washers (shims) of different diameters and thicknesses, which together control how oil flows through the damper under compression.

When the fork compresses, oil is forced through ports at the base of the shim stack. The shims act to control the oil flow in order to stop the fork compressing too suddenly, but they bend out of the way under hard compressions, in order to allow enough oil flow to absorb big impacts.

Imagine the shim stack like a big door being held shut by a spring. The door slows the flow of people (oil) through it (think of slow fork compressions like pedalling), but if people suddenly rush to get through it (think hitting a bump) the door is forced to open up wider, allowing people (oil) to flow through faster.

If the shim stack doesn’t allow enough oil flow under high-speed compressions, the result is excessive feedback through the bars and too little travel is used on harsh bumps — this is known as spiking.

Conversely, if the shim stack is too flexible, the fork will lack support and dive through its travel. For this reason, compression damping shim stacks are endlessly tinkered with by suspension tuners who try to find the ideal compromise between comfort and support — Fox has gone through a few different iterations in recent years.

The damping tune options: VC49, E16 or E18?

If you’ve got a pre-2016 Fox 32, 34 or 36 fork with a FIT4 damper, it’ll have a compression damping tune known as VC49. Basically, this tune uses a shim stack which is pretty “on-off” in the way it opens up.

That means you get quite a lot of feedback through the bars on small chatter, but it opens up quite suddenly, so you don’t get much support for mid-speed compressions. It’s pretty harsh, yet it dumps through the travel too easily on bigger hits.

The EVOL spring uses a transfer port on the inside of the stanchion. As such, the EVOL upgrade requires a different CSU on the 36
The EVOL spring uses a transfer port on the inside of the stanchion. As such, the EVOL upgrade requires a different CSU on the 36

For this reason, Fox developed what it calls the E16 tune. This has a shim stack that opens up far more smoothly, delivering better small-bump sensitivity and increased mid-stroke support too.

When I back-to-back tested these two tunes, keeping all other settings the same, the E16 tune held the fork much higher in its travel during braking-bump-filled steep sections, and seemed to offer better sensitivity and traction on smaller chatter too.

With the E18 tune, Fox hoped to build on what it had learned from the E16 tune, but wanted to make it a little more compliant over harsh hits. It did this by replacing two shims with one slightly stiffer one. According to Fox, this “takes the edge off” bigger hits, by allowing more oil flow at higher shaft speeds.

While the older Fox 36 air spring is travel adjustable and features a transfer port on a thin central shaft
While the older Fox 36 air spring is travel adjustable and features a transfer port on a thin central shaft

As the name suggests, the E18 tune is what comes stock on all 2018 FIT4 forks. The added mid-stroke support from the EVOL spring means the 2018 forks can work better with a slightly less firm damping tune; although the E18 will also benefit less aggressive riders with the older air spring.

Meanwhile, the E16 tune may still be preferable for strong riders, who don’t mind a little more feedback and want more support, especially in conjunction with the non-EVOL spring. The older VC49 tune is probably only going to benefit cross-country riders who want a lot of low-speed threshold damping for pedalling efficiency. According to Fox, “that’s the point of this programme — you can have what you want.”

So, if you’ve got a MY 2016 onwards Fox 32, 34 or 36 fork, you could just send your fork in for a re-valve, but that would be expensive. To make it more cost effective, Fox recommends performing a re-valve when the fork is opened up anyway during a service. Then you can take your pick of the VC49, E16 or E18 damping tune (although the VC49 tune is not recommended for the 36) for an additional cost of around €25, on top of the cost of the fork service.

Spring upgrade options

The Fox Factory Tuning programme allows you to upgrade the compression damping assembly and air spring on older forks to 2018 spec
The Fox Factory Tuning programme allows you to upgrade the compression damping assembly and air spring on older forks to 2018 spec

If you’ve got a 32 or 34 fork, it’s fairly simple to upgrade the spring to the latest EVOL air spring. This means you’ll get a higher negative spring volume, offering a more linear, coil-like start to the stroke, resulting in better off-the-top sensitivity and traction, with more support after sag. At around €40 (again, assuming you’re having a service anyway), this could be a pretty top-value upgrade.

For Fox 36 forks, the EVOL upgrade is more involved. This is because the EVOL spring uses a transfer port that’s built into the inside of the stanchion, rather than on a central rod as in the older (non-EVOL) Fox 36 air spring. As a result, 36 forks require a whole new CSU (crown steerer unit) to get the EVOL air spring.

This will make the EVOL upgrade far more expensive in the Fox 36 than the 34 or 32 unless you want to replace the CSU anyway — perhaps because it’s worn, you want to upgrade to Kashima stanchions or you want to try a different fork offset — in which case, it’s probably worth upgrading to the EVOL spring at the same time.

Do bear in mind that the EVOL spring is not travel-adjustable like the older Fox 36 spring — if you want to change travel down the line you’ll need to swap the spring.

As mentioned above, Fox says the E18 damping tune complements the EVOL air spring and recommends upgrading the damper to E18 when fitting the EVOL spring. Having said that, it’s not compulsory by any means and more aggressive riders may prefer the E16 tune even with the EVOL spring for maximum support.

What’s the bottom line?

During back-to-back testing, the E16 tune felt noticeably more composed and traction-rich than the older VC49, while upgrading to the EVOL spring gives a more stuck-down coil-like feel
During back-to-back testing, the E16 tune felt noticeably more composed and traction-rich than the older VC49, while upgrading to the EVOL spring gives a more stuck-down coil-like feel

The prices of these upgrades are yet to be confirmed and will vary from country to country depending on your national Fox service centre. While you could send your fork in to get a damping and spring upgrade at any time, they’re going to be far more cost-effective if your fork is being taken apart for a service anyway.

In that case, and if the prices we’ve been quoted are realistic, this could be a seriously thrifty way of tuning and upgrading your suspension. Getting a re-valve for as little as €25 sounds like a no-brainer if you’ve got the older VC49 tune. Having ridden them both, the E16 and E18 tunes represent a really significant traction-boosting upgrade over VC49.

For Fox 32 or 34 fork owners especially, the EVOL spring upgrade is well worth considering too as it offers noticeably more initial sensitivity and gradual support. I can think of far worse ways to spend €40 or so.

The Fox Factory Tuning programme is due to roll out in September. For prices, advice, availability and compatibility details, contact the Fox distributor in your country. In the UK that’s Silverfish

Seb Stott

Technical Writer, UK
Seb is a geeky technical writer for BikeRadar, as well as MBUK and What Mountain Bike magazines. Seb's background in experimental physics allows him to pick apart what's really going on with mountain bike components. Years of racing downhill, cross-country and enduro have honed a fast and aggressive riding style, so he can really put gear to the test on the trails, too.
  • Discipline: Mountain
  • Preferred Terrain: Steep!
  • Current Bikes: Focus Sam 3.0, Kona Process 111, Specialized Enduro 29 Elite
  • Dream Bike: Mondraker Crafty with Boost 29" wheels, a 160mm fork and offset bushings for maximum slackness.
  • Beer of Choice: Buckfast ('Bucky' for short)
  • Location: Bristol, UK

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