BMC Speedfox with TrailSync first ride review

All new 120mm trail bike has a trick up its sleeve

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At first glance, BMC’s new Speedfox is a pretty conventional trail bike. It’s available with either 27.5” or 29” wheels depending on frame size. The geometry is pretty conservative, typified by a head angle of 68.25 degrees and if the frame looks familiar that may be because it shares most of its DNA with BMC’s Agonist marathon bike, which was released last week. Only the upper link and an enlarged top tube junction are different, but that’s a clue to something rather special going on inside the frame.


What sets the Speedfox apart from the crowd is a unique, fully-integrated dropper seatpost, which also actuates the shock remote lockout.

The system, which was developed by BMC, is dubbed Trailsync and it allows the shock and seatpost to be controlled simultaneously by a single bar-mounted remote.

With no need of a separate shock remote, this leaves the bar refreshingly uncluttered
Jeremie Reullier

The post itself is a 30mm shaft, which slides directly into the seat tube — this means the frame is not compatible with a conventional seatpost.

The seat tube houses a pair of large nylon bushings and a seal-head at the top, just like you’d find in a suspension fork.  A brass pin sits inside that enlarged top tube/seat tube junction; this stops the post from rotating inside the seat tube and slots into three holes in the post, which fix its height at three distinct positions.

A brass pin sits inside the top tube. This fixes the post in its three set positions and stops it from rotating
Jeremie Reullier

For the large and XL frames, the dropper travel is 120mm; for the small and medium, it’s 80mm and 100mm respectively. For all sizes, the intermediate height sits 35mm below the highest.

There was impressively little fore-aft or rotational play in the seatpost

The base of the post is fixed inside the frame, so in order to adjust the seat height there’s an adjustable collar on top of the post. This allows 35mm of vertical adjustment. If your seat height is out of this range, you’ll first have to cut the post down to the required length like you would a fork steerer.

BMC claims that by using a fully integrated post — with its large shaft diameter, wide bushing overlap and easily serviceable seal head — its post’s long-term reliability should be superb. But that’s not what truly makes it unique.

When the seatpost extends to its maximum position, it pulls on an internal cable that actuates the shock’s remote climb switch. This turns it from ‘open’ to ‘trail’ mode. In other words, the dropper lever also acts as a suspension remote. This is the crux of Trailsync.

The post pulls on a cable which firms up the shock for climbing when in the upper position
Jeremie Reullier

The obvious advantage of this is that there is less clutter on the bars, with fewer cables than having a separate remote dropper and lockout.

It also makes the bike much simpler to ride. There’s no chance of dropping into a descent without remembering to switch off the shock’s lockout (we’ve all done it!). There’s simply less to think about when riding, and less chance of getting it wrong.

Dropper seatpost ride impressions

At the press of one switch the seatpost drops and the shock opens up, allowing you to tear back down without fuss
Jeremie Reullier

There was impressively little fore-aft or rotational play in the seatpost. On the trail, the post’s action reminded me of Specialized’s first generation of Command post.

The return speed is pretty damn fast — although this can be adjusted to some extent by changing the air pressure inside the spring — and the three-hole-and-pin mechanism operates similarly to the Command post too. Finding the middle setting takes a little practice at first, but I soon got the hang of it.

I don’t normally use an intermediate height on a dropper, but I often found myself using the medium position here in order to open up the shock. This is ideal for super technical climbs or lumpy traverses, but when spinning along rough fire-roads I did find myself wishing I could have a fully open shock and a fully extended seatpost simultaneously — the medium height is too low for prolonged pedalling, and the suspension is occasionally too harsh with the seat fully extended.

I can imagine many traditional BMC buyers will miss having a full lockout too, although it is possible to run the cable so the post switches between trail and locked modes, instead of trail and open.

The post head allows for a little height adjustment, but you’ll need to cut the post down to the correct ball-park length first
Jeremie Reullier

Some may also be put off by the need to cut the seatpost down (not so great if you want to lend the bike to a friend), and I would have liked more dropper travel for steep descents.

So the Trailsync system is a compromise, but one that does what you want it to most of the time. There certainly are situations where it’s not ideal, but I get the appeal of only having one button to think about.

You could ask, why not just do away with a shock lockout altogether? Well, as with the Agonist, I was a little surprised at the amount of pedal-bob the Speedfox exhibits when out the saddle with the shock open. BMC makes bold claims about its pedalling efficiency, but I’d say it bobs more than many bikes of this travel. 

There are ways to design suspension systems to be more naturally efficient by increasing the effect of chain-tension on the suspension (known as anti-squat). However, more anti-squat can result in pedal-kickback while reducing suspension sensitivity and traction, especially when pedalling through rough terrain.

The Trailsync system allows for fairly efficient pedalling when the seat is up, without compromising the suspension too much when the seat is lowered and the shock is open.

Overall ride impression

We found the Speedfox’s geometry a little short and steep on technical terrain
Jeremie Reullier

I took the Speedfox down some pretty demanding descents at the foot of the Matterhorn, near Zermatt. On the steep and rocky stuff, the fairly steep head angle and quite short front-centre made the bike feel a little keen to throw you out the front door on steep steps, even with the fork setup pretty firm.

My test bike was fitted with the outgoing model of the RockShox Pike RCT3 fork, whereas the production bikes will get the 2018 model, which should offer more mid-stroke support.

It’s nice to see a fairly short stem (55mm), but I’d have liked a slacker head angle for steep terrain stability. It’s fair to say that by modern standards the handling is on the traditional, rather than super-stable side.

Still, the suspension works well when left open, with impressive suppleness off the top and a nice gradual build-up of support. I probably pushed beyond the envelope of what this bike is designed for on the steep and rocky terrain I rode, but on the more mellow trails it rides well. It’s light, agile and very easy to ride.

The agile handling works well on mellower flow trails
Jeremie Reullier

The relatively long chainstays (445mm in L and XL) put you in a central riding position, making it easier to rail turns with confidence, without making it feel at all sluggish.

The Trailsync system will make the Speedfox particularly well-suited to those who are relatively new to the sport or simply want a bike to get on and ride without any unnecessary distractions.

Speedfox pricing and availability

  • The top-of-the-range Speedfox O1 ONE that I rode will cost €6,999.
  • The base model — which has an all-aluminium frame and a non-dropper seatpost — will cost €1,999.

Availability is expected from July. See for more.

Product Specifications


Name Speedfox
Brand BMC