Racking up wins since the last Olympics as a prototype, SR Suntour’s automatically-controlled TACT electronic suspension has proven itself at the top-tier of cross-country racing. But now, starting with a decisive short track win by Tom Pidcock at the opening round of the 2023 World Cup, SR Suntour TACT e-suspension is almost ready for an official release.
Take a closer look with us from the Nové Město na Moravě track and race pits, as we dive into what makes this upcoming electronic suspension control so unique…
all photos by Cory Benson, copyright Bikerumor.com
Let’s start with a disclaimer that what goes on inside this next-gen SR Suntour TACT e-suspension is still officially undefined. While similar automatically-controlled mountain bike suspension systems from the likes of Fox & RockShox have plenty of visible external sensors, batteries, wires, and separate components that hint at much of their functionality… SR Suntour TACT is almost entirely self-contained. And TACT isn’t quite ready for prime time yet, so SR Suntour is staying tight-lipped about the details for the time being.
But, this prototype suspension tech is being raced on the XC World Cup by multi-discipline INEOS racing powerhouses Tom Pidcock and now Pauline Ferrand-Prévot on their new Pinarellos. Plus, we spotted it on the Scott Spark bike of German racer David List of Lex Ware MTB.
And, we’ve heard interesting comments from riders and mechanics about setup, customization & real function on the trail. Plus, a patent application I’ve dug up suggests some true innovation both in a new sensor and an all-new type of compression valve control!
How does it work?
Like other electronically-controlled suspension, the concept is relatively simple: By collecting sensor data on bike & trail conditions, an electronic suspension controller can automatically open or close the compression damping circuit of your fork and/or shock, so that you are always in the most effective suspension mode for the terrain.
The SR Suntour solution looks to be different in that much of their system is contained just within the body of their Axon 34 Werx TACT fork and Edge Plus TACT shock. Sure both fork & shock are connected to a single wire into the frame – presumably to a central power supply and/or CPU – but there do not appear to be any other external sensors. And there are no external controls.
What’s unique from SR Suntour?
That lack of external controls is certainly one of the most noticeable features, but also hints at the true functionality & reliability of this system. Do you really think that Tom Pidcock would race something he can’t override if he wasn’t confident in it when an Olympic medal or World Cup win were at stake? Of note, yes he won Olympic gold with this back 2021, he won the 2022 Nove Mesto XCO olympic-distance race with it, and on Friday he won the XCC short track here with it, too. The system seems to be controllable and adjustable via a partner app on a mobile phone to select a rider’s desired settings.
But then, you just ride and it promises that your suspension will always be in the correct mode.
Chatting with SR Suntour, they mentioned that during the course of a World Cup cross-country mountain bike race their TACT system will change modes around 1500 times, or around 200x per lap over what is essentially a 80-90 minute race.
But is it just open or closed on impact?
A new type of valve inside!
Talking with a mechanic apparently familiar with the SR Suntour TACT system (but not currently a team testing it), we were told that what really set this new system apart from other automated suspension controllers, was that it wasn’t simply ON-OFF.. Locked or Open. Digging into some patent filings, I found a description of a new type of electronic compression damping control valve that helps explain how & why this could work.
Instead of using the conventional inline needle valve that is either closed or open, SR Suntour may be using a blind-hole valve with a rotating-body that can be configured to have multiple ‘open’ positions from a “medium” or “partially open” setting up to “fully open”. Another benefit of this ‘inventive’ valve design is that it requires less force to actuate and no force to keep closed, meaning less stress & wear, unlike the needle which must resist movement with each impact and can leak under cumulative impacts.
Smart sensors for improved uphill suspension
While all of that sounds good, what might really be the defining feature of the new SR Suntour TACT suspension is hinted at by the Smart Sensor Technology label on the fork and shock. Reading into that same patent, SR Suntour is describing a “inventive damper control arrangement” system that includes “upward lift detection”. That means instead of waiting for a sensor to detect an impact like other automated electronically-controlled suspension, the TACT system would be able to automatically unlock the suspension when a rider pulls up on the handlebar to lift or simply lighten the front wheel to get over an obstacle.
The idea is smoother suspension actuation while climbing rough terrain – like the Nove Mesto track’s steep rooted climbs – in order to reduce rider fatigue and allow them to keep their weight forward for more efficient pedaling & bike control.
This solution also can pre-emptively unlock when the wheel smoothly drops away to be ready for a pending impact.
Where are all of the sensors, actuators, controllers & batteries?
In the fork, there seems to be plenty of space inside the right fork leg to place both the actuator and 3-axis accelerometer sensors, sharing space with the damping function. All of the TACT-equipped Axon 34 Werx forks we’ve seen retain standard rebound damping adjustments on the bottom of the leg (and standard air spring controls on the opposite left leg) suggesting everything is in the top of that right leg. The carbon Werx crown is not open from the bottom, so there could be something hidden in the steerer tube?
As for the rear, an external box bolts onto the Edge shock for automated compression damping controls, while a manual rebound knob is angled off to the side. This Pinarello Dogma XC uses a conventional mount shock, but the Scott Spark that we also saw testing the new suspension uses a trunnion mount. Interestingly, the Scott gets an air valve in a different orientation for access hidden inside the frame, but that control box on the side of the Edge TACT shock doesn’t actually fit inside the Spark, so we only saw it without the standard protective cover.
Both fork and rear shock are plugged into a single wire that disappears into the frame – presumably for power or centralized control. During regular service between races, we saw INEOS mechanics unplug and disconnect the SR Suntour suspension components, but we couldn’t see how complex the wired connections were.
OK, so when can you get SR Suntour TACT?
So far, SR Suntour has been developing and testing their new electronic suspension control for racing under UCI approval as a prototype. But it seems that status is soon to expire, and they’ll need to make it available to the public. That means that already this summer in June 2023, you could get ahold of your own SR Suntour TACT suspension setup, in very limited numbers – think maybe 100 sets available to consumers in 2023. But…
This is a very custom setup that you simply can’t just bolt-on to any bike. SR Suntour’s TACT e-suspension will only work with the few bikes that have already served as test beds during its development. That includes Pidcock’s original BMC Fourstroke, his new Pinarello Dogma XC, and the bold Scott Spark that saw David List of Lex Ware MTB testing.
Any mountain bike racer with the latest versions of these top XC bikes – and plenty of extra cash – could buy a complete SR Suntour TACT e-suspension upgrade kit this summer and have their bike refitted through an official service center. SR Suntour suggests that pricing hasn’t really even been considered yet, but this ultra-limited summer release will likely be expensive. Once they’ve put the system out in the world to more users – and gauged interest – they’ll look at how best to optimize the cost of the integrated technology for the type of riders that could benefit from such suspension automation.
Sure, that’s a lot of info and tech speculation for now. But as for official details from SR Suntour, we expect to know more following Eurobike in June.