Mountain bike suspension can be an intimidating thing to fiddle with, especially if your high-end fork or shock seems to have more dials than the space shuttle. Sure, you know your bike feels like crap over that one rough section of trail, but should you add more or less damping? And are we talking compression or rebound? And was it four clicks or four turns?
Ryland Lueders' free ShockTune app aims to solve the mystery of suspension setup using only your phone. How ShockTune Works
The idea is straightforward enough: By mounting the phone solidly onto your handlebar or seat post, ShockTune uses its accelerometer to measure the forces acting on the bike. Picture yourself riding towards a big ol' rock with the ShockTune app running on your handlebar. When your front tire hits the rock, the phone's accelerometer picks up the impact because, well, it forces the entire bike upwards, no matter how good the suspension is. ShockTune displays that upward movement on a graph; the bigger the spike, the more (or faster) the bike was moved upward by the rock and vice versa.
The thinking here is that the less the bike is moved upward, the better its suspension must be at absorbing the impact. In other words, a smaller spike means a better bike.
What ShockTune Tells You
''There are really two key things to look for in the results graphs,'' Lueders told me when I asked him what all the red and green lines mean. ''First, as you mentioned, minimizing the number of spikes and oscillations.'' We've already talked about what the big spike tells you, but the oscillations are all the smaller spikes on the graph that come afterward. Let's go back to that same rock for this one. You're going to run straight into it again, only this time we're thinking about what happens after the initial impact is absorbed. Let's also pretend that your fork is, for some strange reason, running zero clicks of rebound damping; once the fork takes in the hit from the rock, it'll want to extend very quickly, so much so that it'll keep trying to do it, only to dip into its travel slightly and then extend again. And again. And maybe a bunch more times, too, even though the rock twenty-feet behind you.
Of course, depending on your level of sensitivity, this might be something you've felt before or maybe not, blissfully unaware of the blown damper in your eight-year-old fork. I'm sorta jealous, to be honest. Anyway, you generally want as little of that extending and dipping, AKA oscillations, as possible so that your suspension is ''quiet'' or ''controlled.''
The second thing you're looking for is minimizing the extremes, those big spikes on the graph that signify the bike being moved upwards excessively fast. Remember, a smaller spike means a better setup, and it goes in both directions. Lueders gave me an example of his fork using a bit too much rebound damping, which the graph showed as a large downward spike post-impact, as well as a larger upward spike but fewer oscillations.
''This illustrates the tradeoff we make with excessive rebound damping,
'' Lueders told me. ''That is to say, while the firmer rebound setting nearly eliminates oscillation, it comes at the cost of increased downward velocity after the bump and increased rebound velocity.
One thing ShockTune won't do is tell you which way to turn the dials - you'll have to interpret that yourself - but Lueders said that the app is intended to help riders better understand what their bike is doing under them. ''I was actually increasing the rebound damping on my fork, trying to reduce the rebound pop I was feeling,
'' he said of the experiment above. ''But, in my case, I had actually added too much rebound damping and it started to have the opposite effect of what I intended.
If you're wanting the deep-dive on ShockTune, you can check out Lueders' explainer here
Sounds neato, right? For sure, but there are a few other things to mention, the most notable being that ShockTune is something you use in a controlled environment, not at any point during the ride. Because it's using the accelerometer inside your phone, you have to attach the phone solidly to your bike, but obviously not any of the moving suspension components. If you're evaluating your fork, you'd probably mount it to your handlebar; the shock, you'd attach it to your seat post.
The phone must also be mounted ''perpendicular to one of the axes,'' which is a fancy way of saying get it straight or flat. Once you press record, the accelerometer will also measure everything
it feels, and it will definitely feel you pedaling squares as you sprint towards that rock again. Because of this, you'd want to focus on a single, short section of trail, and try to be as consistent with your speed, line, and body inputs as possible. And the more samples you take, the clearer the picture will be. You can also combine and average your recordings by clicking one button.
Does it Work?
After farting around with mounts and rubber bands that wouldn't keep the phone from shaking when I hit a bump, I made my own solid mount using some reflector pieces, SRAM shifter hardware, and an old Topeak cellphone case that now has an extra speed hole. I used a spirit level to ensure that the phone was as flat as possible, with the homemade mount allowing for angle adjustments to get it just right on every axes. The phone was attached to the Mondraker F-Podium DC's handlebar with RockShox's new SID Ultimate on the front of it, and my artificial bump was as high-tech as it gets: I found a 2x4 in the neighbor's yard and laid it on the road.
First up was running straight into it with the fork unlocked and the ShockTune app recording, and I saw the results as soon as I pressed the stop button: A green spike. Next up, I locked the SID out and rode straight into the 2x4 at roughly the same speed as when the fork was unlocked, only this time the spike was much, much taller because the suspension was too firm. With the fork effectively not able to move, the phone's accelerometer was displaced quicker and more than when the fork was unlocked, which showed itself as an even larger green spike.
I could produce a similar effect using too much rebound damping, too, only inverted on the graph. While ShockTune has some limitations in that the phone needs to be level and the intended impact in near-isolation, the completely free-of-charge app provides some interesting data for those curious about what's happening under them.