Stumpjumper 15 Shock Testing

The Specialized Stumpjumper could be the most popular mountain bike in the world, and the 2025 Stumpjumper 15 is the latest version in its long history. With modern geometry and thoughtful features all about, Specialized has built a bike that’s as easy on the eyes as it is to ride. With such a wide range of customers, the Stumpjumper has to be approachable to every rider, from someone buying their first mountain bike to Specialized racers around the world. I find myself somewhere in between those two, and while I find myself between the tape every summer, I just like goofing off on my bike all year round.

From the first ride, the Stumpjumper 15 has been a comfortable, predictable, and just plain old fun bike that will serve as a test platform for many bike parts to come. Today, we’ll be trying out several of the most popular rear shocks on the new Stumpjumper 15 to figure out which work the best, and which you should upgrade to.

Perhaps the most exciting and polarizing feature of the Stumpjumper 15 is the new Genie shock, which is a collaboration between Specialized and Fox. Armed with a fancy name and big air can, the Genie shock is based on Fox’s Float Shock, and promises coil like performance in the initial stroke, paired with air shock support deep in the travel. Without getting too technical, the Genie has a large air volume in the first 70% of its stroke, giving it a linear coil-esque feeling, similar to other shocks like the Vivid or the Float X2. What sets it apart, is that a portion of the air volume is cut off part way through the travel, giving the shock a smaller volume and making it more progressive. Specialized has magically squeezed two different shocks into the place of one, perhaps the inspiration behind the name?

Before we start switching things out, let’s talk about how the Genie rides. First of all, the Genie is not just a gimmick, and it tells a story about how Specialized wanted the Stumpjumper 15 to be ridden. With excellent small bump sensitivity, the Genie is eager to get into its initial stroke, allowing the rear wheel to get up and out of the way of anything you plow it into. Through general trail riding where you’re just hitting little bumps, rocks, and roots, the Genie smooths out the trail in a way that’s very similar to a Vivid or Float X2 with their oversized air cans. While not quite on the same level of a coil shock’s suppleness, the Genie really shines in this environment, and feels like a magic carpet ride through small bumps and general small trail chatter.

When the hits increase in size, and the Genie goes into progressive mode, it handles those big hits with surprising composure, giving a predictable ramp up that catches you on those big drops or compressions. I played with changing where in the travel the Genie changes volume, and found the stock setting to be the most intuitive and balanced. I also played with adding volume spacers, and just one was plenty. My only gripe with the Genie shock is its lack of adjustability.

We have the Performance model, which has a two position compression lever as well as 13 clicks of LSR. There just wasn’t enough compression damping on the Performance Genie to handle successive hits, and the shock was quickly overwhelmed when going through consistently rough sections of trail and had to keep its composure through several consecutive impacts. More money will get you the Performance Elite or Factory Genie shock, which have three clicks of LSC, but I still think that would be inadequate, but I haven’t ridden either of those shocks. I really wish this bike came with the Float X version of the Genie, with the much wider range of compression adjustments, but that shock is currently only specced on the Levo SL.

This might just be the perfect shock for the Stumpjumper 15. Unfortunately only available on its motor equipped relative; is Speicalized picking a favorite child?

For the majority of riders, the stock Genie shock is just about perfect. With an amazingly supple initial stroke and end stroke support given by the two spring curves they’ve fit in one shock, Specialized makes it clear that this bike is meant to be comfortable and intuitive for everyone that hops on it. Riders that are looking to push the envelope and find both their personal limit as well as the bike’s limit will find that the Genie may not be the best tool for the job. Luckily the very standard 210x55 sizing means that you have lots of shock options to play with.

Mike tested a bunch of 210x55 shocks on the previous gen Stumpjumper EVO, so we have tons of Stumpjumper 15 compatible shocks laying around the shop. This opportunity is too good to pass up, so after a couple of weeks on the Genie, I started playing with all kinds of shocks on the Stumpjumper EVO. First up is the shock that I believe would have been specced on just about every build if it wasn’t for the Genie, a Float X. This particular Float X is taken from Mike’s Stumpjumper EVO frame, and has the Specialized Rx tune, so this should be just about perfect for the Stumpjumper 15. Unsurprisingly, the Float X installed perfectly without any issues, just like the rest of the shocks I tried.

It’s certainly just in my head, but this bike just looks more right with a piggyback equipped shock. Something about the Genie never quite tickled my subjective fancy, and the Float X instantly looked more at home on this rig. On trail, the Float X was both similar and completely different to the Genie. Actually, the more I think about it, the Float X was completely different in every sense. Off the top, the Float X was more hesitant to enter its travel, and felt slightly harsher off the top. With smaller seals and volume this doesn’t come as much of a surprise, but the Float X makes up for this in the increased support with the 10 clicks of LSC that completely change the nature of the shock. I’ve ridden the Float X on a few bikes now, and have found that with any less than all of the compression the Float X will blow through its travel, but when all the way closed, the Float X holds up very nicely to sections of trail that would bully the Genie.

A wider range of compression damping is always welcome.

Overall, the Float X is better suited for hard charging riders, as the compression adjustment gives the shock way more composure through repeated rough hits, and you’ll need to run an extra volume spacer or two because of how linear the Stumpjumper 15’s leverage curve is. Adding an extra volume spacer really livened up the shock, giving it more mid stroke support and keeping it from using all of the travel more than it needed to. I also ran my rebound pretty dang fast, 4 clicks from open, to keep that agile trail bike feeling and keep the shock higher in its travel.

There are a couple Stumpjumper 15 builds that feature a coil shock, which instantly had me a bit confused. All of the Stumpy 15 marketing tells us the bike is so linear that it needs a special proprietary shocks to not blow through the end stroke, thus the Genie was developed. But then Specialized turns around and specs linear coil shocks on their frame with a linear leverage curve, and doesn’t offer any explanation about it. So of course I had to try it for myself, and installed a Vivid Coil at about 25% sag. I chose the Vivid Coil because its adjustable Hydraulic Bottom Out makes it far more suited for linear frame designs than other coil shocks, butI started with it fully open to see what happens.

Like on other bikes, the initial stroke of the Vivid Coil is amazing. A coil shock paired with RockShox’s TouchDown technology is pretty much impossible to beat, and the Stumpjumper 15 with the Vivid Coil does a fantastic job of contouring the rear wheel to the ground. Even though I ran less sag with the Vivid Coil than the other shocks, climbing traction was fantastic, with the bike finding ways to squat and grab traction just about anywhere on the trail. You’ll get more pedal bob, but the lockout lever on the Vivid Coil is second to none, essentially turning the Stumpy into a hardtail for long road climbs.

Do product managers spec coil shocks primarily because they look sick? I wouldn't be surprised.

But like anyone expected, there was a trade off. I didn’t make it more than five corners before pulling over and closing the HBO circuit, and even still, I was using full travel far more often than I would have liked. Closing the HBO definitely helped the situation, but any of the air shocks were a hell of a lot more comfortable any time I had a big impact. I don’t want to be too dramatic, but I don’t recommend that anyone runs a coil shock on the Stumpjumper 15, especially not one without some kind of hydraulic bottom out feature. Specialized specs an Ohlins TTX22m.2 on some builds, and a Fox DHX on other builds, but neither of these shocks have HBO or any special tricks to help in bottom out scenarios. I’m so curious as to why they made that choice, when there are several other options out there that would suit this frame much better.

While I haven’t gotten the chance to try it yet, the Cane Creek Tigon could be the saving grace for coil shocks on the Stumpjumper 15. Armed with an air can that combines the small bump sensitivity of a coil shock with the bottom out support of an air shock, the Tigon could be the exactly what the Stumpy ordered. Stay tuned for further testing.

I’d be lying if I said I wasn’t biased towards the RockShox Vivid from the very start. Ever since it came out, this has been one of my favorite shocks on every bike I’ve ridden it on, and I was itching to get it on the Stumpjumper 15. Before we get to how it rode, let’s quickly touch on Float X2 vs Vivid, and why I didn’t ride the Float X2 on this bike. After riding both big air can equipped DH shocks from Fox and RockShox back to back on other bikes, I’ve come to the conclusion that they are incredibly similar, and the biggest difference between them is their adjustability. With the linear suspension design of the Stumpjumper 15, the HBO equipped Vivid is the smarter choice without a doubt.

A large air can, hydraulic bottom out, and plenty of adjustability seemed to combine the best of all worlds thus far, and the RockShox Vivid is without a doubt my favorite shock I’ve tried. Off the top, the Vivid is very similar to the Genie, but then actually has the support I was looking for in repetitive impacts. The RC2T damper has high and low speed compression, which lets me get a hold on the bigger impacts by adding a couple clicks of both. Once again, the linear suspension of the Stumpy 15 reared its head, and two volume spacers were needed in the Vivid to get the mid stroke support I was looking for. With both of those volume spacers in there, I ran the HBO right in the middle, and while I can still find the end of travel, it’s not a harsh experience.

We’ve got it good, and just about every shock I tried offered amazing performance with their own character. I would happily run the Genie for the rest of my days on the Stumpjumper 15, as Specialized have done a great job designing a shock specific to this platform. 97% of riders, including myself, are going to really enjoy this stock shock, and there’s no immediate need to spend hundreds of dollars on another shock. Especially if you’ve got the Performance Elite or Factory versions of the Genie, there’s enough tunability and progression to charge hard in comfort.

In my opinion, coil shocks just don’t suit the Stumpjumper 15. Specialized has gone out of their way to build a very linear leverage curve, and that’s something that just doesn’t play nicely with coil shocks. If you really want to make a coil shock work, I would highly recommend getting a progressive spring or the fancy air/coil hybrid Cane Creek Tigon. While the Vivid Coil is a great shock on lots of bikes, it did not suit the character of the Stumpjumper 15, and you’re better off spending your money on its air sprung sibling.

Overall, the RockShox Vivid was my favorite shock on the Stumpjumper 15. Combining my favorite features from every shock I tried, the Vivid had a blend of suppleness, support, and composure that is exactly what I was after. When packed with a couple volume spacers and a couple clicks of hydraulic bottom out, the Vivid has both the midstroke support and bottom out resistance I was looking for, and isn’t scared of taking consecutive hits. While the Stumpjumper 15 only has 145mm of travel, the Vivid gives the level of composure I would expect from an enduro bike, and really starts to blur the lines between short and long travel bikes. Anyone looking for maximum performance out of their Stumpjumper 15 should start and end their search with the RockShox Vivid.

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