XC racers will bleed a fork for a 20g service-interval saving. So when Pinkbike’s XC tech gallery from the 2026 XCO World Championships at Val di Sole went up on August 28, one bike in it made no sense on paper: Victor Koretzky’s title-contending Specialized Epic with a 450-gram Rimpact tuned mass damper stuffed into the steerer tube. Half a pound of dead weight, on a discipline where a wheelset launch gets covered because it shaved 300 grams. We wrote that wheelset story about Mavic’s Crossmax Ultimate four days before this one, and the contradiction is the whole point.

Here’s the short version: it’s the same production TMD that’s been quietly winning over World Cup downhill pits for two seasons. Koretzky just became the highest-profile rider to bring it to XC.

Quick Take

Rider / bike	Victor Koretzky, Specialized Epic
Part	Rimpact tuned mass damper, 450g, mounted in the steerer tube
Spotted	Pinkbike’s XC tech gallery, 2026 XCO World Championships, Val di Sole — Aug 28, 2026
Consumer version	Rimpact TMD V2, £199.99 (~$255)
Consumer weight	420g total, 250g suspended tungsten weight on dual springs
Fit	180mm+ steerer tubes, single or dual-crown forks
Where else it’s raced	Elite World Cup DH: Trek Factory Racing, Canyon CLLCTV, Scott Factory DH, Cube Factory Racing, NukeProof Axess Racing; hidden unit on Jackson Goldstone’s Santa Cruz V10
Independent lab data	None published yet — Rimpact’s own accelerometer testing only
Best for	XC racers on rough, high-frequency courses willing to trade grams for hand comfort late in a race
Skip if	You race smooth courses, or you’re not willing to add weight without third-party proof

What Actually Showed Up at Val di Sole

Pinkbike’s gallery is the kind of post that exists to catalog whatever’s bolted to the front of the fastest bikes in the pits, and this year it caught something that didn’t belong in an XC field: a Rimpact TMD, the same 450-gram unit that’s been living in downhill steerer tubes since roughly 2024, now sitting inside Koretzky’s Epic. Nothing about the part is XC-specific. It’s the DH product, unchanged, dropped into a completely different discipline.

That matters more than it sounds like it should. XC is the discipline that measures success in grams saved and watts not wasted. A rider on that circuit choosing to add weight — and not just any weight, a lump of tungsten that does nothing for propulsion — is either chasing something real or making a very expensive mistake in front of every TV camera at Worlds.

What Is a Tuned Mass Damper, Actually?

A tuned mass damper (TMD) is a small weight suspended on springs inside a bike’s steerer tube or frame, designed to absorb high-frequency vibration before it reaches the rider’s hands. It doesn’t reduce impact force from big hits — that’s what suspension does. It targets chatter: the buzzy, fast, low-amplitude vibration that never gets big enough to move a fork through its travel but adds up over a race-length effort.

Rimpact’s own name for the product is arguably not accurate. By the company’s own admission, its TMD is “neither tuned, nor damped” in the strict engineering sense — there’s no hydraulic circuit, no adjustable frequency tuning like you’d find in a skyscraper or a Formula 1 car. It’s a mass and spring responding passively to vibration. Call it a mass damper, not a tuned one. Rimpact still uses “TMD” because that’s what riders search for, and because the category got named before anyone was precise about it.

The Case For It: What Rimpact’s Own Testing Shows

Rimpact has run accelerometer testing at the headtube comparing a bike with the TMD installed against the same bike with a static weight of equal mass bolted in its place — a real control, not just “with vs. without.” The result: total energy reaching the rider was roughly the same in both cases, but the TMD produced a smaller, broader peak instead of one sharp spike. In practice, that’s a lower peak force through the handlebar after each bump, spread over a slightly longer window, which Rimpact frames as less fatigue over a long ride rather than more control on any single hit.

That’s a real, specific claim, and it’s more honest than most marketing copy for this category. It’s also Rimpact’s own lab, Rimpact’s own accelerometers, and Rimpact’s own choice of what to publish. No independent third-party test lab has put a number on this yet — not a magazine, not a university engineering department, nobody without a reason to want the number to look good.

Why This Was a DH Thing Before It Was an XC Thing

TMDs didn’t start at Worlds this week. They’ve been part of the pit-lane furniture in Elite World Cup downhill for two full seasons now — the same pits where SRAM’s wireless DH transmission went from novelty to standard kit. Trek Factory Racing, Canyon CLLCTV, Scott Factory DH, Cube Factory Racing, and NukeProof Axess Racing all run production or team-spec units, and Jackson Goldstone’s Santa Cruz V10 has carried a hidden unit through a run of results that’s hard to argue with.

DH is a more forgiving place to test half a pound of dead weight. A downhill bike like the Specialized Demo already weighs 35-40 pounds, so 450 grams disappears into the build. It’s also a discipline built entirely around high-frequency chatter at speed — square-edge hits, braking bumps, root fields at 30mph — which is exactly the vibration profile a mass damper is built to handle. If a TMD was ever going to prove itself somewhere, DH pit lanes were the obvious lab. XC racing, with courses that mix smooth fire road with rock gardens and a total bike weight under 22 pounds, is a much harder sell.

That’s what makes Koretzky’s Epic notable. We covered a mega-mullet DH prototype at the same Val di Sole Worlds week — tech moving from a niche idea into a World Championship start line. This is closer to the reverse: proven gravity-racing tech moving up into a discipline that’s supposed to reject anything that doesn’t pay for its weight in speed.

Do XC Racers Actually Need This?

Three things determine whether a TMD makes sense on an XC bike, and none of them are “does it look fast in a gallery photo”:

1. Course roughness. Val di Sole’s XCO course has enough technical, root-strewn singletrack to generate real handlebar chatter over a 90-minute race. A smooth, groomed XC course gives a mass damper almost nothing to damp.
2. Race duration. Fatigue-reduction claims compound over time. A 20-minute short-track race isn’t long enough for reduced hand fatigue to show up in a result. A full XCO effort, or anything marathon-length, is.
3. Weight budget elsewhere. Riders who’ve already built to sub-22-pound bikes with wheels like the Crossmax Ultimate have room to spend 450g on something that isn’t rotating or unsprung mass. Riders still chasing weight everywhere else probably shouldn’t spend it here first.

How Much Does a Rimpact TMD Cost, and Will It Fit Your Bike?

The consumer version Rimpact sells — the TMD V2 — runs £199.99, roughly $255 at current exchange rates. It weighs 420g total, built around a 250g suspended tungsten weight riding on dual springs, and it’s designed for 180mm-or-longer steerer tubes on either single-crown or dual-crown forks like the RockShox BoXXer. That length requirement is worth checking before you order: a lot of XC race bikes run shorter head tubes and lower stack, and a steerer that doesn’t clear 180mm won’t accept the full unit without stacking spacers to make room, which adds height you may not want on a race bike.

There’s no XC-specific version. What Koretzky ran is the same part a DH racer would bolt to a 40 fork, just installed in a cross-country frame’s steerer instead.

Who Should Actually Buy One

XC and marathon racers on genuinely rough courses. If your local circuit or your target race has sustained chatter — hardpack root sections, chunky singletrack, anything that vibrates your hands for minutes at a time — this is a plausible, if unproven, way to reduce fatigue late in a long effort.

Riders who’ve already optimized everything else. If your bike is already built to a weight budget you’re happy with and you’re looking for marginal gains that aren’t about grams, 450g of vibration control is at least a defensible next purchase.

Anyone curious rather than committed. At $255, it’s a cheaper experiment than a lot of the componentry XC racers already buy on faith — a single wheel upgrade costs more than this.

Who Should Skip It

Racers on smooth courses. No chatter, nothing to damp. You’re just carrying weight.

Anyone chasing a specific race-weight number. If you’re the rider agonizing over the gram-by-gram breakdown behind a $3,049 wheelset, adding 450g back in a steerer tube is a hard sell until there’s independent data proving it’s worth more than an equivalent weight saved elsewhere.

Anyone who wants third-party proof before spending. Rimpact’s internal testing is more transparent than most, but it’s still the manufacturer marking its own homework. Nobody outside the company has published a number yet.

The Bottom Line

Victor Koretzky running a Rimpact TMD at Worlds is a genuine crossover moment — DH pit-lane tech showing up on a World Championship XC bike, unmodified, on a rider good enough to matter. It’s also one rider, one race weekend, and a manufacturer’s own accelerometer data as the only evidence it does anything. XC racing spent this same week celebrating a wheelset that shed 300 grams to chase a podium; Koretzky spent 450 grams on the opposite bet. Both bets might be right. We just don’t have the independent data yet to say which one pays off on race day, and until that data shows up, this is a $255 experiment for riders on rough courses, not a mandatory upgrade for the rest of the field.

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Reporting sourced from Pinkbike’s XC Tech Randoms gallery and Rimpact. No test unit has been ridden by our team at time of publication.