Review | Rimpact Chain Damper - Flow Mountain Bike

Rimpact, the UK-based brand known for its rim inserts, has expanded its range with the introduction of a chain damper. The Rimpact Chain Damper is designed to reduce the chain forces generated by the upper portion of the chain flailing around in rough terrain, along with reducing pedal kickback forces caused by suspension movement. This is achieved via a floating spider chainring design that bolts in lieu of a conventional SRAM or Shimano chainring.

Who remembers Aaron Gwin’s winning run in Leogang from 2015 without a chain? If you haven’t seen it, it’s worth a watch, as it’s forever scrawled in the history books as one of the most iconic race runs of all time. Some argue that as he couldn’t pedal, he was more focused on maintaining speed, which landed him the win, while others debate that the improved suspension performance by not having a chain gave him the advantage on the brutal Leogang race track. But hang on, why does not having a chain improve suspension performance?

Chain dampers are becoming increasingly popular on World Cup DH & Enduro bikes, but until now the most common product was the O-Chain.

What issues does the Rimpact Chain Damper try to solve?

Chain slap is an unfortunate byproduct of the modern drivetrain when hammering down rough terrain, and frame manufacturers do their best to reduce the noise via carefully moulded chainstay guards that dissipate the force. The lower portion of the chain is typically damped via the spring and clutch mechanism integrated within the modern derailleur, which drastically reduces unwanted chain movement. The upper portion of the chain however is left to flail around, resulting in a noisy drivetrain and feedback through the pedals.

In the modern drivetrain, the lower portion of the chain is damped via the spring and clutch in the derailleur, however the upper portion is typically left to flail around in rough terrain.

Pedal kickback is a little trickier to explain, and we can dive down the rabbit hole into the details. But what is most important is understanding the causes of pedal kickback, why you might want to reduce it, and the effect reducing it has on the ride.

In almost every configuration of suspension designs, when the rear suspension compresses into its travel, the distance between the axle and the bottom bracket becomes greater. This subsequently increases the chain length required between the cassette and cranks, known as ‘chain growth’. As the chain can’t physically lengthen, the forces from the chain pull on the crank, causing your feet to try to rotate backwards to keep the suspension active. Since a large percentage of your weight is transmitted through your feet to the pedals, your body tends to resist that movement. This typically results in a loss of small bump sensitivity, as you essentially restrict the movement of the rear suspension with your feet.

The effects of kickback vary depending on several factors, including wheel speed, hub engagements, and what gear you are in

In summary, at full travel the axle moves away from the bottom bracket, applying tension to the upper portion of the chain and subsequently rotating the cranks backwards

On large impacts, the force from the chain pulling on the cranks is much higher and generally greater than what we can resist with our feet, hence the cranks will rotate backwards allowing the suspension to cycle through its travel. The exact amount of rotation depends on many factors, including suspension design (primarily anti-squat), what gear you are in, the number of hub engagements and the speed of the rear wheel.

On the bike, this results in a tugging feeling through the cranks under more significant impacts and a ‘locked-up’ rear suspension feeling under fast, repetitive, smaller hits. High-pivot suspension platforms with idler pulleys tend to experience far less pedal kickback compared to traditional layouts, although often not eliminated. These sensations are something we have just learnt to ride with, and a lot of folks wouldn’t even know it’s an issue. Don’t believe us? Remove your chain and do a lap. This decouples the rear suspension from the cranks, resulting in zero feedback through the pedals and unhindered suspension.

A lot of folks might be questioning why they can’t just use a lower engagement hub to reduce pedal kickback feedback, and long story short, you can. This however introduces a level of inconsistency, as the amount of feedback you will experience will depend on how many degrees of rotation the freehub has before engaging. Introducing a fixed amount of float at the chainring eliminates that potential inconsistency to effectively manage the feedback through the pedals.

So how do we get that sweet-sweet suspension performance without removing our chains? Insert the Rimpact Chain Damper.

At rest, the Rimpact Chain Damper looks no different to a normal chainring

The 8.4° float is subtle visually, but is very noticable when both climbing and descending

Rimpact isn’t the first to try and reduce forces and noise generated by the upper portion of the chain flailing around. The Ochain damper has been available for several years and is up to its second iteration of the design. These are often seen on the World Cup DH and EDR circuit, which also feature a floating chainring design similar to the Rimpact Chain Damper. Some relatively cheap and novel products have been on the market for quite some time, such as STFU elastomer chain dampers. We’ve had several STFU chain damper modules fitted across a handful of test bikes over the years, which simply, and rather effectively, quietens down drivetrain noise. However, the STFU chain dampers only limit the chain movement via the elastomer guards, and zip-tieing rubber blocks to the frame might not be everyone’s cup of tea.

E-Thirteen has also recently released its Sidekick rear hub, which incorporates a freehub mechanism that disengages when coasting. The brand claims this filters feedback through the pedals caused by chain oscillations and pedal kickback, delivering a quieter and smoother ride. We have a pair of E-Thirteen hoops inbound for testing, so stay tuned for our review.

Rimpact Chain Damper Details

The Rimpact Chain Damper was designed to reduce drivetrain feedback through the pedals. This has been achieved by developing a floating spider chainring design comprising an inner floating chainring and two outer plates, fixed via the direct mount bolts to the crank. On the inside, two springs provide resistance to the float, and four rubber elastomers act as bump stops to soften the engagement. The internals of the mechanism are sealed from the elements with two large x-ring seals that sit between the inner and outer plates.

The 32T SRAM T-Type 8-bolt test unit weighed in at 242g on the scales. For comparison, a 32T SRAM T-Type chainring weighs in at 74g, resulting in a 168g increase from the stock configuration. Seeing as the Rimpact Chain Damper is marketed primarily at the gravity-focussed crowd, we can’t see this weight increase being a deal-breaker.

The Rimpact Chain Damper is currently available in SRAM 3-Bolt and 8-Bolt direct mount patterns, along with Shimano’s own direct mount system.

Key Details

Chainring Size | 30-36 Tooth
Compatibility | SRAM T-Type 8-Bolt, SRAM X-Sync 3-Bolt, Shimano Direct Mount
Degrees of Float | 8.4°
Price | $549.99 AUD
Confirmed Weight | 242g (32t SRAM T-Type 8-Bolt)

Ride Impressions

With a focus on more gravity-orientated riding, the Rimpact Chain Damper was the ideal match for Nick’s Santa Cruz Nomad for testing at Maydena Bike Park and local trails in Hobart. Higher engagement hubs amplify the scenarios where pedal-kickback is experienced, making the Nomad an even better test mule, being fitted with an Industry Nine Hydra rear hub with 690 points of engagement. Fitment of the damper is fairly straightforward and was no different to swapping out a standard chainring, we opted for the T-Type 8-Bolt mounting configuration with a 32T chainring. Once fitted, we did need to add a few shims behind the chain guide on the Nomad, as the chainring sat a few millimetres further out on the drive side.

On the trail, the rear suspension on the Nomad felt far more active on small to medium-size hits, delivering a fluttery feeling through the rear end of the bike, with no perceivable feedback through the cranks. The improved sensitivity of the rear suspension delivered improved rear wheel traction, which was most obvious when holding a line through rock gardens or trails littered with roots. Softening the correlation between the drivetrain and the suspension truly feels as though it unlocks the rear end to perform how it was designed, and fine-tuning the shock settings became more influential after reducing the effect of a rather major variable.

The Rimpact Chain Damper is a sleek piece of kit that fits right in with SRAM’s XO T-Type Transmission.

We have always found the Nomad to be noisy, likely due to the stiff frame and oversized tube profiles accentuating any rattles throughout the bike. Chain slap wasn’t completely muted, however was notably reduced over chattery trails. While a quieter bike doesn’t make it perform any better, it’s one less thing to think about when charging down the trail. Out of curiosity, we performed back-to-back testing on two almost identical bikes, both with Santa Cruz’s VPP suspension platform, one with the Chain Damper and one without. Riding the Megatower without the chain damper felt like blasting heavy metal music, while riding the Nomad with the chain damper was more like enjoying jazz-funk with a martini in hand.

Things do get a little odd once pointed uphill. Even when paired with one of the highest engagement hubs on the market, the inherent float in the chain damper delivers a sensation through the pedals that took a while to become accustomed to. It was most apparent during short efforts up pinch climbs or to bring the front wheel over rocks, the float in the chainring delivers a somewhat sloppy sensation through the cranks. This would be further exaggerated if paired with a lower engagement hub. Once you push through the 8.4° degrees of float, the engagement of the damper is solid, with no notable softness from the rubber elastomers being transferred through the cranks. The float wasn’t noticeable when winching your way up extended steeper climbs with continuous power output.

When spinning along a traverse or mellow climb, we would overcome the float between the 1 o’clock to 5 o’clock and 7 o’clock to 11 o’clock positions, however the springs within the damper would seemingly spring back when the cranks were nearing the dead spot in your pedal stroke. This resulted in a pulsating sensation through the cranks that we just couldn’t get our heads around, similar to that of an oval chainring but amplified.

Flows Verdict

The Rimpact Chain Damper is best suited to gravity-orientated riders looking for unhindered suspension performance. We can foresee the Rimpact Chain Damper fitted to plenty of bikes that frequent bike parks, along with enduro racers who aren’t fussed by the float in the cranks on the climbs. The riders who fall into these categories will benefit from improved suspension sensitivity and reduced feedback through the pedals. On the flip side, those who spend more time on undulating terrain may find the float and pulsating sensation through the cranks pose too much of a drawback to outweigh the suspension benefits.

The boost in small bump sensitivity and reduction in feedback through the pedals is undeniable, and we urge any pedal-kickback non-believers to test one of these out for themselves. It muted almost all of the feedback through the pedals, delivering a calmer ride, and we quickly fell in love with the fluttery feeling of the rear suspension.