It seems you can’t open social media or a magazine these days without seeing a new bike with an idler suspension design, each claiming to be the best mountain bike ever. In fact, if you turn to our mountain bike review section you can read the full reviews of the Deviate Highlander 140 and Forbidden Druid XT mid-travel full-suspension 29ers with, you guessed it… idlers.

How will high-pivoted bikes take to the UK’s singletrack?

Idler pros:

Rearward axle path: By using an idler to help decouple the drivetrain from the suspension layout, frame engineers can use a more rearward axle path, without the associated increase in chain growth and pedal kick-back. Rearward axle paths give the wheel more time to climb the face of the bump, and as the chainstay length increases as the suspension compresses this helps stabilise the bike. No one really discusses what happens as the wheel rebounds though, so maybe a more vertical axle path would be the ideal compromise.

Better control of anti-squat: Anti-squat is the suspension’s ability to resist compression under acceleration, be that pedalling, pumping or cornering. The addition of an idler makes it easier for suspension engineers to fine-tune the bike’s anti-squat characteristics. It also allows the rider to change the chainring size and gearing without changing the degree of anti-squat or pedal kick-back.

Idler cons:

Noise and drag: One of the biggest concerns when adding an idler is increased resistance in the drivetrain. In our experience this isn’t an issue if done correctly. Both bikes in this test were silent and smooth running, and it was only when the chain got covered in grime that the noise level increased. It’s probably no worse than a mucky jockey wheel in your rear derailleur, but because the idler is directly beneath you, you notice it more.

Extra weight: Put simply, idler equipped bikes are always going to be heavier than conventional suspension designs. The most obvious reason being that the longer chain needed to accommodate the idler adds weight. Factor in the idler itself and any additional bearings, mounts and chain guides and it all starts to add up.

Increased anti-rise: The more rearward the axle path, the more the rear suspension will compress under braking. As such the spring rate increases which in turn makes the suspension harder to compress which can reduce traction and lead to a harsher ride. On the plus side, the increased anti- rise helps retain the bike’s geometry better under heavy braking, so depending on your perspective it could also be considered an advantage.

Idlers add extra weight but reduce nasty pedal kick-back

High pivot hype

It’s not just Cannondale, Norco, Deviate and Forbidden who are pumping up the high-pivot hype, spy shots are already circulating of prototype bikes from Devinci, GT and others, all rocking idlers. So once again, what’s old is new, as high-pivot idler designs have been drifting in and out of downhill racing for over two decades with various degrees of success.

Why the sudden proliferation in the enduro bike category? To answer that question we need to wind the clock back 10 years to when SRAM launched XX1, the first mass produced 1×11 drivetrain. Because without it, and the subsequent 1×12 drivetrains, no usable idler equipped enduro bikes would exist today.

But it’s not just the gravity-focused bikes that are taking advantage of 1x drivetrains to rethink longstanding beliefs and further decouple the suspension and drivetrain. Forbidden and Deviate, both early converts, have trail bikes boasting high single-pivot suspension designs with fully rearward axle paths. The basic idea being that the rear wheel moves back and up over the bumps, while the idler eliminates the adverse effects of the associated pedal kick-back that would normally come along for the ride.

So what better head-to-head test, than our recent head-to-head featuring the Deviate Highlander 140 review and the Forbidden Druid XT review? As the name suggests the Deviate Highlander has 140mm travel while the Forbidden Druid pumps out 130mm. Both bikes have full carbon frames and both are built around 150mm forks, although you also have the option to run 160mm forks to further slacken the geometry.

The Forbidden would benefit from a more forgiving quota of travel

Some conclusions

Coming into the test of the Deviate Highlander vs Forbidden Druid we had lofty expectations for both of our high-pivot hopefuls. We were expecting a magic carpet ride that allowed these short-travel 29ers to glide effortlessly across the roughest terrain – suspension that under-promised but over-delivered. After all, the purported benefits of the fully rearward axle path that Deviate and Forbidden both hang their hats on is a compelling one. Unfortunately, it’s not the whole story.

Yes, both bikes are good at handling single, big square-edge hits, but it seems to be at the expense of small bump sensitivity. And while it would be easy to attribute this to the axle path – small bumps come from underneath the wheel, rather than in front of it, and as such should benefit from a more vertical axle path – to do so would be to overplay the axle path’s role in suspension performance. There’s a reason why all of the axle path graphs you see have an exaggerated scale on the horizontal axis: it’s to help highlight their subtle differences.

The Highlander was unable to silence trail chatter

Don’t think for a minute that we’re saying that it doesn’t matter if the axle path is rearward, forward, a combination of both, or even s-shaped. It’s just not that high up in the pecking order of things that influence the rear suspension.

Focusing on the shock tune and spring curve, and how both interact with the leverage rate of the frame, always yields the biggest gains in suspension performance. Reduced friction also plays a key role in optimising suspension, where something as simple as switching from bushings to bearings in the shock eyelets can offer large gains in traction. So while tweaking the axle path, anti-squat, anti-rise and pedal kick-back all offer benefits that shouldn’t be overlooked, somehow they have managed to take centre stage.

And it’s relatively easy to see why this has happened. Mountain bikes in all disciplines have evolved in recent years. Gone are most kooky designs, and bikes from one brand now look and perform very similar to another. Natural selection at its finest. And it’s what makes testing bikes and discerning the subtle differences between them that much more difficult than ever before.

In many ways we’re lucky to be at the pinnacle of mountain bike development, and if you want to stand out or push the limits of performance you need to do something different, as simply introducing a slightly slacker head angle or small increase in reach isn’t going to grab anyone’s attention. So the idler design makes perfect sense. It’s novel and accompanied by a compelling narrative; the rearward axle path gobbles up the bumps and the idler banishes pedal kick-back once and for all.

But both Deviate and Forbidden seem to have lost sight of the fundamentals as the shock tunes on both bikes are way off the mark. Deviate has two things going on. First, the single-lip wiper seals increase friction, especially on the bigger bearings of the rocker link. Also, it’s not had a lot of time to experiment with the new Cane Creek Kitsuma Air shock, which may not be the best fit for the Highlander 140’s leverage rate.

As for the Forbidden, we were fortunate enough to be able to try the Druid with a lighter compression tune as Ace Bicycles still had a Fox DPX2 from when the bike was launched in 2019. And while that took us a step in the right direction, it was still over-damped as we had to run the rebound adjuster wide open and it still wasn’t very fast.

As a trip to BikePark Wales highlighted, you only have the travel you’ve got and no amount of axle path manipulation makes up for more travel. On the rough, fast tails where the Forbidden and Deviate are supposed to excel, we took an absolute beating compared to the week before when riding the exact same sections on the 170mm-travel Nukeproof Giga 290 (review).

That’s not to say that all high-pivot idler bikes will feel this way, as that would be as absurd as saying all four-bar linkage bikes are identical, which clearly isn’t true. That said, success leaves clues. And if you want to ride faster on rougher trails you need more travel. So maybe the Deviate Highlander 150 or the Forbidden Dreadnought would be better options for hardcore trail riders looking for something a little different.