The clutch provides the effect of massively increased spring tension within the shifting mechanism, inducing more tension into the chain and in turn less margin for error with regard to shifting. In other words, it stops the chain flailing wildly on poorly maintained roads. The clutch mechanism can also be disengaged using a thumb actuated lever on the rear mech itself, reducing the tension to that of a normal derailleur or simply for making the process of changing a wheel or chain a little easier.

Why now?

Only a few years ago, attending any niche handmade bicycle show would result in the feeling that fat-tyred bikes were going to take over the world. Thankfully they didn’t, but these days ‘gravel bikes’ are the must-have addition to any bicycle manufacturers line-up, and Shimano has taken notice:

“Riders have been pushing the limits of what a road bike is capable of riding for many years, evolving the sport from racing to encompass greater adventure,” says the Japanese firm. “In recent years we’ve seen a broader definition of what a drop handlebar bike can look like; road wheels followed that by accommodating wider tyres. Now in a natural evolutionary step it’s time for drivetrains to evolve too.”

When shifting mechanically, the increased tension is designed to be hardly noticeable. Once the initial inertia of the clutches grip is overcome it feels much the same as any other mechanical shift. The rear mech yields easily under one’s input at the handlebar but gives the bumps of the road a far harder time.

The advantage of a clutch mechanism having been available to mountain bikers for so long is that the technology is already proven to work at the highest levels of performance. The benefits to professional road cyclists are less obvious – with increased chain tension comes the marginal loss of precious watts – but for the cobbles of the Spring Classics, the extra chain security may may prove advantageous.

Trek-Segafredo’s Degenkolb is rumoured to be taking the RX805 Di2 rear mech into battle at Sunday’s 116th edition of Paris-Roubaix, an event which ‘Dege’ won in 2015. The race is renowned for its harsh terrain, and if Degenkolb’s previous performance is anything to go by, this should be the ultimate test for the new product; any questions about reliability will surely be put to rest.

For the rest of us, Shimano’s new RX800 and RX805 rear derailleurs will be available to consumers from mid-June this year. UK prices are to be confirmed.

Website: Shimano