Design Notes: The Mech
When we set out to design the Mech, we wanted to see how far a mechanical derailleur could be pushed. While the drivetrain industry seemed to be putting all its eggs in the electronic basket, we wanted to make something to challenge this trend and prove that mechanical shifting can meet the demands of modern riders too.
We released the Ratio Mech in November 2025, and following our first Design notes article on Ratio Chainrings, we thought it would be interesting to take a look into the engineering decisions behind the Mech.
A background in upgrades
We started making our upgrade kits because we wanted to use the latest drivetrain innovations on our own bikes without having to replace the whole groupset. This experimentation gave us hands-on experience with a huge range of drivetrain setups; we gained an in-depth understanding of how a bike shifts and where systems tended to fall apart.
Our kits proved popular, but – living in a part of the UK known for being particularly wet – we began finding shifting performance would deteriorate over time.
This got us thinking, why isn’t mechanical shifting able to survive the worst of the Lake District weather?
Shifting expectations
We began looking at the mechanical derailleurs already on the market to find out what caused them to degrade and how the effects could be avoided.
Initially a lot of blame was placed on shifter cables, but it quickly became apparent that this wasn’t the only factor causing poor shifting. We would change the cables when shifting became sluggish, only to find it still wasn’t crisp enough.
We discovered that, often, friction in the derailleur was holding up the shifting. Most mechanical derailleurs came fitted with bushings, and we noticed that water and dirt would contaminate the bushing, causing it to bind.
We wondered, why was all the advancement happening in the electronic shifting world? It seemed mechanical shifting was being left behind as more batteries were fitted to bikes. We had tried electronic shifting and were frustrated with how easy it was to break. Electronic drivetrains were increasingly sold as the solution to poor shifting, with cables framed as the fundamental problem. But from our testing, friction in the derailleur itself was often just as important. There must be a way to make a mechanical derailleur that shifts better.
The brief
On the back of this initial investigation, we had a clear list of exactly what we wanted the derailleur to achieve.
It must:
• hold its own among its battery-powered cousins and perform at least as well as an electronic derailleur
• be fully user-serviceable with replacement parts available
• fit on all bike frames
• be compatible with modern 1x setups across different manufacturers
• have cable routing which works for all bike frames
Python
Before we made a physical derailleur, we used a Python model to simulate the derailleur, chainring, chain and cassette in space. This meant we could tweak the geometry of the derailleur and work through the cassette assessing B gap as we went and quickly iterate different geometries. The model can also cycle through different models and sizes of cassette, so that we could design the Mech for the broadest possible range of compatibility.
Here you can see the Python model shifting through the cassette.
What are the key features of the Mech?
Bearings – the bigger the better!
We mentioned before that a lot of the shifting woes we experienced were caused by the derailleur itself not moving sufficiently freely. The parallelogram linkage of the derailleur is the part that translates the movement of the cable into a gear shift, and we found friction at the pivots of this linkage.
Now, lots of modern derailleurs use 4mm axles with bushings in the linkage of the derailleur, so this was the starting point for our testing. The issue with this solution, however, is that these thinner axles can bend and the bushings can seize after water and mud ingress. The result? Sluggish shifting, notably to harder gears, and indexing inconsistency if the axle bends in an impact.
We started by testing nylon, Teflon, self-lubricating plastic and phosphor bronze bushings by retrofitting them to existing derailleurs, but one solution consistently outperformed the rest: Rolling-element bearings.
It was then a case of testing different bearings. We tried different diameter bearings in plain and stainless steel. Again here, we began by retrofitting bearings to existing derailleurs (Lewis even rode a bike around Spain with a derailleur which had been drilled out to install bearings!) before we began fitting them to early prototypes of the Mech.
We concluded that larger stainless bearings outperformed the other options. We also opted for a larger, 5mm axle to make the linkages stronger, ensuring more precise shifting and greater longevity.
Next it was a question of making sure the new bearings were protected from the elements. Other derailleurs use one-piece links, meaning the axles must slide through afterwards. This leaves a hole which exposes the bushing to dirt. We wanted the bearings to be captive, with the aluminium link protecting the bearing. Our links split in two and close over the axle.
Why derailleur link length matters
Choosing the length of the links gave us another opportunity to prolong the life of the bearings. The links in the Mech are longer than average, meaning the bearings don’t rotate as far for each shift. This means less wear on the bearings and less frictional force on each shift.
Return spring geometry and design
The linkage return spring is a key component in the derailleur, ensuring the derailleur shifts back to smaller sprockets. Shifting to easier gears is made possible by pulling on the cable using the shifter, while shifting to harder gears is reliant on the shifter cable being pulled in the opposite direction by the linkage spring.
Simpler derailleur designs anchor the return spring on two opposite link axles. The result of this mounting option is that the tension on the shift cable varies dramatically across the cassette, so the shift lever feels light in some shifts and heavy in others.
We built another Python model to alter the mounting position of the linkage spring. The position was optimised to ensure more consistent cable tension across the travel, which gives lighter lever feel too. The new spring anchor screws double as the linkage assembly screws, coupling the two halves of the split links we mentioned earlier.
Servicing with a multitool
Another important consideration for the Mech was serviceability. We wanted to make sure customers could service the Mech with a multitool, as there’s nothing worse than not having the right tool for the job, especially when you’re out riding. Everything is held together with sizes 2.5mm, 3mm, 4mm, 5mm, 8mm and T25.
On the Mech, the clutch and cage spring assembly are self-contained, so the cage can be swapped on and off with a single T25 screw. There’s no need to wind up the cage spring. It’s so easy to remove that if you need to take the Mech off the bike you can just leave the cage behind to save breaking the chain.
(Please note: the direct mount version of the Mech is no longer available)
Cage stop
The Mech features our Cage Stop to make removing the rear wheel easier and cleaner. To make this possible, we linked the movement of the cage to the movement of the parallelogram linkage.
To engage the cage lock, simply shift into the smallest sprocket and pull the cage forward until it clicks. We’ve engineering a catch on the cage to hook onto a matching catch on the inner link. When the Mech isn’t in the smallest sprocket, the cage can rotate forwards, and the two catches pass freely. To release, pull the cage forwards again, nudge the linkage inboard and gently allow the cage to rotate back.
One Mech, multiple setup options
The final key feature of the Mech is cross compatibility; it fits all bike frames and works with a wide range of different cassettes.
To ensure compatibility with any frame, we had to prevent tight bends in the cable between the dropout and the Mech. The cable adjuster on the Mech is positioned at just the right distance from the dropout to minimise the amount of exposed cable whilst providing clean routing, even on road and gravel bikes with rear-facing cable ports at the dropout.
We also wanted the Mech to have the broadest possible drivetrain compatibility. This is where fin development was key. The radius of the fin determines how far the derailleur moves for each click of the shifter, effectively allowing a given shifter to work with a cassette which it wasn’t designed to be compatible with. Want to run an older 11 speed SRAM road shifter with the newest SRAM Transmission 12 speed cassette? Easy! Simply fit the Ratio 1×12 Wide Ratchet and the Ratio Mech with Fin C.
The beauty of the modular Mech fins is twofold. Firstly, we’re able to design new fins for new cassette and shifter designs as and when they appear. Secondly, from a rider perspective, drivetrains can be upgraded without the need to buy a new derailleur.
(Please note: the direct mount version of the Mech is no longer available)
The Mech: conclusions
The Mech started with a simple question: why should mechanical shifting have to compromise on performance or durability? By rethinking the fundamentals — friction, spring behaviour, stiffness and serviceability — we were able to build a derailleur designed to continue shifting consistently in the worst conditions, while remaining fully repairable and upgradeable for years to come. Mechanical drivetrains still have a lot of life left in them, and the Mech is our contribution to pushing them forward.
Modular, rebuildable mechanical derailleur.
The Mech is designed for performance, longevity and compatibility. 100% made in the UK.
