Chainring Choice or Shifting Ramps?Jan Heine
The chainring choices of our René Herse cranks are not limited by dedicated shifting ramps, so you can use any gear combinations you like. We have optimized the chainring tooth profile to shift well at all times, and not only twice per crank revolution when a ramp and pin are aligned correctly.
During the development of our cranks, we spent a lot of time testing different prototype chainrings (above), as well as the ramped-and-pinned cranks of other makers (below).
Modern chainrings have ramps and pins on the backside below the teeth. The ramps and pins are located where there is an optimal path for the chain from one ring to the other. For that reason, modern chainrings only work in sets of two (or three for triples).
If you put a small chainring with a different tooth count on the cranks shown above, then the ramps of the big ring no longer line up where they should. That is why the large rings are marked not just with their own size, but also with the size of the small ring that is part of the set. In the photo below, the large ring is a 50/34 ring, with ramps that don’t work with other small chainrings, like a 39-tooth ring.
Most component makers offer very limited chainring choices, otherwise they would have to develop a multitude of chainring pairs. Most double cranksets today are available only with 53/39 and 50/34 chainrings.
Some smaller manufacturers offer ramped chainrings that are not designed in pairs. (They are easily recognizable, because they don’t specify for which small ring they are designed.) These ramps are not very effective and mostly serve to reassure customers who see ramps as an important asset of chainrings.
For many decades, chainrings did not have ramps and pins, and yet they shifted fine. Ramps and pins serve only as “insurance” against bad shifts that occur when the rider doesn’t push the lever far enough, or when they forget to let up on the pedals during the shift. Most of the time, the rider initiates the shift when no ramp is aligned correctly, and the chain just moves to the big ring without the help of ramps and pins. (An exception are Shimano STI triples, which don’t work without ramps and pins.)
For the new René Herse cranks, we had to make a choice: Design a few chainring combinations with ramps that offer insurance against bad shifts, or offer almost unlimited chainring choices without ramps. (The third option, to provide “cosmetic” ramps, was not considered.)
It would be prohibitive to provide ramped chainring pairs for each of the dozens of chainring combinations possible with the new René Herse cranks. We would need to develop no fewer than six 48-tooth chainrings, depending on whether you want to use a small chainring with 32, 34, 36, 38, 42 or 44 teeth. And so on for each chainring size! (Now you can understand why even big makers offer only very few chainring choices.)
Instead, we focused on the tooth profile to make sure the chain has an easy path onto the chainring – not just in a few places where there are ramps and pins, but at any spot in the pedal stroke. We tested a number of tooth profiles with a variety of derailleurs to determine how to optimize the shifts without ramps. In the photo above, you can see how the chain runs diagonally between the teeth at the onset of the shift. We use an asymmetric tooth shape that provides more room for this shift. (The teeth bear the chain load only on one side, so there is no need to have as much material on the other side.)
Here’s a bad shift, just what we don’t want, where the chain rides up on the chainring at first, and only engages after half a chainring revolution! This “prototype tooth shape C” was not selected for production…
The downshift to a smaller chainring is relatively simple (above). The chain simply drops down onto the smaller ring. It works every time, without any ramps, pins or special tooth profiles. Small rings wear faster than big ones, so ours use a different tooth profile from the large ones, one that is optimized for durability.
You probably will not notice the optimized chainring tooth profiles when you install your René Herse cranks, but we hope you will notice the difference once you ride them on your bike. Click here for more information about the René Herse cranks.