Gear types – derailleur & internal
Most people, in North America at least, are familiar with derailleur type gearing on bicycles. Most mountain bikes and road bikes have derailleur gearing, which is characterized by multiple sprockets on the rear wheel and often on the crank, with moveable chain-guides (the derailleurs) which “derail” the chain by moving it sideways to engage with the different sprockets, thus changing the gear ratio (the number of revolutions of the crank to produce a revolution of the wheel).
Instead of derailleur gearing, most of our bikes (except for the CF Commuter) use internal-gear hubs. Unlike derailleurs, internal-gear hubs achieve different gear ratios by a planetary gear system enclosed within a sealed “hub”. In much of the world (but North America to a lesser extent), commuter and urban bicycles are commonly fitted with such systems.
Read more for discussion of the merits and drawbacks of each.
Advantages of internal gears:
One of the greatest advantages of internal-gear hubs is that the moving components are contained in a sealed unit, where they are protected from dirt, water, grime, road salt, debris, and the like. In contrast, the cages (the part with long arms and idler pulleys that tension the chain and take up slack when shifting between gears) of derailleurs are exposed, and vulnerable to being bent, damaged, or broken. Derailleurs, especially the cheaper models, are somewhat infamous for easily being knocked out of adjustment. Internal hubs are notoriously robust in this respect.
Maintenance and Longevity
With a derailleur system, the chain must be able to “snake” sideways during gear changes, and regular cleaning is required for smooth shifting. Additionally, adjusting the limit screws on the derailleur is often necessary to keep the shifting smooth as parts wear and stretch. Internal hub systems shift reliably and smoothly and can go for years without maintenance or adjustment.
Since there are no multiple gear sprockets and idler wheels to pass over, the chain on an internal hub drive always runs in a straight line and is less susceptible to wear. The chain is wider as it does not have to flex sideways, so it is inherently more robust. Strength & longevity are greatly improved, especially in wet or abrasive environments.
Internal gears allow stronger rear wheels because less “dish” is required (since there is only one sprocket to accommodate, as opposed to a cluster of 7 to 10). The spoke angles on the left side and the right side of the wheel are similar, resulting in a stiffer, structurally more stable wheel build.
Internal-gear hubs, unlike derailleurs, can be shifted while stationary, suiting them well to riding in stop-and-go city traffic. Unlike derailleurs they can be shifted from any “gear” to any other instantaneously (without need to progressively move through intermediate ratios).
The lack of a derailleur with its pulleys, exposed gear cluster, and serpentine chain path makes for a simple chain line. The chain cannot jump from the chain wheel and sprocket the way it can with a derailleur.
Linear, low force shifting
Shifting is linear…there is only one shifter; no need to juggle front & rear shifters, and no need to educate riders to avoid the front/rear shift combinations that cause cross-chaining.
Internal-gear shifters need low shifting force, whereas cheaper derailleur type shifters require considerable finger force to overcome spring tension.
Advantages of Derailleurs
Wide gear ratio
Derailleur systems can achieve gear ratio ranges (so-called “speeds”) of over 500% (meaning with one turn of the crank in the highest gear the bike moves a distance 5 times that in the lowest gear). In practice most derailleur systems have ratio ranges more like 350%. The gear ratio range of the Shimano Nexus 8 speed is 311% (rollout, see below, of typically 2.6 to 8.1 meters), the gear ratio range of the Nexus 7 speed is 245%.
High-end derailleurs are lighter than internal gears.
Internal-gear systems (especially the “premium” low friction version we use (see article “E-bike efficiency”) typically cost more than mid-price derailleurs.
Higher mechanical efficiency
Derailleurs can have higher mechanical efficiency (lower friction losses) than internal gear hubs. In practice though, the efficiency of derailleur systems can fall enormously due to dirt & wear. (Ref. Kyle & Berto, “The mechanical efficiency of bicycle derailleur & hub-gear transmissions”, Human Power #52 Summer 2001). For more discussion of this see Technical Article 10, “E-bike efficiency”.
Easier rear wheel removal
Rear wheel removal & replacement for internal-gear bikes requires the additional step of tensioning the chain. Quick release systems for easy wheel removal cannot be incorporated.
Which of our models use which gears?
Except for the “CF Commuter”, all our e-bikes use Shimano Nexus internal-gears. These bikes are designed for simplicity and freedom from maintenance. Our preference is a 7 or 8-speed hub rather than a 3, 4, or 5 speed, to provide a reasonable complement of “granny” gears for riding without any power assist. Covid supply chain disruptions have required us to go for Nexus 7 speed hubs for 2021 and 2022 orders. These have the net effect of eliminating a granny gear, but the electric motor fully compensates for this. For the rider, the internal hub provides simplicity. Most riders of our electric bikes never have need for the very low gears typical of derailleur-equipped mountain bikes. Rather, they use electric power assist to overcome steep terrain or strong headwinds.
Derailleur gearing is, however, used on our carbon hybrid bike, to provide a wider range of gear ratios for those riders who want or feel they need them, and is particularly suited to those who cycle off-road on steep terrain.
When comparing bikes based on their gear ratios a useful number to compare is their “rollout”. “Rollout” is the distance a bicycle travels for one crank revolution … the higher the number, the faster the bike will go for a given cadence, but the harder it will be to pedal. Note that the Carbon Hybrid has low gearing for those riders who want to add lots of pedal-assisted hill climbing, but because these are e-bikes this is not necessary (since the motor can substitute for lower gears for all but the most arduous of hill climbing or the heaviest of rider/payloads). We know that many users of our Carbon Hybrid e-bike will not use the front derailleur (left shifter), but for those who want the lower gearing offered by this shifter (rollout as low as 1.6m) it is there for them!
“Rollout” of 8 speed Nexus hybrid on CanCycle and Easy Rider, metres per crank revolution
“Rollout” of 7 speed Nexus hybrid on CanCycle and Easy Rider, metres per crank revolution 20T
“Rollout” of 8 speed Nexus hybrid on 26” Easy Rider, metres per crank revolution
“Rollout” of 7 speed Nexus hybrid on 26” Easy Rider, metres per crank revolution 18T
“Rollout” of carbon hybrid 22-speed derailleur bike, metres per crank revolution