CVT In Bicycles? Automatic Stepless Shifting Explained In Simple Terms


CVTs are quite common on many types of vehicles and have recently started to make their way into the world of bicycles. But what is a CVT for a bicycle and what are the unique challenges they present? Importantly, which bikes already have a CVT fitted?

CVT bicycles have a Constantly Variable Transmission where the gear automatically changes to maintain constant pedal cadence without rider intervention; during acceleration and deceleration, the gearbox adjusts to the pre-set gear ratio. CVT is best for commuter and recreation bikes because it is simpler and maintenance-free.

What does a CVT mean for bicycles?

From a rider’s point of view, a CVT provides a step-less automatic gear change so that the rider can maintain a constant pedal speed without needing to change gears manually.

CVT stands for Constantly Variable Transmission.

This means that the gear system is always changing (= constantly varying) gear ratios to ensure your pedal speed is always constant.

CVTs are used on almost 100% of motor scooters and snowmobiles and are very common on ATVs, earth moving equipment, and increasingly popular on cars.

However, they are currently used on very few bicycles.

The advantage of CVTs on bicycles is that they are easy to use as there are no or limited controls on the system, and are reliable and durable as they are enclosed from the environment.

Traditional derailleurs are exposed to the elements as well as to external physical forces, which is why they need regular maintenance, such as gear indexing, cleaning, lubing. An enclosed system virtually eliminates these maintenance requirements.

NuVinci transmission

CVT / Step-less shifting vs Automatic Gear Change Bicycles

Let’s first have an introduction of the two main concepts:

CVT / Step-less shifting

An important point to note is the step-less gear change feature of CVTs. In vehicles with CVT, it’s impossible to actually notice when the gear is changing, and really it is continuously changing gears.

While on most bicycles with gears you have a 1st, 2nd, 3rd… etc gears, each of which has a set gear ratio, in a CVT there’s an infinity of gears between the highest and lowest possible gear ratios.

There are also some systems that have a step-less gear change, though are not automatic. For simplicity, we will also categorize them as CVTs here, even though that is not technically correct.

Pros

  • User-friendly interface
  • Variable gear range – not fixed gear ratios like 1, 2, 3, etc.
  • Durable

Cons

  • Limited ability to choose desired gear
  • “direct” efficiency is low
NuVinci step-less grip shifter

Automatic Gear Changes

This is very similar to an Automated Manual Transmission (AMT) on a car and is an automatic stepped gear change. This means the gear change is automatic, with only specific gear ratios that can be selected as used in a manual gear system. 

AMTs bring the benefit of being easy to use, and can be reliable and durable if enclosed.

Pros

  • User-friendly interface
  • More efficient with a direct load
  • Can be durable

Cons

  • Often have a jerky motion as there is no clutch on a bicycle (nor double clutches…)
  • If exposed, not durable

So, which is better?

As a CVT is step-less, this means the pedal speed is continuously maintained, while an AMT can only select from certain defined gear ratios. The major downside of an AMT on a bicycle is that the gear change can be jerky, and also the change can happen just when you didn’t want it to.

Also, as all CVTs are enclosed, the durability is typically higher and the maintenance required lower as the mechanism is protected from the environment.

So, if you are not interested in maintaining your system, and want smooth gear changes, a CVT is the better choice.

Main types of CVT bikes

It’s best to focus on the main types of bicycle CVTs and to check which bikes they are used on. As mentioned the benefits of a CVT most apply to commuter and recreation cycling, so they are the most common types.

Enviolo

Enviolo is a rear hub gear system that was a fork from the now-defunct company NuVinci.  It is popular in Europe, especially on recreation eBikes which use a center-mounted motor. Enviolo is normally fitted as a component by various bike manufacturers.

Technically it is a traction drive, which means is not continuously changing. Enviolo has addressed this with a product advancement that adds an electronic control system that can link to the drive motor to provide a continuous gear change.

Evolo

Evolo is the other fork from NuVinci and is most common in the USA. It appears to be very similar or even the same as Enviolo. Evolo sells its own bikes fitted with their gear system.

Continental

Continental offered a combined center-mounted motor and NuVinci gear system. However, the system had only limited market success and has since been removed from the market.

It was sold as a component to bike manufacturers.

BONUS – SECRET NEW DEVELOPMENTS

Of course, even bicycle gearbox technology doesn’t stand still. So here are sneak peeks at some new CVTs coming to the market shortly:

ratioX

OK, I’m biased as this is my company – ratioX is a center-mounted true CVT that works well with rear-hub motor commuter eBikes. ratioX requires no controls to change gears and is the lightest enclosed gear system available with a wide gear range. ratioX is planned to be sold as a component to various bike manufacturers. ratioX’s technology is largely based on a motor scooter’s, though it needed to be scaled down and inverted to work on a bicycle. The main restriction on this system is that it is hard to change the pedal cadence during a ride.

revonte

revonte is a combined center-mounted motor and IVT (Infinitely Variable Transmission) that has two motors: one that drives, and one that adjusts. It provides a continuously variable gear change with a wide gear ratio and has a controller to change your pedal cadence. The technology is similar to the Hybrid Synergy Drive developed by Toyota for Hybrid cars, and the main question on the product relates to the weight of the overall system. It appears the main target customers are Mountain Bikes for revonte.

Can you convert any bike to use a CVT?

Typically, a bicycle frame is designed for a certain gear change mechanism, so it is difficult to modify any frame to suit a CVT system if it was not designed for that system.

It is recommended to buy a purpose-built bicycle to ensure the safety and function of your ride.

Simon Faneco

Simon is a bicycle engineer and entrepreneur from Australia currently living in Switzerland. He's the inventor of the first true center mounted CVT for bicycles. Follow his invention at ratiox.ch.

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