How to Upgrade a 21 Speed Bicycle to 27 Speed (Complete Shimano Conversion Guide)

Many riders ask if they can upgrade their 21-speed bicycle to a 27-speed setup.

The answer is yes. However, upgrading to 27 speeds is more than simply replacing the gears. Since a 27-speed drivetrain uses a 9-speed cassette, several components must work together to ensure smooth and reliable shifting.

Components Required

A typical 21-speed to 27-speed upgrade requires:

• 9-Speed Cassette

• 9-Speed Rear Derailleur

• 9-Speed Shifter

• 9-Speed Chain

• Front Derailleur (if required)

• Crank (optional)

• Freehub (if upgrading from a 7-speed freewheel)

Individual Components

Shifters

Shimano Acera SL-M3000 3×9-Speed
https://omobikes.com/products/shimano-shifter-m3000-acera-2x9-speed

Shimano Alivio SL-M3100 3×9-Speed
https://omobikes.com/products/shimano-shifter-m-3100-alivio-3-9speed

9-Speed Cassette

https://omobikes.com/products/shimano-cassette-hg-200-9s

Rear Derailleur

Shimano Alivio RD-M3100
https://omobikes.com/products/shimano-alivio-rear-derailleur-rd-m3100-9-speed

Shimano Altus RD-M2000
https://omobikes.com/products/shimano-rd-m2000

Front Derailleur

Shimano Alivio FD-T4000
https://omobikes.com/products/shimano-fd-t4000-alivio-3-9speed-mtb-hybrid-front-derailleur

9-Speed Chain

KMC Z9
https://omobikes.com/products/kmc-z9-bicycle-chain-for-9-18-27-speed

Crank (Optional)

A crank upgrade is not required when converting from 21-speed to 27-speed. However, if your existing crankset is worn out or you'd like to improve performance, you can upgrade to a compatible crankset.

Prowheel
https://omobikes.com/products/prowheel-crankset-for-21-gears-24-27-gears-mtb-hybrid-cycle

Shimano Tourney FC-TY501
https://omobikes.com/products/bicycle-shimano-crankset-fc-ty501-tourney-for-3x6-7-8-speed

Do I Need a Freehub?

If your bicycle currently has a 7-speed freewheel, you will need to convert it to a cassette (freehub) before installing a 9-speed cassette.

Cassette Hub
https://omobikes.com/products/buzzer-alloy-bicycle-hub-sealed-bearing-for-cassette

Need Help?

Not sure which parts your bicycle needs? Send us a photo of your bicycle or your existing drivetrain on WhatsApp, and we'll help you choose the correct components.