Reports of the demise of this Web site are greatly exaggerated! We at sheldonbrown.com thank Harris Cyclery for its support over the years. Harris Cyclery has closed, but we keep going. Keep visiting the site for new and updated articles, and news about possible new affilations.



find us on FB

More Articles by Jobst Brandt
Next: Chain Care, Wear and Skipping
Previous: Alenax Bicycle

spoke

Subject: The Continuously Variable Transmission
From: Jobst Brandt
Date: January 25, 2003

The Continuously Variable Transmission (CVT) is the holy grail of many inventors who are not convinced that it is an impossibility. That is to say, the positive engagement, continuously variable transmission, that does not rely on friction, electrical, or hydraulic ratios but uses mechanical gearing, is not possible. By definition, continuously variable is analog while gears and chains are digital.

The CVT does not exist, and I am convinced it will not. If it were possible, railway locomotives, trucks, buses, and cars would long ago have used them. Strangely, it is in bicycling that the strongest believers of the concept reside... as if there were more money to be made in bicycles. In fact, the bicycle, with its enormously adaptable human motor, doesn't need a CVT. In addition, its low input speed and extremely high torque, make the bicycle an especially difficult gearing challenge. For this reason, high performance bicycles use derailleur chain drive that is found practically nowhere else.

Non-gear CVT's, currently used elsewhere, have poorer efficiency than both planetary gears and derailleur chains. More importantly though, the low-speed high torque of bicycling would require transmissions that would weigh more than the bicycle, making them impractical.

Jobst Brandt

[Continuously-variable transmissions have in fact been introduced by NuVinci. They are heavy compared with geared hubs, but by no means as heavy as Brandt suggests. NuVinci hubs use an assembly of tilting spherical rollers between angled surfaces, and a special oil which resists slippage; nonetheless there is some slippage, and efficiency is somewhat lower than with geared hubs or derailer systems. The main advantage is the ability to "dial in" a pedaling cadence rather than select among sprockets or internal-hub gearing steps..-- John Allen]

Spoke Divider

More Articles by Jobst Brandt
Next: Chain Care, Wear and Skipping
Previous: Alenax Bicycle

Spoke Divider

Spoke Divider

Articles by Sheldon Brown and others
Harris
Home
Beginners Brakes Commuting
Lights
Cycle-
Computers
Do-It-
Yourself
Essays
Family
Cycling
Fixed Gear
Singlespeed
Frames Gears &
Drivetrain
Bicycle
Humor
Bicycle
Glossary
Bicycle
Links
Old
Bikes
Repair
Tips
Tandems Touring What's
New
Wheels Sheldon
Brown

Reports of the demise of this Web site are greatly exaggerated! We at sheldonbrown.com thank Harris Cyclery for its support over the years. Harris Cyclery has closed, but we keep going. Keep visiting the site for new and updated articles, and news about possible new affilations.

Harris Cyclery Home Page

If you would like to make a link or bookmark to this page, the URL is:
https://www.sheldonbrown.com/brandt/continuous.html

Last Updated: by John Allen