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Speeds
Bikes with gear shifts commonly have anywhere from two to 30 different "speeds" altogether. The nomenclature for designating the number of speeds is confusing and somewhat inconsistent.
For bikes with only one gear shift, it's pretty simple. The number of gears is the number of positions.
- If it's an internal-gear hub, the number of speeds is determined by the internal construction of the hub.
- If it is a derailer system, the number of sprockets in the cluster is the number of gears.
When there are two separate gear shifters, it gets confusing. Most newer adult bikes have two derailers and shifters, one for selecting among the sprockets on the rear wheel, the other for selecting the chainwheel in front.
The traditional way for designating the number of speeds with such bikes is to multiply the number of rear positions (sprockets) by the number of front positions (chainwheels.)
- Thus, a bike with 4 rear sprockets and 2 chainwheels was always called an "8 speed" (4 x 2)
- In the late '50s, 5 speed rear clusters became the norm, and these bikes were typically called "10 speeds." For much of the '60s and '70s "10 speed" was practically a synonym for "bicycle."
- In the early 1980s, a 6th rear sprocket became common, so those bikes would be "12 speed." If they had 3 chainrings instead of 2, they would be "18 speed."
Then it started to get confusing!
- In the late 1980s, bikes started to come with 7 sprockets in back, so they would technically be either 14 speed or 21 speed, depending on whether they had 2 or 3 chainwheels. However, it was not unusual for cyclists to refer to these as "7 speed" systems, with the number of chainrings ignored.
- In the early '90s, when the move to 8 sprockets in back occurred, "road" cyclists, who used two chainwheels, commonly referred to their bikes as "8-speed" (nobody remembered the 4 x 2 "8 speeds" from the early '50s.) These bikes could have been called "16 speed" but nobody did. However, touring and mountain cyclists, with 3 chainrings commonly referred to them as "24 speed."
- This pattern seems to have largely continued: Bikes with two chainrings are commonly referred to by just the number in back, these days 9 or 10. Bikes with three chainwheels are more often referred to by the total multiplied number, i.e., 27 speed or 30 speed. Although a bike with 9 in back and two in front could technically be called an "18 speed", nobody does, so as not to cause confusion with 6 x 3 "18 speeds."
It is important to realize that the theoretical number of gears is not the same as the usable number of gears on a dual-derailer system, because there are some gear combinations where the chain angle is so extreme that those gears should not be used. In addition, there are often duplicated gear ratios, so a "27 speed" bike may actually only have 20 distinct, usable gears or so.
See also my article on Gear Shifting and my Gear Calculator Page and my Speeds Page.
