What is it? The Freewheel
Unless the only bicycle you have ever ridden is a fixed-gear bike (or ‘fixie’ as the kids call them), you probably know what a freewheel is. Or, at the very least, what a freehub is. Or, maybe you don’t know what either is. Whether or not you have, though, keep reading because we’re breaking them both down, and we’ll wager that there’s more to the story of the bicycle wheel than you think.
FIRST, THE RATCHET
From the most basic mechanical standpoint, a freewheel is a ratchet. A ratchet is any type of mechanism that permits motion in only one direction while preventing motion in the opposite direction. To accomplish this, a ratchet consists of a gear with asymmetrical teeth that is affixed to some sort of solid structure, or base, along with a pivoting, finger-like structure called a pawl. Why are the gear’s teeth asymmetrical? This allows the gear to spin freely in one direction against the pawl, which, being spring-loaded, is pushed out of the way by the teeth, and then forced back into contact with the gaps between the teeth.
If the gear spins in the opposite direction, the different shape of the asymmetrical teeth push against the pawl, and the gear becomes locked into place. Think of socket wrenches, most of which involve a ratcheting mechanism: you spin the wrench in one direction to tighten a bolt, and when you spin it in the opposite direction, the ratchet enables the socket end (and bolt) to remain fixed as you set up for another tightening action. A cable tie, also called a zip tie, is another wonderful example of a ratchet; loop one end through the other, and a tiny pawl allows the tie to be tightened while preventing it from loosening.
THE OLD FREEWHEEL
An evolution of ye olde fixed-gear bikes from the days of yore, the adaptation of the ratchet to a freewheel rear hub allowed cyclists to stop pedaling and coast. The very first freewheel created for a bicycle is credited to William van Anden of New York, who was issued a U.S. patent on March 23, 1869. Traditional freewheel design involved a single cog-and, later, multiple cogs-surrounding a ratcheting gear mechanism that could spin in the opposite direction of a rolling bicycle wheel. When the bicycle wheel rolls forward, the ratchet gear is actually locked into place, with the chain forcing the ratchet to propel the bike. When the rider stops pedaling and the wheel continues to roll, the ratchet is loose and spins against its pawls. This causes the unmistakable, rapid clicking sound we all know and love, and the reason for various hubs sounding different or louder than others is due to a greater or lesser number of pawls, or possibly disparate materials or profiles used in the construction of either the pawls or the ratchet. These freewheel cog setups would be threaded onto the drive side of a rear hub, along with a set of ball bearings and a variety of caps and seals for durability’s sake. Along with the derailleur, it can be argued that the freewheel helped revolutionize the bicycle, making it more convenient for anyone to go for a ride.
THE NEW STANDARD
If the bulk of your cycling life has occurred within the past three decades, then the word ‘freehub’ may be more familiar to you than ‘freewheel.’ The word ‘freehub’ is actually a registered trademark of Shimano, but in the lexicon of cycling, it has become the widely accepted term for any type of rear hub with a freewheel ratchet mechanism built inside, as opposed to the ratchet residing within the cogset. Look at any modern rear wheel and you’ll see that on one end of the hub is a distinct protuberance, with a series of ridges carved into it. This is the freehub body, and it houses the ratchet and a cartridge bearing. Those ridges are called splines, and they serve as the connection between the cogs of a cassette and the ratcheting freehub body, taking the place of the traditional threaded-on cogs. By the early 1980s, the freehub and cassette combination had overtaken the conventional threaded freewheel and hub in popularity. The primary advantage of freehubs and cassettes over traditional freewheel systems is that the drive-side axle bearing is located farther outward and closer to the rear dropouts of the frame. This reduces stress on the rear axle and improves power-transfer efficiency. Also, power transmitted from the rider’s pedaling action to the rear wheel is distributed more evenly across the width of the freehub body and its splines than a traditional, threaded freewheel.
Creators of contemporary freehubs will often use the term ‘points of engagement’ when describing the efficiency of their product. This refers to the number of pawls and teeth of the hub ratchet working together, or ‘engaged,’ at any given time to propel the bike forward. The more points of engagement, the faster the rear wheel begins propelling the bike forward. The average hub typically has 18 to 36 points of engagement, with some models offering up to 120. To give you a sense of the potential that rear-hub technology still possesses, consider Kappius Components’s Evolution rear hub. It utilizes a 60-tooth drive ring with eight magnetically sprung pawls that are engaged two at a time. What does all that mean? The Kappius Evolution rear hub boasts an astounding 240 points of engagement!
EASY MAINTENANCE
Like every component on your bicycle, the freehub requires occasional maintenance, possibly even replacement after extended use. A good rule of thumb is to disassemble and clean your freehub body every six months to one year, depending on how adverse your typical riding weather is. Check with the manufacturer for exact instructions on how to properly maintain your freehub, but typical service involves removing one or two locking screws, removing the freehub body from the wheel’s hub, followed by cleaning with a mild solvent, and a reapplication of grease to prevent wear. If your freehub requires replacement due to wear or damage, a new one will cost you around $45?$60, depending on the make and model.
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