You may check the thread pitch of a freewheel by threading an ISO left bottom-bracket cup into it (not a right cup, which is left-threaded). If they rock across each other, it is different. If the threads engage tightly all the way across, the thread pitch is the same. Hold the threads of the bottom-bracket cup against those of the hub, and look in between, against the light. Do not force a freewheel - you will ruin the hub.Ī bottom-bracket cup can serve as a thread gauge for a freewheel: Dimensions are usually marked on cups. An ISO/British/Italian freewheel will skim the top of the threads of a French hub and will slip forward if an attempt is made to use it. A French freewheel may start to thread onto an ISO/British/Italian hub but will soon bind. However, for strong riders and on tandems, it is best not to mix and match - freewheels sometimes do strip the threads of aluminium hubs. The older British and Italian standards use the same thread pitch but a very slightly different thread diameter, and are generally interchangeable. Freewheel ThreadingĪll recent freewheels and threaded hubs, regardless of where made, use ISO threading. The bearings center the outer body on the inner body, and allow the inner and outer body to turn freely relative to each other when the cyclist is coasting. The front (right) side of the freewheel has another bearing assembly, not shown in these photos. In the previous photo, part of the inner body's bearing race is visible as a polished arc (blue arrow). The bearing balls roll between this bearing race and one on the inner body. The photo also shows bearing balls in a bearing race, embedded in grease to hold them in place during assembly (also a few bearing balls that got away). This particular freewheel has two pawls directly opposite one another and an odd number of ratchet teeth, 15, so only one pawl engages at a time. When the cyclist is pedaling, the outer body also turns (counterclockwise in the photo), the pawls engage the ratchet teeth and the freewheel is silent. The freewheel makes a characteristic tick-tick-tick sound as the pawls spring into place behind ratchet teeth. When the cyclist coasts, the pawls slip forward (counterclockwise in the photo) over the rachet. The ratchet is the circular stepwise arrangement near the center of the photo. The photo below shows the outer body from the back (left) side. Small wire springs, visible in the photo, rotate the pawls outward. The red arrow points to one of the two pawls of this freewheel. The outer body (the part that holds the sprockets) has been removed. The photo below shows the inner body (the part that threads onto the hub) of a freewheel. Most freewheels achieve this by means of pawls which engage a ratchet. Making only a rear adjustment without also changing the chainring will present noticeable and potentially too drastic of a change to your rollout so a rear adjustment is generally paired with a chainring adjustment at the same time.The outer body of a freewheel can turn freely in one direction relative to the inner body, but not in the other direction. A decrease to your Cog or Freewheel tooth count with give a rider higher top speeds, but less snap out of the gate. In general, an increase to the gearing in the rear (Cog or Freewheel) means a decrease in your rollout and easier pedaling, but lower top speeds. Be certain to understand your rollout and how a tooth count change on the rear impacts that calculation. Cassettes however, still may come with higher end bearings and titanium race to save weight and resistance. Most entry level wheels and BMX bikes come with an installed Freewheel, whereas higher end and custom built BMX bikes are fitted with a Cassette. A Freewheel is a one piece gear with bearings installed that allow a rider to backpedal or coast. A Cog slides onto a rear cassette and is spaced to align the chain with the front chainring. A Cog is a machined or stamped gear with teeth, made from Steel, Chromoly or lightweight Aluminum. Understanding what you need and the difference between Cogs vs Freewheels is the first place to start. We carry both Cogs and Freewheels for your BMX Race Bike.
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