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Re: Bottom Brackets

17 September, 2011 10:26AM
There are indeed several different sorts of bottom brackets. Years ago they were all 5 piece, an axle, two cups and two sets of bearings. Originally the axles were for cottered cranks, then along came alloy cranks and a square tapered axle. In order to increase longetivity and to speed up bike assembly the cartridge type was developed, where the bearings are sealed in a tube fixed to the right-hand side of the assembly and a left hand cup simply holds that side in place. With the advent of the mountain bike it was found that with the additional stresses caused by off-road riding the left hand crank had a tendency to work itself loose. Shimano therefore developed what they called the Octolink bottom bracket where the axle has 8 splines on it and the cranks have corresponding slots. Other manufacturers followed suit (eg Powerspline) but with their own versions, (10 splines), in order not to infringe Shimano's patents. More recently, Shimano have brought out the Hollowtech system. This recognises that the inherent problem of the bicycle is that being so close together, the bearings wear out too quickly. By moving the bearings into a sealed unit outside the bike frame (thus increasing the space between them) it is possible to use larger sealed bearings and decrease the load imposed on them. At the same time this enabled the manufacturers to use a hollow axle which reduces weight.
Currently you will see square tapered axles on the cheaper bikes and the really cheap ones are milled to look from the outside as though they are a cartridge type when they are actually 5 seperate bits. Most mid range bikes will have a cartridge type of bottom bracket, the higher end bikes will have splined cranks. The hollow axle type is reserved for the very top-end bikes used in competition.
Subject Author Posted

Bottom Brackets

Simon T 13 September, 2011 04:17PM

Re: Bottom Brackets

cotterpin 17 September, 2011 10:26AM

Re: Bottom Brackets

Simon T 17 September, 2011 05:49PM


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