The possible lengths for the rear axle are, 126mm (which is used for 6 or 7 speed Road Racing bikes), 130mm (which is used for 6 or in a few cases 7 speed Mountain bikes and 8 speed Road Racing hubs), and 135mm (which is the present, common size for 7 speed Mountain Bike hubs), 140-145mm (for tandem bikes). The rear axle length is measured, like the front axle, from outer axle locknut to outer axle locknut. The type and age of the frameset, dictate the amount of space available for the freewheel or cassette, and therefore the amount of cogs that will fit comfortably on the rear hub. Front axles, it fit in standard fork ends, are 9mm in outer diameter. The axle locknut is the last piece on each side of the axle, (not the axle itself). It is also refered to as the "over lock nut" dimension. The length of all front axles is 100 millimeters, this measured from outer axle locknut edge to outer axle locknut edge. This dimension is used to determine the proper spoke length, relative to the rim you are using, and some believe that the flange thickness is also an influence in building your wheel. The "spoke center circle diameter" is the measurement, center to center, of two spoke holes at the opposite ends of the same side of the same flange. This dimension is given because the spoke hole might be near the edge of the flange or it could be positioned somewhat inward from the edge with the spoke laying over the extra aluminum. The "hub flange outer diameter" is the measurement, outer edge to outer edge, at the opposite ends of the same side of the same flange. Remember, to properly "dish" (center the rim over the middle of the axle's over locknut dimension), you will generally require the drive-side spokes to be 1 or 2 millimeters shorter, if you want to maintain an even wheel dish, and exposed length, on each spoke. As a practical matter, having the front and rear hubs use the same flange size makes it possible to use the same length spokes, front and rear, on three sides of your wheels. Some hubsets use a small flange front and high flange rear so that replacement of spokes on the freewheel side can be done without freewheel removal. Small flange hubs have the advantage of being a little lighter, but as the flange gets smaller, your choices of lacing patterns and spoke number drop off, when the spokes and heads start to interfere with adjacent spokes. ![]() The Hub flange is referred to as having a "small" (low) or a "large" (high) flange. It is the thin area that rises off the ends of the hub. The hub flange is the part of the hub that the spokes actually pass through. The three-piece type has a separate center or "core" tube with, what is generally, an aluminum alloy flange that has been pressed onto it (Nuke Proof, and Bullseye for example). Into the aluminum hub shell a bearing cup race or bearing cartridge is pressed on each side. The one-piece style uses a single aluminum forging, a single piece of machined billet aluminum to form the core of the hub itself. Hubs are usually made using a one-piece or a three-piece designed hub shell. It's for this reason that the hub descriptions are so lengthy, our apologies, but over educating has never been found punishable. Not an inch is traveled on a bike without the hubs revolving, and this is an area of the bike where quality improvement can be noticed. Hubs are another of the primary weight bearing component. Product Overviews | Archive Reviews | Comparison Tables | Tables | Metals Guide | Frank's Picks | News & Gossip ![]() Buyer's Guide / Hub Overview - Bicycle Parts at discount prices / the Buyer's Guide / Bicycle Parts at their finest! / Professional Bicycle Source / Bike Pro
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