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why are mtb rear hubs wider than road hubs? Im sure this started in the 70's for some odd reason, what was it?

thanks
jeremyb
 

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So you did...assume it was to accommodate the needs of tire clearance, cassette width, wheel strength, etc....kinda like on freeride/dh bikes now to have a 150mm spacing.
 

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Why and wherefore

jeremyb said:
why are mtb rear hubs wider than road hubs?
The origin is a comlex of factors, including the fact that early MTBs were based on the old Schwinn baloon tire paper route bikes. Today, the technical justification would be the need for a stronger wheel (wider spacing means less dish) and the need for more clearance at the BB and brake bridge for wide tires. The second point is that since the frame needs to be so wide for tire clearance, it's easy to have the wider dropout spacing and therefore get the stronger wheel.
 

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Why MTB hubs are wider

Kerry Irons said:
The origin is a comlex of factors, including the fact that early MTBs were based on the old Schwinn baloon tire paper route bikes. Today, the technical justification would be the need for a stronger wheel (wider spacing means less dish) and the need for more clearance at the BB and brake bridge for wide tires. The second point is that since the frame needs to be so wide for tire clearance, it's easy to have the wider dropout spacing and therefore get the stronger wheel.
It can't be because Schwinn balloon tire bikes had wider axles, because the original ballooners actually had narrower widths than current MTBs (the used single speed coaster brake hubs, afterall). It can't be because of wider BBs or for clearance for wider tires, because angling the stays out to be a few extra millimeters at the axle by itself will only give a millimeter or so extra clearance at the tire - instead, the chainstays are curved and bent for tire clearance.

The reasons MTB axles are wider are two fold: Firstly, because of the extra chainring, and the wider spacing of the chainstays (for tire clearance), the cranks on an MTB have a wider Q factor and the chainline is likewise moved outward, so the axle is spaced to move the cassette out further as well. Secondly, MTBs typically experience more lateral loading than road bikes, so the reduced dishing allowed by the wider axle has the added advantage of increasing the rear wheel's lateral strength.
 
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