Quote:
Originally Posted by EB
What a "bright" idea!
But why?!
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When this was first developed, the reason behind it was a bit questionable, but it might actually make a difference on a gravel bike.
The lateral stiffness of the rear triangle can be increased if the chainstays are laterally wider at the bottom bracket. This is why systems like BB86 (86.5mm wide BB shell) and BB90 (90mm wide BB shell) were developed. But even with wider BB shells, chainring clearance still limits the width of the right (drive side) chainstays. So often the end of a BB68 or BB90 BB shell sticks outward from the chainstay width on the right side.
So, the makers of BBright figured, "why not make the BB shell and chainstays wider on the left, but leave it the standard width on the right where the chainrings limit clearance?" Thus was born BBright, whose 79mm wide BB shell extends 45mm on the left (like BB90), but only 34mm on the right (like BSA). To maximize BB bearing stance width but still work with standard crank spindles, the left BB cup is internal to the shell, and the right BB cup extends outward from the BB shell.
So, BBright has always been a bit of a mish-mash for road bikes. But on gravel bikes, it might actually make sense. To accomodate wide tires but a relatively narrow chainline and Q-factor of gravel drivetrains, the chainstay on the right has to be quite narrow. In order to give good lateral stiffness, this means the left chainstay has to be much wider. The BBright BB shell accomodates large chainstay width differentials, so it is uniquely suited to gravel bikes.