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SRAM DUB vs 30 mm spindles explained

DUB looks like SRAM's answer to the 30 mm spindle, and it is close, but the 28.99 mm diameter is deliberate: it lets one crank spindle run in every common shell using a single DUB bearing size.

A true 30 mm spindle is stiff but shell-hungry

A 30 mm aluminium spindle is stiffer and lighter than a 24 mm steel spindle, which is why BB30, PF30, BBRight and BB386EVO were all built around it. The problem is that a 30 mm bearing needs a wide shell to sit in, so a 30 mm crank does not fit a narrow BSA or a 41 mm pressfit shell without a reducer bottom bracket that runs the spindle on smaller bearings.

That fragmentation, one crank needing different bearings and cups for every shell, is the problem DUB set out to solve.

DUB is 28.99 mm on purpose

DUB, SRAM's Durable Unified Bottom bracket, uses a 28.99 mm spindle. That diameter is small enough to pass through the bearings used in a 41 mm pressfit shell yet large enough to keep most of the stiffness of a 30 mm spindle. Crucially, every DUB bottom bracket uses the same DUB bearing, so one DUB crank can be fitted to BSA, T47, BB86, BB92, PF30, BB30 and more by choosing the matching DUB bottom bracket for that shell.

So DUB is not a 30 mm spindle and not a 24 mm spindle: it is a third size chosen so that one crank family covers every frame with one bearing.

Fitting a DUB crank

Pick the DUB bottom bracket that matches your shell standard, threaded or pressfit, road or mountain width, and the DUB crank drops in. You cannot run a DUB crank in a 30 mm or 24 mm bottom bracket, because the bearing bore is specific to the 28.99 mm spindle.

Confirm your shell first, then choose the DUB bottom bracket for that shell.

Related

Sources: Park Tool: Bottom Bracket Standards · Wheels Manufacturing bottom bracket fitment reference · Crankset (Wikipedia, CC BY-SA)