This post compares the advantages and disadvantages of DUB and Hollowtech bottom brackets.
Bottom Bracket – a mechanism of cups and bearings allowing a spindle connected to the cranks to spin smoothly. The bottom bracket is installed in the so-called bottom bracket shell – the point where the seat tube and the downtube meet.
Hollowtech Bottom Bracket – A Shimano bottom bracket operating with outboard (external) bearings allowing the use of a hollow spindle of a much larger diameter.
DUB Bottom Bracket – A SRAM bottom bracket operating with external bearings. DUB stands for Durable Unified Bottom Bracket. The goal of DUB bottom brackets is to make the selection process easier by offering a more unified standard.
The Advantages of Hollowtech Bottom Brackets
- Larger/Thicker Ball Bearings
Hollowtech bottom brackets come with a spindle that’s 24mm in diameter. Conversely, the spindle of DUB bottom brackets is 28.99mm in diameter.
The bearings used by Hollowtech bottom brackets are 25x37x7mm in size (inner diameter/outer diameter/thickness). Those of DUB bottom brackets are 29x40x6.8mm.
The bearings of DUB bottom brackets have bigger overall dimensions due to the larger diameter of the spindle. However, we also have to look at the relation between the inside and outside diameter of the bearings.
The size difference between the inner and outside diameter of HT bottom brackets is 12mm whereas that of DUB bottom brackets is 11mm. This means that Hollowtech bottom brackets have 1mm more space for larger ball bearings. Larger ball bearings = potentially longer bearing life.
Also, Hollowtech bearings are 0.2mm thicker. This is a very small difference but deserves a mention.
- More Common Spindle Size
24mm spindles that Hollowtech bottom brackets operate with are more common than the 28.99mm DUB spindles. Consequently, the rider can choose from a greater variety of cranksets.
The Advantages of DUB Bottom Brackets
- Made for oversized spindles
The larger spindles that DUB bottom brackets are made for have two potential benefits – extra stiffness and lower weight.
Most of a tube’s strength comes from its walls/periphery. Consequently, when all parameters are equal (material, wall thickness…etc.) tubes with a larger diameter are stronger and stiffer than tubes with a smaller diameter.
The larger diameter of DUB spindles allows the production of axles that are just as strong as those with a smaller diameter while weighing less.
The table below compares the weight of Hollowtech and DUB bottom brackets:
|DUB BB386 Road
|Shimano XTR SM-BB93
|Shimano Deore XT BB-MT800
|SRAM DUB T47
|Shimano Saint SM-BB80
|Shimano Dura-Ace SM-BB92-41B
|Shimano Dura Ace BB-R9100
|DUB Pressfit BB92
Conclusion: DUB bottom brackets tend to be ever so slightly heavier than Hollowtech models. The difference, however, is too small to matter unless one is trying to assemble the lightest possible bicycle.
The Difference Is Not Substantial
Truth be told, the practical (perceivable) difference between a DUB bottom bracket and a Hollowtech one is not substantial. Both are modern bottom brackets with external bearings that come in plenty of models capable of satisfying any frame. Consequently, the choice comes down to:
Cranks Are More Important Than Bottom Brackets
Bottom brackets are an important bicycle component, but at the end of the day, they are not as important as the crankset in the long run. Therefore, one should first choose a crankset and only then review the bottom bracket opportunities in front of him.
It’s better to have an average bottom bracket and a nice crankset than the opposite. Quality cranksets are expected to last a lot longer if not the life of a bicycle. (Of course, this applies to cranks allowing you to replace the chainrings).
Meanwhile, bottom brackets will go bad sooner or later due to bearing wear and are normally replaced more frequently than the crankset.