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I am assembling a bike on my own and came a cross the topic spacers for bottom bracket/crank.

I am installing a Shimano FC-R7100 crank with the bottom bracket model SM-BBR60.

By taking a look at the dealer's manual, I didn't see anywhere if I need spacers and how many. How can I know if I need spacers for my bottom bracket / crank?

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With modern cranksets, you will know you need spacers if the manual says you do, and if spacers came with your bottom bracket. Shimano and Campagnolo cranks don't use spacers, which is why the dealer's manual says nothing.

SRAM DUB cranks use spacers. A spacer kit is included with the BB, and the manual will tell you which spacers to use. For example, on a road BSA shell, you need 2.5mm spacers between the cup and the frame on both sides, and an additional 4.5mm outer right spacer that goes between the BB cup and the crank. On a 73mm shell, you only need the 4.5mm outer spacer on the right.

Shimano instead makes 68mm and 73mm versions of its BSA BB. Campy handles this by not making any MTB components.

Generally, if buying a third party BB, you will just supply your BB shell information. If the manufacturer needs spacers for certain arrangements, the listing will probably say so, or your dealer would let you know. If you're buying online, then you would want to read the listing closely. For example, on Chris King's site, they say that spacer kits are required, and that they're included with the purchase price (they don't seem to sell BBs direct). For example, their ThreadFit 24 BB has one spacer kit for most 24mm cranks, and a second spacer kit for the old SRAM GXP standard. If you look on Competitive Cyclist's listing for CK BBs, you might miss the fact that a spacer kit is included as a free gift with purchase.

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  • I'm unclear. Are crank spacers to be used in addition to, instead of, 3mm/6mm boost chainrings—or are the two issues otherwise entirely unrelated?
    – Sam7919
    Commented Aug 17, 2023 at 20:52
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    @Sam no idea tbh, as I don’t do MTBs
    – Weiwen Ng
    Commented Aug 17, 2023 at 20:57

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