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Why some botom bracket have center sleeves, and others don't?

I'm looking for BSA - DUB bottom bracket and so far the Sram ones have this centar sleeve, but many after market ones don't.

Any pros and cons between the two styles?
 

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Pre-Dub standard, the Sram cranks didn't have preload adjustment and the SRAM BBs with that sleeve created the EXACT spacing you'd need to have the crank preload perfect every time after you tightened the cranks down.

Now that we have Dub, well I used a BB without the sleeve with some new Dub cranks and after I installed the BB with no spacers I didn't have enough preload adjustment to get rid of slack. Then I added some spacers I had, the same 2.5mm under each cup. I could then set preload, except since the slack all comes out of one side the cranks were not at all centered to the frame. The left side crank where the preload adjuster is was like 5mm further away from the frame downtube than the other side. Be careful when doing this because you can accidentally grind your chainring right in to your chainstay.

Then I placed both of my 2.5mm spacers under the right hand side bearing cup and then after I adjusted preload the cranks were dead centered to the frame downtube. I don't mind this process and it allowed me to run my preferred BB brand (Hawk) but you might find this tedious.
 
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