I’m upgrading my wifes’ bike from 9 to 10spd shimano. Do I need to replace the chainring and BB w/the new 10spd or is her 9spd stuff going to work? thanks
I’m not sure I understand your question. Are you upgrading or not? I think you mean, can I use my existing front chainring with the new rear derailer?
In short, yes. The new DA front derailler is very nice and the new BB is integrated on the OUTSIDE like the original BMX bike and MTB components (i.e. XTR) and is VERY nice, light and stiff.
Remember, you must use the new, thinner, 10sp chain.
What I meant is can I only replace the cassettes, r. derailleur, chain, shifters or do I also have to upgrade the chainrings, BB and cranks?
No, current 9 speed will work. Again, the new DA crank is all integrated and the BB, chainring and cranks are now only 2 pieces - very stiff and light.
Your 9sp crank, bb and chainrings will work fine with the 10sp system.
In fact you can use the same old rear deraileur if you want to. the 10-speed front is better though b/c the cage is a bit narrower.
i have 10-speed on my tri-bike and i swaped it from 9 without changing the crankset at all.