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is it possible to put a bb with hallow tech on this bike can the square tapered BB be replaced with one that i can use my two piece crankset with?

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The new bottom bracket will fit as long as it is of the same thread and type. The Trek uses an English thread bearing. Shimano also says that you must use a mountain bottom bracket with a mountain crank. The new crank must be pretty close to the same tooth count as the original. The front derailleur is designed to work with a limited range of ring gears. If you are in the 40-44 tooth range you will be fine with the original derailleur. It may require some adjusting as the chain line most likely will be slightly different. I recently did a similar swap and I had to move around the bearing spacers to adjust the chain line.

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The most comprehensive guide on bottom brackets online I know of is here.

You can replace the square taper bottom bracket with a Hollowtech II bottom bracket and use a compatible crankset with that bottom bracket. The particular crank you choose should be such that your derailleurs are able to handle it.

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  • so a bb30 should work ?
    – wvc121270
    Mar 29 '15 at 19:40
  • No. For bb30/pf30 you need a frame which is designed for that standard. Things you can do are in the "conventional threaded" section of the guide. Note that BB386 Evo comes in threaded and pressfit versions.
    – Batman
    Mar 29 '15 at 19:42
  • ya the bb30 threads right in but its way to wide thanks for your help ill try to figure it out
    – wvc121270
    Mar 29 '15 at 19:52
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    BB30 is a pressfit system. It won't work in a trek 4300.
    – Batman
    Mar 29 '15 at 19:55

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