73mm BB Shell in a TT frame?

I have recently picked up an old (2015) Dassi TT frame. I've been slowly building it up until getting to the BB. It has a 73mm BB shell inside the frame, not a 68mm. What chainsets, if any, can I use on this bike? I have a Vision Trimax Carbon chainset (24mm spindle) I was planning on using, but the BB comes up too wide.

Why would a TT frame come with such a wide BB shell? The previous owner had it from new and claims nothing has been changed

It's definitely not a shim stuck to the outside, it's a full shell

If worst comes to worst, what's the best way to trim the width down to 68?



  • webboo
    webboo Posts: 6,087
    You can get an FSA IsIs BB in a 73mm width. It’s the type with splines on the ends of the bb I. e. the axle is part of the bb rather than part of the chain set. I guess you could get the the old square taper bb’s in a 73mm width as well.
  • i.bhamra
    i.bhamra Posts: 304
    You could probably shave 2.5mm each side with a facing tool but would need to be sure the crank arms would still clear the chainstays sufficiently. I guess a square taper BB and appropriate chainset would be another option. Not sure about other chainset options but I'm sure someone on here will know!

    It seems odd it has a 73mm shell, I'm assuming it is internally threaded and not PF?
  • david37
    david37 Posts: 1,313
    edited March 2021
    hmm I thought id replied here to this, perhaps I didn't send so here it comes again

    The two main press fit 73mm road BB standards are BB30a and PF30a . BB30a has a 42mm inner diameter and PF30a has 46mm. NB THIS IS NORMALLY A CANNONDALE DESIGN.

    If the BB is threaded it will be a T47 BB

    you can buy a wheelsmfring or similar BB that will fit the frame and allow you to fit whatever road cranks you have without an adapter.

    If you're unsure what to buy take some measurements ID and BBwidth and tell sigma sport along with the crank you want to use and they will send you the right thing.

    Fitting is a piece of pish

    Your bike is fine

    I recommend the wheels system, ive never had any issues when they're installed properly.
  • david37
    david37 Posts: 1,313
    here is a link to choosing the correct T47 bottom bracket
  • i.bhamra
    i.bhamra Posts: 304
    Nice informative post @david37 I'm not the OP ans it's not my problem but I have learned something and feel like I should say thanks. So, thanks!