i have a 68mm threaded bb with shimano 105 cranks. looking at Rotor or Praxis gravel just for something different, they are 30mm axle. advice please on which of the 68mm, 30 threaded bottom brackets would be recommended ( if any)

I wouldn’t. Sorry.

Check the bearing sizes – e.g. Rotor and Wheels Manufacturing use standard 6806 bearings in comparison to Race Face which are smaller and don’t last as long IME.

thanks simon, as dovebiker says, some have bigger (better) bearings? but after that what are the negatives?

The big negative for me is that there isn’t room in the BB for the plastic sleeve with a 30mm axle, so the back side of the bearings is nowhere near as well protected from any crud and water that makes it into the frame (which is usually a surprising amount IME).

I’m no Shimano fanboi, but their cranks Do. Just. Work…

After much creaking of a Praxis/BB30ish combo I’ve switched out for a Shimano crank and creaking is gone. Wish I could have avoided the BB30. LBS also said that a lot of the problems I’ve had are due to the 30mm axle and very little space for the BB.

The need for the BB tube depends on frame construction and whether water can run down the seat tube and collect in the BB shell and contaminate the bearings from the inside out. BB30 is the worst as the bearings actually sit in water.

I’m no Shimano fanboi, but their cranks Do. Just. Work…

Yep. GRX range gives a few gravel choices 1x, 2x, 400, 600, 800.

I’ve read the same negatives about Praxis but mine has been generally OK. 30mm in a traditional threaded BB. I have to change bearings more frequently than on other bikes but I maybe also treat this one worse. And bearing replacement is a piece of cake. I chose it because I was being a tart and wanted the spiderless look for cheap. There are probably better options to achieve the same now and I do much prefer the Shimano design.

Mine creaked when I had a fraction too much spacer in there. And that stuffed the bearings. Changed bearings and reduced spacer size and all has been fine. Visible gap to the sprung washer now.

thanks for the info, i just fancied something different for a change ! Rotor do a crank with 24mm axle, but a bit more spendy