differences in shimano bottom brackets

[AngryScientist]

i'm not too shimano informed, so:

whats the difference between a 5700, 6700 and 7900 bottom bracket??

[dave thompson]

Fundamentally, nothing. Finish, weight and marginally better materials in each succeeding name mainly. 5700 is very good for a start but IMO Ultegra and Dura Ace are little better as far as bottom brackets go. All seem to work exceedingly well and are fully interchangeable with each other and their respective components.

[slidey]

Honestly, I don't know but I have and still use BB7900 and it works very well for me. It's very stiff when paired with my DA7800 crankset. Can't make out any noticeable difference from BB7800 at all.

For a brief period, I had also used the BB6700 with the 6750 crankset and call me picky, but I could feel a certain lack of stiffness in comparison to the above-mentioned setup.

In any case, they're so inexpensive that you might as well always go for BB7900. They're cross- and backward-compatible across Shimano cranks (Hollowtech 2).

[AngryScientist]

thanks Dave, that's kind of what i thought. i have a rotor crankset incoming, and a brand new 5700 BB in the parts bin (from where i have literally no idea). so they'll work fine for now.

[nahtnoj]

For a brief period, I had also used the BB6700 with the 6750 crankset and call me picky, but I could feel a certain lack of stiffness in comparison to the above-mentioned setup.



The reason has nothing to do with the bottom bracket. The 7800 crank has a steel spindle, while the 6700 has an aluminium one.

[apeescape]

I dont think shimano makes a crank with an aluminum spindle.... I think the difference is in the quality of the aluminum and the forging process. I know the 6750 will have stiffer rings than the 7800

[nahtnoj]

You're right. DA has a higher quality steel spindle than Ultegra, which is also steel...

[slidey]

Well, as per my experience - the 7800 crankset with 7900BB was noticeably stiffer (can't quantify how much) than the 6750 crankset with the 6700BB.

So, yeah...don't think your statement holds true for every case.

I know the 6750 will have stiffer rings than the 7800

[rice rocket]

You sure about that? Shimano will tell you straight up that the Ultegra is stiffer, but heavier than their Dura-Ace crank.

[slidey]

I am sure, yes...it's just what I experienced.

The only thing that could have misled me is that prior to the 6750 and since then I've only ever used 7800 cranks. And, I did pick up on the difference in the change of setup and didn't prefer it.

You sure about that? Shimano will tell you straight up that the Ultegra is stiffer, but heavier than their Dura-Ace crank.

[Mr Cabletwitch]

I've been told the only difference in bottom brackets is the bearings used so use what you have and eventually replace the bearings with Enduros.... This is what I did.