best BB for gxp bottom bracket replacement?

[tv_vt]

I've read the comments before about excessive friction in the outboard bottom brackets, but have noticed it now firsthand on a gxp bottom bracket for a Truvativ crank. If I spin it hard, it'll go one revolution. An octalink BB on another bike seems to have much less friction when I spin it.

Any suggestions for a replacement bottom bracket? Don't think Shimano or Campy are compatible, or FSA for that matter. Is a SRAM the only choice? Is ceramic really worth the dough?

Thanks,

Thom

[David Kirk]

Do you know that the BB is properly faced? That type of drag sounds like the BB isn't faced.


The bearings won't matter if they aren't parallel to each other.

Dave

[dnades]

I've got the same thing going on with a Force crank and gxp bottom bracket. I even tightened it to the bottom end of the torque recommendation. It is very stiff. The most I can get it to go around is about 2.5 times with a really hard push. The paperwork says that it'll loosen up over time and since it hasn't been ridden yet I can't say that it won't but it sure is stiff. Did I mention it was stiff? Everything went together real well and the cups met the bottom bracket evenly when tightened. I guess I could get it checked out. TV vt let me know what you end up finding out about your bottom bracket(ie getting it faced as DK suggests). If I spin my chorus ut crank with same amount of force it goes around and around ad nauseum(different frame though).

DK- any lo-tech way of checking the faces short of a stiff crank?

[David Kirk]

DK- any lo-tech way of checking the faces short of a stiff crank?

Low tech is relative. If you have a real set of calipers you can measure the BB width at 4 places around it. A good facing should give a difference of .002" max.

Do you have some calipers or know someone who does?

It shouldn't matter how tightly the crank is torqued. There is no side load on the bearings relative to each other. All lateral location is handled by one side so exact BB width doesn't matter. I just installed a Force crank and BB on Karin's new bike and it spins smooth and long.


Dave

[pdxmech13]

the cups on my serotta are within .06 and the regular gxp bb is one of the smoothest I have felt to date.

[tv_vt]

It's a Look carbon frame, so I'm not sure it can be faced. But I thought one of the good things about the gxp bb's were that the frame didn't need to be perfectly faced.

I kinda wonder if the seals on the outside of the bearings create drag.

I may just spring for a new Team gxp and give it a try - they're only $35 thru Excelsports. The crank is a 177.5mm compact, so it's hard to replace with anything else - there aren't too many options out there for that combo (unless I want to spring for a new DA7900 crank at $700 or so a pop).

Thanks for the replies.

Thom

[labratmatt]

I too have had good luck with the GXP bottom brackets. Mine spins smoothly and easily.

[Louis]

A good facing should give a difference of .002" max.

Wow. Those Kirks sure are built to tight tolerances.

Let's assume a 68mm BB shell.

68 mm = 2.677165 in

0.002 / 2.677165 = 0.0747 %

PS I would think that it's pretty tough knowing for sure that the calipers are truly on opposite sides of the shell. Rotating them just a bit so they are no longer parallel to the shell axis could easily throw off the measurement.

[dnades]

Well I'll have to check my assembly of the crank and see what is going on. Clearly if you guys are having no problems it is probably something I did while putting it together. A note: this crank came with a narrow plastic spacer ring which I did not install. I couldn't find any information about it on the directions. I found a reference to it in regards to sram's mountain bike cranks but not the force cranks.

thanks again

john

[benb]

I reinstalled my GXP BB & Rival Cranks tonight on my Serotta...

- I once again noted the threads on the GXP BB are very precise.. they thread all the way in with no use of a tool other then to do the final torquing. (This is not true with either the DA BB I have nor the the XT BB I had in for a hillclimb this weekend)

- No spacer ring on the crank.. my bike was shipped from Serotta to Quality and the SRAM stuff was put on.. definitely no spacer ring.

- After cleaning, regreasing, and reassembling with no chain on the bike if I spin the cranks they spin about 4-5 rotations before coming to a stop. (About the same as my other combos)