[tidi]

my mate has 7800 group on his bike. when in big ring, big cog so totally crossed the angle the chain comes off the front ring appears severe and makes a grinding noise.
i know it ain't best practice to ride in that gear which he doesn't but it sounds awful.
it's a double crankset.
my questions are
1, could someone have put a triple bb in
2, how would i know if it is a triple bb?
kind regards

 

[Salsa_Lover]

The 7800 BB is the same for all cranksets, the spindle length is on the crank itself.

 

[tidi]

thanx a lot..

 

[bdaghisallo1]

Does your mate have a frame with short chainstays? That would definitely contribute to non-optimal chain path angles. If so, not much to do about that but buy a new frame.

 

[tihsepa]

Does your mate have a frame with short chainstays? That would definitely contribute to non-optimal chain path angles. If so, not much to do about that but buy a new frame.

Or not crosschain.



My idea is cheaper.

 

[MR_GRUMPY]

It's the chainline.

Some bikes have screwed up chainlines. My main bike is able to ride in the big-big without any noise at all. If I try that on my TT bike, the chain will actually fall off the big ring, onto the small ring, after a few minutes. My other bike is somewhere in the middle.
.
.
.

 

[tidi]

thanx guys. i don't know the length if the stays but they appear short enough for small to medium size frames. his frame size would be an xl.
glad to hear some frames just have bad chain lines cause this has me stumped.