New crank set, but what length bottom bracket??
Darra8
Posts: 721
Hi Guys,
I'm quite sure this has been asked many times before, but i have looked for the right answers, but get different lengths.
At the moment i have a 113mm BB and my acera cranks are, after tightening them up, are almost touching the BB housing. This is also stopping me getting the front mech to go far enough in to drop the chain onto the inner ring. I am also thinking of upgrading the crank to alivio at the same time, but have looked on different websites and one says 113 and the other says 118 BB lengths. As i already have 113 and it would seem that it's a little short, maybe 118 would be better. But the questions is will 5mm longer be enough, should i go for 121/122?
Hope someone can help.
Steve
I'm quite sure this has been asked many times before, but i have looked for the right answers, but get different lengths.
At the moment i have a 113mm BB and my acera cranks are, after tightening them up, are almost touching the BB housing. This is also stopping me getting the front mech to go far enough in to drop the chain onto the inner ring. I am also thinking of upgrading the crank to alivio at the same time, but have looked on different websites and one says 113 and the other says 118 BB lengths. As i already have 113 and it would seem that it's a little short, maybe 118 would be better. But the questions is will 5mm longer be enough, should i go for 121/122?
Hope someone can help.
Steve
40 year old pussy who "still" hates the thought of falling off!!
0
Comments
-
What is the exact model of crank ie code? Will say on it somewhere (FC m311 for example)0
-
The acera crank i have at the moment is FCM 381 The crank i'm thinking of upgrading to is alivio FC-MC411-S. Both are square taper40 year old pussy who "still" hates the thought of falling off!!0
-
The 411 appears to need a 123mm axle for a 47.5 chainline.0
-
This is what makes it so confusing. 2 different websites said 113 or 118 :?
Also, what does 47.5 chainline mean?
Cheers,
Steve40 year old pussy who "still" hates the thought of falling off!!0 -
I got that from the Shimano site - though it may have been an older model. Site is down at the minute though.
Best bet is to look up front chainline!0 -
The chainline is the distance from the centre of the middle chainring (or inner chainring if a double) to the centre of the seat tube.
Shimano usually recommend 43.5mm for a road double, 45mm for a road triple, 47.5mm for a hybrid, and 47.5mm or 50mm for an MTB.
I set my chainline as small as possible which is easy with square taper bottom brackets due to lots of different axle lengths being available. As long as the chain doesn't rub anything when on small/small, and the cranks and chainrings don't rub the chainstays.0 -
I prefer the shorter line too - running octalink on my Zaskar LE, and a shorter BB. I think it favours technical riding and therfore the chai nangle that results from shorter gears.0
