Myosmith

I recently swapped the stock crankset on my Giant Boulder SE with an Shimano Alivio crankset. All works well except that there is about a 1 cm space between the crank and the bottom bracket, even with the crank bolts fully tightened.

I looked online and found that the Alivio cranks list a spindle length of 113 and I think mine is probably about 122, though I haven't pulled it out to measure accurately. I've ridden the bike that way a few times and it seems to work fine, but it looks funny to me to have that gap.

Is there a mechanical reason the bottom bracket should be changed to a 113 or is it OK to ride as is?

bradtx

Myosmith, It might optimize the chainline to use the correct BB.

Brad

Capecodder

You need 47.5mm from the center of the seat tube to the middle chainring. This will give you the correct chainline, and a 113mm BB is in order.

Myosmith

Thanks for the info.

Capecodder,

Is that 47.5 mm consistent across bike brands and models with triples? If so, that will be a very handy number to add to my notebook.

bradtx

Myosmith, Here's a link: https://sheldonbrown.com/chainline.html . Generally a shorter chainline measurement is preferred to lesson the Q factor, or the distance the feet ar spaced apart. It is somewhat dependent on the frame and crankset WRT interferance.

Brad

fietsbob

IsProfile, .. Lower profile design, moves the planes the chainrings sit, out,
relative to where it sits on the end spindle/ BB axle.
as a result of the shape the crank arms, spider.. are made