Determining Correct Size Bottom Bracket??

[biggiec]

I recently purchased a 2001 team GT i-drive frame, and i have never built a bike up from scratch before. I want to use Deore LX cranks, the M572 model, but im not sure what size BB i need for my frame. I know you need to use an es-51 bb, but i dont know what size to get A site selling a parts kit for this particular frame includes a 68 x 113mm BB, so i assume that size BB will work for my frame. What do these dimension mean? Is the 68 number the diameter and cant be substituted, and the 113 the length, wich you can use different lengths?? I was also reading that with this particular crank you need to use a longer bb. Thank for any info.

 

[dabac]

Is the 68 number the diameter and cant be substituted, and the 113 the length, wich you can use different lengths?? I was also reading that with this particular crank you need to use a longer bb. Thank for any info.

68 is the length of the bearing (a.k.a "shell), i.e. the part that screws into the frame. 113 is the overall length of the axle, the part that the cranks attaches to. Depending on your crank arms you might need a longer BB not to get cleareance issues with the chainstays and to get a working chain line.
I don't know what'll happen if you start playing around with the shell size, probably some combo's will work while other won't.

If you're not sure what dimension you need this is the sort of thing that I'd consider leaving to the LBS, if they don't know either they can try different sizes until they find the right one and still only charge you for one part + labor. Unless you have a very understanding LBS that'll let you return parts that have been assembled, in that case you can do your trial-and-error yourself if you don't get it right the first time.

 

[boudreaux]

I recently purchased a 2001 team GT i-drive frame, and i have never built a bike up from scratch before. I want to use Deore LX cranks, the M572 model, but im not sure what size BB i need for my frame. I know you need to use an es-51 bb, but i dont know what size to get A site selling a parts kit for this particular frame includes a 68 x 113mm BB, so i assume that size BB will work for my frame. What do these dimension mean? Is the 68 number the diameter and cant be substituted, and the 113 the length, wich you can use different lengths?? I was also reading that with this particular crank you need to use a longer bb. Thank for any info.

A 572 crank uses a 121 or 126mm spindle and a shell width of 68 or 73mm depending on your the shell idth of your frame.