Bottom bracket axle length ?

Sharky

Guru
Location
Kent
I had the same problem when converting a frame back to square taper. I took it to my LBS who probably had all the different sizes on the their shelves and they fitted the correct one and charged a very modest amount for fitting. Second time round, when it needed replacing again, I was able to order the exact same length and fitted it myself.
 

Ajax Bay

Veteran
Location
East Devon
I'm assuming you mean (square taper) BB length not spindle length. Measure the bottom bracket with a set of calipers. Road frame will be 68mm (nearly always) and an MTB 73mm. Buy a UN55 with spindle length (eg 113mm) correct for the intended chainset and chain line, and fit.
 
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RufusChucklebutty

Senior Member
I'm assuming you mean (square taper) BB length not spindle length. Measure the bottom bracket with a set of calipers. Road frame will be 68mm (nearly always) and an MTB 73mm. Buy a UN55 with spindle length (eg 113mm) correct for the intended chainset and chain line, and fit.
My question was not the diameter , but the length of the spindle if you have no factory data to go on ?
 

Ajax Bay

Veteran
Location
East Devon
My question was not the diameter , but the length of the spindle if you have no factory data to go on ?
My answer (68mm, maybe 73mm) is not the diameter either - but do you know whether it's 68 or 73? You asked "How do you determine the correct length square taper bottom bracket cartridge for a bare frame". I offered you additional info to help you get to the spindle length answer, in case that's what you were actually asking, and said it depended on the chainset you plan to use. What chainset do you plan to use? What is the OLN of the rear dropouts (ie where the rear wheel goes in)?
 

davidphilips

Über Member
Location
Onabike
Think what is the important measurement is the distance from the frame to the center of the chainset, problem is some square taper chainsets go on to the bottom bracket further than others (different makes or bit of wear?) as far as i remember set the distance center of frame to center of chainset (if double or triple chainset) to about 44.5mm, Way to set this measurement is with lenght of bottom bracket.
l and error unless you are lucky
Fixed wheel or single speed bikes i am sure will differ. This distance is important to get a good chain line.
 

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RufusChucklebutty

Senior Member
I make my bikes from salvaged and recycled bikes that are thrown away ,cannibalising them , most of the parts other than frames I have are generic or unidentifiable, I rarely get high end state of the art parts .
 
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