Bottom Bracket Size

Bimboveloce

New Member
Hi,
I have a Specialized Crosstrail Sport 2011 model and I am rebuilding most of the running gear.
The bottom bracket is noisy and I wanted to replace it but I am unsure of the size. The old one is 68 x113 but I want to ensure this is the correct size as I know the bike has been mistreated.
Does anyone know the correct size of the bottom bracket for a Specialized Crosstrail Sport 2011?
Thanks in advance
Tony
 

Ajax Bay

Veteran
Location
East Devon
:welcome:
The '68' is the width of the BB shell of the bike: cannot be affected by 'mistreatment'.
113 is the length of a square taper spindle: 113mm and whether that's 'correct' will depend on the chainset you have fitted. What is that and confirm type of BB (H2, square taper)? Then go an look for a new version of that chainset and it should specify the spindle length required (square taper). A couple of mm either way probably wont matter (more caveats available on application).

https://www.specialized.com/gb/en/crosstrail-ltd-disc/p/33500?color=36257-33500&searchText=9214-8102
Chainset Shimano FCM-543LK
The Shimano FCM-543LK pdf is here: https://si.shimano.com/pdfs/ev/EV-FC-M543-K-2682.pdf but it won't have "113" on it, sfaik.
 
OP
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Bimboveloce

New Member
Hi Ajax Bay,
Thank you for your reply.
I'm sorry but I don't understand some of your terminology. When you mention chains what is this? BB, H2 Square Taper? I know the bottom bracket is a square taper. All gear, front derailleur, rear derailleur, chain, crank, gear shift cables have been replaced if that helps.
Regards
Tony
 

si_c

Veteran
Location
Wirral
You need a Shimano Bottom Bracket (BB) which has a square taper fitting to the chainset. The Shimano model you need is a BB UN55 size 68x113 as you noted in your first post.
 

Ajax Bay

Veteran
Location
East Devon
Agree with @si_c , but the UN-55 has been discontinued and its replacement in the Shimano stable is the UN-300:
https://www.tweekscycles.com/uk/shimano-bb-un300-square-tapered-bottom-bracket-2012876/
OP - lots of pictures in this: https://bike.bikegremlin.com/1634/bicycle-bottom-bracket-standards-explained/ to add to your knowledge base.
I couldn't be sure what chainset you have (the one with two cranks and sprockets on the front) and the bike spec I found listed the Hollowtech2 chainset. You subsequently shared that yours was square taper - so UN-300. But you still haven't shared what the chainset is, so if you fear the bike has been 'mistreated' (as you put it) and a different chainset has been put onto the 'old' 68-113 BB, then tell us what the chainset is. "crank. . . [has] been replaced" by who?
 
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Bimboveloce

New Member
Thanks, the chain set has 3 sprockets, 26,36-48 teeth sprockets. I have replaced all of the gear mentioned on the previous posts.
Thanks in advance.
 
OP
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Bimboveloce

New Member
Thanks I appreciate the offer, unfortunately I have purchased one from Amazon as it came the next day. Will be fitting the cranks at the weekend as the bottom bracket is now in.
On the test fit of the crank, it doesn't go far on the bottom bracket square taper, is this correct?
 

Ajax Bay

Veteran
Location
East Devon
Depends what you mean by "far". When just fitted on by hand the end of the spindle will be maybe 3-5mm below the 'level' of the (square) hole in the crank. Screwing up the crank bolts will 'pull' the crank further and firmly onto the spindle (a mere smear of grease, tighten, hit crank (along spindle axis line) with a rubber mallet, tighten again). The design and the forces a square taper interface deals with actually means that, when ridden/turned with moment, the crank creeps up the spindle's facets very slightly.
More here: https://www.sheldonbrown.com/brandt/installing-cranks.html
 
Location
London
Agree with @si_c , but the UN-55 has been discontinued and its replacement in the Shimano stable is the UN-300:
I only learned this recently.
Somewhat concerned as like many I always rated the UN55.
Anyone any idea if the UN300 is as good?
Must admit to being puzzled as to why shimano replaced something so well established that just worked.
 

Ajax Bay

Veteran
Location
East Devon
like many I always rated the UN55. Anyone any idea if the UN300 is as good?
Me too. No idea, and I can't see that anyone can have a useful view, unless they've done seious miles since it was rolled out and they installed one immediately. Maybe it's just renaming but it has a "chain line stabilizer" - not sure if that's a 'thing' - looks like a rubber washer with no clear function.
https://bike.shimano.com/en-EU/product/component/tourney-tx800/BB-UN300.html
Have a few UN-55s in spares box but about to get a UN-300 @ 110mm as that's the length I need for a new build (with Spa Cycles triple chainset). I'll try to remember to let people know once it's done 10Mm (this time next year, maybe).
 
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Bimboveloce

New Member
Thank you for all the replies.
I have now fitted the running gear, derailleurs front and rear, bottom bracket, cassette, crank etc, now need to set up derailleurs, challenging me thinks and a sticking from disc brake. Any ideas how to take apart for servicing? it is hydraulic.
Thanks in advance.
Tony
 

Tripster

Senior Member
Location
North West
Me too. No idea, and I can't see that anyone can have a useful view, unless they've done seious miles since it was rolled out and they installed one immediately. Maybe it's just renaming but it has a "chain line stabilizer" - not sure if that's a 'thing' - looks like a rubber washer with no clear function.
https://bike.shimano.com/en-EU/product/component/tourney-tx800/BB-UN300.html
Have a few UN-55s in spares box but about to get a UN-300 @ 110mm as that's the length I need for a new build (with Spa Cycles triple chainset). I'll try to remember to let people know once it's done 10Mm (this time next year, maybe).
Interesting the replacement BB from Shimano has no shoulder on non drive side like the UN55 and looks more like the TH industries one I just replaced
 
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