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chian line botom bracket crankset questions

Old 10-25-12, 01:58 PM
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chian line botom bracket crankset questions

bike 95 gt arette
current altus cranset. 68mm bottom bracket
steel frame
triple


want deore or or stx lx or xt cransk set (lighter prettier)

on ebay i often see bottom brackets with cranksets in the $40 range seems like a good price (used) assuming the bottom bracket it ok

i also assume the chain line for my bike is about 47 because its an altus which is mtbike set.

so are most shimano mtbike sets 47mm chain lines?
and I think to get a 47mm chain line the bottom bracket MUST MATCH THE CRANKSET.

so a given lx crankset may need one length bottom bracket and another stx might need a different one to end up with the same chain line. right?

so if I am buying a crank set without a bottom bracket
a) iw will likely need to change the bottom bracket from my altus c90 even though its smooth
b) it will depend on the crankset even if I only considered sq taper

are the above true if I am looking at bontrager or truvative, but with different lengths to get my 47mm chain line.
should I avoid octalink or isis, or only if it doesn't have a bb. (I think I should)
if I find a shimano hollowtech (fixed spindle to crank) i will jump on it but I think its out of my price range


I know I want 175mm cranks. i am 5'10"
does a 4 tooth difference on the big ring matter much. most i see are 44 32 22. should I hold out in my search for a 48 (this is for a hybrid on road almost exclusively)
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Old 10-25-12, 02:04 PM
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also what is mega exo. I am seeing a lot of fsa gossamer cheap. with the bracket. is it compatible?
I alos assume that with my 7 speed cassette I am fine with anyth 7 or 8 speed 9 speed ok too?

Last edited by scooterfrog; 10-25-12 at 02:19 PM.
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Old 10-25-12, 02:20 PM
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chain line is from the center line of the Bike, to center of the rear cluster.
a parallel line, if an even # of speeds its between two.
that is Both ends..
if a 9 speed and a triple crank, there is a chain ring and cog lined up.

if an 8 speed and a double it's the gap between , half way between each.

in crankset design there are Low Profile and wider types
the low profile comes in to meet a short spindle..
wider profile the spindle is longer , the crank arm may be at a right angle
to the BB axis.
Older TA and Campag are like that.

External BB types eliminate adjustments,
so simplify by reducing choice. the BB spindle-tube is fixed to the right crank arm.

Last edited by fietsbob; 10-25-12 at 02:27 PM.
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Old 10-25-12, 03:37 PM
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ok
i was looking for practical answers. but your informaiton helps
so if I use a 9sp triple in the front will my wider 7sp chain work ok or will it get hung up,

if I want to maintain an acceptable (whatever the word is) for my bike which i think needs to be 44-47mm as a hybrid with mtb componnets do I need to get cranks first and then the bottom bracket

if a crank set is mtb and comes with a bb is it safe to assume the (word above that I don't know) will be about right for my bike.

if most free hubs are the same width and the old are the same isn't the center cog almost always in the same place? Maybe 7 speed is a bit inbound of 8+ speed because the freehub body is shorter (or need a spacer)

does this not depend on my frame at all. bb width being the only concern (i suppose short chain stays might matter but mine are particularly short)

maybe I am asking the wrong questions.

Last edited by scooterfrog; 10-25-12 at 04:18 PM. Reason: it was confusing
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Old 10-25-12, 04:20 PM
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new question
assuming a 68mm dd shell
which comes first the crank or the bottom bracket length (spindle) once this is cleared up the rest may follow.
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Old 10-25-12, 04:29 PM
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new question
assuming a 68mm bb shell
which comes first the crank or the bottom bracket length (spindle) once this is cleared up the rest may follow.
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Old 10-25-12, 04:32 PM
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on sheldond brows database link of bb mine says this
[TABLE="class: tgrid"]
[TR]
[TH]Model
[/TH]
[TH]Single/
Double/
Triple[/TH]
[TH]Length[/TH]
[TH]Type:
Square/
Splined[/TH]
[TH]Chainline[/TH]
[TH]Chainring
Clearance[/TH]
[TH]Right
Crank
Clearance[/TH]
[TH]Left
Crank
Clearance[/TH]
[TH]Tread
(Q factor)[/TH]
[TH]BCD[/TH]
[TH]Notes[/TH]
[/TR]
[/TABLE]


[TABLE="class: tgrid"]
[TR]
[TD]Altus CT90
[/TD]
[TD]Triple[/TD]
[TD]116-121[/TD]
[TD]Square[/TD]
[TD]47.5-50[/TD]
[TH="colspan: 5"]Recalled! Do Not Use!
See Shimano dealer for free replacement.[/TH]
[TD]Compact 1995
[/TD]
[/TR]
[/TABLE]
where 47.5 is listed as the chain line on my crank. do I want maintain that?
whats a compact triple.

am I talking to myself again
do you think I can actually get a free replacement still
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