bb size confusion

Callistus Valerius said:

Thinking about replacing a shimano 600 double crank, with an isis
compact. Pulled out the bb, and it's a bb-un70 square, with no length size
on the bb. The shell is the standard 68, and I measured from one end to the
spindle to the other and came out with 115. So I check Sheldon's BB size
pagehttp://www.sheldonbrown.com/bbsize.html#ultegra and on his chart I see
under 600 ultegra 6400 and length I see this --- 113 (115) ?? Now the 115
number matches my number, but is the 113 the number I use to replace the BB
with? So would it be a 68x113. Even if I didn't change to isis, and just
wanted to replace the square bb, with a new one, would it be a 68x113, or
would I have to scrounge ebay for a bb they don't make anymore.

2mm? Don't lose any sleep over it.

Callistus Valerius said:

Thinking about replacing a shimano 600 double crank, with an isis
compact. Pulled out the bb, and it's a bb-un70 square, with no length size
on the bb. The shell is the standard 68, and I measured from one end to the
spindle to the other and came out with 115. So I check Sheldon's BB size
pagehttp://www.sheldonbrown.com/bbsize.html#ultegra and on his chart I see
under 600 ultegra 6400 and length I see this --- 113 (115) ?? Now the 115
number matches my number, but is the 113 the number I use to replace the BB
with? So would it be a 68x113. Even if I didn't change to isis, and just
wanted to replace the square bb, with a new one, would it be a 68x113, or
would I have to scrounge ebay for a bb they don't make anymore.

The length of the Isis BB has to match the requirements of the Shimano
crank and not your old BB. You have to refer to the maker of your
cranks to find out the necessary size of Isis BB to install. However,
I think that there are only two sizes right now so you only need to
get the narrow one.

Quoted message said:

Callistus Valerius said:

Thinking about replacing a shimano 600 double crank, with an isis
compact. Pulled out the bb, and it's a bb-un70 square, with no length size
on the bb. The shell is the standard 68, and I measured from one end to the
spindle to the other and came out with 115. So I check Sheldon's BB size
pagehttp://www.sheldonbrown.com/bbsize.html#ultegra and on his chart I see
under 600 ultegra 6400 and length I see this --- 113 (115) ?? Now the 115
number matches my number, but is the 113 the number I use to replace the BB
with? So would it be a 68x113. Even if I didn't change to isis, and just
wanted to replace the square bb, with a new one, would it be a 68x113, or
would I have to scrounge ebay for a bb they don't make anymore.

The length of the Isis BB has to match the requirements of the Shimano
crank and not your old BB. You have to refer to the maker of your
cranks to find out the necessary size of Isis BB to install. However,
I think that there are only two sizes right now so you only need to
get the narrow one.

Yes a BB should match the crank requirements and the BB shell width, a
previous cranks setup dimensions are not relevant except in direct
comparison to the same crank and manufacturers suggestions.

If you are not changing the crank just swapping out the BB that was
there and it worked fine, get the same again.

A Shimano crank with an Isis BB?
Have I missed a recent development?

Marcus

Callistus Valerius said:

Thinking about replacing a shimano 600 double crank, with an isis
compact.

-----------------------
The BB length has to match the new cranks. Road doubles have pretty
much standardized to 108mm, so you'll probably need a 68x108mm if you
are sticking with a double. Check the crankset first.

A lot of people are a little down on ISIS because the bearings don't
seem to be as durable as the new EXO designs that put the bearings
wider and bigger. So,you may want to consider stepping up to something
like Shimano hollowtechII, or FSA EXO designs if you are going to
replace BB and crankset anyway.

Callistus Valerius said:

Thinking about replacing a shimano 600 double crank, with an isis
compact. Pulled out the bb, and it's a bb-un70 square, with no length size
on the bb. The shell is the standard 68, and I measured from one end to the
spindle to the other and came out with 115. So I check Sheldon's BB size
page http://www.sheldonbrown.com/bbsize.html#ultegra and on his chart I see
under 600 ultegra 6400 and length I see this --- 113 (115) ?? Now the 115
number matches my number, but is the 113 the number I use to replace the BB
with? So would it be a 68x113. Even if I didn't change to isis, and just
wanted to replace the square bb, with a new one, would it be a 68x113, or
would I have to scrounge ebay for a bb they don't make anymore.

A perennial question:
Cup thread matches frame; spindle dimensions match crank.

If your old spindle length fits the new crank, it was a random match.
Cranks generally are shorter over time, once 127mm now as short as
102mm. Crank designers have a wide variety of ways to get the chainrings
in the right (same) place and that is not easy to observe. Buy the
spindle when you buy the cranks.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Quoted message said:

The BB length has to match the new cranks. Road doubles have pretty
much standardized to 108mm, so you'll probably need a 68x108mm if you
are sticking with a double. Check the crankset first.

---------
So 108 for a double, 118 for a triple, so what would a 113 be for? Now I'm
guessing it's for a seat tube that isn't standard, bigger, so the chain line
is farther out?

Quoted message said:

A lot of people are a little down on ISIS because the bearings don't
seem to be as durable as the new EXO designs that put the bearings
wider and bigger. So,you may want to consider stepping up to something
like Shimano hollowtechII, or FSA EXO designs if you are going to
replace BB and crankset anyway.

----------
are they as easy to put on as an isis is?

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

So 108 for a double, 118 for a triple, so what would a 113 be for? Now I'm
guessing it's for a seat tube that isn't standard, bigger, so the chain line
is farther out?

Manufacturers set the spindle length according to the needs of the
particular crank. There is no rigid standard. Shimano and Campagnolo
especially have always had numerous exceptions to even their own typical
spindle lengths. The spindle length means nothing except that it is
what the crank maker needed for that particular crank and it probably
has nothing to do with the frame. Probably...

Since ISIS seems to have more or less followed a basic standard for
spindle lengths, any particular ISIS road double is very likely to
require a 108mm spindle length. Of course, if you try to do something
off the wall like put a road crank on a MTB frame, then you are in
uncharted territory and you will need to use what works. Old frames
and/or frames imported from certain countries may have their own
requirements.

A Muzi said:

If your old spindle length fits the new crank, it was a random match.
Cranks generally are shorter over time, once 127mm now as short as
102mm. Crank designers have a wide variety of ways to get the chainrings
in the right (same) place and that is not easy to observe. Buy the
spindle when you buy the cranks.

Which is what makes buying and using used cranks of uncertain origin such fun.

--
Dane Buson - [email hidden]
"Bureaucracy is a giant mechanism operated by pygmies."
-Honore' De Balzac

Quoted message said:

A Muzi said:

If your old spindle length fits the new crank, it was a random match.
Cranks generally are shorter over time, once 127mm now as short as
102mm. Crank designers have a wide variety of ways to get the chainrings
in the right (same) place and that is not easy to observe. Buy the
spindle when you buy the cranks.

Dane Buson said:

Which is what makes buying and using used cranks of uncertain origin such fun.

Hence an endless series of inquiries here. It's knowable but not simple.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

Let's say you want to "guestimate" a bottom bracket width for an older
(70's and early 80's) crankset in a 68 mm shell. Older cranksets have
a 3mm drive-side offset so you'd add 3mm to the older size to get the
modern symmetric sized cartridge bottom bracket :

vintage high-end forged road cranks : modern 115 cartridge (=112 vintage)

== campagnolo and clones road double

vintage low-end riveted road crank : modern 130 cartridge (=126 + 3
vintage double)

== sugino maxy riveted cranks

mighty-tour forged cranks are about halfway between maxy and
campagnolo.

These guestimates would not be far from the mark. For single-speed
usage, subtract 3-4mm to move the outer chainring inwards by half a
chain-width. For triple usage, add 3-4 mm to move the innter
chainring outwards by half a chain-width. That can get you started.

- Don Gillies
San Diego, CA

Vintage high-end cranks : campagnolo, dura-ace, shimano-600, sugino
mighty, etc., used 112-113 asymmetric spindles which are 3 mm longer
on the drive side (known as a "3 mm drive-side offset"😉.

Your crank has been updated to a symmetric bottom bracket so you add 3
mm which ends up showing up on the non-drive side to get 115 (well,
116 technically but 1 mm is a trivial difference in chainline and 116
mm BB's are rare). You need a new 115(common) or 116(uncommon) mm
symmetric bottom bracket as a replacement.

If you're buying a new crankset, just ask the seller what size it
needs for your application. All you really need is the double size,
you can subtract or add 3-4mm for single or triple applications,
respectively.

Newer BB's are all over the map : 102 mm for pro-level campy
record/chorus, 110 mm for lower-end campy, and 109 mm for most track
applications. And, if its 109 for track, you want to add 3-4mm for
road-double applications. In general, cheaper cranks need wider
bottom brackets because the more metal is used to build a cheaper
crankarm head, using weaker metals, and according to lower tolerances.
in some cases arms are riveted to spiders, adding another 3-4mm to the
overall crankset width.

- Don Gillies
San Diego, CA