BB Compatibility with Bicycle

Do some more checking. You can find a sealed cartridge bracket with that
spindle length. A shorter spindle length will probably not function
properly (ie chainrings not clearing chainstay) Is your bike a triple?
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Quoted message said:

I am trying to change out the bb which has an existing spindle length
of 122.5mm. The diameter is 73mm. The bb I want is Shimano UN-73 which
is offered in 113mm spindle length and 73mm diameter. My question is:
will the Shimano fit? I have a GF Zebrano hybrid bike. Thanks for your
help. I did a search and I couldn't find anything online or in the
groups.

Steven

No it won't fit, it's too short. 9.5mm, about 1/3 inch would most
likely leave the crank arm or chain ring rubbing on the frame.

Shimano bottom brackets ARE available in many different lengths (107
109 110 113 115 117 119 122.5 127 131, etc) , look for one of about
122.5 mm to match the one you removed. They also offer different
quality levels, although the main difference is weight. Some use
steel, plastic, or aluminum for part of the construction. All the
shimano bbs are pretty reliable.

the diameter is not 73 mm. that is the spec for the width of the
bottom bracket shell part of the frame. 68 70 or 73 are common. It
doesn't have to be exact, just close.

What you want based on your question is a 73 x 122.5.

Bottom brackets typically are 2 different diameters. The size you are
working with and a much larger size common in department store bikes,
old schwinnns, some bmx bikes. There is no confusing bb axles or
cranks between the two.

the next bit of fun is the end of the bb axles. 4 sided / square taper
is common for older bikes. newer higher end racing equipment uses a
completely different shape. Some are called octalink.

Newer square taper crank arms tend to use shorter axles too. If you
are not changing crank arms, look for the same length of axle you took
out.

The reason to match up the bb axle length is to keep the crank in the
same relative position to the derailer, chain line and frame. Too
short and the crank will rub on the frame. Too long and the front
derailer might not be able to shift to the largest chainring. Way
different and the overall shifting will suffer.

Expect to need to do minor adjustments on the front derailer when you
change bottom brackets.

Quoted message said:

I am trying to change out the bb which has an existing spindle length
of 122.5mm. The diameter is 73mm. The bb I want is Shimano UN-73 which
is offered in 113mm spindle length and 73mm diameter. My question is:
will the Shimano fit? I have a GF Zebrano hybrid bike. Thanks for your
help. I did a search and I couldn't find anything online or in the
groups.

Steven

Ok, I'm going to answer my own question so hopefully others in the
future can be helped. The diameter of 73mm is the number that matters
the most. If I purchase a new bottom bracket, it has to be 73mm in
diameter. The new spindle length can vary. It can be 122.5mm or it can
be 113mm. It depends on the model of my choosing.

So the answer to my question is yes, the Shimano bb that I want to
purchase will fit into my bike because it is 73mm in diameter.

Thanks to the bike shop in Pleasanton on Santa Rita Rd for explaining
to me.

Steven

Excuse me, I got it slightly wrong. 73mm is the width, not the
diameter. Doesn't matter anyways, I got the gist of it. The basic
answer is yes the Shimano will fit my bike.

Steven

Quoted message said:

Excuse me, I got it slightly wrong. 73mm is the width, not the
diameter. Doesn't matter anyways, I got the gist of it. The basic
answer is yes the Shimano will fit my bike.

Steven

Perhaps you ignored the previous posts. While the bottom bracket width
may fit your bike, the shorter spindle is likely to cause you problems.
The shorter spindle will bring the cranks and the chainrings closer to
the frame. If you don't have enough clearance, the chainrings or the
crank will hit the frame. Even if it doesn't hit the frame, you will
have to readjust your front derailler or you will drop the chain onto
your foot when you try to shift to the big chainring.

You are better off buying the correct size.

-Buck

Quoted message said:

You are better off buying the correct size.> -Buck

I guess that would entail buying the same spec unit that I have on now?

The problem I kept having was chain suck. Haven't had it yet since I
exchanged my old bike for my new one (thank god!), but I'm worried that
it might happen again.

I was reading that a change in geometry might actually be helpful in
this case because of the way the original specs were setup. My bike is
notorious for chain suck. I talked with LBS serviceman and he said that
all Gary Fishers, Trek, and so forth have design issues which are more
likely to cause chain suck.

Quoted message said:

From the research I have done, the source of the problem is the chain

rings. That's what I'm trying to change.

Steven

Quoted message said:

Quoted message said:

You are better off buying the correct size.> -Buck

I guess that would entail buying the same spec unit that I have on now?

Yes.

Quoted message said:

The problem I kept having was chain suck. Haven't had it yet since I
exchanged my old bike for my new one (thank god!), but I'm worried that
it might happen again.

I was reading that a change in geometry might actually be helpful in
this case because of the way the original specs were setup. My bike is
notorious for chain suck. I talked with LBS serviceman and he said that
all Gary Fishers, Trek, and so forth have design issues which are more
likely to cause chain suck.

Quoted message said:

From the research I have done, the source of the problem is the chain

rings. That's what I'm trying to change.

I think your LBS service guy is yanking your chain.

You can change the chain rings without changing the geometry of the
bike or the cranks. Take a look at this website for some ideas on
correcting the problem:
http://www.fagan.co.za/Bikes/Csuck/

If you really need a new set of chainrings, you may be able to get some
more life out of them by flipping them over. Just remember that you
should also replaced the stretched chain and perhaps even the cogs at
the same time. In the future, keep an eye on your chain wear and
replace it when worn so it doesn't cause the damage to more expensive
parts.

-Buck

Quoted message said:

I am trying to change out the bb which has an existing spindle length
of 122.5mm. The diameter is 73mm. The bb I want is Shimano UN-73 which
is offered in 113mm spindle length and 73mm diameter. My question is:
will the Shimano fit? I have a GF Zebrano hybrid bike. Thanks for your
help. I did a search and I couldn't find anything online or in the
groups.

Steven

Un-73 BBs come in a variety of lengths, including 122.5 Get the same
one you are replacing..i have one-call me

http://www.vechhios.com

Quoted message said:

Un-73 BBs come in a variety of lengths, including 122.5 Get the same
one you are replacing..i have one-call me

http://www.vechhios.com

Your website link does not work. And thanks to the guys that have
helped out. You guys are so kind. 🙂

So far so good, I've decided to hold off on buying any parts until I
experience at least one incidence of chain suck but so far it hasn't
happened. I have purchased a good size bottle of degreaser however, for
cleaning my chain. Gotta love that Finish Line chain cleaner do-hickey.
It really gets the job done for squeaky clean chains.

Steven

Quoted message said:

Un-73 BBs come in a variety of lengths, including 122.5 Get the same
one you are replacing..i have one-call me

Quoted message said:

From the research I have done, the UN-73 BBs do indeed come in 122.5

length. Unfortunately they are not offered in a 73mm width along with
the 122.5 length which is what I need. Thanks anyways, maybe I'll go
with Truvativ.

Steven