Swap triple crank to double - outer ring hits frame



M

monkeyboy

Guest
Hello,

I recently purchased a bianchi axis for a commuter bike. It came with a
175mm-triple. I would like to swap it with a shimano 600 or 105,
172.5mm-double I currently have. When I try to mount the crank, the
large chain ring rubs on the chain stay.

I'm not sure what the best fix is. It looks like you can't find a
172.5mm-triple unless your at the high end of the component range, and
they are expensive. Could a new bottom bracket fix the problem? Are
there different tapers on the bottom brackets that determine where the
crank mounts?

Thanks,

Frank

PS

I want to make the change for a couple of reasons. I have two other
bikes each with 172.5mm cranks, I'd like to keep things the same for
all. Also, I have some road sized, 130 bcd, chain rings to use as
spares. The triple came with a 48 as the largest and has a 110 bcd.
 

Weisse Luft

New Member
May 28, 2004
1,306
0
0
monkeyboy said:
Hello,

I recently purchased a bianchi axis for a commuter bike. It came with a
175mm-triple. I would like to swap it with a shimano 600 or 105,
172.5mm-double I currently have. When I try to mount the crank, the
large chain ring rubs on the chain stay.

I'm not sure what the best fix is. It looks like you can't find a
172.5mm-triple unless your at the high end of the component range, and
they are expensive. Could a new bottom bracket fix the problem? Are
there different tapers on the bottom brackets that determine where the
crank mounts?

Thanks,

Frank

PS

I want to make the change for a couple of reasons. I have two other
bikes each with 172.5mm cranks, I'd like to keep things the same for
all. Also, I have some road sized, 130 bcd, chain rings to use as
spares. The triple came with a 48 as the largest and has a 110 bcd.

Get the double BB and all will be fine. Yes, triple BB's are narrower, making the outer ring too close to the chinstay on some bikes.
 

davidd86

New Member
Nov 29, 2004
126
0
0
I think it depends on the brand as to whether the double's longer than the triple. But Weisse's right, get the next size up in BBs and you'll be set. I had the same problem as you do; using a Campy double with the 111mm BB, the big ring rubbed on the chainstay. I just swapped it out for a 115.5 that's supposed to be used with their triples. All is well. The 2.25mm on each side isn't enough to notice or materially foul up the chainline.



Weisse Luft said:
Get the double BB and all will be fine. Yes, triple BB's are narrower, making the outer ring too close to the chinstay on some bikes.
 
monkeyboy wrote:
> Hello,
>
> I recently purchased a bianchi axis for a commuter bike. It came with

a
> 175mm-triple. I would like to swap it with a shimano 600 or 105,
> 172.5mm-double I currently have. When I try to mount the crank, the
> large chain ring rubs on the chain stay.
>
> I'm not sure what the best fix is. It looks like you can't find a
> 172.5mm-triple unless your at the high end of the component range,

and
> they are expensive. Could a new bottom bracket fix the problem? Are
> there different tapers on the bottom brackets that determine where

the
> crank mounts?
>
> Thanks,
>
> Frank
>
> PS
>
> I want to make the change for a couple of reasons. I have two other
> bikes each with 172.5mm cranks, I'd like to keep things the same for
> all. Also, I have some road sized, 130 bcd, chain rings to use as
> spares. The triple came with a 48 as the largest and has a 110 bcd.


Well, you should be able to make the 600 or 105 fit, but you will
probably need a longer BB. I couch this in "maybe" terms because the
bike may well be designed in part around the particular crankset.

Further, remember that you're increasing Q-factor by putting in a wider
BB. The standard for 600/Ultegra cranks was 113mm, the standard for
105sc cranks was 107mm.

If clearance is tight, you could try something like a 105sc on a 115
(or longer) BB...but you are paying for it in Q-factor.

You might just want to try the stock cranks and see if they aren't OK
for you as is...
 
Q

Qui si parla Campagnolo

Guest
Luft writes-<< Get the double BB and all will be fine. Yes, triple BB's are
narrower,
making the outer ring too close to the chinstay on some bikes. >><BR><BR>

I say-I don't get this. Triple BBs are always longer and a longer BB spindle is
what this gent needs. He is going from a triple to a double, not the other way
around. The way-wide chainstay on the Bianchi is the problem.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"
 
T

Terry Morse

Guest
Someone wrote:

> Well, you should be able to make the 600 or 105 fit, but you will
> probably need a longer BB. I couch this in "maybe" terms because the
> bike may well be designed in part around the particular crankset.


Another potential fix is to insert a spacer between the right side
bottom bracket cut and the frame. This only works if you have enough
clearance for the left side crank.

You can purchase BB spacers of varying size at loosescrews.com.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/
 
P

Peter Cole

Guest
"monkeyboy" <[email protected]> wrote in message
news:[email protected]
> Hello,
>
> I recently purchased a bianchi axis for a commuter bike. It came with a
> 175mm-triple. I would like to swap it with a shimano 600 or 105,
> 172.5mm-double I currently have. When I try to mount the crank, the
> large chain ring rubs on the chain stay.
>
> I'm not sure what the best fix is. It looks like you can't find a
> 172.5mm-triple unless your at the high end of the component range, and
> they are expensive. Could a new bottom bracket fix the problem?


Ye, Sheldon Brown has a BB size index, you can look up your crank.
http://www.sheldonbrown.com/bbsize.html
 
M

Mark Janeba

Guest
Qui si parla Campagnolo wrote:
> Luft writes-<< Get the double BB and all will be fine. Yes, triple BB's are
> narrower,
> making the outer ring too close to the chinstay on some bikes. >><BR><BR>
>
> I say-I don't get this. Triple BBs are always longer and a longer BB spindle is
> what this gent needs. He is going from a triple to a double, not the other way
> around. The way-wide chainstay on the Bianchi is the problem.


I agree. Is the chainstay spreading at some really big angle?
Everyone's talking about the *big* chainring hitting the chainstay - I'm
used to seeing the little ring hit first.

Mark Janeba
 
W

Werehatrack

Guest
On 20 Dec 2004 05:29:16 -0800, "monkeyboy" <[email protected]>
wrote:

>Hello,
>
>I recently purchased a bianchi axis for a commuter bike. It came with a
>175mm-triple. I would like to swap it with a shimano 600 or 105,
>172.5mm-double I currently have. When I try to mount the crank, the
>large chain ring rubs on the chain stay.


This can be due to one of three things. The 172 crank may have a
larger chainring, or the 172 crank may require a different BB with
wider spacing, or the 172 crank may have a wallowed taper.

>I'm not sure what the best fix is. It looks like you can't find a
>172.5mm-triple unless your at the high end of the component range, and
>they are expensive. Could a new bottom bracket fix the problem?


Yes, if it's just a matter of the crank/chainring/frame combination
needing a wider BB.

>Are
>there different tapers on the bottom brackets that determine where the
>crank mounts?


No. The shaft lengths are different.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.
 
J

Jim Hall

Guest
monkeyboy wrote:

>Hello,
>
>I recently purchased a bianchi axis for a commuter bike. It came with a
>175mm-triple. I would like to swap it with a shimano 600 or 105,
>172.5mm-double I currently have. When I try to mount the crank, the
>large chain ring rubs on the chain stay.
>
>I'm not sure what the best fix is. It looks like you can't find a
>172.5mm-triple unless your at the high end of the component range, and
>they are expensive. Could a new bottom bracket fix the problem? Are
>there different tapers on the bottom brackets that determine where the
>crank mounts?
>
>Thanks,
>
>Frank
>most shimano triples use a 118 mm width BB, while doubles need 109 mm
>
>



>PS
>
>I want to make the change for a couple of reasons. I have two other
>bikes each with 172.5mm cranks, I'd like to keep things the same for
>all. Also, I have some road sized, 130 bcd, chain rings to use as
>spares. The triple came with a 48 as the largest and has a 110 bcd.
>
>
>
 
Mark Janeba wrote:
> > around. The way-wide chainstay on the Bianchi is the problem.

>
> I agree. Is the chainstay spreading at some really big angle?
> Everyone's talking about the *big* chainring hitting the chainstay -

I'm
> used to seeing the little ring hit first.
>


The OP identifies the bike as a Bianchi Axis, but doesn't say what kind
of crankset was originally on the bike. If the original crankset had
smaller chainrings (typical in a newer bike), then switching to a
double crankset with larger "road" chainrings might mean the chainrings
and chainstay are trying to occupy the same space.

A couple solutions come to mind: install a smaller outer chainring on
the "road" double crank (48 tooth would match the original, I believe)
or remove the small chainring from the original crank and install it on
the shorter bottom bracket.

Jeff
 
D

David L. Johnson

Guest
On Mon, 20 Dec 2004 06:10:22 -0800, marchantshapiro wrote:

>
> Well, you should be able to make the 600 or 105 fit, but you will
> probably need a longer BB. I couch this in "maybe" terms because the
> bike may well be designed in part around the particular crankset.


Nonsense. It's much more likely that the cranks he is trying to put on
are simply designed for a longer bottom bracket. Simple thing to change
out. The rest of the bike could not care less what brand crank is
used.


>
> Further, remember that you're increasing Q-factor by putting in a wider
> BB. The standard for 600/Ultegra cranks was 113mm, the standard for
> 105sc cranks was 107mm.


But the relationship between Q-factor and bottom bracket length is not
that simple. It depends on where, relative to the pedal, the tapers are
supposed to meet the crank. Some are further out, others are closer in.
It also depends on the brand; if the original crank is Campagnolo, the
Shimano will not fit right. Find what length bottom bracket you need
(Sheldon Brown's site has the information), and replace the bottom bracket.

--

David L. Johnson

__o | A mathematician is a machine for turning coffee into theorems.
_`\(,_ | -- Paul Erdos
(_)/ (_) |
 
M

monkeyboy

Guest
monkeyboy wrote:
> Hello,
>
> I recently purchased a bianchi axis for a commuter bike. It came with

a
> 175mm-triple. I would like to swap it with a shimano 600 or 105,
> 172.5mm-double ...


Thanks to all who responed. I took another look at the frame, it's not
symetric. The drive side has a stiffening member welded in. The chain
ring was rubbing on the weld bead. The current bottom bracket was a
110.5mm, I pulled a 113mm from an old frame and all works fine. I'll
probably get a 115mm for a little additional clearance.
Thanks again,

Frank