Tech question on MTB derailleur

[amirm]

Hi all:

I need some education on front derailleurs. In particular, I want to know about the swing mechanism. What's the difference between top and bottom swing? What difference does it make? How can I work out mine is top or bottom swing?

I have a Deore derailleur, and as part of upgrading the drivetrain, I want to put a new XT. The seller asks me to specify the swing type. Obviously, I'm not buying the part at my LBS. Can someone help?

Cheers,
Amir.

 

[amirm]

Originally posted by amirm
Hi all:

I need some education on front derailleurs. In particular, I want to know about the swing mechanism. What's the difference between top and bottom swing? What difference does it make? How can I work out mine is top or bottom swing?

I have a Deore derailleur, and as part of upgrading the drivetrain, I want to put a new XT. The seller asks me to specify the swing type. Obviously, I'm not buying the part at my LBS. Can someone help?

Cheers,
Amir.

Never mind, I worked it out. Mine is a top swing.

Cheers.

 

[flyingdutch]

Originally posted by amirm
Never mind, I worked it out. Mine is a top swing.

Cheers.

shouldnt it be 'top-pull' or bottom-pull' ???

ie which orientation the cable pulls on the mech from

From my (albeit totally un-researched and off the cuff) memory it would seem that the majority of mtb front mechs are top-pull to keep the cable protected from mud/road-grime if it were going round under the BB

anyone wanna clarify that?

 

[amirm]

Originally posted by flyingdutch
shouldnt it be 'top-pull' or bottom-pull' ???

ie which orientation the cable pulls on the mech from

From my (albeit totally un-researched and off the cuff) memory it would seem that the majority of mtb front mechs are top-pull to keep the cable protected from mud/road-grime if it were going round under the BB

anyone wanna clarify that?

You're right about the routing. However, some manufacturers still prefer routing through the down tube and under BB (including mine). Shimano has recently moved to make dual pull structure which one mech can be used in either way.

However, top and bottom swing refers to the position of the swing arm in refernce to the clamp. Due to space restriction, eg in duallies and some compact frames, top swing mech has become popular as the clamp can sit really close to BB. Shimano manufacture two versions of each front derailleurs which are both dual pull and multi-clamp. That is, they can fit any of the three mainstream seat tube sizes and they can use either routing direction. The difference is only in the swing geometry. A traditional hard-tail should be able to use either version. In my case, I am going with the M760 derailleur which is top swing. M761 is bottom swing.

It seems swing geometry has not been an issue on roadies, and they all seem to use the bottom-pull bottom-swing set up.

Hope this clarifies a little.

Cheers,
Amir.

 

[Nick Payne]

Nope. Bottom-pull derailleurs can be either top swing or
bottom swing. eg the Deore XT FD-M750 and FD-M751.

Nick

flyingdutch wrote:

> amirm wrote:
> > Never mind, I worked it out. Mine is a top swing.
> > Cheers.
>
>
>
> shouldnt it be 'top-pull' or bottom-pull' ???

 

[Peter Signorini]

"amirm" <[email protected]> wrote in message
news:[email protected]...

> However, top and bottom swing refers to the position of
> the swing arm in refernce to the clamp. Due to space
> restriction, eg in duallies and some compact frames, top
> swing mech has become popular as the clamp can sit really
> close to BB.

<snip>

> The difference is only in the swing geometry.

There's more to it than that, as some derailleurs are
BB mounted with no clamp, bottom swing and cable
routing under the BB. These are used for dualies with
an interupted/minimal seat tube where a clamp-mount
cannot be used.

Cheers Peter

 

[flyingdutch]

Boy, that Singlespeed is lookin' good

 

[amirm]

Originally posted by Peter Signorini
"amirm" <[email protected]> wrote in message
news:[email protected]...

> However, top and bottom swing refers to the position of
> the swing arm in refernce to the clamp. Due to space
> restriction, eg in duallies and some compact frames, top
> swing mech has become popular as the clamp can sit really
> close to BB.

<snip>

> The difference is only in the swing geometry.

There's more to it than that, as some derailleurs are
BB mounted with no clamp, bottom swing and cable
routing under the BB. These are used for dualies with
an interupted/minimal seat tube where a clamp-mount
cannot be used.

Cheers Peter

Peter:

It's interesting you said that. Someone also said that in general bottom swing shifts better than top swing. So when this third group of BB-mounted derailleurs came around, they went for bottom swing and not top swing. This is consistent with road bikes using bottom swing. So one can conclude that top swing is a solution to address restricted requirements of specific set-ups, eg duallies, and it's not necessarily as good.

Cheers,
Amir.