Front derailleur - Quick Q

[letmetalktomark]

Hi All,

Need a front derailleur for one of my bikes and the BB mounted ones caught my eye.

Any advantages/disadvantages to running one of these over a conventional ST mounted one? They look cleaner/less cluttered when mounted.

Just wondering……

 

[cherrybomb]

I've never had one, but don't you need a different bottom bracket to fit them? :?

 

[Anthony]

So far as I am aware there's no option in this - i.e., if your seatpost has a stud to screw an E-type mech into, then you just about must use an E-type mech, because the designer provided the stud for a purpose (which may be that the seatpost is shaped or inappropriate for clamping). And if your seat post doesn't have a stud then you can't use an E-type mech.

You use a standard bb, but the ring that fits between the bb and the bb shell is c2mm thick, so shifts the bb 2mm to the right, which may or may not matter to you if you're a chainline freak. Or if your left side crank arm is within 2mm of touching the chainstay, in which case you'll need a bb with a longer axle.

 

[yo-eddy]

If you want to try

http://www.retrobike.co.uk/forum/viewto ... 156#157156

 

[letmetalktomark]

If you want to try

http://www.retrobike.co.uk/forum/viewto ... 156#157156

Thats what got me thinking

 

[stew-b]

if your seatpost has a stud

you mean seat tube,dont confuse the guy even more

 

[letmetalktomark]

No worries I knew what you meant!

Still a tad confused though.....


My brothers Gary Fisher has one of these that is solely held by a regular square taper shimano BB. It does rest against the seat tube but isn't held by a bolt.

Presumabley if I can live with a slight ofset circa 3mm (as above) I wold be okay?

M

 

[Iwasgoodonce]

I don't mean to hijack the thread, but could one of these be the answer to my inability to find a suitable braze on front mech for my E-Stay CroMega?

 

[Anthony]

I don't understand - see below an M739 E-type mech. The ring that fits around the bb is perfectly plain. Immediately above it is the hole that you put the bolt through to connect it rigidly to the seat tube. Without that bolt it would be free to rotate around the bb every time you change gear (and in fact you wouldn't change gear and you wouldn't be able to tension the cable).

 

[stew-b]

some cheap shimano front mechs use the bb and have a bent bit of steel to rest around the seat tube to stop it spinning instead of the bolt idea.