Correct front derailleur band mount size

[Fleshpiston]

Evening,

I've forgotten what size front derailleur will fit my frame. My frame uses a 31.6mm seatpost. Anyone know what's the correct band size i should buy. The 7900 Dura Ace front derailleurs with a band mount come in 28.6mm, 31.8mm and 34.9mm.

Advance thanks.

[familyguy]

Evening,

I've forgotten what size front derailleur will fit my frame. My frame uses a 31.6mm seatpost. Anyone know what's the correct band size i should buy. The 7900 Dura Ace front derailleurs with a band mount come in 28.6mm, 31.8mm and 34.9mm.

Advance thanks.

Probably 34.9, assuming aluminium frame. My Mongoose is 31.6 post and 34.9 clamp. Unlikely to get a 0.1 al tube to not crush like...welll...foil.

Jim

[Fleshpiston]

Jim...i think you're right...i changed the battery in the digital callipers and measured the diameter of the seatpost tube...its 35.25mm...so it must need a 34.9mm band since its an aluminium frame.

ps i need to record all these stats in a little black book.

[biker jk]

For what it's worth my titanium frame uses a 34.9mm clamp front derailleur mount and a 31.6mm seat post.

[Fleshpiston]

Thanks biker...every bit of info is always helpful

[rustychisel]

Yep, 34.9mm would be my guess.

They're tricky little buggers sometimes with regards to installing and torquing correctly. Too much and you can crush the seattube, a little too undertensioned and you risk the front derailleur dropping onto the chainrings with fairly fatal results for a Campagnolo Record FD. Ahem, ask me how I know.

[Fleshpiston]

Buddy, i agree. I just wanted to be sure before i order one. c r c sells them for $87 and is the cheapest online. I'm guessing that since my new cranks are also 53/39, then the new front derailleur will be mounted in the exact same spot as the old one. I have a torque wrench, so do you think 2-3Nm will be adequate force

They're tricky little buggers sometimes with regards to installing and torquing correctly. Ahem, ask me how I know.

Please tell. I wish my frame was setup for braze on. Braze on looks like a better setup with regards to FD placement.

Keep on rollin,
Brad

[rustychisel]

Brad, sorry, missed this.

There's another thread on the principal drawback with brazed on FD mounts. The other drawback is the lack of angular adjustment - I've seen some frames where the brazed ear is up to 20º off angle.

I don't often use a torque wrench for such things because in some regards it's better to 'feel' the result. Everyone's different, but I like to give the FD a good tweak and see if it's likely to move under normal load. Also, all carbon tubes are not equal and I fear crushing them, so I usually put one wrap of electrical tape in the correct position before mounting the clamp. I fancy it gives the clamp something to 'grip, or bit into' which isn't the carbon. It's very much a 'go by feel' sort of job, but others disagree. If you use a torque wrench then I really do suggest snugging the bolt up by hand, then using the torque wrench to assess where you are, then trying to shift the thing with your hand to see how tight it need be.

[Fleshpiston]

Brad, sorry, missed this.

No problemo buddy. Btw, all good points in your above post.

Thanks for sharing,
Brad