Bicycle Mechanics - Tiagra FD clamp size - different size

Yesterday I removed my front derailer to swap it over to my new frame. I then found out that the clamp size was different. Previous bike was 34.9 seat tube, new one is 31.8. I decided to head to the LBS today for a new FD, but after doing some reading, I learn I may not have to.

The Tiagra came off a 2005 Lemond Reno. It sounds like it's just a braze-on derailer mounted to a clamp, so all I really might need is a new clamp. Is this correct?

Sorry, lots of questions in the last few days as I run into complications swapping my parts over!

The Tiagra came off a 2005 Lemond Reno. It sounds like it's just a braze-on derailer mounted to a clamp, so all I really might need is a new clamp. Is this correct?

Sorry, lots of questions in the last few days as I run into complications swapping my parts over!

So what's it look like? If it looks like there's a 5mm allen bolt that holds the body of the derailleur onto the clamp, you're in luck. Full retail on just the clamp part is around $12.00.

Incidentally, how's your seatpost fit?

So what's it look like? If it looks like there's a 5mm allen bolt that holds the body of the derailleur onto the clamp, you're in luck. Full retail on just the clamp part is around $12.00.

Incidentally, how's your seatpost fit?

Well that's the thing, I don't have it beside me, it's at home. I was planning to just get a new FD, but after some reading discovered that it might not be necessary. It sounds to me like the 31.8 and 34.9 Tiagra FDs are the same, a braze on, just with a different clamp. I was hoping to get confirmation so I could run by the LBS without having to go home first.

And the seatpost is the same size, no problem there.

Well that's the thing, I don't have it beside me, it's at home. I was planning to just get a new FD, but after some reading discovered that it might not be necessary. It sounds to me like the 31.8 and 34.9 Tiagra FDs are the same, a braze on, just with a different clamp. I was hoping to get confirmation so I could run by the LBS without having to go home first.

And the seatpost is the same size, no problem there.

Bad news. I have a couple of bikes with Tiagra front derailleurs in my basement so I just walked down to check. One's a 28.6 clamp, the other's a 31.8. Neither bolts onto a separate clamp.

Yesterday I removed my front derailer to swap it over to my new frame. I then found out that the clamp size was different. Previous bike was 34.9 seat tube, new one is 31.8. I decided to head to the LBS today for a new FD, but after doing some reading, I learn I may not have to.

The Tiagra came off a 2005 Lemond Reno. It sounds like it's just a braze-on derailer mounted to a clamp, so all I really might need is a new clamp. Is this correct?

Very likely. I don't think the Tiagra comes in a clamp-on 34.9. Suitable clamps are readily available for about US$12.

Sheldon "Clamp-On" Brown

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