[rixter67]

If the seat post is 30.8mm, would it be safe to say that the front derailleur size is 31.8mm??

 

[duc135]

Definitely not.

If the seat post is 30.8mm, would it be safe to say that the front derailleur size is 31.8mm??

It's pretty safe to SAY it all you'd like, but not to do it. Unless your bike is made up of some exotic material that they can make the tube 0.5mm thick then, my guess is that you will actually need a 34.9mm FD clamp.

 

[rixter67]

It's pretty safe to SAY it all you'd like, but not to do it. Unless your bike is made up of some exotic material that they can make the tube 0.5mm thick then, my guess is that you will actually need a 34.9mm FD clamp.

duc, the bike is a Giant Iguana Disc 2003. Do you know what the clamp size might be? I have been told 1 1/8" and another shop said 1 3/8"...... confusing.

 

[Speedub.Nate]

duc, the bike is a Giant Iguana Disc 2003. Do you know what the clamp size might be? I have been told 1 1/8" and another shop said 1 3/8"...... confusing.

1-3/8 / 34.9mm, almost for sure. You can pull the seat post binder off and possibly find a number inscribed on it to verify (either 34.9 or 35.0), or if you have the old derailleur (I'm assuming you don't have calipers to measure with), pull it off and find the diameter stamped on the inside of the clamp.

But if it's a giant using a 30.8 seat post, it's almost certainly a 34.9mm tube.

 

[papajohn]

Use a ruler

duc, the bike is a Giant Iguana Disc 2003. Do you know what the clamp size might be? I have been told 1 1/8" and another shop said 1 3/8"...... confusing.

You can measure the exterior width of the seat tube with a ruler. Or use an adjustable crescent wrench as a caliper and barely snug it down on the outside of the seat tube and measure the diameter that way.

John W.

 

[rixter67]

Thanks for the help guys. I didn't think about the wrench bit, but that would make sense.

It is just confusing to try to get answers and have people telling you different things. You have helped a great deal.

 

[Speedub.Nate]

use an adjustable crescent wrench as a caliper

Nice! I'm filing that one under "Useful Stuff".

 

[duc135]

duc, the bike is a Giant Iguana Disc 2003. Do you know what the clamp size might be? I have been told 1 1/8" and another shop said 1 3/8"...... confusing.

Not sure what the clamp size is, but if the seatpost is 30.8 then my guess is that the clamp would also be 34.9/35.0mm equates to 1 3/8". 30.8mm is just shy of 1 1/4" so there's no way it could be a 1 1/8" clamp. Just to throw a wrench in the works, I know Salsa also makes a 36 mm clamp, but that's a very rare size from what I've been told. "Usually" the FD clamp size is the same as the seatpost clamp size. Hope this helps.

Please take all of my words with caution as I am not a professional by any means nor am I familiar with the Iguana. I'm pretty confident that if I steer you wrong all someone much more knowledgeable will put me in my place. I have, though, very successfully built six bikes from the frame up and do all the maintenance on my bikes as well as for all of my friends. Good luck with your bike project.

Duc

 

[Ebo]

If the seat post is 30.8mm, would it be safe to say that the front derailleur size is 31.8mm??

I would also have to go with the 34.9 / 1 3/8th clamp size. One of my bikes has a 30.4 seatpost with a 31.8 / 1 1/4" clamp. Another has a 30.9 seatpost with a 34.9 / 1 3/8" clamp. Just my 2 cents. I too like the crescent wrench idea, although I have a caliper to use.

 

[papajohn]

"Usually" the FD clamp size is the same as the seatpost clamp size. Hope this helps.
Duc

I have four bikes, by Titus, Ellsworth and Turner that all have 32mm seatpost clamps (for 27.2mm seatposts) and use 34.9mm clamp diameters for the FD, so I am not at all sure that your statement above is a good general rule.

John

 

[duc135]

I have four bikes, by Titus, Ellsworth and Turner that all have 32mm seatpost clamps (for 27.2mm seatposts) and use 34.9mm clamp diameters for the FD, so I am not at all sure that your statement above is a good general rule.

John

Like I said, I'm sure someone much more knowledgeable than me will put me in my place.

Thanks for the info John, now I know better.

Duc