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Are there multiple clamp diameters for a Shimano Front Derailleur?

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Are there multiple clamp diameters for a Shimano Front Derailleur?

Old 04-14-10, 02:31 PM
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Are there multiple clamp diameters for a Shimano Front Derailleur?

I had been previously having problems with a chain skipping on the rear cog but is now falling off the front chain ring (I replaced the chain and cassette). Happens whenever I stomp on the pedals.

I think the front cage on the FD is beyond adjustment and was going to replace. (my fault in probably bending it during transport)

Anyway I saw an FD-5404 on eBay but it mentioned a clamp diameter of 31.8mm (1 1/4"). My seat tube circumference is ~115mm (4.5") which if I calculated that correctly equals 36.6mm (1.43") in diameter.
I cannot imagine there would be that many clamp sizes for budget derailleurs - this is a 105 triple. But will that FD fit my seat tube? Anyone know for sure?
Thanx

I went to the Shimano website but it doesn't mention different clamp widths
https://techdocs.shimano.com/media/te...9830603724.pdf
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Old 04-14-10, 02:36 PM
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Shimano fd's tend to come as a 34.9 then have "front derailleur band installation band diameters" (adapters) in 31.8 and 28.6. They are mentioned in the Shimano instructions you linked. Might want to make sure what your seat tube diameter is...what frame is it?
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Old 04-14-10, 02:45 PM
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Careful though: eBay sellers often don't include accessories and adapters. Ask the seller first.
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Old 04-14-10, 03:05 PM
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Originally Posted by bikinfool
Shimano fd's tend to come as a 34.9 then have "front derailleur band installation band diameters" (adapters) in 31.8 and 28.6. They are mentioned in the Shimano instructions you linked. Might want to make sure what your seat tube diameter is...what frame is it?
LeMond Reno 2004 or 05. (I carefully measured the circumference to 4.5" = 36.6mm diameter and I could be off by an 0.0125".
You pointed out the "S" and "M" on the link which I am hoping means they are referencing adapters available for Small and Medium widths.
Though that standard 34.9 = 110mm circumference and my seat tube diameter is def wider than that.
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Old 04-14-10, 03:31 PM
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I find it hard to believe that bike has larger than a 34.9 seat tube...what's your measuring method?
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Old 04-14-10, 03:47 PM
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Get yourself a vernier caliper for measuring the tube. You can find them as cheap as $10 or 10X that much. I have a $10 one I bought at Home Depot or Sears and it is plenty accurate enough for any bike-related measurement I've encountered so far. My nephew's a pro mechanic and I think his cost a couple hundred.
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Old 04-14-10, 06:48 PM
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Originally Posted by bikinfool
I find it hard to believe that bike has larger than a 34.9 seat tube...what's your measuring method?
I'd love to find out I am wrong. (and btw, the tube does not seem extraordinarily thick. Also I am referring to the seat tube and not a seat post.)
My method:
I used a twist tie and wrapped it around and measured the length - 114mm then went online and used the conversion to calculate diameter.
I might remove the damn FD just to confirm.
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Old 04-14-10, 07:27 PM
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Originally Posted by SteelCan
I'd love to find out I am wrong. (and btw, the tube does not seem extraordinarily thick. Also I am referring to the seat tube and not a seat post.)
My method:
I used a twist tie and wrapped it around and measured the length - 114mm then went online and used the conversion to calculate diameter.
I might remove the damn FD just to confirm.

Removing the derailleur is probably easier than measuring. The diameter is usually cast into the inside of the clamp: 34.9mm = 1 3/8", 31.8mm = 1 1/4", 28.6mm = 1 1/8". Most front derailleurs are either made with these size clamps or are built with the largest and use shims to fit smaller.

I find it hard to believe that there's a seat tube larger than 1 3/8".
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Old 04-14-10, 08:27 PM
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an easy way to measure the clamp diameter is to put a cresent wrench around the tube close the wrench so it is snug on the frame, then measure the distance between the opening.

or if you have a open end wrenches see if the 1-1/8, 1-1/4 or 1-3/8 fits around the tube.

I just tried the second method on 6 bikes in my basement and that method works fine. Only on seat tube was bigger than 1-3/8" and that frame has a fd braze-on

Last edited by cyclist2000; 04-14-10 at 08:32 PM.
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Old 04-14-10, 08:28 PM
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Originally Posted by Jeff Wills
I find it hard to believe that there's a seat tube larger than 1 3/8".
Well there IS a seat tube larger than 1 3/8th. Mine is 1.43"
I went to remove the FD to check the size and immediately realized why my measurement showing 114-5mm circumference does not violate mathematical laws (my conversion from circumference to diameter) There is a gap of about a 1/4" where the bolt threads the clamp together. Still went ahead and removed the FD and it was stamped 34.9mm.
Thanx all for the comments.
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Old 04-15-10, 10:31 AM
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Originally Posted by SteelCan
Well there IS a seat tube larger than 1 3/8th. Mine is 1.43"
I went to remove the FD to check the size and immediately realized why my measurement showing 114-5mm circumference does not violate mathematical laws (my conversion from circumference to diameter) There is a gap of about a 1/4" where the bolt threads the clamp together. Still went ahead and removed the FD and it was stamped 34.9mm.
Thanx all for the comments.
As honest as your twist tie is, I am sure he is not quite as accurate as a $10 vernier caliper. The clamp on a Shimano front derailleur is genreally rigid and will not fasten to a seap tube with any variation in size. And there is always a gap of a few mm (~1/4"). If your derailleur says 34.9 then I will bet you one million dollars your seat tube is closer to 34.9mm than to 36.6.

Get your hand on some calipers and send me the cheque.
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Old 04-15-10, 11:44 AM
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Originally Posted by LarDasse74
If your derailleur says 34.9 then I will bet you one million dollars your seat tube is closer to 34.9mm than to 36.6..
We are talking about a difference of just over 5mm (5.3407075111027mm) in circumference or 1.70xxxxxxxmm in diameter which would make the over/under number 35.75000000000001mm

I don't have One Million dollars but I would go through the effort of raising it if you put your 1 Million in US$$ in an escrow account of an agreed upon 3rd party if that money was bound by your wager and could not be rescinded.

However if you are really a sporting person and convinced that I was imprecise in either my measuring method or conversion, I'm willing to wager a wheelset mfr'd by Road Forum's PSImet up to $500.

When you respond, we will both send him a $500 payment by CC and the winner gets his CC credited back.

(We can work out the verification of the seat tube diameter with the mod on this board - and allow him to choose a bikefo member to verify the diameter of the seat tube or maybe some documentation we can find onlline about LeMond Reno's seat tube width)


Anyway I'd make this wager and you would be paying for the wheelset.

* No games about sanding down the original paint to get to the Aluminum tubing.
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Old 04-15-10, 11:54 AM
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Originally Posted by SteelCan
We are talking about a difference of just over 5mm (5.3407075111027mm) in circumference or 1.70xxxxxxxmm in diameter which would make the over/under number 35.75000000000001mm

I don't have One Million dollars but I would go through the effort of raising it if you put your 1 Million in US$$ in an escrow account of an agreed upon 3rd party if that money was bound by your wager and could not be rescinded.

However if you are really a sporting person and convinced that I was imprecise in either my measuring method or conversion, I'm willing to wager a wheelset mfr'd by Road Forum's PSImet up to $500.

When you respond, we will both send him a $500 payment by CC and the winner gets his CC credited back.

(We can work out the verification of the seat tube diameter with the mod on this board - and allow him to choose a bikefo member to verify the diameter of the seat tube or maybe some documentation we can find onlline about LeMond Reno's seat tube width)


Anyway I'd make this wager and you would be paying for the wheelset.

* No games about sanding down the original paint to get to the Aluminum tubing.
Very well thought out, but lets just get a proper measurement and then we can decide what we are willing to bet
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Old 04-15-10, 12:31 PM
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It is possible that the seat tube the OP measured is larger than 34.9mm standard spec. I've seen some bikes where the seat tube is indeed over-sized, and is then crimped down to a smaller diameter to accommodate a FD band. These were usually entry-level priced bikes.
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Old 04-15-10, 07:49 PM
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Is the seat tube being measured at where the FD clamps? Some seat tubes have varying diameters throughout their lengths. It's where the clamp goes that matters.

Also, the difference between 34.9 and 36.6mm is significant. To illustrate, have you ever tried to jam a seat post even 1mm larger too big into a seat tube (hell, even .2mm is difficult). Or, tried to stick a MTB shifter with a 22.2mm clamp on a drop bar with 23.8mm diameter?
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Old 04-15-10, 07:59 PM
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Originally Posted by JiveTurkey
Is the seat tube being measured at where the FD clamps? Some seat tubes have varying diameters throughout their lengths. It's where the clamp goes that matters.
Also, the difference between 34.9 and 36.6mm is significant. To illustrate, have you ever tried to jam a seat post even 1mm larger too big into a seat tube (hell, even .2mm is difficult). Or, tried to stick a MTB shifter with a 22.2mm clamp on a drop bar with 23.8mm diameter?
1st Yes, the tube was measured where the FD would mount. (BTW the tube is the same size with a sleight taper as it joins the top tube)
2nd The comparison you make is not apples to apples. There can often be allowances for size when going OVER the tube than trying to squeeze INSIDE. (spacing washers for example)
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Old 04-15-10, 09:37 PM
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Well I'm glad you figured out you have a 34.9 clamp size despite your twistie tie....
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