nycbianchi

I measure the diameter of my seat tube at about 33mm (it's a 2006 Bianchi 928 Carbon frame). Am I better off getting a 34.9 clamp and using a shim, or getting a 31.8 clamp and tightening it as far as it will go, laving a little gap where the clamp doesn't close completely?

joejack951

How did you measure the diameter? It should not be that far off.

nycbianchi

I was using a (fairly cheap) caliper. Do you think it could be off by that much? FWIW, the seat tube actually tapers, getting thinner closer to the bottom bracket. So it doesn't seem to be an exact dimension.

nycbianchi

Hey look! I just flipped from "Member" to "Senior Member"! Does that mean I'm now qualified to answer my own question? I don't feel smarter...

joejack951

Well, you did sort of answer your own question here. Measure where the FD will mount. That's the area that matters. Look at the picture here for an idea of where to measure:

https://www.bianchiusa.com/06-bicycle...8-ultegra.html

nycbianchi

I was trying to eyeball the right spot. I just fiddled with it some more and I think it's closer to the 31.8 dimension. If it's a tad wider, and the clamp does not perfectly close, is that okay?

operator

It's either 31.8 or you didn't measure correctly. If it's carbon/AL and you attempt to clamp something narrower in it you will destroy the frame. If it'll even close.

joejack951

There will be a little gap when it's fully tight even at the right size. As Operator pointed out, if the clamp was actually too small, you wouldn't even be able to close it enough to get the screw started. If it was too big, it wouldn't even begin to tighten. If the measurement seems close to 31.8mm, then get that size clamp. Or better yet, buy a braze-on derailler and 31.8mm adapter. Worst case, if you somehow got it wrong, all you need is a new adapter. Also, if you want to move the components to another bike, you'll only need a new adapter, not a whole new FD.

operator

This is a good suggestion +1

Shimagnolo

It means that instead of Pcad totally ignoring you, he will now occasionally insult you.
(Not unlike Dr Cox on "Scrubs").

operator

This the mechanics forum, we don't care about no pcads. They don't post anything worth reading in the road forum anyways.

nycbianchi

You guys are all so helpful, I feel I should give you the full details. Let me just say at the outset that I'm not proud about this; OCP is a sickness and if anything you should have sympathy.

So here it is: I actually already have a FD clamp on the bike, and it works just fine. In fact it's an adapter clamp, so it can be replaced without changing the FD. And that's where the trouble began. Because it's a SILVER clamp. And my bike is BLACK. And to add insult to injury it's a SHIMANO clamp and my bike is CAMPY! So you can see my problem. I figured hey, for $20 I get a nice black Campy clamp, or maybe a generic crabon-black one, and I will no longer be tortured by the incongruous sight of that silver Shimano thing on my beautiful ride. (Yes, I can actually hear your eyes rolling as you read this. Again, I am not proud of this.)

SO ... I take off the clamp and see that it's a 34.9mm, but I also see that it's got a plastic shim in there. And I wonder: did the mechanic who built my bike use this because he preferred to tighten a 34.9 down on some relatively soft plastic rather than force a 31.8 directly onto the precious crabon frame? Or was the 34.9 the only thing he had lying around the shop, and he put them shim in there as kluge?

So I measure the frame and see that it's smack dab in the middle -- 33mm -- and my curiosity only grows. Which is when I posted on BF and that brings us here today.

Is the plastic inner-ring thing always present to protect the frame? Should I replace the 34.9 with another 34.9 since that seems to be working? Or should I put a 31.8 nice and snug on the 33mm frame since I have my choice of any size I want on the interwebs?

Please don't judge.

Steev

If it's the original parts, its possible that is a special sized shim. The best thing to do here is replicate what you have that works. Use 34.9mm and the shim you have.

nycbianchi

Nope, it's not the original parts. But I like your thinking -- if it's working with the shim and the 34.9, just replicate that. I'm not (quite) OCP enough to risk the frame just to get rid of a barely-visible shim.

strop

ROFL ... I thought I was the only one. I refused to put a silver clamp on mine, in fact I refused to use a secondary clamp at all which means I ended up with a 31.8 Ultegra SL clamp-on and the corresponding Shimano shim to take it down to 28.6.

and I think we're called OCD, not OCP :-D

PS: If you really want to do it right Shimano have their dark grey clamp for their Di2 series for a mere $60 and I'm sure it weighs less than a Kate Moss snack.

operator

We have this exact frame in the shop. I will measure this tomorrow.

JanMM

Obsessive Compulsive Disorder. Obsessive Compulsive Personality. Obsessive Compulsive Personality Disorder.
My bike has a black Teflon-coated RD cable and silver stainless FD cable - that bothers me a little bit but I haven't acted on it.

HillRider

A few seconds with a black Sharpie and every thing will match.

BTW, to the OP, a similar few minutes with a rattle can of gloss black and your silver adapter clamp is now black and the Shimano name pretty well hidden.

joejack951

I have similar issues. I delayed a bike build because I had to have a black braze-on mount for my front derailler that fit the frame without (very important) a shim. Problem Solvers makes black and silver clamps in every size you might need unlike Shimano who only makes silver and require a shim for a 28.6mm seat tube, like the one on my short lived Gunnar. Luckily, all I needed was a new 34.9mm adapter to reuse the front derailler on my new bike.

Black Sharpie only works for touching up black spokes and nipples. There's too much surface area on a FD clamp. It would be much too noticeable for my discerning tastes

Nevermind, you were talking about the cable.

nycbianchi

But ... that's ... that's ... cheating! Frankly, I'm caught trying to decide whether I should stay true to my CF mania with a CF (or CF-looking) clamp or stay true to my Campy mania with a genuine Campy clamp. What you speak of is ... just ... blasphemy ...

nycbianchi

While I'm at it -- how do I know how tight to make a FD clamp on a CF frame? I assume I should be using a torque wrench, but what is the proper tension amount? I did a quick search on BF but didn't see this addressed...

strop

Shimano's recommendation is to consult the frame manufacturer. Makes sense as it clearly depends on the frame itself not just that it's CF.

A variation on an old joke applies. Tighten until you hear a slight 'crunch' sound, then back off half a turn :-D

joejack951

Shimano spec's 5-7 N*m and so does Problem Solvers for their braze-on adapters. Honestly, when I tried to hit 5 N*m attaching the FD to my new carbon frame, it felt too tight. I stopped somewhere around 4 or so. Hasn't moved yet (~1000 miles). I had no weird feeling torquing to spec when clamping a FD to a steel frame though. Call me a wuss.

[edit] I checked the online Shimano tech docs and saw their recommendation about carbon frames. I never noticed that before. Anyone know when they added that bit of information? [edit]

Ex Pres 

I had an IBOC Crit with the same problem. I solved it with a Shimano (IIRC) 31.8 clamp. It came with a metal insert and plastic 'sleeve' that installed in either side of the clamp. I sleeved one side and left the other nekkid. It worked perfectly.

Worse was the 28.0 seat post spec'd for the frame

nycbianchi

Post-script to this thread: I replaced the 34.9 alloy Shimano clamp with this crabon fibre clamp, also a 34.9. The new clamp nestled into the Shimano shims perfectly (is there a standard clamp width? I guess so.) and frankly it looks great.

For $20 and about 15 minutes of fiddling it was incredibly satisfying. The carbon mesh matches my frame perfectly.