gearbasher

A friend asked if I could help him replace his Brooks Swallow because he broke the seat rails. He said this was the second time he broke the rails on a Swallow. He asked me what I thought caused it. Both rails broke at the back of the seat clamp. To me, it looks like they snapped in an upward motion. They guy isn't heavy (maybe 170). I asked him if he ever tensioned the saddle. He said he never did and it's about six years old. Could lack of tension be the cause? I can't think of anything else.

purpurite

Wild. What seatpost is he using? There is a lot of distress on the rails NOT where it is broken. I'm wondering what the post to rails interface looked like before it broke.

gearbasher

I'm not sure. There was no brand on it. But, the clamp looks exactly like this Ritchey. The bolts were very tight. Well, tighter than I would have made them.

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chain_whipped

Clamp crimped. Chromed rail has compromised steel. The corrosion depicted along with the crimping caused a stress riser. In time, the inevitable happens.

The coated Brooks rails will look crummy in time but doesn't have the compromised steel that chrome causes.

Brooks also offered for the Swallow (and other models) a titanium railed frame that won't corrode, but they stopped production for that particular model. It too has limits for rider weight.

79pmooney

That seatpost looks to have a shortish clamp. Longer clamp, less force at the clamp edge when you are not seating right over the clamp. Excess clamping pressure will add to what the clamp edges do in that off-clamp-center seating position when you hit a bump. Also, look at the seatpost clamp itself. And the clamp edges, front and back, both top and bottom although bottom is more critical - are they nice, generous rounds or near square? You want a nice, generous rounds. Square concentrates the load at exactly the points stressed in my first two points above.

A fine round file will make turning sharp edges into gentle rounds easy. The rounds on that Ritchey post look good. (I'm not surprised. He knows his stuff.) If your friend is heavy or a bike killer, a post with a long fore and aft clamp will be a benefit. Seeking a post setback to best center the clamp in the rails can also help (though the current marks look pretty close to center).

I ride ti railed seats. If I don't pay attention to the above, it costs me bucks and a ride home. (And this is all covered in first semester sophomore year engineering. Yes, the most rugged rails don't break when abused. But some of us ignore rail durability while seeking comfort, etc. when we buy seats. We can give those rails better living conditions. m )

Bad Lag

I'll bet you a buck there is a stress riser in the seat clamp that means all the loading happens at the back, right where it broke. It isn't the seat (or seats), it's the clamp.

Inspect it carefully and maybe even hone the clamping surfaces, especially the trailing edges, before reusing it.

oneclick 

Did it creak at all before failure - the discolouration of the lower break looks like corrosion - if so it would have happened first, taken some time for the second, and might have complained a bit in the meantime.

Garthr

If the post wasn't a Ritchey it could have been a like twin parallel bolt Kalloy SP-376. Kalloy heads are notorious for having a short clamping area on the rails. I won't use them for that reason alone. I have those classic Ritchey posts, the rail clamp is large and the edges are smooth and free of abrupt edges. Plus it holds the seat very well without the need for undue torque. So if the person who broke their rails because of over tightening the clamp, I doubt it was Ritchey.

AdventureManCO 

I have often thought about the small bearing surface that some seatpost clamps have for the saddle rails, and wonder if a very small cro-mo or alloy 2-part 'shim' in the shape of a half-circle tube, super thin, and about the size of the saddle rail, sandwiched on both the top and bottom of the rails in between the seatpost clamp, could alleviate those stress riser points. Would weigh next to nothing, and help distribute the load across the rail.

I looked and saw nothing like this, but if I ever get a ti-railed saddle, I'm going to fab some up just for extra insurance.

gearbasher

He didn't say anything about it creaking. I looked up the Kalloy SP-376. It definitely wasn't that post. The strange thing was: the rail at the bottom of my pic, broke just inside the clamp area. You can see the line where the end of the clamp was just after the break. In fact, when I saw it, I asked him if that rail broke first and he slid the saddle forward in the clamp to try to get more life out of it. He said he didn't.

mpetry912 

I'm in favor of the seatpost clamp theory here, either the clamp was over tightened or the clamping area was very small, possibly a burr on the edge of the clamp caused a stress riser on the rails.

I have seen a very nice looking "Ritchey" seatpost that was a counterfeit item and it was junk. It would not sufficently clamp the saddle rails, the clamp was poorly designed. Fake parts are out there, they look genuine but they are not.

Another thought - does the rider "un-weight" going over bumps ? I hear people saying they want to ride lightweight wheels and other parts "are those wheels OK for a 240 lb rider" ?

My response is that it's all about riding style. Some people are very easy on equipment. Others, not so much

/markp

repechage

The lower rail in the image shows dark, the upper rail bright, it was the last to go. My hunch was the saddle was more flexible and comfortable for a time.
‘while the clamp position is not extreme, my thought the position on the saddle was.
‘I am of the opinion that on these the post clamp should be centered on the overall length of the saddle or best, the clamp at the center of the load.

there was a reason that old track riders used a support “rod” from the nose to the top tube.

gearbasher

We'll, he said the first Swallow he broke happened when he "accidently" slammed into a pothole without getting off the saddle. So, maybe he isn't that easy on equipment.

I guess I should have mentioned that he is using a "set-back" post. When we were adjusting the position of the new saddle, I told him I like to keep my Brooks saddles slightly nose up. He said he did the same thing to keep from sliding forward onto the nose. My theory is: He is probably sitting too far forward on the saddle. On top of that, since he never tensioned it, it's like he's sitting in a hammock. Because of this, when he hits bumps, the force is pulling the heel plate forward. This is what caused the rails to snap in a (what appeared to be) upward motion. Well, it sounds good to me.

Anyhow, I think I'll kill all the birds with one stone. I'll suggest he gets a new post with no set-back and a wider clamping area. Move his saddle forward a bit. And, tension it when it gets "soft".