broken setpost bolt

[RJS]

Easton single bolt seat post, one of the section had this fail today, he was thinking of replacing the bolt as he had had one fail before at about the same mileage, (about 25,000), how unusual is this? It was a stainless bolt, any recommendations for a replacement bolt or post? He came down on the chain ring, so a series of holes in his knee, hospital were uncertain if it was fractured, probably not, he has to go back next week. Saving grace, he was not far from home so his wife was able to rescue him, and he was on a cycle path not the road where he could have been run over, ( the same path as NAs previous crash, this path is getting a bit of a reputation )
Cheers.
Rob.

[NATURAL ANKLING]

Hi,

Easton single bolt seat post, one of the section had this fail today, he was thinking of replacing the bolt as he had had one fail before at about the same mileage, (about 25,000), how unusual is this? It was a stainless bolt, any recommendations for a replacement bolt or post? He came down on the chain ring, so a series of holes in his knee, hospital were uncertain if it was fractured, probably not, he has to go back next week. Saving grace, he was not far from home so his wife was able to rescue him, and he was on a cycle path not the road where he could have been run over, ( the same path as NAs previous crash, this path is getting a bit of a reputation )
Cheers.
Rob.

Sorry to hear about your mate , hope he is OK

Which bolt in frame or under rails?
Either, I would not use a stainless steel bolt on critical parts that go in to steel (steel nut / female thread)
Aluminium nut thread would strip first more often, so bolt material would not be critical.
They stretch the threads rather easy, the nut would be ok but not the bolt.
The threads stretch then bind then twist and weaken.......................
Frame pinch bolts do get bent by nature of design, so care here is always needed.
And don't grease the thread.
25 K, if its looking well used then maybe prudent to replace periodically, but only if the bolt has been tightened often, in normal service there should be no problem.


Help if the model was posted pics ?
Ah I see the model.

Is it titanium?

I don't know that make at all, but looks like performance stuff, due to price, though the single bolt looks conventional design?

[bikepacker]

Easton single bolt seat post, one of the section had this fail today, he was thinking of replacing the bolt as he had had one fail before at about the same mileage, (about 25,000), how unusual is this? It was a stainless bolt, any recommendations for a replacement bolt or post? He came down on the chain ring, so a series of holes in his knee, hospital were uncertain if it was fractured, probably not, he has to go back next week. Saving grace, he was not far from home so his wife was able to rescue him, and he was on a cycle path not the road where he could have been run over, ( the same path as NAs previous crash, this path is getting a bit of a reputation )
Cheers.
Rob.

I had a seatpost bolt snap one Sunday cycling south of Macon in France. My injuries were not has bad as his but I can still feel the crossbar hitting between my legs.

My recommendation for a replacement bolt is to get a high tensile steel one. At one time they were the normal bolt used on seatposts, it does now seem many manufactures are using the less strong stainless ones.

[MikeF]

SS has various grades, and now does seem to be used in places wheel it shouldn't be as it can be brittle. (Brucey will no doubt supply technical details). Was the seat bolt done up too tight?
There now seems to be a fad for stainless steel gardening tools eg forks and spades. These snap quite easily instead of bending. Beware!

[Brucey]

most bolts have some kind of marking on the head, to indicate the bolt quality/manufacturer, stainless steel or not.

IME it is unusual for stainless steel bolts to be specified as standard fitment on seat pins; plated ones are much more commonly found. If there are any pictures of the bolt or details of the seat pin model that would be helpful.

A single bolt seat pin might last indefinitely with some riders where it might last a shorter period of time with others; bolt tension/loading, saddle setback, rider weight, and perhaps most importantly riding style make a huge difference to the fatigue loads that the bolt sees. Some riders bounce in the saddle more than others, with every pedal stroke there can be an appreciable load cycle.

25000 miles is a very long way if conditions are unfavourable, and it is still a long way even if they are not. With some seat posts (eg Thompson ones) it is recommended that they are binned after 10K miles.

I'm glad that your chum wasn't very badly injured; the potential consequences of such a failure don't bear thinking about.

cheers

[freiston]

Probably nothing to do with the issue reported by the OP but I'll add it on the off-chance it is of relevance to the OP or anyone else... My frame pinch bolt wasn't gripping the seat post tight enough when I first got my bike. On a preliminary ride to get the seat and bars fine-tuned, I got frustrated with the seat post moving and over-tightened the bolt to the extent that it snapped. The replacement wouldn't grip either. A closer inspection showed that the fully closed bolt/nut combo was too long for the frame eyes. I solved the issue with a spacer washer on the nut side.

[RJS]

Yeah, it was the post to saddle rails bolt that broke, seems it may (probably) not have been stainless. Friend is looking at a new post, twin bolt I suspect, there's a big selection, any suggestions for a good choice?
Cheers.
Rob.

[Brucey]

Yeah, it was the post to saddle rails bolt that broke, seems it may (probably) not have been stainless. Friend is looking at a new post, twin bolt I suspect, there's a big selection, any suggestions for a good choice?
Cheers.
Rob.

depends how much he wants to spend, what setback/weight etc he is after. Like you say, there are lots!

One thing I cannot stress highly enough is that if the clamp is in any way reliant upon friction (as it is in many single bolt designs), it is very important not to get any lubricant on the friction faces; a little anti-seize on the bolt(s) is OK but ordinary grease often separates (so oil leaks out of it) and too much of anything is asking for trouble.

Respect the manufacturer's torque settings, too.

cheers

[NATURAL ANKLING]

Hi,
Once I got rid of those old pressed tin jobbies in my youth, I have only had a dropping seat post to frame say twice in 45 years and then because I was midway in adjustment and forgot to torque up, frame clamp.
Once on the turbo, there was no pain or discomfort as it came on gradual and I was in full swing so I barely noticed till a few minutes from end, so continued to finish and some two or more inches lost

The modern one bolt design I find great and had never had an incident.
But as said long overhang and even a normally abusive rider may just bring on a failure in time.

I know nothing of twin bolt designs............but a quick gander at some, and some look over complicated and might lend to other problems.
I guess your mate no longer trusts one bolt so two is a logical even if not necessarily more reliable step?

Edited-

Must be me I just thought...........................my tourer is as far forward as it will go...I even took a file to the clamp............ .................
Before writing in these post I had already decided to change the post as I have run out of adjustment, I will make that a priority.
Another that probably lends some weight to riding style.....

[Brucey]

BTW single-bolt seat pins often get into an evil cycle of slippage-bolt overtightening- more slippage. With many designs the overtightening results in the clamps deforming, which in turn means that the serrations (or whatever) won't work either. If the bolt is too tight, it may also fatigue more quickly.

It is possible to re-file the serrations in many clamp pieces, and restore function that way. However many seat pins allow little access to the lower part of the clamp; the serrations are in a recess.

However there are a couple of repairs that allow a single position to be maintained securely, even with a damaged single-bolt seat pin. First find the correct tilt angle and mark up the pieces so that the exact alignment is known.

1) you can file/dremel a deeper groove in both pieces (in line with one of the original serrations) and lay a length of spoke in the groove; the result will be more secure than the serrations were originally. Or...

2) with the lower part of the clamp only bolted to the seat pin at the correct angle, drill one or two blind 2mm dia holes down through the clamp into the top of the seat pin (where the two parts are in intimate contact). Fit short dowels (made from old 14g spoke) into the holes, and reassemble the clamp and saddle without further disturbing the lower part of the clamp.

With either method, a new angle setting requires that new holes/grooves are made, or that the saddle rails are bent slightly, or that a different saddle is used.

cheers

[NATURAL ANKLING]

Hi,
Sorry, my adjustment I was talking about was filing a small radius on the saddle rail groove in the clamping half, as the saddle rail was shoved all the way onto the clamp, I gained a few mm say five.

I think maybe the problem with OP's mate is more likely what you might have suggested, with the evil cycle, does anyone else remember the hand whacking your old saddle with the constantly failing pressed tin clamps.

Two bolt clamps, there appears many designs, I must be missing out on something....I am assuming its to give a nice precise adjustment of saddle angle......without copying some others patent.

[Brucey]

also...... I forgot to mention that the usual bolt specification for a single-bolt seat pin is an M8x1.25mm threaded caphead, usually of a standard form, which is also readily available in stainless steel etc.

If you are worried about breaking bolts, one method is to fit a stainless steel bolt, and to replace it once every ten thousand miles or so. Standard stainless steel bolts will cost about a quid each, or so.

IME stainless steel bolts of A2-70 grade are tougher and more fatigue resistant than 8.8 grade bolts, because they are more ductile, they work-harden appreciably, and of course are less likely to suffer environmentally assisted cracking.

A few styles of seat pin use a standard threaded bolt with a smaller head size than usual. It isn't difficult to grind the head of a standard bolt to fit.

cheers

[NATURAL ANKLING]

Hi,
I am just not sure
https://www.bikerumor.com/2012/09/04/er ... her-grips/

[CJ]

Aluminium nut thread would strip first more often, so bolt material would not be critical.

Not so. It is possible for a high-tensile bolt to realise its full strength in a nut made from far weaker material - it just needs a long enough length of thread engagement, i.e. a thick enough nut.

If you do a bit of research (as I did a while ago) to see what's available strength wise in bolts made from various materials, stainless steel compares rather poorly. It may be possible to get special bolts made out of special grades of stainless, but off the shelf is merely so-so. The commonly available grades are A2 and A4; and whilst you might suppose the bigger number to be better - it certainly costs more - what you're mostly getting for the extra money is better corrosion resistance. For whilst A4 may have a higher yield strength, it's more susceptible to fatigue and cracking. So if it's for a boat bobbing about on the briny, buy A4. But for a bicycle being battered by"the rocky roadsteads of this parish": A2 is probably a safer bet and certainly cheaper.

Here's a little table I made, comparing the Ultimate Tensile Strengths of commonly available bolt specifications.

Mark Material - comments ______________ UTS (MPa)
5.8 Mid carbon steel - cheapest decent bolt___ 520
8.8 High carbon steel - a fairly good bolt _____ 800
10.9 Cro-Mo steel - a strong bolt __________ 1040
12.9 High-tensile steel - seriously strong ____ 1220
A2 304 Stainless (18/8 : Cr/Ni) ____________ 700
A4 316 Stainless (16/10/2 : Cr/Ni/Mo) _______ 800
__ 6/4 Titanium _________________________ 950
__ 7075 T6 Aluminium ___________________ 570

(Edit: Underscores work better than spaces!)

You can see that if you want something to replace steel that doesn't rust, titanium is a far better bet than stainless AND half the weight to boot! What's not to like about that? And if you want to save even more weight: aluminium will do well enough for all the less highly stressed fasteners such as bottle cages and mudguards.

But I wouldn't use either of those for a single-bolt seatpost. For anything safety critical there is no substitute for a (readily available from any good tool store) high-tensile 12.9 grade steel socket screw. Okay it will rust, but thanks to all the carbon, nickel, chrome, molybdenum, vanadium etc. in there, high-tensile steel doesn't rust too badly and a dab of Hammerite will probably keep it looking reasonably presentable.

[Brucey]

except that..... in some applications a bolt will not be seated correctly at the head end or will be subject to weird service loading. In the former instance the bolt can start to yield in bending and at this point all bets are off; the basic tensile strength of the bolt is only one of the properties one need be concerned with.

This may means that;

1) in applications where the bolt may yield (even slightly) in bending as it is tightened, or in service, the behaviour of the material the bolt is made of in yield is very important. Also

2) in fatigue, the behaviour of the bolt is influenced (in ways that may be unexpected) by details of the bolt manufacture method, and may no longer be closely related to the raw tensile strength of the bolt. Details such as rolled vs cut threads, the properties of the material, the potential for residual stress relaxation, the surface finish, the inclusion population of the steel, the corrosion susceptibility all may influence the behaviour of the bolt in real-world fatigue.

All this means that in an application such as a single bolt seat pin, it is not only the raw strength of the bolt that is important. In particular if the bolt head seating is not perfectly square to the bolt axis, the bolt may yield slightly every time it is retightened; in this circumstance I would far sooner have a ductile, work-hardening bolt material than one that is less ductile, even if the latter is stronger.

A good number of fasteners that are used on bicycles fall into the same category; stem clamps, stem face plates, seat pin clamps, seat binder bolts, cable clamps etc all contain safety critical fasteners that may be subject to low cycle bending as they are tightened, and then see fatigue loading in service. Simply fitting 'strong bolts' may often lead to more fastener problems, not less.

Note that in certain applications, the use of 12.9 grade bolts is forbidden, because they are so much more susceptible to hydrogen embrittlement and/or stress corrosion cracking. I don't think that normal bicycle conditions fall into this category but then again I've seen a fair number of parts in high strength steel fail in ways that would only be likely if there had been environmentally assisted cracking of some kind, too.

cheers