Jackm08

To make a long story short the bolt that holds my saddle to seat post has now broken twice. The first time was a really bad fall, the second time, I was lucky. The first time it happened there was a persistent squeaking noise that I could not figure out the source until it broke. This was the bolt that came with the bike. I brought to my local bike shop and they simply told me to buy a new steel bolt. I did. Yesterday it broke without warning.

My question to the group is, is there a special bolt that I should be using? I am concerned that a very expensive bike is about to take up residency on my indoor trainer as I cannot trust it. I can provide photos if it is of value.

Barry2 

EDIT: Just noticed... Post #1... Welcome to Bike Forums.
Fair warning.. It can get weird around here.

Quality bolts are "graded".
Higher the number, higher the spec.
If you purchased a random ungraded steel bolt then I'm not surprised it failed.

Buy a bolt, the best bolt you can bag, not a bargain bolt, by becoming belligerent and better briefed about bolts.

Barry

(Sorry, just in the mood)

Barry2 

Oh, and when you turn to tighten the target bolt, use the correct torque.

But that's a discussion for another day

Barry

Jackm08

Thank you very much. Very relieved to get this advice

smd4

Did you grease the bolts prior to installing them?

Jackm08

I did....and I was not shy with it

Andrew R Stewart 

Binder bolts can break from a few reasons, IME the most common is because the bolt is no longer able to remain straight as the enough tightness level is reached. In an ideal world the faces/seats of the clamp/lug/boss will remain parallel, side to side. So as the bolt draws together the two sides of the clamp/lug ears/binder barrel the bolt will see no bending. The reality is that this nearly never happens. Very few clamps/lug ears/binder barrels are preset non straight when in a relaxed state so that after tightening the bolt and securing the post the bolt is held straight. The more layers (separate clamps) or the more slop between the post and tube ID (more room to take up) the greater the amount of likely bolt bending will happen. Add in the greater tolerances of a non round post/ seat tube and clamping system and the amount of slop just builds up. In time the binder slot can too often close up and at this point the bolt head is only contacting the clamp's seat at one point under the head, UNLESS the bolt bends to allow the head to seat fully against the seat. Just like when one bends a paperclip back and forth the bolt will work harden and crack. So a broken bolt generally is showing a deeper issue even if the rider doesn't know it. Andy

Jackm08

Which inevitably leads us back to replacing the seat post which is not an option due to availability. From your comment, it assumes that the seat post is the issue, and if so, there are no guarantees that a replacement seat post would resolve the issue as it too may be badly machined?

Barry2's suggestion to upgrade the bolt seems a logical one. If a bolt is strong enough for a bulldozer surely it would keep a 150lb rider on a bike?

Am I missing something?

Barry2 

Jack,
What is the model and year of the bike ?

Barry

grumpus

You want to be sure you use a high tensile bolt, these are often described as grade 8.8. There's usually a good selection on eBay; generic fasteners can be cheaper than cycle-specific items, but be sure that the thread pitch is correct.

Andrew R Stewart 

Some companies, and their contractors, do a better job at matching the aero post and seat tube and associated clamp shapes and dimensions, others less so. I can't offer many options to brand/design specific products when no one else offers an alternative. Nor can I agree with bikes having non round seat posts. What I can do is to help you understand why the bolt likely broke. Sorry if that effort wasn't enough.

I never said anything about the smarts or stupidity of going to higher grade bolts. But trying that to me is a no brainer if one can find a suitable higher grade one (and hopefully the bolt isn't also non standard in it's design). Andy

Jackm08

Hi Barry,

It is a Ridley, Phaeton.T. The year is 2012.

Barry2 

LOL.... I went searching for an OEM Seatpost bolt/clamp for your bike.
Those are tough to find, and I'm an IT guy.

But upon re-reading you actual post (not the subject), you are referring to the Saddle Clamp Bolt.
The single bolt at the top of the Seatpost that retains the saddle, is highly stressed.

Go buy a Graded bolt from a reliable source. Nothing fancy.. no Titanium, no Alloy, just a good ol' bolt.

Was the second bolt that broke marked as graded?

Barry

Jackm08

Hi Barry2/Grumpus,

Everything you mention is accurate. The bolt issue is the one that goes from the saddle housing into the seat post. I looked at the one that broke and it was indeed 8.8. That was very unnerving to learn. I just ordered 12.9. In addition, I am trying to get a hold of Ridley to see what they have to say. It has been about a week and they have not replied, so who knows where that will go.

Barry2, ok, so I am an IT guy too and went on the hunt to replace seat post as Andrew alluded to. I did find a used one on eBay. The guy was asking around $200 plus Shipping and Handling which was a viable organ from my body. As I mentioned to Andrew my concern was that if this bad design or machining, then all I will end up with is the same problem, $200 lighter and one less kidney. For now I am not going down that road.

So where do I go from here:
1. Hope for a reply from Ridley
2. Reattach the seat post with 12.9 grade bolts and replace them every year
3. Attach zip ties from the seat post to the saddle so if the bolt goes the saddle will remain so I can at least stop the bike without hitting the pavement.

If you see anything wrong with this approach, or if there is something I missed I would appreciate your opinion.

If all that fails, convince the wife I need a new bike.

Thanks to all who have offered an opinion.

Barry2 

Did you purchase the replacement bolt from a reputable source?
Meaning a dealer of hardware, not of everything.

Barry

Jackm08

The 8.8 grade M8-40mm bolt was purchased from a place that specializes in bolts. The replacement 12.9 grade was purchased through Amazon. Most places around here only sell imperial, not metric

Barry2 

Amazon is a purveyor of everything!
Very much… you pays your money, you takes your choice
However if the look down the right side of the product page, there is often a link to the actual underlying seller.

Please do look and determine it is a source you like.

Barry