Accident Following Seat Bolt Shearing

Dellsinho

Happened to me a couple of months back, although I did have the saddle a bit far back then, so more leverage on the back of the saddle when I hit a pothole. The bolts on mine were orientated the other way to your other half's, so the front one popped but the saddle was held on still by the back one. Also managed to stay upright, but took me a while to work out what on earth had just happened.

I ended up pushing my bike the rest of the way only to find when I got to work, I'd lost the clamp plate somewhere in the road. Went back to the scene a few days later to find it and sure enough it was there in the gutter, quite scuffed and no longer black in colour. Popped it back on with a new bolt - does the job again.

I'm assuming I overtightened it which lead to the failure.

Hope your other half is alright, sounds nasty.

keef66

ajfish wrote:

I just thought that they are stronger regardless of the fact that they are also resistant to corrosion.

I'm a biologist, so outside my area of expertise, but as I understand it not neccessarily so...

"It is a common misconception that stainless steel is stronger than regular steel. In fact, due to the low carbon content, stainless steel cannot be hardened. Therefore when compared with regular steel it is slightly stronger than an un-hardened (grade 2) steel fastener but significantly weaker than hardened steel fasteners"

From

http://www.boltdepot.com/fastener-infor ... rials.aspx

samthesham

Hi, my girlfriend had a similar incident last night riding my Trek 7.3. Fortunately we were only a mile from home and she wasnt going fast...a nasty shock tho! The supplied Bontrager Nebula seat is only connected to the seat post via a M7 bolt (unusual size, USA) and this has sheared off. I had already ordered two replacements before a mate said he could drill out the holding bar to a more conventional M8 size. Trek riders take care!!!!

ajfish

Since having this accident we have come across a number of others who have experienced similar falls as a result of the seat post bolts failing.
I have to say that, on this occasion Scott took the situation seriously and took the bike back for inspection. While not admitting liablilty they said that the failure could be put down to one of four things. From memory, as I don't have the documentation here; 1. Incorrect fiting of the saddle, 2. Faulty bolts 3. Incorrect fitting of the bolts, 4. improper use of the bike.
They said that, in their opinion the cause is likely to have been caused by faulty bolts but without having these analysed, a cost of which would be down to us, they cannot conclude that this was the case. On balance they elected to offer a new seat post, saddle, helmet and handlebars but acceptance of this would mean that the girlfriend had to sign a declaration not to take any further action against them. Viewing this as better than a flick on a naked buttock with a wet tea towel she decided that it best to accept.
I was impressed with how Scott took this on board. They could have easily washed their hands of it, which is what Pedalon in Tadley appeared to try to do which is where the bike was purchased. Their attitude was very defensive.
I would buy a Scott bike as a result of their customer service, but do remain a bit concerned that the seat bolt issue could still remain a problem.

mick_cornick

Had this happen on my MTB, luckily I stayed upright but had to cycle about 6 miles without a saddle to get home! Bike shop told me it is a common failure mode but mine was a single bolt.

steggy123

Hi there, i have just snapped my second in 3 years, on an MTB round the local trails. First time i held it together but not so lucky this morning, a few holes in my knee and elbow, could have been a lot lot worse. No one is around that time and lots of trees a about. Didnt even sit down hard on it just aftera short hump.

My saddle came a little loose early in the week and i just tightened it up, not hard. It was creaking a bit this morning..so with hindsight some warning signs.

Im not the lightest of fellahs but getting lighter the more i cycle but I am a big bloke generally. Bolt is a single one. Do you think i would be ok if i simply swapped it every six months, would i be better with double bolts and what would be the proper torque settings please. i have been lucky twice. Dont really want to roll the dice again. many thanks. ian

sloppyschleckonds

Thread is useless without pictures of girlfriend

reacher

Take the bolts to an engineer and ask him what they are made from would be my first port of call, because as been said the thread should have stripped first if over tightened, something has been done wrong their I would say, no way should 2 go at exactly the same time, either that are it's a one in a million fluke accident

Moonbiker

Ive has the same thing happen.

Had to ride 15 miles home without using saddle.

paulbnix

Hope your partner is ok now.

I had one bolt snap on my FSA K Force seatpost - it was the rear bolt and it snapped near the top end.

Luckily I was only moving slowly.

Unfortunately the saddle slipped sideways and the rest of the bolt that was sticking up penetrated the lycra in my shorts.

It was a right sod to keep moving while trying to pull the shorts off the bolt - I didn't want to sit down on it :-(

A selection of tie wraps were sort of successful in securing the saddle for the ride home.

lesfirth

I am not a metallurgist but to me the first photo the OP has posted shows two distinct areas of the broken bolts. A silvery bit and a dark bit. On the left hand bolt the silvery bit extends about 75% of the area with a dark bit near the top. On the right bolt the silvery bit is 90% with a little dark bit at the top.
IMHO the silvery bit is a some sort of fatigue crack that has developed over a long time.The dark bit is not cracked.The dark bit is holding the saddle on. The OPs GF said the saddle felt funny. That was the 10% of the right hand bolt breaking. The added stress to the left bolt then broke the 25% of sound metal of that one.
In future I will be a bit more careful checking the tightness of all bolts on my bikes from time to time.I think a check with an allen key would have broken the right hand bolt.