Quality saddle and seat post

Question

I own Scott Voltage YZ 25 for around 10 years. I've been using it daily (city ride mostly). Around 6 years ago, my original saddle, and seat-post were stolen, therefore I had them replaced, but not with the original parts. Here is the old picture of my bike with the original seat:

This year, as I gained some weight, I heard that my saddle would crunch when ever I'd put some pressure on it (road bumps, etc). What I did to "fix" it, was just strengthening the screw connecting saddle and seat-post. It was fine, as it didn't crunch anymore.

Almost two months ago, tragedy happened. As I was riding home, my saddle suddenly broke, and I instantly fell and broke my fibula bone (was left with a metal plate in my foot). When I examined what exactly happened, I saw that the screw which was holding the saddle and seat-post broke in half.

I never thought that this can actually happen. Was I able to prevent it?

My main question is, which seat-post and saddle would you recommend me? Something that would be considered safe, and something that can handle 100kg. (220lbs)

Answer 1

100kg is not super heavy and well within the range of rider weights that bicycles and bike components are designed for. A decent quality seat and seat post should not break underneath you.

Some saddles probably do have a specified rider weight limit, in the same way the most bicycles do. I quickly looked for some information and found that Fi'zi:k actually explicitly states they have no rider weight limit on any of their products. I also looked at WTB but have found no information at this time.

Looking at the picture you supplied, and the description of what happened, I may be able to offer some insight. The seat in the picture is positioned very far back. If the seat that broke was positioned in the same way, your weight would have been acting behind the seatpost and trying to rotate it backwards rather than pushing straight down on the rails and post. You may have also over-tightened clamping bolt. These two factors would have over-stressed the bolt and caused it to snap.

I guess you fell off the back of the bike behind the seatpost, which would have been fortunate as you avoided being impaled on the post as well as breaking your leg.

Answer 2

What you describe sound like a failure by fatigue, not due to overload. What caused the bolt to fatigue and ultimately crack? It can of course be the seat geometry with heightened stress to the back - however, this force compresses the saddle post joint that contains the bolt. If the bolt is tightened, the downward forces are dealt with by the joint and do not affect the bolt at all.

If it came loose, the bolt would be compressed by downward forces. This is not a big issue, bolts do not compress willingly and also tolerate compression quite well.

However, incorrectly tightened, there is also play in the joint (that you heard as creaking). This causes torsional forces on every pedal stroke. Bolts do not like and do not tolerate torsional forces. They get weak and snap: Just remember this ol' bugger that had its threads firmly stuck and stripped its head while you were trying to remove it...

Re-tightening the bolt was likely thtorsionale correct fix, but came late: Now the part of the bolt that was already weakened by torsion was stressed by tension. Tension is not a problem normally, this is what bolts are designed for, but this bit of stretching in the already weakened part was quite likely leading to the bolt snapping.

In essence, most saddles and seat posts out there should be fine for your weight. Just make sure everything is fixed tightly.