In a time period of around 4 months I have broken 3 seatposts. Just broke my 3rd one today. (actually…it could be the 4th, eh i’m not counting).
I do street and trials and have been doing alot of on wheel things lately. Anyway I broke it by just jumping up and pulling on the handle to attempt a double flip then it broke.
The break is just under the bit at the top where the saddle is bolted onto, rite at the very stem of the cylinder. I could get pics if that would help.
Hope someone can tell me whats happening
EDIT: I forgot to tell you that the seatposts that have been broken are all KH seatposts 27.2 except for one that was an already used chromoly seatpost that I got from Christian Huriwai.
Pat and I always break them in the exact same spot. Just seems like that’s where the stress from pulling up on the handle is. The post I have on now is holding up pretty well, though… It has survived many tripleflips (and attempts)
The only seat post I’ve broke it was at the same place as yours. See in Post your broken Uni parts here… almost every seatpost break at the same place, exept for the Qu-ax Reinforced post.
You are applying a twisting (torsion) force to the post and the material is becoming fatigue at it’s weakest point, the weld. This is why KH has started using a sleeve and pin (forged style) and K1 is using a gusset (Pitfighter).
Aluminum is not that strong in shear, if you doubt what I’m saying, try tearing an aluminum can, then try the same with a tin can.
Even the best aluminum posts are still breaking, so the best answer is to get a steel post or if you can afford one, a Ti post.
BTW, my Ti frame builder was asking me if I thought there was a market for Ti seat posts. The cost would be over $100, but you’d get a seat post that was strong as steel and light as aluminum.
The reason why they’re breaking is because that’s the current weak spot in unicycles that get lots of seat yanking. The combination of pulling up and pushing down (or just pulling up) is what eventually wears down the metal.
The posts probably aren’t breaking at the weld, it’s usually just in front of it. If welds are breaking it means the welds are faulty. In my experience with no-name and Miyata posts, the metal always tore, but not the welds. But often the stress area is where the weld is, so the metal tears at the edge of the weld.
My solution to this in the past, when alternative parts were not available, was to get a gusset welded onto the post. The strongest approach, back in the Miyata/Torker LX seat days, was to extend the seat plate to the front bumper bolts, then attach a gusset under that. But a small gusset can still do the same job on a KH/Schwinn style post. All you need is someone who can weld and a couple of triangles of tough metal (to match what the post is made of). May as well do the back when you do the front, so it doesn’t die that way someday either.
But then the seats will start to break… I think the new KH seats and posts are built to address this weak area, and will last much, much longer than the older stuff.
Here’s the seat post on my old DM ATU. Steel Miyata post with extra plate at the front and a big gusset. This is overkill, but would be great for someone who does nothing but Trials or big jumps/drops.
+1
I don’t really have a problem with seatpost (mine is seats). I guess its cause I have cromo post on my unis. Bad thing about cromo is that it bends.
I think the new KH seats and posts are built to address this weak area, and will last much, much longer than the older stuff.
To bad the SW bases are no longer available.