Unfortunately there is no such thing as un unbreakable product, everything gives with time and use. I’d have to say that the carbon fibre base is still the strongest option out of the products that currently exist. To design a stronger base would probably result in a higher cost. Perhaps in a few years we may see aerogel seat bases.
Nice work! I was looking at the pictures trying to figure out why it failed. You may be able to increase the failure load of the seat if you put a thin rubber shim between the seat and the top of the seat post base. Something near 40-50 on the shore A scale. When testing composites we often have to do this sort of thing as the test fixture is much much stiffer than the composite. Because the part of the seat post that clamps to the seat is so much stiffer than the seat it takes all the load right up to the edge of the steel plate. Then all the load transfers suddenly to the seat base. The rubber makes the transition more gradual. You would only need a few millimeters. I don’t know if this would impart a squishy unconnected feel to the uni (probably no more than an airseat), but it is worth a try (mess with the rubber hardness and thickness. www.mcmaster.com is a great source for rubber sheets. We cut them to shape with a water jet, but tin snips should cut it well. Another option is to perforate the steel plate so that the stiffness of the plate is reduced to closer of that of the carbon fiber composite. Just a few suggestions that I would try. They may or may not work. It sucks when expensive things break.
I imagine a couple of thicknesses of DH tube would work, what do you think Gauss?
But it looks to me as though the seat failed at the lower lip and then the failure travelled up to the adapter. The lower lip is where all the seat flex stress would be; is it not? Perhaps the seat winding needs a few layers of fibers over the lower lip that go in a different direction.
the rubber pad to disperse the stresses caused by the stiff plate mounted to the seatbase would work well to pad the Carbon fiber. another good way to reduct the likelyhood of something like this happening would be to grind or file the sharper edges of your mounting bracket.
i took my seat apart within days of first building it and noticed that the plate at the top of my seatpost had scratched or cut the bottom of my seat base. i know that this will eventually lead to failure, buti just have to deal with that, but i rounded off the edges that created the scratch and i think things will be fine for a while anyway.
as far as the crack starting on the edge, or lip… my seat base was very rough around its edges, not very well manufactured in my opinion… i took a disk sander and smoothed out the lips all around the seat base. with a few different peices of sand paper i was able to create a smooth uniform edges all the way aournd.
the jagged edges as they were created alot of little stress risers, or places where all the stress in the seat was focused. never thought about it causeing failure, but it makes sense.
my biggest comlaint about the “carbon fiber” seat base is that it appears to actually be a fiberglass core with a layer of vacumed molded CF on the bottom, and a horribly hand layed layer on top.
where the edges ar ground and where the holed are drilled and filed, you can easily see that the middle is a white-ish color…
for the money i was expecting real carbon fiber all the way through, not a peice of plastic with two layers!
if these bases were the same thickness they are now but 100 percent CF, they would be far stiffer and probably more durable.
Ryan, sorry about the bending. hope you’ve got a good job this summer. that thing i promissed you will be on it’s way very soon, i’ve got one for jeff too. sorry about the wait. later
>Perhaps in a few years we may see aerogel seat bases.
I’ve come across aerogel professionally while doing some research.
Aerogel is very very light (can go down to 0.003 times the density of
water), it is strong for its weight but it is weak for its volume. It
doesn’t look like a good seat base material.
Klaas Bil - Newsgroup Addict
“No two crotches are alike. If they are, I don’t want to know about it. - John Foss, on seat comfort.”
Yes, someone had to be the first to break one. Bummer. But judging from a cursory glance at the photos, it doesn’t look like the carbon was thin or anything like that. More likely you just used it real hard.
I wonder if a Reeder handle or similar would have helped? The break at the front was probably the result of millions of hops. The handle may have moved the stresses on the seat to a different area, making it last longer. Or they may have concentrated the forces, making the seat fail earlier.
Your next possible step is to look into the frame-attached handles being made by Carol Dingemans. Look for a thread by Max on the subject. This takes the stress off the seat (at least as applies to the front) and moves it to the frame. Probably cheaper and easier to replace, too.
(added later) That is, unless your breakage is the result of seated landing on big drops. Ouch. Probably not, because you might have mentioned something like that. Try not to land on the seat! But whatever you’re doing, it’s clearly out there at the far end of ‘extreme’ territory!
I do almost all of my hopping, and gapping seat-out front, except for rolling hops, which i seldom practice. This makes me think that the seat-post handles wouldn’t be a great idea, also, i have a big problems with breaking and bending seatposts. so i think that it would just add more stress.
I cut a piece out of a old thick tube, and mounted it under the bracket of my seat post, (i re-built the seat with the CF base i was going to use for my MUni), so i’ll see how well it works. I might also add some other rubbery materials i found, once i get a seatpost that isn’t severely bent on -the post -the bracket
and - dislocating from the welds.
The bases are sold at an extremely low margin and low cost for a handmade carbon component. The glass infill is there to give extra stength and charatoristics that the carbon alone would not give. It is true that a seat totally made from Carbon at that thickness would be stronger but consider this… the glass costs almost nothing… look how thick it is and now think what the seats would cost if they were all carbon!
The seats are manufactured by Hansell Composites. Martin Hansell is a long time friend of mine and came to the industry through working in the composite research department of ICI. So he really does know his stuff! What you don’t see is his calculations on the weaves and patterns of the cloths to give optimum charictoristics. He is also someone I can be blunt with
Ryan contacted us regarding the seat and it is clear it has had a hard life… I am hunting for a rejected seat I saw lying around in Martin’s shop which was extra thick, it should help. But it is worth reminding people that Carbon fibre does have a life and it is reletively short, you should not expect a composite structure like a seat base (or a carbon unicycle) to be at full strenght over 2 years!
I think the conclusion was that he was landing very hard on the rear of the saddle. He had several seatposts fail in the time that he had the one seatbase.
Nothing would have survived except for thicker carbon base for Ryan. I think it can be fair to say that Ryan is taking the sport to a higher level and taking more risks… please don’t hurt yourself Ryan! We have produced almost 300 seatbases in over 3 years and only one has failed so far and that was Not a bad record. Would people like an all carbon fibre seatbase at the same thickness? I will get some quoted if people would be interested.