Pivotal seatposts? an idea from BMX...

Hey, this is a fairly recent new concept in the BMX world and it was started by FBM Bike Co… so other brands have to pay some royalties/fees/tax to FBM to be able to use this technology for their seatposts.

Basically how it works is as such, if you didn’t already know:

The seatpost is like that, all one piece, NO WELDS! So it’s stronger than our current welded style ones for a start. Then, the convenient part of this design is that as you see in the centre of the splined plate there is a threaded hole.

So, imagine, the seat base that fits onto this seatpost has a similar splined pattern underneath so that is sits snug on top of the plate, and you can adjust the angle quite easily by sliding the seat base up or down some splines.

Then, here’s the magic: the saddle has a little pouch in the middle of it where you can open the two little rubber ‘gates’ and inside sits a fat allen bolt which screws down through the saddle and into the seatpost, connecting it.

It’s very convenient and somehow reminds me of the Thomson/S.Wallis join.

If this were to be applied to unis, it would be an advance in that:
-no welds on seatpost (less local weakspots)
-seems cheap to produce judging by the price of current pivotal bmx posts
-convenient bolting and adjusting angle of saddle

Here are problems we encounter:
-May be fiddly to get these produced for unis (legal issues with FBM etc.)
-single bolt connecting might not be a strong join for the stresses involved with hopping with the saddle.

I’ve been thinking about this for a while, but meh, could be interesting, and I already have thought of the pros and cons of this design but discuss it amongst yourselves. I’d like to see other people’s view on this.

I think the single bolt might be a problem… a double bolt should work though…

good luck making it double bolt.

I know that the single bolt may not be strong enough. You can get those bolts in titanium though, interestingly.

doesnt tompson do the same thing?

don’t think so… might be wrong though.

Im not sure but ill check. I dont have a thomson so Im not positive…

yes, almost all seatpost have an “angle adjuster,” but w/ pivotals, there are NO seat rails, the “angle adjustment” is between the seat and post, not post and the guts, which attach to the rails of a seat, which then “pivot” on the post.

i agree that the single may be a bit weak, but i think that there must be ways to strengthen that up

It won’t be too weak as the single bolt can be larger than those used in rail posts, bigger diameter bolt = more surface area to grab on. I think it’s a design that should be tried before easily dismissed by people that have no idea what they’re talking about. Don’t assume that a single bolt is weak, that’s like saying drilled rims suck, which is also false.

i agree that dismissal would be retarded, but the way some people(NOT ME) break posts, it could be a potential problem for those “hard core” riders

Here is an idea.

Make a custom plate that bolts onto the seat, and screws into the Pivotal post.

It will take a bit to adjust, but I’m sure it will work fine.

This way you don’t have to produce a new seat, and can test the strength of existing posts before making stronger Unicycle specific posts.

I know it’s quite hard to find a post long enough for a Unicycle, usually they’re super short because they’re designed for BMX.

Longest post I could find in 1 minute of searching is 235mm long.

pivotal.JPG

I think a single bolt would be fine, especially a fat one like in the picture.

The bolt holds the splines together, and most of the pressure is taken up by the splines.

i like your idea dan. not only would it make it good for the testing time, but then people could use their existing seats. only thing is that it brings the “guts” problem back.

Right. I don’t think the bolt would be the weak point. On the seat example shown, looks like the seat itself might be the weak point. But a unicycle saddle would have to be molded specially to work with that system, so this could be addressed in that process.

Molds are expensive.

It would look the same as a regular Unicycle post.

There is enough room under the post to hide the Pivotal bolt.

The Pivotal design has the advantage of eliminating the rails and joining in on an emerging bicycle standard (although possibly a short lived standard). You shouldn’t have problems with it slipping. It is designed with BMX abuse in mind. The splines are stout and as long as the bolt is tight it is not going to slip.

Limitation is the adjustability. You are limited to the angles dictated by the splines. You can’t do a fine adjustment of saddle angle. For a trials saddle it isn’t a big deal but for a Coker saddle I have been known to fiddle with the saddle angle in very fine increments till I get it feeling just right. I don’t want a saddle standard that makes it impossible to fine tune the saddle angle in minute increments.

Just to throw out an alternative. There is also a proprietary seatpost/saddle standard knows as I-Beam. I believe it was designed by SDG. Kore and some other manufacturers have I-Beam saddles and seatposts available. It has been used for lightweight roadie saddles, DH MTB saddles, and BMX saddles.

The design of the I-Beam seatpost can vary as long as the guts hold the saddle. I’ve seen I-Beam seatposts with different designs for the guts and angle adjustment. Some would hold up to unicycle abuse and others wouldn’t.

Another nice find, JC! Since the I-Beam posts are readily available, anyone who makes carbon seat bases (strictly for personal consumption, you know, not to re-sell them or anything) might try adding the beam, and voila’, a new uni standard! Plus you could make the saddles a little narrower.

I could of swore I heard about this before, and I think Kris even talked about the post before. Ill have to search.

Also, not to dismiss the Single Bolt Theory (one bolt that tightens everything in sight!), but for uni applications, that system would require manufacture by the BMX companies of longer posts, something they’re not likely to be too interested in.

i’ve heard of some longer BMX posts.

i could definitely see that kind of post being universal for unicycles. an adapter would not be too hard at all to create, and the most comfortable seat i’ve ridden had a crease down the middle… … …

Ive got an Animal pivotal post and seat on my bmx, its really nice n convenient.

i reckon the bases cud be modified a bit and all wud be good for unis.

and to whoever said bmx companies wont produce posts in our sizes and lengths… well lol, the point of this thread is that in future maybe 3-5 years time unis can adopt this on their own and have brands like nimbus produce these etc…

of course there will b some money u need to pay to fbm for them to allow u to use their patented design