Seat post trouble

now the count of broken miyata seat posts is up to 3, 2of which happened in the last 2 weeks. the most recent just bent foreward really far, and the other 2 broke right off, just underneath the bracket.

I am trying to find a solution to this.

so far, i found an old bike seat post that is a really tight fit to get over. i’m thinking that if i can get it over, it will end my bending problems. But what about the breaking off?
I was thinking of somehow welding a little piece of old, broken post on the front. but then i couldn’t use the other idea. i think i’ve finally rested on something that attaches to this bit of seatpost, then goes foreward, and bolts on under the mounting bolts (that attach the post).

does anyone have any idea on how i would do this, or any other ideas of how to fix it?

Thanks Alot,

-Ryan

Goodness me! What are you doing? I’ve never broken a seat post yet, although my friend bent one when he fell and landed across the uni.

If you try to strengthen a tube either by putting a core in it or a sleeve on the outside of it, you will introduce a weak spot where the reinforcement stops. There will be a ‘discontinuity’ in the strength and flexibility of the tube, and it will tend to snap at that point.

This is one reason why old fashioned ‘lugged’ bicycle frames were replaced with ‘lugless’ frames. And why ‘double butted’ tubes were brought out instead of single butted.

Better to develop a riding style which doesn’t put sudden loads on the tube in the wrong direction?

Have you tried the GB4 seatpost?
<http://www.unicycle.com/shopping/shopexd.asp?id=608>
It’s stronger than the Miyta post and the welding at the mounting bracket is stronger too.

is it different material than the miyata post?

-ryan

Yes. But I’m not sure what tubing he is using.

You could email George Barnes and ask him (he’s the GB in the GB4). His forum name is gbarnes. Look him up in the forum members list.

His email address is also on his web site
http://www.public.iastate.edu/~gbarnes/

I have tried reinforcing mine with a metal tube fitting tightly inside the seat post. I didn’t work because the post had already begun to bend, but maybe it wouldn’t have if the reinforcement had been there to begin with.

Morten

The picture of the GB Seat post looks like it is designed to elevate the front of the seat, is that true?

Also, I think I remember Jagur saying you could take a 27.2 post and fit it over the 22.2 post and it fit well. I could be wrong on the dimensions, though.

Ahh, poor fool. You are obviously not acquainted with Ryan’s trials riding… shame on you! The pleasure-emitting sensory sections of your brain are mad at you for not exposing you to this video. Watch and learn Mike, watch and learn.

As for developing a different style, out of the question!! Many people would be disappointed, just read the threads on Ryan’s riding.

Later,
Eli.

Yes.
<http://www.public.iastate.edu/~gbarnes/gb4/seatpost/seatpost.html&gt;

Don’t try to keep fixing your old Pinto, it’s time for a different car!

I have broken many Miyata posts, though always where the top plate joins to the tube. They’re just made of low grade metal, and not intended for us adults to beat on them the way we do. The GBarnes post is an easy replacement, or if you want to go the full way, get the Kinport rail adapter, then a “real” bicycle seat post of your choice. Make sure you get the proper diameter to match your frame.

Ryan,

I add laser cut seatplates to chromed steel BMX seatposts. The BMX posts I use appear to be thicker/stronger than the OEM Miyata post.

I can’t guarantee you won’t be able to bend this post, but I’m sure it will hold up better than a Miyata.

I do guarantee anything I weld. If you break a weld, I will fix/replace the part at my cost. In your case, I would probably beef up that joint with a gusset too. This has been done before to more than a few OEM Miyata posts.

OK, I watched and learned. :astonished: I admire not only the skills demonstrated, but the dedication and even courage which must have gone into developing those skills. It’s something I could never do. It’s also something I wouldn’t choose to do, but that’s me. Still, as the young people say, ‘Respect is due.’

But to revert to the original question, how to stop the seat post from breaking…

Firstly, there are things which could be done to the riding style to reduce the strain on the seat post. This might put some limits on the height of jumps or drops, or it might simply be a change to weight distribution and the way that the impact is absorbed during a landing - this last bit I do know about, as a dancer. There is skill in all that Ryan does, but there would also be skill in doing “less” but in a more mechanically sympathetic style. There is an element of choice.

But assuming that there is going to be no significant change in style, then here’s an ‘engineering’ suggestion: I notice from most of the movie that the seat is seldom used as a seat. It is used primarily as a handle, and is sometimes held at the front, sometimes at the side, and sometimes at the back. It is then subjected to lifting and landing forces which are ‘off centre’ on the seat post. This is no doubt a large part of the reason for the high mortality rate for seat posts.

So, if it’s seldom used as a seat, and usually used as a handle, WHY NOT… redesign it so that it looks and works like a handle, but has a secondary function as a seat? Seriously.

The strain on the ‘seat post’ will cause least damage when it is straight along the axis of the tube - when the tube is being ‘stretched’ or ‘compressed’ rather than twisted or bent.

So imagine a post with a D handle at the top, almost like a spade or shovel handle. This would provide an excellent grip, and would align the lifting/landing forces in the right direction in relation to the post.

The straight part of the D (uppermost) could be extended a short distance each way, and slightly padded, so that it would provide a bum support (rather than a comfortable seat) for those times when the uni is being ridden as a uni.

Look at trials bicycles, or, for that matter, trials motorcycles - the seat is vestigal, with the whole design tailored to the fact that the seat is only used as a seat for a tiny percentage of the time.

Anyway, what do I know? I’m just some old duffer who thinks wheels are round so they roll better. ;0)

I’ve fixed four bent seatposts by sawing off the post from the baseplate and welding on a BMX 22.2mm OD seat post. These BMX seatposts are known as ‘candlewicks’ as they are just a straight piece of tube with no bike-type seat clamp on the end. They are very strong and also inexpensive (mine cost me US$7).

Miyata seatposts bend quite easily as they are not extruded tube but welded seam construction. A welded seam tube is made from a rectangle of steel rolled into a cylinder and welded together. If you look on the inside of your Miyata seatpost you’ll be able to see the seam.

Hope this helps
Tony

This is probably where things will eventually go, in the area of Trials. For more conventional riding, the seat part will stay pretty important.

But this involves recreating the thing from scratch. Really, a stronger seat post will do the job in the short run.

The Miyata, like 99% of all unicycles made, is intended for light riding by children on an average of 8-12 years old. Just as you would not race on a department store kid’s bike, you should not expect miracles from a Miyata post. It’s fine for what it’s made for, but it’s very weak when it comes to Trials.

As people do more pushing and pulling on unicycle seats, and as handles get bigger and further from the post, the strain on seat posts will continue to increase. I bent the post that came with my Wilder (from a very odd dismount). We simply ask a lot of those poor posts.

For me the ultimate Trials unicycle would not have a handle attached to a seat, which is attached to a post or bracket. That’s too much hardware. The seat could be a lightweight thing intended to support your butt and nothing else. As long as there’s a handle there, it should be built to take all the strain, and it should be attached directly to the seat post or frame. This should make for a lighter unicycle in the long run.

Someday I’d like to experiment with some designs for such hardware…