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-   -   explain seat position dynamics (http://www.unicyclist.com/forums/showthread.php?t=120678)

aj1500 2017-09-06 06:20 PM

explain seat position dynamics
 
I know I can just move my seat around and see what feels best as far as comfort and balance but can someone help me understand the dynamics in moving the seat front to back. I think I understand it has to do with changing the trail on the wheel but at what point would you find yourself needing to move the seat.
at the moment I have mine as far back as it can go, this lifting the nose higher
how would it act if a move it to the center or more toward the front

Kwikkash 2017-09-06 06:52 PM

something i discovered
 
I'm also experimenting with saddle set up. I don't have your answer, however I did find some very useful info on seat and bar setup at Unicycle.com assembly instructions. Go under Kris Holm seats. They talk about seat and T bar set up concepts. Jeff C

juggleaddict 2017-09-06 07:53 PM

I gather you're using the standard style seatpost and not a 2 bolt KH post or pivotal post.
These style posts have a little less adjustment than some other styles, and they're a little harder to adjust. I typically have mine tilting as far up as possible when using that style post. If you could control the tilt infinitely, too far back causes too much saddle width between your legs, and would cause chaffing and discomfort. Too far forward and you'll put too much pressure on your perineum, causing numbness and (you guessed it) discomfort. you have 2 sit bones (you can feel them pretty easily, they're part of your pelvis), and the idea of saddle adjustment is to get the pressure on those. Unicycles are trickier than bicycles because you need the control from your thighs for control and you don't want to slide forward on the saddle. To further complicate things, you're in a standing position on a unicycle, not sitting as you would be on a bicycle (unless you're using a low handlebar). You want enough tilt that you don't have pressure on your perineum, but not so much that you're pushing your thighs apart. This is a tricky balance.

If you look at bicycle saddles, you'll notice that they have many different widths to choose from based off your sit bone width, and that female saddles are typically wider than male saddles. There are some pretty obvious anatomical reasons for this. Unicycle saddles don't have that many sizes, so adjusting the tilt properly is your best bet to get the right fit. Usually I shift position around while riding to find a comfortable spot. Flat saddles are more finicky to fit for me, but more comfortable once you get them adjusted.

aj1500 2017-09-06 08:16 PM

so your saying it really is more about the comfort of the rider

MrImpossible 2017-09-06 08:44 PM

Your center of gravity is always going to end up in the same place, over the wheel - otherwise you wouldn't be balanced anymore.

So when you slide the seat forward, and ride, you'll end up rotating the whole frame back until your butt is back in the same position relative to the wheel. All that really changes is what part of the seat you are sitting on, and what angle the seat is at.

A lot of folks like the saddle slid forward as far as possible because you end up sitting on the relatively wide back part, which is now more level. The flat seats work well for this because you can sit on the back part without the front part curving up into your private parts...

aj1500 2017-09-06 08:55 PM

well I feel better knowing it's just that simple. not sure what I was thinking

I learned how to ride the first time when I lived in Atlanta. we lived in the Marietta area, riding there is a world of difference from Savannah. No hills here
to speak of. I have to admit, for now I'm glad of that

finnspin 2017-09-08 06:18 AM

While I agree with the previous answers for riding, I'd like to add one bit of actual seat position dynamic for the record. You'll notice many flatland/street unicyclists have their seat pointed down (you can flip Kh seatposts backwards to achieve a very "nose down" saddle)

Example:
http://www.unicyclist.com/forums/att...1&d=1325349474

This does two things:
1. your private parts are less likely to be hit.
2. and equally important, it changes the way the unicycle flips and does rolling hops. By moving the handle more downward, it enables you to pull harder and thereby jump higher and flip faster.

It also makes sitting in the saddle for longer periods uncomfortable, which is why most Trial/street/flat riders often push their uni and walk instead of riding.

UniMyra 2017-09-08 06:24 AM

I remember a similar discussion several years ago, and I'm a bit counfused myself. I thought GizmoDuck had a good point: http://www.unicyclist.com/forums/showthread.php?t=94121

johnfoss 2017-09-08 10:55 PM

Funny, that old thread went nowhere and people seemed to lose interest. I probably didn't weigh in on it because we were away in Italy for the Unicon trip, I think.

I don't agree with Ken's initial hypothesis, that adjusting the seat just changes the frame angle. It doesn't, at least not on the old Schwinns (which use the same post and bolt pattern as today's KH and most other brands). In my first few months of (actual) riding, my friend and I had already tried many variations on seat position. Our initial conclusion was that none of them really helped (today's seats are much better). But we both agreed that pushing the seat all the way forward, making the nose high, was our preferred setting with those seats. Especially on the giraffes. This put our weight a little further back on the seat, where it was widening out, and offered a little more support from our "buttockal soft tissues".

In the now, I'm still giving the Kris Holm Zero saddle a chance. I haven't found an angle I like; I get a certain amount of time on it that's fine, but after that it just gets less and less pleasant, no matter how I shift around on it. I think this "chance" period will last until my Kris Holm One saddle arrives. :)

In any case, changing the seat angle really does change the seat angle. Even if you had a set of rails on top of your seat post and could do long adjustments, the angle of the seat in relation to your anatomy would change, and it does matter. I think the optimum angle on any seat is going to be a combination of the seat type, plus your personal anatomy. In other words, something that will be very personal, and require experimentation on your part.

In case the OP's question was not answered already, the adjustments built into standard unicycle seatposts are not intended to change trail or rake; all of that "balances out" to your center of mass. The only meaningful thing that changes is the angle of saddle vs. crotch.

aracer 2017-09-10 05:35 PM

Quote:

Originally Posted by johnfoss (Post 1687815)
Funny, that old thread went nowhere and people seemed to lose interest. I probably didn't weigh in on it because we were away in Italy for the Unicon trip, I think.

I don't agree with Ken's initial hypothesis, that adjusting the seat just changes the frame angle.

I agree with you John - and I'm surprised I didn't weigh in either as I was on here then and usually comment on saddle angle discussions!

Ken is half right though - changing the saddle angle does just change the frame angle, but only if you realise that changing the frame angle moves the seat forwards and backwards (which I don't think he did). Because moving the seat forwards and backwards has exactly the same effect as changing the seat angle (and vice versa) - calling unibokk ;)

johnfoss 2017-09-11 03:56 AM

Quote:

Originally Posted by johnfoss (Post 1687815)
In the now, I'm still giving the Kris Holm Zero saddle a chance.

UPDATE:
Nope to the KH Zero. After going 20 miles yesterday, my crotch told me it's had enough and I agreed. It still looks brand new and has low miles. Anyone interested in a used one? Today I rode my old Coker with 125mm cranks and an ancient air seat, on a carbon base, held together by an old Roach seat cover. Ahhh.

I've ordered the KH One saddle, and hope it's a worthy improvement on the Zero!

BTW, I get how the Zero supports you on your sit bones, but that position only works for me when I'm "in the drops" and eventually my arms and neck get tired. I need a saddle that's also usable in the upright seating position...


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