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-   -   Seat Angle Adjustment- why is it even needed??? (http://www.unicyclist.com/forums/showthread.php?t=94121)

GizmoDuck 2012-08-12 02:08 PM

Seat Angle Adjustment- why is it even needed???
 
I've been thinking about this for a while, and can't figure out the logic behind seat angle adjustment on a unicycle.

When you sit down, the seat should find some equillibrium with your buttocks/crotch.

It doesn't matter if you have the seat angled upwards or downwards or flat, what you change is the angle of the frame underneath you once you sit down.

Why add extra weight and complexity by having angle adjustment (either by having curvature or a complex bicycle angle adjustment system)? You could also have an integrated all in one seatbase/seatpost that would save weight.

More importantly, for short people, it decreases stack height and means you don't have to cut down the seat tube as much.

harper 2012-08-12 02:51 PM

Ken-

Your center of mass must be in the same line as the axle of the unicycle and the center of the saddle. You can adjust the angle of the saddle with respect to that line and it shifts the position of the force distribution on the saddle. I think what you're missing is that if the rotation of the saddle only affected the angle of the frame when you were on the unicycle, your center of mass would no longer be directly over the axle.

GizmoDuck 2012-08-12 03:05 PM

Quote:

Originally Posted by harper (Post 1530497)
Ken-

Your center of mass must be in the same line as the axle of the unicycle and the center of the saddle. You can adjust the angle of the saddle with respect to that line and it shifts the position of the force distribution on the saddle. I think what you're missing is that if the rotation of the saddle only affected the angle of the frame when you were on the unicycle, your center of mass would no longer be directly over the axle.

Your centre of mass should be over the axle whether you have the seat at +45 degrees or 0 degrees or -45 degrees with respect to the frame.

Once you sit down and start riding, the centre of mass and the saddle angle are constant, what moves is the angle of the frame (depending on saddle tilt with respect to the frame).

On a bike, the saddle is fixed at an certain angle to the ground, because it has two fixed points (both wheels) stopping rotation of the saddle. On a unicycle, the frame rotates around the axle so whatever seat angle you start with is irrelevant once you sit on it and start riding.

tholub 2012-08-12 03:11 PM

Quote:

Originally Posted by GizmoDuck (Post 1530505)
Your centre of mass should be over the axle whether you have the seat at +45 degrees or 0 degrees or -45 degrees with respect to the frame.

Once you sit down and start riding, the centre of mass and the saddle angle are constant, what moves is the angle of the frame (depending on saddle tilt with respect to the frame).

On a bike, the saddle is fixed at an certain angle to the ground, because it has two fixed points (both wheels) stopping rotation of the saddle. On a unicycle, the frame rotates around the axle so whatever seat angle you start with is irrelevant once you sit on it and start riding.

Did you do anything to test this hypothesis, like tilting your seat all the way up and all the way down to see if it feels any different?

It does.

GizmoDuck 2012-08-12 03:16 PM

Quote:

Originally Posted by tholub (Post 1530506)
Did you do anything to test this hypothesis, like tilting your seat all the way up and all the way down to see if it feels any different?

It does.

It's a mainly a thought experiment.

But from the limited tilt I can get with a unicycle seat, I haven't noticed much difference, except in how much my thighs rub against the fork crown.

If you notice any difference, it must be because you are taking extra weight with your legs. So at the extreme, if a seat was completely vertical with respect to the frame, someone would have to stand on the pedals in order to ride. But that means it's no longer a seat- it's an ultimate wheel with handlebars.

Alucard 2012-08-12 03:49 PM

1 Attachment(s)
Hi GizmoDuck
I"ve been trying to ride for just over two years now. This is the angle of dangle of my seat. I find this position the most comfy. I can sit in the saddle for about an hour and a half before feeling any discomfort. Hee hee, you'd think with it angled like that I'd be an expert at dismounting backwards gracefully :p, but no such luck, not yet anyway. :)

Attachment 54775

Alucard

finnspin 2012-08-12 03:59 PM

I don't know for Tour/Muni riding, but for Flat/Street you will see riders with a lot of different angles, which all have their pros and cons. If the front of the saddle is really low, it's much easier for Flips, but harder for roll tricks and Unispins, when you put your seat in a "normal" way or with a pretty high front part, you have much more stability and control for SI riding, and it graps better for rolls, but there is a higher chance that badly landed Flips may hurt, and fliptricks are somehow harder..I can't really explain why, it has something to do with the way you can pull/push the saddle.

GizmoDuck 2012-08-12 04:16 PM

Quote:

Originally Posted by finnspin (Post 1530515)
I don't know for Tour/Muni riding, but for Flat/Street you will see riders with a lot of different angles, which all have their pros and cons. If the front of the saddle is really low, it's much easier for Flips, but harder for roll tricks and Unispins, when you put your seat in a "normal" way or with a pretty high front part, you have much more stability and control for SI riding, and it graps better for rolls, but there is a higher chance that badly landed Flips may hurt, and fliptricks are somehow harder..I can't really explain why, it has something to do with the way you can pull/push the saddle.

Ah, but you're no longer sitting on it when performing those tricks right? As soon as you take the weight off the seat, what I said no longer applies.

In Flat/Street, seat angle is more relevant for keeping it out of the way when executing a trick.

Mikefule 2012-08-12 04:30 PM

If you could not adjust the angle of your saddle relative to the seat post:

You could adjust the angle of your saddle relative to the ground by tilting the frame back (or forwards) beneath you as you rode.

This would indeed get the saddle at a comfortable angle for your backside.

However, it would also put your hips further back (or forwards) which might mean that your legs were in a less comfortable position for pedalling.

Also, if your hips were moved a few inches backwards, relative to the tyre's contact patch with the ground, you would need to lean your upper body further forward to compensate. Otherwise you would simply tip over.

So to get the saddle at a comfortable angle, you would end up with every other part of your legs and upper body being forced into a position to compensate.

Or you could just do what we do: adjust the saddle to an angle that is comfortable for your butt when you are in a comfortable riding position...

GizmoDuck 2012-08-12 04:35 PM

Quote:

Originally Posted by Mikefule (Post 1530520)
If you could not adjust the angle of your saddle relative to the seat post:

You could adjust the angle of your saddle relative to the ground by tilting the frame back (or forwards) beneath you as you rode.

This would indeed get the saddle at a comfortable angle for your backside.

However, it would also put your hips further back (or forwards) which might mean that your legs were in a less comfortable position for pedalling.

Also, if your hips were moved a few inches backwards, relative to the tyre's contact patch with the ground, you would need to lean your upper body further forward to compensate. Otherwise you would simply tip over.

So to get the saddle at a comfortable angle, you would end up with every other part of your legs and upper body being forced into a position to compensate.

Or you could just do what we do: adjust the saddle to an angle that is comfortable for your butt when you are in a comfortable riding position...

Sorry, I'm not sure I understand what you are saying?

The angle of the frame automatically adjusts to the angle of the seat, not the other way around. ie the saddle angle (with respect to the ground) and your centre of gravity when riding are constants, the variables are the frame angle.

GizmoDuck 2012-08-12 04:41 PM

I also suspect that what people get when they adjust seat angle is not so much a change in seat angle (with respect to the ground) when riding, but a height adjustment.

Perhaps that is what is noticed in terms of comfort or handling, but you might get the same effect from raising or lowering the seatpost.

Mikefule 2012-08-12 05:32 PM

Quote:

Originally Posted by GizmoDuck (Post 1530524)
Sorry, I'm not sure I understand what you are saying?

The angle of the frame automatically adjusts to the angle of the seat, not the other way around. ie the saddle angle (with respect to the ground) and your centre of gravity when riding are constants, the variables are the frame angle.

Yes, but how do you get your centre of gravity over the axle if your arse is 3 inches further back? By leaning forwards.

It's all about what you would have to do to your entire body position to get your centre of gravity back over the axle if you tilted the frame/seat backwards as a means to adjust the angle of the saddle.

If the saddle moves backwards, your arse moves backwards with it. If your arse moves backwards, then something else has to move forwards to compensate.

Do you want to ride like this:

|
|
O


or like this:
\
/
O

US readers: "arse" = "butt" or "ass".

GizmoDuck 2012-08-12 05:35 PM

Quote:

Originally Posted by Mikefule (Post 1530536)
Yes, but how do you get your centre of gravity over the axle if your arse is 3 inches further back? By leaning forwards.

Why would it be 3 inches further back?

GizmoDuck 2012-08-12 06:08 PM

Quote:

Originally Posted by Mikefule (Post 1530536)
Yes, but how do you get your centre of gravity over the axle if your arse is 3 inches further back? By leaning forwards.

Actually, I see what you and Harper are saying.

So from T to T, if you assume that the saddle will stay the same angle to the ground or wheel axle, you would either angle your body more if your buttocks were fixed to a certain position on the seat, or shift your position along the seat.

However, you could have a seat that allows simple forward and backward adjustment, and that would give an equivalent effect to saddle tilt.

ImFalling 2012-08-12 10:51 PM

Quote:

Originally Posted by GizmoDuck (Post 1530542)
However, you could have a seat that allows simple forward and backward adjustment, and that would give an equivalent effect to saddle tilt.

Yes. But given that seats are all curved, moving the seat forward/backwards means changing the angle between the nose and the pressure point. Its just semantics.

And seats vary in width, so moving the seat forward/backwards allows one to find a spot that matches the width of the sit bones more correctly.


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