It could be the shape of the foam. On a bike seat, it tapers down the sides from the wide section quite differently to a unicycle seat- we tend to stick on a flat slab of foam and think that’s all there is to it.
Do you think if the rear end of a bicycle seat, matched with the front end of a unicycle seat, will result in your ischial tuberosities being supported by the wide section?
I think bike seats support your sit bones because you’re in more-or-less a sitting position, bent at the waist. The position of the handlebars and pedals, both forward of the seat, cause this.
On a uni, you’re pretty much in a standing position with pedals directly below you. A handlebar can help get you leaning forward, but you have to go to pretty far extremes to approximate a bike posture, and it only works for road unis.
Moving the seatpost doesn’t change anything except structural details of how you build things; your butt is going to end up in the exact same position relative to the pedals and handlebar. If you move the seatpost back, when you start riding it will have to rotate forward until the seat is in the same place as before (or else you wouldn’t be balanced). Putting the seatpost right under your butt might make for a more robust seat with less flex at the connection, but flex might even be a good thing for suspension purposes.
So far the best I’ve been able to do for offroad is a less padded, flatter seat with a modest handlebar extension to get a little lean, with my butt pressed backwards into the seat a little, instead of straight down. But it’s not that great, especially on easier trails where I spend s lot of time sitting.
Does everyone here use bicycle shorts? I was worried about my rear the first couple days I rode, but then pulled out my Pearle Izumi bib shorts and haven’t thought much about the seat since.
anyone tried one of these on a uni?
I have one on my hybrid bike and I like it but I havent been brave enough to fit it to the uni yet
That Spiderflex lacks anything between your legs. From a comfort viewpoint, that’s nice.
Ive only been riding 8 weeks, but I couldn’t mount with a saddle like that as I grip mine between my thighs to freemount. Also, wouldn’t the seatpost fall down when you stood up on the pedals to add power?
Don’t see me feeling confident enough to try anything like that on my Uni anytime soon 
Bicycle shorts, two pairs here (for longer rides) on my street unis.
One pair for the normal rounds, pair of jeans for commuting (only few hundred meters on the uni) or walking the dog (5 km round) on my Muni.
Greeting
Byc
The reviews of the Spiderflex and the Hobson seats read almost the same. “Hands must stay on handlebars to maintain control” This may be an issue on a uni. Other than that small item:p, reviews are positive.
Funny you should ask…cuz I spent most of this morning widening one of my ghetto seats using minicell foam. I’ll post some pics later this weekend, going for a long ride tomorrow if it warms up.
Oh, and since I’m married to an engineer, I sat down with here and discussed whether moving the saddle forward on the post would change anything and she said “YES” 
A shortened seat, with a more severe transition from the seating area to waist, like a comfort bike seat but with a wider and continuous width waist vs a dumbell shape. I think we need a waist for support, but we certainly don’t need as much as we have, maybe half as long, and a rail mount so we can adjust the trim of the saddle…
If I can find a donor bike seat that is stiff enough, I’d like to try adding additional foam to the waist and see if I can make a bike seat usable, then build a handlebar mount that attaches to the rails. Adding width to the waist and nose on a bike seat is probably more resilient than adding width to the sit area of a uni seat.
I ride with just a plastic handle on my MUni and commuting Unis a lot, and find I’m usually quite bent over, definitely not an upright position.
Try showing her the pics I posted at Flatfish NNC CF Base - #40 by aracer and see what she thinks - I am also an engineer 
I did and I made some drawings while she looked on, so when in doubt, try it out, which is what I did
Seriously, there is nothing like testing a theory, because we are often misled by what we have learned, make assumptions, etc…
When I found myself sitting on the waist of my flat seats and had to use an upturned saddle to push my pelvis back on the seat, I realized that there was more to the formula than simply flattening a seat.
Today, I built up the waist of a seat so the wider portion of the seat was carried forward. I found that I was now sitting on padding and balancing in the sweet spot; the waist. Essentially I had moved my pelvis forward on the seat without relying on an upturned saddle to hold me in place.
Now whether a forward shifted seat post or a rearers shifted seat base mount would do the same, that’s the harder theory to test…so I’m starting work on bike seats tomorrow…
But first things first: Can you all measure the distance between your IT (sit bones)?
I measured mine at 110-115mm. I wonder if this is wider than average, which would explain why some folks are more comfortable on a stock seat. I’m not a huge guy by any means, but I have some good birthing hips 
The KH Freeride base is 135mm wide, the Freeride foam is 150mm wide (note that it rounds over the edge at ~ 125mm.
I measured a bunch of mountain bike seats, all had a similar width to the KH seat, ~150mm.
A “comfort seat” we have mounted on a spin bike was a whopping 190mm wide (rounding over at ~ 170mm) and it was so much more comfortable to sit on when I was upright, whereas the bike seats felt a lot like a unicycle seat; just wide enough to work, but not wide enough to be comfortable.
It appears that my “arse bones” are too wide for a uni seat. Even with flat foam I only have ~10mm of foam on either side, which is why it feels like my ITs are sitting on edges of the seat; because they are! The problem is even worse when I sit on the waist of the seat, because then my ITs are not supported at all!!
I wonder if the reason uni seats are narrow, other than mimicing bike seats, is so that it’s easier to dismount to the rear? Not that adding 40mm would make a huge difference, but it would be harder to get your legs around the seat as you dismount; I tend to get off forward, so not a problem for me
I like playing with gear, esp making new stuff out of old stuff, it’s like McGuyver or something
@Aracer, I figured out why we disagree:
Your diagrams are correct IF I want to ride a flat seat with an upturned nose, in which case I can make the flat seat work, BUT if I want to run a flat seat without an upturned nose, then I need a way to move the seat forward or move the wider portion of the seat forward.
No - you’re still missing the point. My pictures show how rotating the seat so that the nose is pointed up is exactly the same as moving it forwards on the seatpost.
Or to put it another way, moving a seat forwards on the seatpost is exactly the same as rotating the nose upwards.
I could go and test that out on my uni, but I wouldn’t really learn anything, as my pictures explain it just as well.
Note that I’m not suggesting that you turn the nose of the saddle up in order to ride with an upturned nose, I’m suggesting you turn the nose of the saddle up in order to move it (the wider part) forwards. You try it and see with your uni if you don’t believe the pictures - turn the nose up on the saddle, and then rotate the whole uni until the saddle is flat again.
Or get your wife to look at my pictures and explanation again if you’ll trust her rather than me, as either she didn’t understand the point, or you didn’t understand what she told you.
I realize what you’re saying, and in theory the upturned nose should allow the seat to flatten out as the frame angles forward, but in reality it does not work that way.
“Try it?”
Dude, I have been trying it, that’s what this thread is about!
I now have two ghetto flat seats and one Flatfish, three different foam set ups:
Flatfish + Nimbus Gel
Ghetto + Freeride “cut down”
Ghetto + Nimbus flat with minicell wings and a 1/2" minicell top sheet.
The nicest feeling seat is the Nimbus Gel, but it sufferes from being too narrow
The Ghetto Freeride has been my go to seat for the past month, it has suffered a multitude of modifications and is now at a “best stop now” situation.
The Ghetto minicell seat I built today and will ride tomorrow, more once I get it out of the trail.
I was looking at bike seats on line to get an idea of what is out there, so for starters I measured my “sit bone” spacing, this is the seperation between your ITs when in your “riding position”.
One of the interesting comments I read on the Specialized tech page was that an upright position increases the seperation between you ITs, so a person who has medium spacing 110-130mm will go up from a 145mm “medium width seat” to a 155mm “wide width seat”.
My spacing is considered wide, so I’d go up to an “extra wide seat” which is >155mm. An extra wide seat is your basic “big booty” recreation seat that comes on upright bikes :o
As if I didn’t already have enough to be embarrased about, now I’m gay because I ride a unicycle and fat because I use a extra wide seat 
I’m looking at the Specialized seats because they come in more than one width, so I can compare how they feel… and if I can try them out for size on my Thomson seat posts, the only remaining issue is mounting a handle.
I’m gonna start with bolting a piece of handle bar between the seat rails, then depending on how much flex I get with that set up, next I’m looking at getting an adjustable length stoker stem.
This is so much fun! And to think it all started with a flatfish 
That quote is signature worthy.
quoted
Those are pretty good pics! The one with the goofy frame does a nice job showing how the seat-to-wheel connection details don’t much matter.
… and I’m an engineer, too! What a nerdy bunch we are.
In which case, moving the seat (or at least the wide part) forwards isn’t going to help you, as you’ll end up with exactly the same upturned nose as if you’d turned the nose up - just with a different angle of frame. Your problem isn’t having a seat with the wide part in the right place, but that you’re not actually sitting on the seat in the way you think you are.
Umm, so when I reach under my arse and mark the points where I sit, I’m not actually doing that correctly?
Okay, pray tell how I would do it correctly?
Look, it ain’t rocket science, I can feel where I’m sitting, I can place my fingers in the exact locations where my sit bones are “sitting”, and you’re saying what?
My sit bones want to be approx 2" behind the seat post, so my plan is to build a seat pad or use a bike seat that places the widest area of the padding at this point.
The only problem I can see is that my pelvis (sit bones) will continue to creep forward as I move the padding forward, in which case I will have to use padding or nose tilting to hold pmy pelvis back.
I should note that ride with a handle and use it for support 99% of the time.
Well, it turns out that unicycle seats are designed differently than bicycle seats for a good reason
Using a Thomson seat post, I installed a variety of seats, from a “racing road model” all the way up to an “upright wide body” seat. What I found was that the wider seats were more comfortable than the narrower seats, but this was due more to the width and padding in the waist and nose. Ultimately, to maximize comfort, I had to tilt the bike seats upwards as I have done with my flat seats, even then the bike seat was not even close to as comfortable as my flat seats.
In a sense, the following comment by Aracer is true: "… you’re not actually sitting on the seat in the way you think you are. "
We may be sitting on our ischial tuberosities, but ONLY because the waist of the seat keeps us sitting there, otherwise our pelvis will roll forward, the unicycle will rotate backwards, and we end up sitting on our “taint”. This is why uni seats are designed with a wide padded waist and an upturned nose.
The reason a bicyclist can sit the way they do, on their ischial tuberosities, is because they can rest (and resist gravity) by using bars. A touring unicyclist could in theory adopt the same body position by using “bicycle like” bars, but the unicycle will still rotate under the pelvis, so for unicyclists a bicycle seat is an imperfect match.
There is some opportunity for updating the classic shape of the unicycle seat, but the emphasis might be better placed on redesigning the waist and nose to support and provide comfort at the taint than trying to place the rider more on their ischial tuberosities. Like Gizmo suggested, the wide rear of the seat is probably not necessary.
At this point the Flatfish with a semi flat Nimbus Gel pad is my preferred seat, I run it at ~8-10 degrees nose up, it is relatively comfortable (better than any standard uni seat, not as good as a bike seat on a bike).
One thought I had is that a high hand position might also work to change the body posture and take some pressure off the taint area, this is something I’m working on with my next generation of handles.