Hi.
When I’m riding my 29", I lean to the right. When looking down, I tend to see the right side of my wheel.
I turned my seatpost front to back and rode my unicycle so the frame is in the other direction (and my pedals unscrew 
), I noticed I leant to the left and I saw the left side of my wheel when looking down, so I think my problem doesn’t come from the seatpost nor the saddle. If it was the case, I would be leaning in the same direction.
I’m not sure how to proceed in order to determine where does this issue come from, there is nothing wrong when I look at my unicycle, no deformation at all, at least to the naked eyes.
Any idea? 
I can take some pictures if that helps.
Is wheel exactly in the center of the frame?
To check frame, you can try to remove wheel and seatpost, so you can put it standing on the floor. Place next to wall, mark positions of legs and top tube, then turn it 180 degrees and check again.
Just an idea, probably you can do something similar without taking uni apart.
There is 1 to 2mm difference between the rim and each frame “arm”, the distance is different if I turn the wheel a little but it is never inverted, so there is somewhere 1 to 2mm asymmetry. Could be the frame. Do you think such a little difference could create such a loss of balance if I’m sit higher on the seat.
I take a picture and use photoshop rulers to see if there is asymmetry (not much), sorry for the huge picture :
Picture without the rulers: http://i.imgur.com/WvBreEP.jpg
Any thought ?
That’s pretty dead on. 1-2mm shouldn’t even be noticeable with a tire that wide. The tire itself could almost have that much variation in it. do you happen to be riding on a cambered road? Try riding down a path where you feel like you’re off center, then turn around and ride back down the same path backwards. Do you feel the same thing? I think you covered that with the saddle flop, but if you did and out, then changed the saddle and rode back, you would experience the same thing.
There are so many little things that can throw off your balance, especially when you are a new rider. One thing to pay attention to is your foot placement. make sure that your feet are spaced equally on the pedals. If one foot is further out than the other it can make the unicycle feel lopsided.
Hi,
Thank you for your replies. 
I don’t consider myself as a “new” rider as I’ve ridden my 29" for about 2 years before this issue came up.
I tried another thing: I flipped the wheel front to back (wheel + cranks & pedals) to see if the issue came from lower than the frame. I tried and leaned to the left. I rode back on the same road part and I was still leaning to the left. I noticed that my pedals were unscrewing (of course, I flipped the wheel) so I turned my seat front to back (so the pedals would be on the right side) and came home… Leaning to the right.
So I guess the issue comes from somewhere around the wheel. The next step will be swapping the cranks (still riding the unicycle in the right direction!) to see if it’s coming from the wheel itself. So frustrating.
one other hunch, try changing the pressure of the tire. Also check the bead of the tire. (looks like it’s fine from the picture, but I’m grasping at straws at this point) I’ve only had it happen on a bike once, but the bead slipped into the rim when I hit a bump, which very slightly collapsed that side of the tire. Good luck! hopefully with enough poking you’ll figure it out. I would be interested to hear back and see what you find.
