How to stabilise the bicycle seatpost and saddle when it is all the way up? It is a standard column bicycle seat and I realised maybe I should have it raised to top (I can still stand the bicycle up using my toes) but the saddle rocks as there is no column to stop it moving and it doesn't have any other supports.

I don't want it fixed forever but still want the saddle to be stable, with minimal movement. How can I do that?


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The movement is 1 mm. I will correct this later.
Your seat post is not all the way up, it's too far up.

If you need the saddle at that height you need a longer seat post. As mentioned in comments there is usually a 'minumum insertion' point marked on the post.

Don't ride the bike with the seat post too far out of the seat tube. It's dangerous as the seat post may collapse under you and you risk damaging the top of the seat tube even is that does not happen.