Awhile back, the seat post on my bicycle bent over.
The seat post is a hollow metal tube located just underneathe the bike seat or bicycle saddle.
How do you fix this problem?
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The safest option is to just replace the seatpost. They're not too expensive. You need to match the OD exactly, and get one at least as long as the old seatpost.
If your seatpost is steel, it is possible to un-bend them using a lot of leverage and a bench vise. You need a metal tube at least 1 metre long, and 2 metres is ideal.
Note, you cannot straighten a pipe by hammering - that will squash the tube and make it out-of-round.
If your seatpost is aluminium, it is likely to crack on straightening, or even if it gets to straight will be significantly weaker. In this case, replacement is your only option.
It is possible to reinforce a seatpost by knocking in an inner pipe of suitable diameter. However this only works if the seatpost is straight or very close to straight and doesn't have a flare on the end. This also increases weight. Using a solid rod works, but doesn't add much more strength than a pipe, and adds significantly more weight.
Measure the diameter (also known as the "width") of the seat post or saddle pipe.
Calipers can be used for measuring diameters.
Order stainless steel round bar cut to length, from an internet based web store or retailer.
Stainless steel round bar is solid metal in the middle. Solid metal cylinders do not bend as easily as hollow opened ended tubes which are full of air.
Slide the solid steel round bar into the bicycle frame where the old seat post used to be.
A hole might need to be drilled on a drill press. Put the metal rod on top of a recta gulair block with a v-shaoed notch cut into the block in order to hold the round bar stationary while drilling the hole.
The hole would be for seat saddles which have a bolt passing though the inside of the seat post.
Seats with a clamp work better than seats which have a bolt passing though the seat post.
I replaced the seat post on a shwin town and country adult tricycle with solid steel round bar. The solid steel round bar works.