Going beyond seatpost limit

[pmprego]

Hi,

My bike "broke". I was going to use my wife's bike but even 1cm below my preferred saddle height, I'm already 2cm beyond the seatpost limit (is an aluminium seatpost - decatlhon bike).

I'm 70kg and will only be doing asphalt. Is it a really bad idea to go beyond the seatpost limit or... Doable for one or twice?

Thanks!!

[ms6073]

Exceeding the max extension line allows the post to exert great leverage on the seat tube which will subject the seat tube to undue stress. On a steel or alloy frame, the inner bore of the tube can deform effecting the seat post clamp's ability to properly retain the post whereas on a carbon frame, it will most likely lead to stress risers that destroy the tube's structural integrity.

[C36]

Hi,

My bike "broke". I was going to use my wife's bike but even 1cm below my preferred saddle height, I'm already 2cm beyond the seatpost limit (is an aluminium seatpost - decatlhon bike).

I'm 70kg and will only be doing asphalt. Is it a really bad idea to go beyond the seatpost limit or... Doable for one or twice?

Thanks!!

Aluminium or carbon frame? Is it bellow the top tube junction? Below the seat stays ? How much length do you have on the frame?

[ghisallo2003]

Exceeding the max extension line allows the post to exert great leverage on the seat tube which will subject the seat tube to undue stress. On a steel or alloy frame, the inner bore of the tube can deform effecting the seat post clamp's ability to properly retain the post whereas on a carbon frame, it will most likely lead to stress risers that destroy the tube's structural integrity.

I think this is a simple but safe rule, but the exact minimum insertion, I believe, depends on the frame rather than the post. Some frames clamp in a limited area: for example by having a step in tube thickness that you can feel with your finger. It is hard to imagine that the length of seat post below this area, entirely untouched by the frame, has an impact on the set up. There is furthermore not a restriction on overall seat post length, so this is not a question of leverage. On the other hand, some frames, particularly older, have a length of seat-tube above the top-tube/seat stay cluster, and it is preferable to have seat post insertion below this cluster area, regardless of the seat post minimum line.

So overall, more complicated I think than a simple line on the seat post.

[ghostinthemachine]

Just waiting for another thread in a couple of weeks...

"My wifes frame broke, do you think it was because i had the seatpin too far out."

[pmprego]

Just waiting for another thread in a couple of weeks...

"My wifes frame broke, do you think it was because i had the seatpin too far out."

I realized that I had another 27.2mm seatpost in tha house (the trainer). A regular 300mm seatpost not this 250mm decatlhon ultra-mini seatpost. Problem averted.

Nonetheless, the consensus clearly indicates it'd not be a good idea. Duly noted.

[ABogle]

You'd think the brand would be conservative with the min insert line, but it'd be you taking a chance. When it comes to torque for example I remember Dave Rome on cyclingtips saying that when some of the older BMC frames quoted a certain torque figure as the max, they literally meant the max, not recommended, not max with a buffer.

[Treptay]

I wouldn't ride it like that. Seatposts are not that expensive, better to spend some money on one, than to destroy a frame