Seatpost minimum insertion

[Moodyman]

Hello,

I've been riding one of my bikes for three years with the seat post 3-4 mm past it's minimum insertion point. It's just makes the bottom of the top tube at (TT/DT intersection) but does not pass it. Is this ok or should but a longer seatpost in? I am 100kg plus.

 

[black'n'yellow]

shouldn't you have asked this three years ago..?

 

[Chris S]

The fact that it's not snapped within the past 3 years suggests that you can get away with it. But does 3-4mm honesly make that much difference to your riding position? Shoe soles can vary in thickness by more than that. Why not drop the post down to its minimum insertion point and see if you notice any difference?

 

[accountantpete]

They usually over-engineer stuff by 1/3rd and I suspect they move the min insertion mark up by a similar margin.

The main issue I would have thought is the angle of the seat tube.

 

[black'n'yellow]

The fact that it's not snapped within the past 3 years suggests that you can get away with it. But does 3-4mm honesly make that much difference to your riding position? Shoe soles can vary in thickness by more than that. Why not drop the post down to its minimum insertion point and see if you notice any difference?

you will notice a 3mm difference...could be the difference between the right position or the wrong one.

 

[theclaud]

Get a longer seatpost. Seatpost failure injuries aren't funny.

 

[Moodyman]

Get a longer seatpost. Seatpost failure injuries aren't funny.

Yes,I'm aware that they are potentially serious, but I've long held the view like AccountPete that they built in a safety margin. I check it weekly for potential cracks - and sought advice from two reputable LBSs. Both have said the same as AP, but that I shouldn't go any higher.

And yes, 3-4 mm is very much noticeableR. It's the difference between a niggle in one knee and a perfect fit.

 

[Rob3rt]

It's not the seatpost failing you need to worry about so much as the frame giving out!

 

[Chris S]

you will notice a 3mm difference...could be the difference between the right position or the wrong one.

Images of princesses, peas and mattreses spring to mind. I'm definitely a commoner!

 

[theclaud]

Yes,I'm aware that they are potentially serious, but I've long held the view like AccountPete that they built in a safety margin. I check it weekly for potential cracks - and sought advice from two reputable LBSs. Both have said the same as AP, but that I shouldn't go any higher.

And yes, 3-4 mm is very much noticeableR. It's the difference between a niggle in one knee and a perfect fit.

I think you're right, and Rob3ert is probably right that it's the frame at risk, but then eliminating safety margins with regard to frame failure doesn't seem a very good idea. Why not just get a longer seatpost?

 

[Rob3rt]

I am not sure that you mean theclaud, I am pretty sure that a frame will also have a safety margin built in. But you should refer to the manual/manufacturer re. how much post must be within the frame because the min insertion on a seat post, may not necessarily meet the requirement of the frame set so you may already be approaching the safety margin of the frame, then if you go and do as the OP has done and raise it an additional 3-4mm you may end up outside of that margin of the frame, even if you are within the margin of the seatpost. Probably pretty rare that a seatpost's marked min insertion is off far enough to pose significant risk, but it is worth checking if you are on the limit.

The min insertion marked on the seat post refers to the minimum amount of the post that must be inserted into the frame to avoid the seatpost failing. It does not refer to the the frame failing.

If in doubt, make sure you get a seatpost long enough to sit in the frame a couple of cm lower than the bottom of the seat tube and top tube intersection (obviously you need to use some judgement here because frames have different geometries). I like to have 1/3 of the post or a bit more at least inside the frame.

If you are a weight weenie, buy a longer post, make sure your setup is as close to perfection as possible, then chop off the post so that you only have as much as the min insertion within the frame. Will achieve best fit for minimum weight.

 

[marzjennings]

It's not the seatpost failing you need to worry about so much as the frame giving out!

Having cracked a couple of frames at the seat tube/top tube I always ensure there's a couple of cm's extra seat post set in the seat tube.

I think the OP has been lucky so far nothing has broken or bent.

 

[gavintc]

I think you are mad riding with a seat post sticking past the min insertion line at 100kg - that is pushing on for 16st in old money. The frame could well crack when you least want it. Get a longer post - they are not that pricey.

 

[Moodyman]

I think you are mad riding with a seat post sticking past the min insertion line at 100kg - that is pushing on for 16st in old money. The frame could well crack when you least want it. Get a longer post - they are not that pricey.

This is why, despite assurances from two LBSs, I'm still riding in fear of
breaking the frame at the ST/TT joint.

I agree the're inexpensive when you equate to the risk of failure so will be getting a longer post.

Thanks all.

 

[mickle]

What kind of frame?
What frame material?
What diameter seat post?
What make of post?
What style of riding?
Integrated or separate seat clamp?
Lay back or in-line?
What riding position (bolt upright, flat back or somewhere in between)?
What age frame and post?
Butted seat tube?
What distance from bottom of seat post to min insert line?
What distance from top of seat tube to top of top tube ?
What arrangement seat cluster?
What tolerances seat post/seat tube?
Burr free seat tube?
Scratch free seat post?
Ever been over tightened?
Corrosion?
Front or rear slotted?
Heavy backpack?
Rack mounted rack?
Clutching at straws now?