Minimum seat post insertion

[Plum Hill]

I've been using a Campy 250mm carbon seat post in a Serotta carbon HSG. The post is installed with the minimum amount of insertion, 60mm.
While at the LBS for some fit work, they pulled the seat post. One owner squaked there wasn't enough post in the frame. The other said it was OK on my lugged frame but would have cracked a typical molded carbon frame.
Any learned opinions?
Tipping the scale in the low 190s.

[ultraman6970]

Depends a lot of the seatpost, there is a reason why the seatposts come with insertion marks, the reason for the insertion mark, just because i have seen this , is because the seatpost rocks back and forth, and if it goes too high above the insertion marks you risk to crack the bicycle seat tube.

Honestly never seen an aluminum seat post to crack because was too high above the insertion mark, but steel frames yes, seen quite a few to crack.

With carbon seatposts the situation changes a little bit tho, material is different and the mark is there more than nothing because you really can crack the seatpost if too high. Never seen an steel frame to crack the seat tube because the carbon seatpost is above the insertion marks, but seen carbon frames developing cracks due to a seatpost (carbon or aluminum) that is too high due to the rocking.

[oldpotatoe]

I've been using a Campy 250mm carbon seat post in a Serotta carbon HSG. The post is installed with the minimum amount of insertion, 60mm.
While at the LBS for some fit work, they pulled the seat post. One owner squaked there wasn't enough post in the frame. The other said it was OK on my lugged frame but would have cracked a typical molded carbon frame.
Any learned opinions?
Tipping the scale in the low 190s.

Does the frame have an external seat post clamp? If it does, turn it around 180 degrees or get a Campagnolo one.

[EricEstlund]

Minimum insertion marks are based on the diameter and length of the post and are the minimin insertion the CPSC deems safe for the post.

Minimum insertion for the frame is a different matter in application. It's common practice to run the post at least past the depth of the top tube- for frames with extended seat collars this may be well past the posts marked minimum insertion.

[SoCalSteve]

Doesn't tapered wall seatposts play into this equation as well? Thinner in the middle to save weight and clamping insertion marks are very important to pay attention to as that where the material is built up?

[CampyorBust]

I always thought the rule of thumb on lugged frames was that the seat post should at the very least clear the bottom of the seat tube lug, with ideally 1cm or more. I have never had frame damage with my Aero Campy seat post which regrettably are almost always just a hair too short for my frames. If I don't clear the lug by at least 1cm I will go to a longer seat post, I just don't want to risk it. Riding my Campy carbon post well within the insertion requirements, no problems but I am lighter than you.

[Plum Hill]

Hard to put into words, but seat post does extend past the lug. Bottom of post is a bit more than one centimeter past the top tube.
I may pick up an Enve straight post as we're trying to get more weight on the front wheel. It's definitely long enough.

Thanks to everyone.

[doomridesout]

Resurrecting a dead thread to ask a similar question: I picked up a really short Eriksen Sweetpost here on the forum for my Ti Hampsten-- it's got no min. insert and I'm not worried about the post, but I'm wanting to make sure that I've got enough in the frame. The post juuuuuust barely clears the bottom of the top tube/seat tube weld (by about 5mm). There's about 6 cm of the post in the frame below the clamp. There's only a fistful of post showing and I only weigh 140. Am I overthinking this? I would feel a lot better if I had 2 cm of post below the bottom of the top tube weld, but it only clears that junction by a tiny bit. What sayeth the peanut gallery?

[apple]

Fine by me. I had a 330mm seatpost that I ran above the "minimum insertion mark" for years. Technically I needed a 350 to get below the mark, but the 330 allowed me to get the bottom of the seatpost *just* below the bottom of where the top tube met the seat tube.

This has always been the standard as far as I recall, as long as the bottom of the seatpost is below the bottom of the top tube where it welds into the seat tube, you're good. 1/2cm should be fine, as it was for me for years until I got a 350mm seatpost.

[pdmtong]

The post juuuuuust barely clears the bottom of the top tube/seat tube weld (by about 5mm). There's about 6 cm of the post in the frame below the clamp. There's only a fistful of post showing and I only weigh 140. Am I overthinking this? I would feel a lot better if I had 2 cm of post below the bottom of the top tube weld, but it only clears that junction by a tiny bit. What sayeth the peanut gallery?

with 6cm inserted, 5mm below the bottom of the top tube, and you at 140#s I would say fine.

if you were 180 I would say not fine, and want the added 2cm you speak of.

it also depends on how heavy you ride. take care to avoid hard shots while seated. duh!

[oldpotatoe]

Resurrecting a dead thread to ask a similar question: I picked up a really short Eriksen Sweetpost here on the forum for my Ti Hampsten-- it's got no min. insert and I'm not worried about the post, but I'm wanting to make sure that I've got enough in the frame. The post juuuuuust barely clears the bottom of the top tube/seat tube weld (by about 5mm). There's about 6 cm of the post in the frame below the clamp. There's only a fistful of post showing and I only weigh 140. Am I overthinking this? I would feel a lot better if I had 2 cm of post below the bottom of the top tube weld, but it only clears that junction by a tiny bit. What sayeth the peanut gallery?

'General' rule of thumb-twice the width of the top tube below the top tube, seat tube weld.

"Probably' be fine but it would be a shame to hurt a bike frame for a 'pre owned' seat post.

[Peter P.]

Not enough. Buy a proper length post and alleviate all worry.

[pdmtong]

Your situation is in the gray area. It probably would be ok but who truly knows?

5mm isn't much. What if your measure is slightly off? Had you said the post bottom is even with the tubes lower plane I would say that's cutting it too close for me. You need that leverage agains the TT to not torque on the frame

Ride softly at 140#s swings me towards probably

It's the Internet. The only way to ride without thought is to have a longer post that's buried further