How much seat post is too much seat post?

[CassidyAce]

My '96 Palisades Trail (alloy frame) has been a faithful servant; it was on winter commuting duties last week and I noticed nasty creaking/cracking noises as I shifted my weight on the saddle. It's got 26cm of exposed seat post (collar to rails), so there should be about 14cm of seat post in the seat tube, and I'm wondering if that leverage is stressing the frame. I'm not overweight, so that's not the problem, and I can manually reproduce the effect by pushing down on the front a rear of the saddle. I can see a little flex in the seat post and perhaps a little in the seat tube. I have tried a different seat post and a different saddle, and the noise remains. I cannot see any cracks, though. Yet.

As I said, the bike has been a faithful servant, so I don't want to break it. So, are these noises the product of acceptable flex or a sign that I should pass the bike on to a shorter rider before I damage it? It is twenty-five year-old alloy, after all. Anyone got any ideas?

 

[jimo746]

Mike Muz would be the person to ask regarding excessive seatpost length

It could be the saddle rails or clamp atop the seatpost making the noise.
I'd take it all apart, clean, lubricate, and carry on.
I don't think 26cm of exposed seatpost is excessive tbh.

 

[CassidyAce]

26cm is fine in the Rockhopper but that's a steel frame. I did clean the post and saddle rails: no change. I'll have a look at the clamp, though. Thank you.

 

[longun]

Itll be fine,as long as the min insertion mark is around the seatstay and top tube junctions the risk is low imho

 

[mk one]

As long as the post is in far enough, below the bottom of the top tube and seat stay junctions it should be fine. The creaking could be a number of things, though the cracking noises i would be more concerned with. If they are still there with a different post/saddle in i would have a really close look at the frame.

 

[CassidyAce]

The min insertion mark will be near the bottom of the junction of the seat tube and top tube, and there should be about 9 or 10cm of seat post below that. However, the creaking and cracking noises have persisted with a brand new seat post and change of saddle. There is a smidgen of visible fore and aft movement in the seat post (the new one) when weight is applied to the front and rear of the saddle but there is no downward slippage. I'll check the frame more carefully for hairline cracks when the light's good; I haven't noticed anything yet. My concern is that there is nothing visible yet but that there might be soon. That would be a shame: I owe the bike more than it owes me.

 

[clubby]

Seat clamp or welded on tabs? If separate seat clamp, do you have another you could try?

 

[CassidyAce]

Tabs tightened with a QR pin. I gave it a good look over this evening. No cracks: . A surprising amount of flex in the alloy seat post. I say 'surprising' but I've never really tried to look at how much my seat posts flex. I assumed that a 30mm diameter alloy tube that's strong enough to sit on probably wouldn't flex visibly. Anyhow, it does but silently, so: . However, there was a little bit of scope for tightening both the seat post QR pin and the saddle rail clamp without using unwise force, so I've tried those and I'll test ride it tomorrow. If that sorts it out, I'll feel like an idiot but a happy idiot.

 

[mk one]

Give the inside of the seat tube a clean/wipe out too.

 

[CassidyAce]

Give the inside of the seat tube a clean/wipe out too.

Good point.