Steel frame, Alloy seatpost - minimum insertion?

[badgerjockey]

I have a steel road bike - Genesis Equilibrium 20, which was bought second hand after someone custom built it.

It looks like they used their old Ritchey V2 seatpost in it which had approx the bottom 5cm cut off it.

I also discovered an ever so slight bulging of the seat tube on the frame an inch or two down from the top tube-seatstay junction. Is this normal or cause for worry?

They way I have the seatpost setup at the moment gives me an insertion into the seatube of about 9.5cm.

Any thoughts would be great.

H

 

[TheDoctor]

Most seatposts have a minimum insertion marked on them - usually about 7cm IIRC.
9.5 cm inserted should be more than enough.
About the bulge - it *could* be that the last owner had a too-short post in and has damaged the tube, but since you're now using a longer seat post then you won't be stressing the same point. Keep an eye on it - if the bulge turns into a crack or a split then that's bad.
Fortunately steel tends to give way fairly gracefully, so it won't just snap.

 

[Globalti]

An even bulge in a steel tube isn't too much of a stress riser, some tubes are deliberately "dented" to create space for the wheel. Don't know the engineering term for this.

 

[TheDoctor]

Me neither.
Even a crack isn't catastrophic - a hole drilled at each end will stop it propagating.

 

[badgerjockey]

OK, just fiddled with the seatpost and now I have 8.5cm insertion, about 2.5-3cm of it is below the bottom of the top tube-seatstay junction. This is the exact same place as where the bulge is.

Am I jeopardising my frame by continuing with this? Or should I just man up and shell out for a seatpost that someone hasn't taken a hacksaw to?