I've cut my current giant seatpost down in my '07 trance so not sure whqt length it was before and I am currently looking at a 2nd hand thomson (in-line not layback too) seatpost.
I reckon that at normal saddle up position I'd have about 8cm left in the frame. This comes out at the bottom of the toptube/seat tube join.
http://www.giant-bicycles.com/_upload_us/bikes/models/zooms/2007/Trance-1.jpg
I'd also have to push the saddle rearwards on the rails.
£25 posted…

Its not going to be far down into the frame enough is it?

No! 100mm at least I would say, but if you're a really light rider then you could take a chance, what does manufacturer say, be guided by them.

giant say 80mm

Bottom of seatpost should be below seattube/toptube junction as a guide.

If your leaving only 8cm of a 410mm post in the frame then maybe the frame is a bit small. 😕

I usually take mine out completely.

If your leaving only 8cm of a 410mm post in the frame then maybe the frame is a bit small.

There's no 'maybe' about it…….
But he doesn't say how long his post is!

Bit late getting back to this thread! post is 280mm long – not 410mm. hence the £25 posted.
interesting that giant say 80mm to leave it. makes sense with the frame and where 80mm takes you down to.
maybe i will go for it!