Help I need a loooong seatpost

[Over The Hill]

I have a cheap and cheerful folding bike that I use for the last mile or so of my commute. It is by Salcano and is Alloy framed, Great for the job, got it cheap on Ebay
Here is a picture of one like it on Ebay now.
http://cgi.ebay.co.uk/SALCANO-EASY-...ryZ33503QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Problem I have is that I cannot get the saddle high enough to be comfortable as the stem is too short. It has a standard 350 long 27.2 dia stem. I am only 5' 9" and even with the stem out too much I feel it needs a good 50mm more. As the frame is so short it needs more reach than a standard seatpost.
So I have been trying to get a longer seatpost but been having no luck. All I really want is a 450 long seatpost and thought of a budget of up to £20 should get something. Alloy if I can but would be happy with anything that size.
LBS1 Looked blankly at me.
LBS2 Said i could not fit a longer seatpost as I would break the frame (but could not tell me how he got to this conclusion) I can see I am creating a longer lever but as I am only 12 stone I think it is within the frames limits.
Halfords not worth bothering with.
On line Ebay has nothing and Wiggle Evans Parker and Ribble all only go up to 400 long.
After that I am stuck!

Firstly can anyone see any reason why I should not put a longer seatpost on the bike and assuming it is not a problem in theory, does anyone know where i can get a 450 long seatpost.

 

[ufkacbln]

400 mm is the longest you will get from a main dealer.

What is the diameter you require?

If compatible then you might gain from looking at some of the Folding bike catalogues such as Dahon. Some unicycles also have long posts.

Unfortunately these posts tend to be wider (30 - 34 mm) then the 27.2 or similar that most bikes use.

 

[Steve Austin]

This comes up quite a lot with some MTB's. The longest post that regularly get5 suggested is a Roox, at 410. any longer and they start putting too much leverage on the frame and you're putting to much tension on the top weld. not a good idea

 

[Keith Oates]

If you really want to try out a longer seat post go to a hardware store and buy a section of Stainlees Steel pipe of the same OD. A freind of mine did that in China and the bike is still going as far as I know!!!!!!!!!!!!!!!!!!!!!!