Seatpost - urgent enquiry!!

[mat777]

Hi everyone

I have a 2001 Giant XTC DS1 alloy frame which looked to take a 27.9 seatpost as the frame had a really thick seat tube wall. I have seen a 30.8 post on offer very cheaply, and upon closer inspection the the seat tube on the bike looks to be a normal thickness tube for 30.8 or .9, sleeved down like so:



My question is - is the sleeve critical to the strength of the tube? I will be running a high saddle on a long tube, so I dont want to end up bending or ovaling out the frame tube by running the larger diameter post with no sleeve. Will I be better off putting the sleeve back and waiting for a thinner tube to come along at the right price?

[syko89]

Is that not just a shim so you can run either the thinner or thicker seatpost?

Your new seatpost should have indicators on how high it can sit without putting too much stress on the frame.

Edited by syko89 on Thursday 17th January 10:33

[mat777]

syko89 said:

Is that not just a shim so you can run either the thinner or thicker seatpost?

Well thats what I'm not sure about - it doesnt say whether its a shim or whether its structurally integral... and its a £1200 frame as stake.

though on a side note, said narrower diameter of 27.9 seems a lot harder to find a post for

[gradeA]

Giant typically use a 30.9mm seatpost - DO NOT use a 30.8mm. 30.9mm posts are cheap and easy to acquire.

There will be less chance of damaging the frame by using the correct size post and not using the shim. Typical rule of thumb is that the post insertion into the frame should go at least an inch below the bottom of the top tube to seat tube junction.

Giant Connect SL 30.9mm 400mm seatpost

[mat777]

Thanks gradeA.

Does the 0.1mm make a really big difference then even if i was to put a layer of tape round the post and tighten up the clamp fully?

ETA... oops, my mistake - turns out it was a 30.9 I had been looking at all along - a 220mm SDG USA alloy post. This should be fine then if I insert it far enough?

Edited by mat777 on Thursday 17th January 10:45

[gradeA]

220mm is really short - allowing for 4" in the frame, that only allows you about 5" out of the frame, and you said you run it quite high?

Sysyem EX 400mm £13.50 delivered
Cheap, decent enough post, plenty long enough and the right size. Job done.

Giant inline for £22
Or a pukka Giant one to keep it looking nice.

[mat777]

Nuts, I've bought the 220mm one now as It had a saddle on it already and was only 9.99

The frame says min depth 80mm, I reckon I could run between 100 and 130mm in the frame as I've just checked against my other bike - that does have the saddly right up but it is a medium frame and the giant is a large, plus the other bike is ridden on the road so has the saddle high anyway, whereas on the giant i'd have it low to hang off the back when doing DH stuff. I dont often sit down on off road rides anyway so as long as I have enough length sticking out to mount a mudguard i'd be happy anyway