GT Seatpost sizing and seat tube bolt sourcing

[damiena]

Hi

Can someone advise me please on seatpost sizing?

I have I believe a 1997 GT Karakoram frame. It has 1997 stamped on the forks and I presume these are original. I looked up the original spec in 1997 and it says a 26.8mm seatpost.

I have measured the internal diameter of the seat tube at 29mm (not with calipers). This feels slightly too big for a 26.8mm seatpost - how much will the seat tube bolt clamp in the tube? Does a 26.8mm post sound right?

Second question - The tube has an integrated clamp, I've yet to find a bolt that will fit through it as most bolts appear to be 8mm and it looks like I need a 6mm bolt. Any advice on a suitable bolt I should be looking for?



TIA
Damien

 

[hamster]

Seatpost has to be MAX 0.2mm smaller than the seat tube inside diameter. Ideally the seat tube slides in smoothly like a piston - with a nice clean seat tube like yours, that's what you should aim for.
The best way to check is with a conical seat tube gauge; GOOD bike shops will have one. You can try to measure with a vernier, but it's still a bit on the trial and error side.

 

[damiena]

Seatpost has to be MAX 0.2mm smaller than the seat tube inside diameter. Ideally the seat tube slides in smoothly like a piston - with a nice clean seat tube like yours, that's what you should aim for.
The best way to check is with a conical seat tube gauge; GOOD bike shops will have one. You can try to measure with a vernier, but it's still a bit on the trial and error side.

Many thanks for the advice, much appreciated.

 

[CraigB5]

Re:

Watching with interest as I would also like to know where replacement bolts may be sourced for a ‘99 Zaskar with integral clamp.

 

[d8mok]

Re: Re:

Watching with interest as I would also like to know where replacement bolts may be sourced for a ‘99 Zaskar with integral clamp.

I’ve had this issue a couple of times on Zaskars (98+) and ended up buying a cheap steel GT full bike to split and use the bolt . Extreme I know but you end up in profit and get the bolt.

 

[fast & curious]

Similar question: my 94 GT Tequesta has a 26.8mm seat post, however I struggle to tighten the clamp. I seem to loose a millimeter height here and there with every trip. Shall I try 27.2?

Also would be pretty handy as there are some dropper posts in 27.2. (I am pretty tall. My Tequesta is a 22", the largest GT steel frame size. Yet the seat post is about 20cm out ...)