Seatpost - is it a 26.2 or isn't it?

[Xesh]

The thing to remember about frames is that the top of the seat tube opens up slightly when there's no collar on it, so measuring the diameter will give you a rough idea of the seatpost size. I usually try a size up and one down to be certain.

Don't forget the manufacturing tolerances of the seatpost come into this as well. Rarely are seatposts the exact size that's printed on them. For example the Specialized S-Works Pave carbon seatpost (27.2mm diameter) has an acceptable tolerance range from 27.05mm to 27.25mm.

This means if your frame is 27.25mm and you get a seatpost that's 27.05mm it'll be slightly loose in the frame.

 

[sylus]

Yog

If you need to test and want to try I have an old 26.4 you can try for just the postage

 

[weeman_mtb]

I've got one of these NOS Saracens up the loft waiting for me to finish it, definately a 26.4mm seatpost.

 

[Yog Sothoth]

Cheers weeman, I think you're right. Saracen must've chosen an obscure diameter back in the day.

Sylus that's really good of you. How much postage and are you on paypal - I could do an instant payment?

Think I'll try the coke can approach first - as long as it's not visible it'll be fine by me. I don't want to buy a new seatpost just yet, having bought this one.

 

[sylus]

Let me know, it might be as you said trying the coke can as a shim then confirming what weeman said and if so then choosing the one you want with the now correct info.

As to the offer to send you one I have it's an old kalloy 26.4 and you could have it for nothing as it's a bit scratchy..as to the post obviously it would be by the cheapest means ..would anyone know the postage on a 2nd class posted seat tube?

 

[silverclaws]

I had that recently with a '91 Saracen frame, some berk had fitted a 25mm seat pin wrapped in bodge tape and then tightened up the cinch bolt so much it cracked the frame at the bottom of the slot.

I had an old Saracen Kalloy seat pin which should have fitted, but it didn't until I discovered the corrosion inside the tube and where the crack was, the metal was folded in. That sorted and the crack stop drilled the Kalloy 25.8mm seat pin fitted perfectly, Saracen back to Saracen. I use the 'USE' seat pin, as I always hated the lack of adjustment the Saracen Kalloy post didn't have bitd.

I also use verniers, but in that case it was a pair of inside calipers and the vernier used on that, hardly that accurate, as it is feel against spring pressure, but near enough, near as dammit, a case of go or no go and fine grade emery. But if absolute accuracy, or as near as one can get with the correct measuring equipment, well I believe the ISO standard is at 20 degrees Celsius. Remembering of course different materials expand and contract at different temperatures and rates.

But isn't that what engineering was about bitd, getting something as near as possible to work, then adjust to fit, I suppose modern production methods demand things to fit without hassle for speed of production and less reliance on skilled engineers.

 

[shedobits]

I took my newly found frame to my friendly LBS and bought what fitted best.