seat post steel frame

[harrybarry]

Just before i order a seat post for my seat framed old hydrid i want to check the size with you lads in the know, the bike came with out one.

i have measured the frame and it seems to be 25 mm diameter does that sound right as all the posts i see on evil bay are 31.5 or 27.5.

Cheers chaps

 

[upsidedown]

Have a look on www.sheldonbrown.com in the seatpost entry in the glossary. There's a database of seatpost sizes for different manufacturers.

 

[PpPete]

This Ebay seller has a whole range of weird sizes at reasonable prices:
http://stores.ebay.co.uk/BANKRUPT-SURPLUS-BIKES-BITS?_rdc=1
I've had a couple of 26.4mm ones off him recently for rebuilds on kid's bikes.

The trouble with measuring is that you need to be accurate to 0.2 mm ! This is difficult enough if you take an old seat post out to measure, the only way to be sure is with a vernier caliper (or a digital one). The seat tube on an old steel hybrid is unlikely to be perfectly round so you need to take several measurements with a caliper and average them.

Alternatively I believe LBS often have a tool to check ....

 

[tyred]

Definitely best to take it to a shop. It may be that someone has overtightened the clamp in the past, squeezing the top of the seat tube. It may be worthwhile to spread it a little with a large flat screwdriver. The best way of finding one to fit is to try it and a decent bike shop should have something in most common sizes. Just be careful if testing with one of the older type plain pipe seat posts as it can drop into the frame and you will have good fun getting it out again.

25mm would be unusual (i had great fun and games getting a 25mm one for my 1960s Batavus, ended up buying one from German ebay). I expect you have a 1" seatpost, common in the more budget steel frames like old 3 speeds and older MTBs. A basic 1" chromed steel seatpost should be easy to find for a few quid.

If you do end up with one slightly too small, it's not the end of the world as a old coke tin makes an excellent and cheap shim but never force a too large post into the frame.