Find out seatpost size?
- Thread starter bigfella
- Start date
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mickle
innit
- Location
- 53.933606, -1.076131
I very strongly suspect you are looking at an inch. (25.4mm)
Depends on the tubing. For a steel seat tube in standard 28.6mm diameter in a good quality tubing like 531, the most common seatpin size should be 27.2mm, but there are other sizes like 26.8mm etc. Old alu frames like the Alan or Vitus which had seat tubes in standard 28.6mm diameter but had thicker walls used 25mm seatpins.
Big John
Guru
I've found that doing an accurate measure is virtually impossible. I always take my old seat post into the shop if I'm after a new one and say "I want one this size please". Usually works. Or........they check it against another seat tube, tell you the right size, you say you'll think about it, then buy one off the net. Now I would NEVER do a thing like that ;O)
e-rider
Banned member
- Location
- South West
From the original post it sounds like you're measuring the internal diameter of the seatpost! You should try measuring the external diameter of the seatpost or the internal diameter of the SEAT-TUBE of the frame.
bigfella said:What you take me for! The frame came with no seatpost and I used a vernier caliper to measure the internal diameter of the seat tube.
But you did say "I have used a vernier calliper to measure the internal diameter of the seatpost of my old racing bike project"
You probably meant seattube
e-rider
Banned member
- Location
- South West
so, now we have that sorted it could be either:
25.0
25.4
25.8
26.0
26.2
25.8 and 26.0 will be very difficult to find these days - maybe impossible.
25.4 is still quite common and the most likely according to your measurements
25.0
25.4
25.8
26.0
26.2
25.8 and 26.0 will be very difficult to find these days - maybe impossible.
25.4 is still quite common and the most likely according to your measurements
e-rider
Banned member
- Location
- South West
sorry, 25.8 is from the 70s and earlier.
26.0 is more recent.
26.0 is more recent.
PatrickPending
Legendary Member
- Location
- Leicester
once youve decided on trhe right size, there's a good range of diameters to be found here
http://www.edinburghbicycle.com/ebw...9&f_SortOrderID=1&f_bct=c003154c003138c003277
i've bought a couple of hard(ish) to find posts from them range from 25.2mm upwards
hope this helps
http://www.edinburghbicycle.com/ebw...9&f_SortOrderID=1&f_bct=c003154c003138c003277
i've bought a couple of hard(ish) to find posts from them range from 25.2mm upwards
hope this helps
Piemaster
Guru
- Location
- UK City of Culture
bigfella said:
Hmm. A difference of 0.3mm. There is a pencil on the desk with 0.5mm lead in it, not a lot is it? It is tricky to measure accurately internal diameters with a vernier, holding it at 90 degrees to the tube and applying the same finger pressure for each measurement. If the tube is perfectly round as well. It has been subjected to heat when being built so there may be a tad difference there.
Personally I wouldn't fret too much over what it is to that degree, as long as it goes into the seat tube with using brute force and doesn't rattle around when its in there.
Gerry Attrick
Lincolnshire Mountain Rescue Consultant
It's complicated because the seat tube without a post is unlikely to be exactly round due to the pinch bolt squeezing it out of shape. Then if you take out the pinch bolt you end up with a duff reading. Strongly suggest trying likely seat posts to get a good fit. Don't try and make do with a nearest is good enough, you will cream cracker the frame or yourself.
