seat pin sizes

cartesr

Hi
just doing a fixed conversion with a second hand road frame, not sure of the seat pin size required so tried a campag one from my Ribble and it doesnt fit. The Ribble is roughly 27.2. I measured the other frame with some calipers and its 26.76 or 26.52 depending om where I put the calipers inside. So Im confused should I be looking for a 26mm seat pin or 25mm. Anybody out there any idea what size is required

cheers

nicklouse

and what is the make and modle and year of your frame.

seat posts have a number of sizes changing by 0.2mm at each step.

so more info or LBS time for a measurement.

cartesr

Hi thanks for your response

the frame is italian ive been told its a Barechi and was made in the early 90's its made fom cloumbus aelle tubing, thats all I know Im afraid

cheers

Monty Dog

There are countless sizes of seatpost sizes for steel frames - knowing the type of tubeset can help - 27.2, 27.0 and 26.4 are probably the most popular. From what you say, sounds like a 26.4mm is what you need - your LBS may have a tapered seatpost gauge, which has a series of graduated dimensions - stick it in the frame and go for the dimension just below the seat collar. Alternatively, go for a 25mm post and use a shim from the likes of USE - means you never have to worry about the post getting stuck either.

cartesr

thanks very much for the advice ill ask my lbs if they do have a measuring device , if not ill get a 26.4

regards

gundersen

then you will need a coke can

if i remember correctly columbus aelle is 26.8

cartesr

cheers for the advice

Monty Dog

If you buy a 26.8 post, which will have a nominal diamter of 26.5 - 26.6mm, given your dimensions it might be a bit of a squeeze. Before you trash a new post, may be worth getting your LBS to check the size and perhaps running a reamer down the tube to get it 'round' and the right size.

cartesr

Hi

Im very confused now, so a 26.8 seat pin isnt 26.8 then?

I tried the seat pin from my MTB last night which is 26.4 (stated on the pin) and they is a fair amount of play when inserted in. When tighten up its easily koved from side to side
but doesnt slide down on its own accord but I guess 26.4 isnt really 26.4.

I think Im going to have to take it to my lbs,

again thanks for your help

nicklouse

think about it. if they were exactly the same size they would not fit together.

there is a certain tolerance to allow fit. the pin will be, to use easy numbers, 10mm+0-0,1 and the teat tube 10mm+0,1-0 as an example. i dont actually know what the real tollerances are.

Monty Dog

The diameter refers to the actual internal diameter of the frame tube - there needs to be a small clearance between the post and the tube for it to slide easily in position - for a seat post this is probably about 0.1mm to give a little room for clamping and to ensure you can get it out again. Any difference bigger than about 0.25mm is considered a 'free' fit. As said, you'd be better off going to your LBS to check the diameter and perhaps getting them to run a reamer down it - steel tubes in particular can become internally corroded which can make them smaller in diameter and can jam a post.