Trek 520 seat post size
 

What is the seat post diameter on Trek 520's ?
I assumed they were all 27.2 mm
I bought an older 520 I am restoring and it has a 28.6 post now.
Maybe the previous owner used a smaller post and munched down on the clamp, anyway I am checking it out...................

I think my 83 520 is Reynolds 501. It's not 27.2., if I recall correctly.

My 520 says Reynolds 531. I found a site vintage-trek.com and am looking to see what I can find. They started making the Trek 520 touring bikes
in 1983 it looks like. Mine has cantilever brakes. So far I don't see info on the seat post diameters.

It looks like I may have a Trek 620. The catalog data says the 520 is Reynolds 501 and the 620 is 531 which is what mine is.
I think I will find the serial number and see if I can narrow it down to the year.

84 is 501 also.

I would imagine any 520-620-720 would be 27.2.

I think ALL old Treks are 27.2- but I seem to recall of a very very select few 27.4. Maybe. Or maybe I’m thinking Paramounts.

My 1990 Trek 520 was a 26.8 seatpost.