Seat post woes 27.2 too big - 27.0 too small!
Posted: 15 Nov 2010, 5:35pm
Hi, I have recently brought what I think is a mid eighties steel road frame with reynolds 531c main frame tubing which I am in the process of building up with many of the old parts for a previous 531 galaxy frame which had to be retired after it developed a cracked down tube.
I had been using a 27.0 seat post in the old 531 frame which fitted well/worked fine. I assumed/hoped I would be able to swap the same seatpost over to the new frame but the fit is too loose in the 531c frame. Even with the seat post bolt well tightened up with the seat post slot sides nearly touching when tightened, I found on the first test ride that the my old 27.0 post was twisting about in the new 531c frame. When not riding the bike and with the seat post clamp undone, you can feel some play in the fit of the 27.0 post in the frame even with the post (which is quite long at 400mm x 27.0) is pushed all the way down into the frame (it is 400mm long). I assumed that I therefore needed a 27.2 seat post and purchased another USE 400mm x 27.2 post (cheap at £16.00 but have used these posts of several other bikes and they have been problem free) but now find that this post wont' go into the seat tube past the first 4cm or so even with a good film of grease and having cleaned up the inside of the seat tube as far as I can.
It seems that I actually probably need a post of about 27.1 but I don't think this size is made? Do you think I need to get the seat tube "cleaned up" at a bike shop? I gather good shops often have some kind of special tool that they can use to clean up the inside of the seat tube which might help the 27.2 to fit better/to slide down further as it should or could I perhaps alternatively purchase a seat post shim to use with the 27.0 post which would add the equivalent of .1mm diameter that I seem to need?
From googling about most info I can find seems to suggest that the 531c seat post diameter should be 27.2 but there is not way that the 27.2 post that I have will fit in as it is and by feeling down the tube as far as I can with fingers it seems very smooth inside with no rust. I have measured the diameter of both the posts that I have (one stamped 27.0 and the other 27.2) with callipers and taken several readings and averaged them both out - the 27.2 post actually measures on average 27.098, the 27.0 post averages 26.27 which makes the actual difference in diameter between the two 0.828mm. I thought if I could find a shim of that would add about .4mm diameter this would hopefully be a midway point that would work/hold tight. In googling for shims, I see that some are designed to make 27.2 seat posts "bigger", the next size down seem to be shims that start at 25.00 and go up in increments of 0.2 mm or so and therefore was assuming that if I buy a shim sized 25.0 - 25.4mm this might work? Any advice/anyone else's past experiences of getting round this as cheaply as possible would be much appreciated as this is now the last part I need to fit before I can start using the bike. I did wonder about making a coke can shim but worry about this getting lost down the seat tube and ending up causing more problems!
Thanks in advance for any advice or thoughts.
Robert
I had been using a 27.0 seat post in the old 531 frame which fitted well/worked fine. I assumed/hoped I would be able to swap the same seatpost over to the new frame but the fit is too loose in the 531c frame. Even with the seat post bolt well tightened up with the seat post slot sides nearly touching when tightened, I found on the first test ride that the my old 27.0 post was twisting about in the new 531c frame. When not riding the bike and with the seat post clamp undone, you can feel some play in the fit of the 27.0 post in the frame even with the post (which is quite long at 400mm x 27.0) is pushed all the way down into the frame (it is 400mm long). I assumed that I therefore needed a 27.2 seat post and purchased another USE 400mm x 27.2 post (cheap at £16.00 but have used these posts of several other bikes and they have been problem free) but now find that this post wont' go into the seat tube past the first 4cm or so even with a good film of grease and having cleaned up the inside of the seat tube as far as I can.
It seems that I actually probably need a post of about 27.1 but I don't think this size is made? Do you think I need to get the seat tube "cleaned up" at a bike shop? I gather good shops often have some kind of special tool that they can use to clean up the inside of the seat tube which might help the 27.2 to fit better/to slide down further as it should or could I perhaps alternatively purchase a seat post shim to use with the 27.0 post which would add the equivalent of .1mm diameter that I seem to need?
From googling about most info I can find seems to suggest that the 531c seat post diameter should be 27.2 but there is not way that the 27.2 post that I have will fit in as it is and by feeling down the tube as far as I can with fingers it seems very smooth inside with no rust. I have measured the diameter of both the posts that I have (one stamped 27.0 and the other 27.2) with callipers and taken several readings and averaged them both out - the 27.2 post actually measures on average 27.098, the 27.0 post averages 26.27 which makes the actual difference in diameter between the two 0.828mm. I thought if I could find a shim of that would add about .4mm diameter this would hopefully be a midway point that would work/hold tight. In googling for shims, I see that some are designed to make 27.2 seat posts "bigger", the next size down seem to be shims that start at 25.00 and go up in increments of 0.2 mm or so and therefore was assuming that if I buy a shim sized 25.0 - 25.4mm this might work? Any advice/anyone else's past experiences of getting round this as cheaply as possible would be much appreciated as this is now the last part I need to fit before I can start using the bike. I did wonder about making a coke can shim but worry about this getting lost down the seat tube and ending up causing more problems!
Thanks in advance for any advice or thoughts.
Robert