Advertise on Bikeforums.net



User Tag List

Results 1 to 10 of 10
  1. #1
    Junior Member
    Join Date
    Sep 2008
    Posts
    11
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Miyata seat post q

    I'm looking for some help with a vintage Miyata frame. The bike is a 1987 215 ST. This is the low low end touring model for that year. The bike did not come with a seat post. The posts that I happen to have lying around are to small to fit into frame by about .010 of inch. The opening in the frame is about 1.060.
    the modern seat posts I have are all 1.070. Did they make smaller seat posts/frame openings back then?
    Thanks for any help.

    I'm rebuilding 2 vintage Miyatas. One for myself one for my daughter.

  2. #2
    Senior Member SweetLou's Avatar
    Join Date
    Jul 2007
    Posts
    2,114
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Seat posts come in many sizes. I am not sure what size is used for the Miyata 215. I think you should take to bike to your LBS, so that they can measure the seat tube and get the correct size seat post.

  3. #3
    Senior Member
    Join Date
    Nov 2004
    Posts
    9,998
    Mentioned
    9 Post(s)
    Tagged
    1 Thread(s)
    Miyata's butted frames typically use 26.8mm (approx. 1.055") seatposts. During this period, Miyata manufactured their own tubesets and chose to use a double butted seat tube, unlike most other tubing manufacturers, who used single butted seat tubes. Single butted tubes are butted (i.e. thicker) only at the bottom of the tube, where it inserts into the bottom bracket shell, because of the higher stresses at that location. Miyata's extra butt at the top of the seat tube, means it uses a smaller seat post than most single butted tubes.

    The advantage of having the extra butt, in conjunction with in-house tube manufacture, meant that Miyata could control the top butt diameter, so that they only had to stock one size of seatpost, regardless of the thickness of the un-butted section of the tube. Bicycle brands who used tubing with single butted seat tubes could also stock a single seat post size, but to do so they had to ream or hone the seat tube to size of the thinnest gauge tube, an operation which added extra cost. The only other major tubing manufactuer who regulalry used double butted seat tubes was Tange.

  4. #4
    Death fork? Naaaah!! top506's Avatar
    Join Date
    Nov 2005
    Location
    The other Maine, north of RT 2
    My Bikes
    '71 Gitane Super Corsa, '73 Atala Giro d'Italia, '73 Schwinn Super Sport, '76 Viscount Aerospace Pro, '81 Miyata 710, '81 Lotus Classique, '84 Ross Signature 290s, '84 Shogun 500, '85 Miele Gara, '87 Miyata 512, '89 Centurion Ironman, many more
    Posts
    3,133
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    Concur with T-Mar. All 5 Miyatas that I've owned took 26.8mm seat posts.
    Top
    You know it's going to be a good day when the stem and seatpost come right out.

  5. #5
    Disraeli Gears Charles Wahl's Avatar
    Join Date
    Jul 2007
    Location
    NYC
    My Bikes
    Riding: 1960s Falcon commuter; Queued: 1977 Bob Jackson, 1983 Serotta Club Special, 1984 Motobécane Team Champion, 1983 Guerciotti SLX, 1974 Harding (like Holdsworth Pro), 1974 Peugeot PX10LE, 1970s Jeunet Franche-Comté, 1974 Raleigh International
    Posts
    3,009
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by top506 View Post
    Concur with T-Mar. All 5 Miyatas that I've owned took 26.8mm seat posts.
    Which OP's measured opening size corresponds to. 1.060" = just shy of 27 mm, and subtract 0.2 mm for clearance, you have 26.8.

  6. #6
    My bikes became Vintage OLDYELLR's Avatar
    Join Date
    Aug 2005
    Location
    Ontario, Canada
    Posts
    1,096
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by top506 View Post
    Concur with T-Mar. All 5 Miyatas that I've owned took 26.8mm seat posts.
    Top
    I have a mid-eighties ladies' Miyata 310 with the seat post stamped 26.7, about 220mm long. The sticker on the seat tube says "MIYATA Cr-Mo CHROME MOLYBDENUM DOUBLE BUTTED TUBES" but I don't have any gauges handy to see if the seat tube is butted at the top. The "upper downtube" on these frames joins the seat tube just below the mid-point. I expect ladies' frames are the exception to the rule.
    1981 Nishiki Ultimate
    1977 Nishiki Landau
    1967 Jeunet Captivante track bike
    1951 Claud Butler New Allrounder under construction
    "index shifters = frets on a fiddle"

  7. #7
    Stop reading my posts! unworthy1's Avatar
    Join Date
    Sep 2004
    Posts
    8,383
    Mentioned
    10 Post(s)
    Tagged
    0 Thread(s)
    and if T-Mar's explanation isn't enough, Sheldon Brown's database of seatpost sizes shows every *steel* framed Miyata (except for 2) takes a 26.8 post.
    The exceptions are 1:
    a Mtn. bike and 2:
    a 610 which takes a 26.7! (and has the exclamation mark indicating how rare a size that is! I have never seen a seatpost marked 26.7, he doesn't say if it's a female frame or not)

  8. #8
    Senior Member
    Join Date
    Jul 2006
    Location
    Ontario
    Posts
    280
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by OLDYELLR View Post
    I have a mid-eighties ladies' Miyata 310 with the seat post stamped 26.7, about 220mm long. The sticker on the seat tube says "MIYATA Cr-Mo CHROME MOLYBDENUM DOUBLE BUTTED TUBES"
    I have a 1984 men's Miyata 310 and the seat post is also stamped 26.7; very strange size.

  9. #9
    Senior Member
    Join Date
    Nov 2004
    Posts
    9,998
    Mentioned
    9 Post(s)
    Tagged
    1 Thread(s)
    Any any seat post ending in a odd number is rare. Seat posts are normally manufactured in even numbered, 0.2mm increments. A difference of 0.1mm from the 26.8mm standard is not significant, as the binder slot would only have to cinched an extra 0.3mm. I can only speculate on the reason for these odd sized posts, but I doubt the seat tube's top butt is 0.05mm thicker than the standard. More likely, the post was manufactured slightly undersize and rather than rework them the manufacturer stamped the true size, knowing than the difference would not affect fit or function. Knowing the Japanese approach to quality, I suspect they probably even notified Miyata and received approval before shipping the posts.

  10. #10
    Junior Member
    Join Date
    Sep 2008
    Posts
    11
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    26.8mm Roger that! Off to nashbar.....
    Thanks guys.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •