SBDU Ilkeston TI-Raleigh 1980 Metric Reynolds 753 Seatpin Size

SBDU Ilkeston Metric Reynolds 753 Seat Pin Size – The Truth

There are many stories about the SBDU and even more about Reynolds 753 tubing. Most of these stories travel the internet, changing and evolving each time they are told. Something as simple as which seat pin size should fit a 753 frame is one of those stories. It causes the most confusion and creates some of the longest discussions whenever it is raised. Everyone seems to have an opinion about what is right; few ever seem to agree. My latest addition, SB3800, means that I may now have a couple of frames that could finally settle the seat pin debate.

In my recent blog post about the 1975 introduction of Reynolds 753, I had a couple of theories about seat pin size and why some owners reported differences. The general belief has always been that the lighter gauge (801) 753 tubing was used for frames up to a specific size, these frames would take a 27.0 mm seat pin. Larger frames would be built with the slightly heavier gauge (803), these frames would take a 26.8 mm seat pin. The frame size where the gauge change was meant to happen was thought to be in the region of 58/59 cm.

I never believed this. I just didn’t think it was that clear cut. Even though at the time, I had three metric 753 frames of 57 cm or less, which all had a 27.0 mm seat pin, and that appeared to prove the story was right, I still wasn’t convinced that it was a simple case of using a certain gauge based on frame size alone.

I wasn’t convinced because the SBDU built custom frames, and a custom frame means selecting a tube set that matches the person and the type of riding that person did. So many SBDU documents used phrases like “Built in the appropriate gauge of 753 for rider and programme of races”, “lighter gauge can be used where suitable”, “the tubing used is 753 to the appropriate gauge for the size and weight of the rider and the severity of courses to be ridden”. Those phrases made my mind up, the 753 gauge and frame size assumption just didn’t stand up, unfortunately, I had no proof.

I now have a fourth metric Reynolds 753 SBDU frame that may prove my theory…

SB3800 is a metric tubed 57 cm 1980 Reynolds 753 frame. It has Prugnat 62D head lugs and an RGF bottom bracket shell, single taper seat stays that fasten to the side of the seat lug with oversize seat stay caps. It requires a band on front mech and has a single set of bottle bosses. It has braze on gear lever bosses and standard cable stops. The rear ends are drilled Campagnolo 1010/B Portacatena.

SB3800 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753
SB3800 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753

SB4059 is a metric tubed 57 cm 1980 Reynolds 753 frame. It has Prugnat 62D head lugs and an RGF bottom bracket shell, single taper seat stays that fasten to the side of the seat lug with oversize seat stay caps. It requires a band on front mech and has a single set of bottle bosses. It has braze on gear lever bosses and standard cable stops. The rear ends are drilled Campagnolo 1010/B Portacatena.

SB4059 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753
SB4059 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753

I didn’t need to write all that about SB4059, I could have just said it was identical to SB3800, but writing it here does hopefully get across just how identical they both are. They are the same frame! There is no difference in style or geometry! All tube lengths are the same! All frame details are the same! If bikes could have a twin then these two frames would be twins.

But they each take a different size seat pin…

SB4059 is 27.0 mm
SB3800 is 26.8 mm

…and that is the reason why the stories about Reynolds 753 seat pins are not correct. These two frames show that it wasn’t a clear cut change over for tube gauge depending on the frame size.

Tube gauge was selected for the rider and not the frame size. Seat pin size is a result of tube gauge and not frame size.

Because SB3800 is made from the heavier and slightly thicker gauge of tube, I would expect the frame to weigh a little bit more than SB4059. A heavier, thicker gauge means an increase in wall thickness and therefore a heavier frame.

SB3800 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753 Frame Weight
SB3800 SBDU Ilkeston TI-Raleigh 1980 57 cm Metric Reynolds 753 Frame Weight
SB4059 57 cm 1980 Metric 801 Reynolds 753 27.0 mm Seat Pin = 1645 grams
SB3800 57 cm 1980 Metric 803 Reynolds 753 26.8 mm Seat Pin = 1739 grams

SB3800 and SB4059 both clearly demonstrate that you cannot assume Reynolds 753 seat pin size for a specific frame size.

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Written by Neil McGowran

Blogger of all things to do with the Specialist Bicycle Development Unit (SBDU) and TI-Raleigh Ilkeston.

8 comments

  1. Dear Neal,
    I own a early 753 Team Pro (SB 805) in original excellent condition. Size 55 embossed under BB.
    It has all specs of a 753 as the Haden forkcrown, drilled 1010A rear dropouts etc.
    But the seatpostdiameter is definetely 27.2 cm. And ithe post is not jammed in or set tight or whatever.
    Just exacetely matching for a 27.2 seatpost. Any idea ?

    1. Hi Bernd
      Thanks for getting in touch. Do you have SB805 or SB806? I’ve seen SB806 which is 55cm. This was the whole point of my post, 753 came in several butted sizes with several wall thicknesses. The thinnest 753 seat tube wall was 0.3mm. This gives the 27.0mm seat pin. If your frame is 753 and takes a 27.2 seat pin that makes your seat tube wall thickness only 0.2mm

      753 was a metric diameter tube, so the outside diameter of a metric 753 seat tube is 28.0mm (plus a little more for paint). Check the diameter of your seat tube. Imperial size was 28.6 (plus a little for paint)

      If your frame is 753 and definately takes a good fit 27.2mm post (and that post is accurately measured at 27.2 because I’ve seen lots of variations), then your frame may have been reamed. SB805/806 was an early 753 from 1976 and may fall into the unverified stories I’ve heard about workshops reaming the tubes.

      The later 753R that came out in 1982 increased the outside diameter of 753 to 28.6 and came ready for a 27.2 seat pin.

      Do some measuring of the outside of the seat tube and check what the size is?

      Neil

    1. Hi Wouter

      Yes, there are a few 27.2 early 753 frames (Metric). There are some who insist that there were only 2 sizes (27 & 26.8) and that the seat pin size was rigorously determined by the frame size, but I didn’t believe that and wrote the post. I’ve seen the geometry spec for Gerrie’s SBDU bike and it is listed as being built with “753 lt” which I assume to be “753 light”. It would be interesting to measure the outside diameter of the seat tube on your bike to 100% confirm it is metric. If it has an accurately sized 27.2 seat pin fitted then the seat tube butt at the top of the tube will be 0.2mm (seat tubes are single butted with the thicker butt at the BB end).

      Cheers
      Neil

  2. Hi Neil , I use to own 100% original SB557 , Reynolds 753 1975/6. Seat pillar size 27.2
    I have also seen Henk Lubberding’s 1977 team bike 753. 27.2

    1. Hi Mark

      How are you? Do you still have you collection?

      The point of my post was just to debunk the myth that a definite line was drawn between frame sizes and that anything below that line was 27.0 and everything above the line was 26.8

      The 27.2 story is something else… There are so many stories, like yours that also mention 27.2 – unfortuantely, I’ve only had experience of Metric 753 with 27 & 26.8 – I have both in the same frame size and is why I’ve been able to verify them and write the post.

      I believe Henk rode something like a 59/59.5 frame? If the std metric 753 theory is applied, that frame should have a 26.8 pin, so 27.2 is incredible, if it is original.

      I haven’t physically had a metric 753 with 27.2 in my possesion but would love to get my hands on one to provide even more detail to what was available.

      The problem is that a metric 28.0mm tube with a 27.2mm seat pin gives a wall thickness of 0.2mm (according to Reynolds seat pin data and calculations) – a 27mm pin gives 0.3mm and 26.8 gives 0.4mm – so as you can see, 0.2 is incredibly thin (especially on a large frame like Henks).

      I can’t say if it is possible or not as SBDU essentially had free rein to design whatever butting and wall thickness they wanted, as they, together with Reynolds, designed & tested 753. If a 0.2 wall 753 tube existed then it must have had very limited use.

      It is also possible that SBDU had Imperial 753 tubing before it became commercially available in 1982 (because they designed it, and, as you’ll know, SBDU didn’t stick to any type of rigid schemes). Several early apparent 753 frames exist with Carlton Capella lugs, but those lugs were said to be Imperial only (I don’t know if that is true, but that came from Mike Mullett), that means those tubes were either 531DB or early Imperial 753 with a 0.5 wall thickness? Both of those options would give a 27.2 seat pin size. Henks 77 frame that I think you are referring to has Capella lugs, which are meant to be an Imperial fit and which would give a 27.2 pin.

      Issues crop in with frames like SB557, a very early SB numbered 753, which has a 27.2 pin. It may have been original, but did you own it new from 1976? If you didn’t then you cannot 100% say that it has not been altered… and that is the continuing problem.

      Cheers
      Neil

      1. Hi Neil, please take a look on Flickr website and look at my photos. Type in Markkenpol to see my bike photos. There are some good photos showing the Henk Lubberding’s team bike I sprayed plus many other fine examples. Unfortunately I no longer own these but I’m still very interested and in personal contact with some of the builders from Ilkeston factory.
        I use to be a member of the SBDU website but I can no longer find it.
        I must say you have made a wonderful job of the bikes and a great presentation of photos,
        Mark Kennedy

      2. Thanks Mark, I’ll take a look, and thanks for your comments too.

        When I started researching my SBDU frames back in 2012, the Yahoo group was very active and you probably had the best and most varied collection. Sadly the group doesn’t seem as active with chat now, 242 conversations this year compared with 1300+ back in 2012.

        https://groups.yahoo.com/neo/groups/TI_RALEIGH_TEAM_PROS/info

        I was very tempted when you sold you bikes, especially in Henk’s 83 bike, but just couldn’t afford at the time.

        But again, thanks for you comments, nice to hear from you.
        Cheers
        Neil

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