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.
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.
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.
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.