The SBDU and Their Use of Reynolds 753 Reynolds 753R and Reynolds 753T

There has always been lots said on the subject of Reynolds 753, and that doesn’t surprise me. This tubing had such an impact on the sport of cycling; the frames and their riders were breaking records before anyone even knew 753 existed! 753 frames are still sought after 40+ years following their introduction. You can’t go a day without the subject of 753 cropping up on the internet and the online debates and discussions mean that there are always stories and different opinions. But are these stories real and are the opinions accurate? What is truth and what is myth? What are these stories? Have I done enough research and accumulated enough data to either prove or debunk them?

The SBDU was integral in the development and use of Reynolds 753, therefore it goes without saying that many of these stories have been influenced by SBDU frames and their owners. These are some of the stories I hear the most about Reynolds 753…

1. Early Reynolds 753 was Metric diameter only, with seat pins of 26.8 or 27.0mm
2. Seat pin size for SBDU frames built from early Reynolds 753 was determined by frame size
3. In 1982 the SBDU changed from Metric Reynolds 753 to Imperial 753
4. You can’t fillet braze Reynolds 753

Story No.1

Early Reynolds 753 was Metric diameter only with seat pins of 26.8 or 27.0mm

Was this true? This story, especially seat pin size has been talked about so much without any real conclusions.

Based on every single piece of Reynolds documentation that I’ve seen from the period, this appears to be a true story, the first 753 was Metric. Early Reynolds 753 did come in various gauge sizes (wall thickness), but the outer diameter was always listed as Metric. Reynolds documentation listed 801, 802 & 804 gauge 753. The SBDU also used 803 gauge. All 4 of those types are listed with the same Metric outer diameters.

Reynolds own documentation should surely nail this one, shouldn’t it? If Metric was the only diameter that Reynolds documented then that must mean that the story has to be true? Doesn’t it..?

But this story is linked to the SBDU so the facts behind it aren’t straightforward. One massive thing I have learned is that the SBDU was anything but predictable and you can never say never with anything linked to the SBDU! The SBDU were also different to other builders because they worked with Reynolds and helped to develop 753 – that is a relationship that no other builder had.

The only thing that casts a doubt over the Metric diameter story is that at least half a dozen frames exist that seem to contradict it. This handful of frames may prove that Metric 753 was not the only 753 tubing in existence. These frames all have a 753 frame transfer and all exhibit some frame features of period SBDU 753 frames with drilled 1010/B rear ends and stiffening tangs on the inside of the fork blades. But, they also exhibit significant features which aren’t expected on Metric 753, features that are more associated with Imperial diameter tubing such as Reynolds 531.

The first significant ‘Imperial’ feature is the lug type, they have been built with a lug called ‘Capella’, made by Carlton. These lugs have been modified and the shape has been cut to a slightly different design, but they are undeniably Capella lugs. Capella lugs are known to be Imperial diameter size. So how can Metric size 753 tubes fit into Imperial size lugs – they are both different diameters, some tubes would be too small for the lugs and some would be too big?

Although Capella lugs were actually used by the SBDU, they were definately not the ‘norm’. A small amount of SBDU frames were built with Capella lugs, and these are all built with Imperial diameter 531 Double Butted tubing… except this handful of mysterious examples…

The second significant feature is that the seat pin size on this handful of frames is 27.2 mm which is the size you would expect from a 0.5 mm single butted 28.6 mm diameter Imperial tube. The Capella lugs and 27.2 seat pin are a match, but don’t fit with Metric tubing. If these frames had a Metric diameter seat tube of 28.0 mm and the 27.2 mm seat pin size is correct, it means the internal wall thickness of the seat tube would need to be 0.2 mm (this is thinner than the thinnest 753 which was 0.3 mm). See my blog post on seat pin and frame tube gauge.

Do these Imperial features mean that Imperial diameter 753 frames may have been built by the SBDU several years before Imperial 753 was officially introduced by Reynolds under the name of 753R?

I don’t have one of these frames in my collection so I’ve never been able to measure, investigate and document them. So at the moment, my thoughts are only guess work at best, but educated guess work! Here are my theories on these bikes… and these theories take into account that the SBDU, as frame builders, had privileged early developmental access to 753 and the Reynolds Tube Company. They did, after all, work with Reynolds to develop the 753 tube.

Theory One

Because of the Imperial features of these frames, are they just 531 frames, but built with the features you see on a 753 frame, and finished with a 753 frame transfer? Drilled ends and fork blade stiffeners can be fitted to any type of tubing so these features cannot be used as a guarantee of tubing type. So are they 531 frames…? Are they 753 frames…? Based on frame features alone, I just don’t know…

Theory Two

During the design process to develop 753 tubing, was one of the design options an Imperial size version (equivalent to the later 753R)? Did Reynolds and the SBDU develop 753 tubes in Imperial diameters but scrapped it in favour of the Metric system and Metric dimensions?

This theory may actually have some substance behind it!

The early 1970s and especially 1973/74 was significant for the Metric system. The UK joined the EEC in 1973 and committed to adopting the Metric system. Various UK industries over the coming years started to fully switch to Metric. This is also the same period that the SBDU was created and the search started for a new tube type. Does this mean that 753 started as Imperial in the design stage but ended up as Metric for it’s release in 1975 to fit in the UK’s decision on the Metric system. But did a few of these developmental Imperial size 753 tube sets exist in a corner of the SBDU that they later built into these frames?

Theory Three

Are these frames a type of hybrid 753? Are they a standard gauge 531 tube that has gone through a heat treatment process to increase the tube strength while retaining the 531 gauge? Reynolds 753 and 531 have different internal wall thickness, but did they simply apply heat treatment to some 531 tubes to gain a stronger tube? This would mean that these frames were Imperial diameter, standard butted 531 tubes but with significantly increased strength due to the heat treatment; technically no longer Reynolds 531, but essentially, a heavier gauge 753?

Unfortunately, as I said, I’ve never had one of these frames in my workshop, I haven’t been able to get any tube dimensions or frame weights so they remain a mystery. They all have 753 frame transfers, they all have some 753 frame features, they all take a 27.2 seat pin and all have Carlton Capella lugs.

Were they a developmental Imperial size 753 that was never released because the UK joined the EEC and committed to the Metric system? Were they just heat treated, standard gauge 531? Were they just standard 531?

Verdict: Neither Proved or Debunked (for now, until I get one of these frames..!)

Story No.2

Seat pin size for SBDU frames built from early Reynolds 753 was determined by frame size

Was this true?

I’ve already covered this story in an earlier blog post “Metric 753 Seat Pin Size”. The story was always told that Metric SBDU 753 frames had a ‘cut off’, or ‘switch over’ size where the tubing gauge changed from 801 gauge (requiring a 27.0mm seat pin) to 803 gauge (requiring a 26.8mm seat pin). It was believed to be around a 58/59cm frame.

What I found is that this story is generally true. In fact, all my 57cm Metric 753 frames conformed to the story, they all took a 27.0mm pin… this was fine, until I got my hands on SB3800, another 57cm Metric 753… this frame took a 26.8mm pin, contrary to the story. I also have other examples of frames in my sample data that confirm this.

SBDU frame set literature always refers to the most appropriate gauge of tube selected for the rider and race program. These statements appear across the literature and show clearly that, where appropriate, a small but heavy or rough rider may require the heavier 803 gauge, and likewise, a tall but light pedal spinner, may be suitable for the lighter gauge 801.

Verdict: Story Debunked

Tube gauge (and the resulting seat pin size) was selected for the rider and type of racing. Tube gauge and seat pin size was not simply determined by frame size. There may have been a ‘stock’ tube gauge for a ‘stock’ frame size, but a discussion about rider and usage probably took place to see if the ‘stock’ gauge was the most appropriate.

Story No.3

In 1982 the SBDU changed from Metric Reynolds 753 to Imperial 753

For clarification, the story is that the first SBDU Reynolds 753 frames were based on Metric external diameter tubes until Reynolds updated the range in 1982 and introduced a version of 753 which was based on Imperial external diameter tubes. The way in which this story is told suggests that there was a switch over period from Metric tubed SBDU 753 frames to Imperial tubed SBDU 753 frames, with Imperial taking over.

This story about post 1982 753 is confused because Reynolds split the classification of 753 into two different types. Up until this point, 753 had always just been known as ‘753’. Even though early 753 used different gauge tubes, frames were all equally identified by the same iconic frame transfer, just ‘753‘.

Reynolds divided the new 753 into ‘753R‘ with the ‘R‘ meaning ‘Race‘ and marketed as a tube for road frames, and ‘753T‘ where the ‘T‘ stood for ‘Track‘ and was marketed as a lighter gauge tube for Track use. This classification really stuck with some people and 753T was always seen as a Track specific tube, with road bikes using 753R. But the finer print of each tube in the Reynolds documentation went a little further into the description of R & T.

• 753T was described as for ‘Pursuit and Time Trials’
• 753R was described as for ‘Road Racing, Cyclo Cross and Sprint’

However, a tube is just a tube, regardless of how it is defined in any marketing material, and any tube can be considered for any discipline and for any frame. The best custom frame design should mean that the most appropriate tube should be used for the specific person and the required use.

The SBDU definately specified 753T as an option for Time Trial and Road Frames. This is the wording and frame detail specification from the 1985 SBDU frame set descriptions.

So why am I going on so much about 753T when this is a story and Metric and Imperial tubing? It is because 753T is a Metric diameter tube! The vast majority, if not all of Reynolds documentation about post 82 753 seems to reference 753R Imperial dimensions. Almost nothing exists about the specification of 753T. The only dimension data I’ve ever found for Reynolds 753T is in the Paterek Manual for Bicycle Frame Builders and was dated 1984. It listed 753T as Metric tubing with the following tube spec…

            Outer Diameter (Wall Thickness)
Top Tube    26.0 (0.7/0.3/0.7)
Seat Tube   28.0 (0.7/0.3)
Down Tube   28.0 (0.8/0.5/0.8)
Seat Stays  12.0/16.0/11.0 Double Tapered (0.5)
Chain Stays 22.0/13.0 (0.6)

This is my 1985 frame, SB7121. I recently wrote a blog post about this and how it was built from 753T. You can see clearly see a 1985 frame but with Metric dimensions.

Verdict: Story debunked

From 1975 to 1982, 753 was a Metric tube (apart from those few mystery frames in Story 1). After 1982 an imperial version of 753 was introduced and took over as the main 753 tube set, but it did not mean the end of Metric diameter 753.

I think the new dual definition of 753R as ‘Race’ and 753T as ‘Track’ confused things and the wording used when people talk about the switch over period of SBDU frames in 1982 has influenced this story and the opinions that people have. Imperial was introduced but Metric did not disappear.

Story No.4

You can’t fillet braze Reynolds 753

I see this story crop up occasionally on forums.

Brass is typically the filler rod used on lugged steel frames, it works really well and melts and flows at a temperature that does not cause damage to a normal steel frame tube. Brass can also be used to build a lugless ‘fillet brazed’ frame because brass can be used to build up an external bead or ‘fillet’ around the tube joint. Tubes are mitred as normal and fitted against each other with a small tack of brass holding them together. Once the alignment has been double checked, more brass can be added to the exterior of the join and built up into a bead of brass. The bead is then smoothed with a file and emery cloth to form a smooth and almost seamless, flowing transition from one tube into another.

But with Reynolds 753, you cannot use Brass to join the tubes. The temperature required to melt the brass and allow it to flow is too high. 753 is heat treated tubing with a high tensile strength, and excessive heat on 753 removes that strength. Therefore Silver is used because it flows at a temperature well below brass and below the point that would damage the strength of 753 tubes. The problem with silver is that it is very soft, it melts very quickly and is often described as ‘free flowing’. It doesn’t have the same properties of brass that allow it to ‘pool’ and build up into a fillet join.

But my recent acquisition of SB4409, a 753 Dynaflite shows that you can in fact use silver to fillet braze a 753 frame, but you have to have some excellent skills to be able to do this. So how was Silver used to fillet braze these frames?

The answer is really clever. Mike Mullett who was the SBDU workshop manager in the late 70s and early 80s, and who built SB4409, described the process…

“The tubes were mitred accurately and a ring of the normal Silver Flo 66 was bent to shape, very free flowing used for the lugged frames, and placed INSIDE the tube. It was then “teased” out with the torch until a sparkle of the silver solder appeared on the outside. After the joint had cooled, ArgoFlo was used which was a very pasty LOWER TEMPERATURE silver solder. As the name implies it had an element of gold in its make up. It was then possible to build up the significant fillet without melting the initial Silver Flo 66. Yes 753 could be fillet brazed by a builder with enough torch talent.”

A really clever process but requiring great skill to achieve.

Verdict: Story Debunked

It was possible to fillet braze Reynolds 753, It certainly wasn’t the ‘norm’ but it was possible.

Conclusion

I think I’ve managed to give convincing arguments about 3 of the most common stories surrounding Reynolds 753 and the SBDU. I haven’t given up on the other, the early Metric/Imperial 753 frames… I’m still working on that, and hopefully I’ll be able to bring that to a conclusion at some point in the future.

Don’t instantly believe everything you read online about Reynolds 753. The SBDU may have had access to some bespoke tubes and gauges of 753 because of their involvement in the early 753 development work that were not commercially released by Reynolds to other builders and that does confuse things when certain tubing topics arise. Check as much as you can and gather as much information as you can before deciding on what you feel is and isn’t fact. Even my entire blog post is a story, you might agree with it… you might disagree… However, it is supported by lots of information taken from original manufacturers documents, it is based on checks and measurements against actual Reynolds 753 Metric and Imperial SBDU frames and includes first hand testimony and descriptions of build processes from people who built these frames.