I’ve wanted to write this post for a while, and I’ve tried to start and structure it a few times, but it has been difficult getting to grips with the scale of the subject. There was often either too much conflicting information or sometimes a complete lack of information about Reynolds tubes. Hopefully I’ve got a good grasp now, although it has still taken longer than expected to get all of this out of my head and crammed into a short, informative and hopefully coherent blog post.

My previous timeline post about the SBDU frame details and frame numbers was all about how the SBDU used specific features that could be used to define periods of frame construction – the use of certain lugs and tube finishes that tell you something about the age or model of an SBDU frame; a scalloped seat stay cap or Cinelli seat lug can tell you something about what you are looking at. That post is constantly evolving and is receiving regular updates whenever I get new information.

One aspect of SBDU frames that I didn’t cover in that timeline was the frame tube. The tubes that connect the lugs and frame details together, and how these tubes changed over the period of Ilkeston as Reynolds introduced various changes. This post isn’t a history of the Reynolds company or a comprehensive account of its tubing, that is just too huge for me to take on.

I wanted to write one post that covered everything, but after just one minute of thinking about that, I saw how impossible that was going to be. To stop myself from rambling and writing a mammoth blog post, I’ve decided to cover Reynolds and the SBDU in several smaller timeline posts which I’ll group together under their own section of the blog. These posts are going to be a brief overview of some of the subtle differences you might not have thought about or noticed on an SBDU frame.

To look at Reynolds tubing for the period of Ilkeston I need to consider the years from 1974 to 1987. For me, that is 2 distinct periods of Reynolds and their tubes…

The period from 1974 up to 1982/83 – and then from 1983 to 1987

Why those periods?

There are many more periods of Reynolds history before and after these dates but these 2 periods that pivot around 1982 are the ones that specifically cover the production of the SBDU at Ilkeston. In 1982, Reynolds and the SBDU introduced several changes. Not just the new tubing names and transfers but also different tube sets and chain/seat stay profiles; some of these profile changes went on to influence some aspects of frame design.

This initial post is specifically about the very early production of 531 frames; before the public arrival of Reynolds 753 & 531SL.

Reynolds 531 TDF 1975 TI-Raleigh SBDU Ilkeston
Reynolds 531 TDF 1975 TI-Raleigh SBDU Ilkeston

As always, before I move on, here are some caveats on this blog post.

  1. I did not work for Reynolds or the SBDU. My information in this post is based on published Reynolds data and physical measurements of SBDU frames
  2. My sample of frames is tiny compared to total frame production. There may be frames that differ and conflict with my own research
  3. Some Reynolds information is still missing but as time goes on, if I find it, I’ll add it

So lets start with SB frames available to the public in 1974 & 1975…

Reynolds Frame Transfers 1974 – 1975…

This period was fairly simple – by far the simplest period to cover. Production for SBDU SB frames was Reynolds 531 Butted Tubes supplied by the Reynolds Tube Company Ltd.

The only slight difference you may see on original SBDU frames in this period is the Reynolds frame transfer.

In 1973 Reynolds introduced the gold colour name panel to the base of the 531 frame transfer. The transfers below are the original ‘pre 73’ transfer without the name and address detail panel. These appear in the Reynolds Top Tubes publication from 1972.

Reynolds Top Tubes 1972 Raleigh SB4059 TI-Raleigh SBDU Ilkeston
Reynolds Top Tubes 1972 Raleigh SB4059 TI-Raleigh SBDU Ilkeston

The Reynolds Top Tubes publication from 1973 shows the new transfer with the extended gold panel with the company name and address- “Manufactured by Reynolds Tube Co Ltd”. Although Reynolds had been part of the TI (Tube Investments) group since 1928, they did not adopt the TI-Reynolds company name or the TI-Reynolds name on the 531 Butted Tube transfer until later in the 1970s.

(Both of the Top Tube publications show the ‘4 Stars‘ **531** transfer – I’ll mention that a little later. Although it existed, it doesn’t yet feature on SBDU frames and appears further through the SBDU timeline).

Reynolds Top Tubes 1973 Raleigh SB4059 TI-Raleigh SBDU Ilkeston
Reynolds Top Tubes 1973 Raleigh SB4059 TI-Raleigh SBDU Ilkeston

This publication from Reynolds confirms the date of the transfer change as 1st July 1973.

Reynolds Catalogue Raleigh SB4059 TI-Raleigh SBDU Ilkeston
Reynolds Catalogue Raleigh SB4059 TI-Raleigh SBDU Ilkeston

This is my 1975 original paint Reynolds 531 track frame. It displays the post 1973 frame transfer with the name and address panel.

TI Raleigh 531 Track Frame SBDU 1975
TI Raleigh 531 Track Frame SBDU 1975

There must have been a surplus of tube sets and/or transfers, as the pre 1973 design has been seen on authenticated original (Non SBDU) frames dating from the late 70s and early 80s. There are also a few frames in the SBDU timeline that claim to be in original condition and that have the pre 1973 transfer, yet they were built, according to the frame number, in 1976. Sadly, the majority of the original paint finish SBDU frames I have seen have Reynolds frame transfers that are either 90% missing or so badly damaged that it is impossible to see if they are pre or post 1973.

So far in this post I have only referenced the Reynolds frame transfer. That is because the predominant paint scheme was the black, red and yellow ‘Team’ colours of the TI-Raleigh team. This scheme was normally fitted with ‘TI’ circular fork blade transfers. Although they were produced by Reynolds, their fork blade transfers were generally fitted later in the SBDU timeline; typically post 1982.

For a period correct restoration of an Ilkeston SBDU Reynolds 531 frame from 1974 or 75, either of the Reynolds diagonal 531 frame transfers (pre or post 73 with or without the name panel) would be considered correct. As for fork blades in this period, frames in the TI livery would have a circular TI fork blade transfer.

Reynolds Frame Tubes, Blades and Stays 1974 – 1975…

Again, this isn’t a history of Reynolds but it is nice to know the basics.

There had been several incarnations of tubing but by the start of the SBDU, Reynolds 531 Butted Tubing was considered the best tube for bicycle manufacturing. From the invention and patenting of the butting process in October 1897 and the incorporation of the “The Patent Butted Tube Company Limited” in December 1898, there have been several types; from ‘B/AA’ and ‘A’ quality through to ‘HM’  (High Manganese), to the introduction of ‘531’ quality in 1935.

There are a couple of explanations as to how ‘531’ – (five | three | one) was named. The first was that it was noticed during the production of the steel that composite parts had a ratio of approx 5:3:1. The other was to do with its strength, 53 tonnes per square inch (53:1). Most Reynolds literature mention the 531 ratio story, but however it came about, ‘531’ became its name when it was registered as a trademark.

Reynolds 531, like many other options I’ll talk about in later posts, came in different gauges. But predominantly, the butted tube set that everyone knows, came in the following profile…

Frame Tubes

These are the 4 tubes often called the front triangle (yes, a 4 sided triangle?). Once you get past the mis-matched geometry definition, you can look at the 4 tubes that make up the triangle. This is the top tube (TT), down tube, sometimes called bottom tube (DT), seat tube (ST) and head tube (HT)

Reynolds period literature has the following profile* specs for their imperial** size frame tubes

TT - 25.4 diameter | 0.8/0.5 thickness | 21/24 gauge | double butted
DT - 28.6 diameter | 0.9/0.6 thickness | 20/23 gauge | double butted
ST - 28.6 diameter | 0.8/0.5 thickness | 21/24 gauge | single butted
HT - 31.7 diameter | 0.9 thickness     | 20 gauge    | plain gauge
*various gauges and lengths were available from Reynolds - spec above was std
**metric tubing was available from Reynolds TT 26 /DT 28 /ST 28 /HT 32 diameter
Reynolds 531 Butted Tubing Frame Tube Spec TI-Raleigh SBDU Ilkeston
Reynolds 531 Butted Tubing Frame Tube Spec TI-Raleigh SBDU Ilkeston

Seat Stays

Seat stays had a taper from the top (seat lug end) down to the bottom (drop out) – a ‘single taper’. The literature of the period gave a few different options for the external tube size.

Top diameter 16 / 14 / 13
Tip diameter 11 / 10 / 9.5

0.9 thickness | 20 gauge | plain gauge

As well as options for tube diameter, Reynolds had several options for the tip of the seat stay… Open Ended, Domed and Domed and Slotted.

Reynolds 531 Seat Stay Tube Spec TI-Raleigh SBDU Ilkeston
Reynolds 531 Seat Stay Tube Spec TI-Raleigh SBDU Ilkeston

During this period, the SBDU finished the top of the seat stay with a flat, flush fitted plain end cap for the very early frames, before moving to the scalloped finish (see my frame detail timeline).

There is nothing I can find regarding what seat stay tip end option was preferred on the raw seat stay. However, I’m certain that the ‘Open Ended’ tip option was used as the basis of the detail used. This option fits in with the signature finish that was used at Ilkeston. SBDU didn’t use a domed end seat stay (or chain stay/fork blade for that matter). SBDU used a filed and chamfered edge on the ends of all their stays and blades.

A saw is used to cut a slot and then a round file is used to achieve the chamfer. This is something I copied on my own frame build. Here are a couple of pics of my chain stay ends and a period SBDU rear drop out.

Reynolds 531 Seat Stay Tip Chamfer TI-Raleigh SBDU Ilkeston
Reynolds 531 Seat Stay Tip Chamfer TI-Raleigh SBDU Ilkeston
  • My period 531 SBDU seat stays measure 16mm + at the top and 10mm + at the tip

Note that I’m measuring a combination of tube and paint so measurements will be on the ‘+’ side of those quoted in the Reynolds data sheets. Because this is a ‘taper’, measurements may also be subject to a degree of change from bike to bike as seat stays will be cut at certain points to suit the size of frame.

Chain Stays

Reynolds produced 531 chain stays in several profiles and with similar tip options to the seat stays. The dimensions in the period literature are given as…

BB diameter  22.2 / 22
Tip diameter 13 / 12 / 11 / 9.5

0.8 thickness | 21 gauge | plain gauge
Reynolds 531 Chain Stay Tube Spec TI-Raleigh SBDU Ilkeston
Reynolds 531 Chain Stay Tube Spec TI-Raleigh SBDU Ilkeston

A basic round stay can be manipulated and formed into shape by frame builders using a dimple die or other shaping and forming tool or process. These can be sophisticated jigs and presses or simple shaped wooden blocks with force applied – they both achieve the same thing – creating an indentation to the round surface of the stay so that a tyre or chain ring can clear the tube. Chain stays can be made to suit different lengths and clearances depending on usage and tyre choice.

The chain stays on my period SBDU 531 road frame appear to match the ‘fluted’ and ‘fluted and indented’ options. I don’t know at this point if these are pre-formed from Reynolds or made to shape by the SBDU.

  • The LH (non drive side) is shaped on the tyre side and round on the outside as there is no clearance issue on the outside of the non drive side chain stay.
  • The RH (drive side) is shaped on the tyre side and also on the outside (chain set).
  • My period 531 SBDU chain stays measure 22.2mm + at the BB and 12mm + at the tip

Fork Blades and Steering Column

Reynolds fork blades in this early period had a narrow oval profile. This is a narrow oval shape of 16mm compared to the later and wider 20mm New Continental Oval and existing Columbus Oval.

‘Domed’, ‘Domed and Slotted’ and ‘Open’ tips were offered in the same style as chain and seat stays. 531 blades were offered in different lengths and either straight or pre-raked. Several pre raked options were available.

Blade diameter at crown  29 x 16 | oval
Blade diameter at tip    10.5 / 12 / 13 | round
Blade thickness          1.2/0.8 | 18/21 gauge | single butted taper gauge

Steerer thickness        1.6/2.3 | 16/13 gauge | single butted
Reynolds 531 Taper Gauge Blade and Butted Steerer Tube Spec TI-Raleigh SBDU Ilkeston
Reynolds 531 Taper Gauge Blade and Butted Steerer Tube Spec TI-Raleigh SBDU Ilkeston

A butted frame tube has its advantages of retaining strength at the joint and keeping weight down in the middle of the tube, but a fork blade has different requirements. A fork blade needs strength and rigidity at the crown to deal with the forces of cornering and braking but needs to still perform and have resilience to give the perfect ride. The Reynolds taper gauge method ensures that even after tapering, the end of the blade does not become thicker than at the butt. Once the tube is tapered, it is shaped into its oval.

SBDU fork blade tips were finished in the same style as the chain and seat stays so it appears that the normal open end blade option was used.

Reynolds 531 Blade Tip Finish TI-Raleigh SBDU Ilkeston
Reynolds 531 Blade Tip Finish TI-Raleigh SBDU Ilkeston

Different fork rakes were used for different purposes and frame size/designs, but the standard fork rake for an SBDU road frame was 42mm.

Bringing all this data together, the normal 531 Butted frame for the 1974/75 period had the following spec

Diameter (mm) | Thickness (mm) | Gauge (SWG)* | Tube Profile

Top tube   - 25.4     | 0.8/0.5 | 21/24 | double butted
Down tube  - 28.6     | 0.9/0.6 | 20/23 | double butted
Seat tube  - 28.6     | 0.8/0.5 | 21/24 | single butted
Head tube  - 31.7     | 0.9     | 20    | plain gauge
Seat stay  - 16/12    | 0.9     | 20    | plain gauge single taper
Chain stay - 22.2/12  | 0.8     | 21    | plain gauge round & fluted 
Fork blade - 29x16/12 | 1.2/0.8 | 18/21 | single butted taper gauge
Steerer    - 25.4     | 1.6/2.3 | 16/13 | single butted

SWG - Standard Wire Gauge for Sheet Metal & Wire

SBDU wasn’t just about building top class frames, they were also working with Reynolds in the research and design of other tube sets and materials such as Reynolds 753; and that is what I cover in my next post covering 1975 and 1976.

Reynolds Information Sources

Reynolds Top Tubes Publications 1972 & 1973
Veterans Cycle Club Online Library (VCC)

Recommended Reading

The Custom Bicycle - Kolin and de la Rosa (British builders including TI-Raleigh)
BIKE! - Moore & Benson (A good chapter of the history of Reynolds)

Other posts in my Timeline series

SBDU Frame Number & Frame Detail Timeline SBDU frame detail from 1974 to 1987

About the Author Neil McGowran

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

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