Metric Diameter Tubing? Reynolds 753 Raleigh SBDU Ilkeston 1978 Road Frame SB1995

“Never assume with the SBDU”. That is a phrase I say a lot. It is a mantra I repeat when I’m assessing SBDU frames and bikes. Winding the clock back to 1978 you would think it was safe to assume that the Reynolds 753 tubing type on your frame would be Metric diameter. But remember the mantra, “Never assume with the SBDU”, “Never assume with the SBDU”, “Never assume with the SBDU”.

SB1995 is a recent arrival so I’m moving on with my normal process to document it. I’ve already looked at its features and came up with rock solid provenance for its build and renovation date.

The first step in my process is to weigh the frame stripped of all it’s fittings. It was when I dropped the fork out of the frame to remove the headset cups that I noticed a nice detail… the original owner’s initials, ‘MG’, stamped by the SBDU instead of the usual frame number.

Frame Weight

Frame weight can be random and I’ve written about it before. Weight is a product of frame design, so it is dependant on choice of tubing gauge, fittings and geometry. Even though it’s unpredictable, trying to predict it can still be a good game.

This is the style of Reynolds 753 transfer that SB1995 will have had when it was built. My frame is from 1978 so the name detail box would have been slightly different, it would have had the later 1977 – 1982 “TI-Reynolds” name. Although 753 at the time was typically Metric, I do have a couple of examples of 753 frames, built in the same era, that are Imperial. But those Imperial frames, and others that I’ve seen, are fitted with Carlton Capella lugs. SB664 and SH377T are two examples from my collection.

SB1995 doesn’t have Capella lugs, so based on its build date and its use of the standard period Prugnat S4 lugs, it’s a fair assumption to make that it is a Metric frame. It is a very similar looking frame to many others in my collection. I’ve got lists of frame weights from the data I’ve collected so I thought I would play the guessing game and see if I could judge where SB1995 would sit in that list based on similar period Metric 753 frames.

This is an example list filtered to show a sample of my Reynolds 753 frames.

SB#	Period	Tubing	Diameter	Pin	Size	Weight	Stays	Lugs	BB	Ends	Type
SB632	Pre 82	753	Metric	27.0	52	1552	Flat	Prugnat S4	RGF 4 Slot	Custom Track Drilled	Track Pursuit
SB1500	Pre 82	753	Metric	27.0	56	1582	Oversize	Prugnat S4	RGF 4 Slot	1060 Sport Drilled	Time Trial
SB3505	Pre 82	753	Metric	26.8	52	1585	Oversize	Prugnat 62D	RGF 2 Slot	1010/B Portacatena Drilled	Road
SB2692	Pre 82	753	Metric	27.0	56	1629	Oversize	Prugnat S4	RGF 4 Slot	1060 Sport Drilled	Time Trial
SB4059	Pre 82	753	Metric	27.0	57	1633	Oversize	Prugnat 62D	RGF 2 Slot	1010/B Portacatena Drilled	Road
SB6398	Post 82	753R	Imperial	27.2	57	1648	Fast Back	Prugnat 62D	Cinelli SCM	Shimano (Vertical) Drilled	Road
SB8945	Post 82	753R	Imperial	27.4	58	1673	Oversize	Cinelli	Cinelli Super Corsa	Shimano (Vertical)	Road
SB7121	Post 82	753T	Metric	26.8	54	1678	Oversize	Prugnat 62D	Cinelli SCM	1010/B	Time Trial
SB8851	Post 82	753R	Imperial	27.2	54.5	1684	Oversize	Cinelli	Cinelli Super Corsa	Shimano (Vertical)	Road
SB5377	Pre 82	753	Metric	27.0	57	1687	Oversize	Prugnat 62D	Cinelli CCM	1010/B Portacatena Drilled	Road
SB9000	Post 82	753R	Imperial	27.2	61.5	1713	Fast Back	Custom	Custom	Shimano UFP-10	Low Profile Track
SB3800	Pre 82	753	Metric	26.8	57	1739	Oversize	Prugnat 62D	RGF 2 Slot	1010/B Portacatena Drilled	Road
SB8868	Post 82	753R	Imperial	27.4	59.5	1756	Oversize	Cinelli	Cinelli Super Corsa	1010/B	Road
SB3327	Pre 82	753	Metric	26.8	56	1789	Oversize	Prugnat S4	RGF 4 Slot	1060 Sport Drilled	Time Trial
SH377T	Pre 82	753	Imperial	27.2	56.5	1799	Oversize	Capella	RGF 4 Slot	1053 Track Drilled	Track Pursuit
SB7657	Post 82	753R	Imperial	27.2	58.5	1876	Oversize	Prugnat 62D	Cinelli SCM	1010 with added eyes	Randonneur
SB664	Pre 82	753	Imperial	27.2	61	1888	Flat Plate	Capella	RGF 4 Slot	1010/B (Early)	Time Trial

SB1500 is very light for a 56cm frame and at only 1582 grams, it is my 2nd lightest frame, it is incredibly light for its size; I’m sure there is something hidden in the tubing gauge of that frame that has kept the weight down, so I discounted that one for my weight guessing game. SB2692 is also 56cm and is much more of a typical period Metric 753 frame, weighing 1629 grams. These two are both time trial frames and there are subtle differences between SBDU road and time trial frames in this period so those differences are taken into account too.

I thought that as it has the same 4 slot RGF BB and Prugnat S4 lugs as SB2692, but is slightly smaller at 55cm, and is a road frame with subtle differences that might add a small amount of weight, SB1995 might come in at something between 1600 and 1635 grams. The scales proved I was wrong…

SB1995 tipped the scales at 1728 grams, so although it is a smaller frame, it is almost 100 grams heavier than SB2692.

Sweat the Small Stuff

Now I know I said I normally strip every item off my frames before weighing them, but on this occasion I left the Raleigh BB cable guide in place to preserve the original SBDU rivet. That might sound like overkill on the detail, but it is an original detail and I want to do whatever I can to preserve it. To record the weight precisely, I know that a Raleigh plastic guide with a rivet in situ is 3 grams. That small detail brings the weight of SB1995 down to 1725 grams.

From my experience of handing and documenting these frames, I’ve noted a couple of reasons why a frame might weigh 100 grams heavier than other frames of a similar size and tube type. One is tube gauge (the tube wall thickness) and the other is outer tube diameter. Both of these factors can add a small amount of metal and therefore a small amount of weight.

Reason One: Seat Pin Size

Seat pin size is a good way of determining tube gauge. Could this be a Metric 753 frame that requires a 26.8mm seat pin rather than the normal 27.0mm pin? Is this the reason for the extra 100 grams? Seat pins are things I have in abundance. It’s always good to have a range of pins from 26.6mm up to 27.4mm; these sizes should cover most Reynolds seat tubes.

The 26.8mm pin I used dropped straight in! When I say it dropped straight in, it literally wobbled and slid all the way in, barely touching the sides of the tube. The 26.8mm pin was far too loose for SB1995 to be a heavier gauge Metric 753.

The second reason that could explain the difference in weight is tube diameter. Could SB1995 have larger diameter tubes and therefore be an Imperial tube frame?

Reason Two: Tube Diameter

Metric Diameter Tubing Dimensions

Starting with period Metric 753 tubing dimensions. Metric has a slightly bigger top tube but smaller seat and down tubes compared to Imperial.

Tube	Diameter (mm)	Diameter (Equivalent inch)
Top Tube	26.0	-
Seat Tube	28.0	-
Down Tube	28.0	-

The tube diameters given in the table above will be based on bare metal, so any measurement I take will be slightly larger than the figures above due to paint, it won’t be much, but will still be slightly larger.

Having my collection is great, I can call on so many frames to use as examples. The measurements below are from SB1500 – this is an amazing Metric diameter tubed 1977 frame from the SBDU with original SBDU paint. As you can see, all the measurements are slightly larger than the bare tube diameter, but they are all 100% Metric.

Imperial Diameter Tubing Dimensions

The thing I find funny about Imperial diameter tubing is that it usually has its size quoted using Metric units. For example, an Imperial diameter seat tube of 1 1/8 inch will often be quoted as 28.6mm. They are both correct but not many now actually quote tube size using Imperial units. I even measure and record Imperial tubes in Metric units too!

An Imperial tubeset will have a slightly smaller diameter top tube compared to Metric but has larger seat and down tubes.

Tube	Diameter (Inch)	Diameter (Equivalent mm)
Top Tube	1	25.4
Seat Tube	1 1/8	28.6
Down Tube	1 1/8	28.6

This is SB8851, another frame in my collection and another SBDU frame with original paint. This one is built with Imperial Reynolds 753R. The tube diameters again are all slightly larger than the bare metal Imperial size.

So how does SB1995 compare… is it Metric or Imperial? Here are the measurements…

SB1995 1978 Imperial Tube Reynolds 753 Road Frame

And there is the answer. SB1995 is definately an Imperial tubed Reynolds 753 frame but from an era of Metric 753 tubing and that is why my weight estimation was slightly wrong. This is an example of the SBDU at its non-understandable best! The relationship the SBDU had with TI-Reynolds and also their use of and access to different types of Reynolds 753 tubing is so difficult to pin down.

Now that I know it is Imperial tubing, it’s frame weight is much more understandable. It falls in line with my other early period Imperial 753 frames.

Frame Number	Size (cm)	Weight (grams)	Year	Tube Diameter	Frame Lug
SB1995	55	1725	1978	Imperial	Prugnat S4
SH377T	56.5	1799	1977	Imperial	Carlton Capella
SB664	61	1888	1976	Imperial	Carlton Capella

I’ve seen quite a few early period Imperial 753 frames, it isn’t something new. But they have all tended to be noticeable because they have been built with Capella lugs, so SB1995, with its standard looking Prugnat S4 lug type is different, and something I need to add to my brain.

SB1995 is a completely normal looking period Metric Reynolds 753 frame with an RGF BB shell with 4 slots, Prugnat S4 lugs, semi sloping fork crown, 1010/B drilled ends and single taper seat stays… but built with Imperial tubes!

And so the mantra needs to be repeated…

“Never assume with the SBDU”

Repeat, “Never assume with the SBDU”

And repeat again, “Never assume with the SBDU”

Next up will be confirming the seat pin size – should I assume a normal Imperial seat pin size of 27.2mm?

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