The “Services des Courses” frameset is described by the SBDU at Ilkeston as “…out and out ‘Team Issue’ framesets embodying our current thinking on design and construction…”
That means my frame, SB6560, should reflect the geometry and design of one of the most successful teams of the 70s and 80s. I guess that means I should measure my frame and see what the design and geometry is.
Getting set up and ready to measure frame geometry takes a little time. I’m not doing anything technical with perfectly flat surface tables but I am using a solid work bench that is relatively level – I can compensate for any small discrepancies and make things level with settings on my electronic gauges.
Wheel and tyre choice together with the lower stack height of the headset all work together to position the frame in the right place. Most lower stack heights are in the 11 to 14 mm range – this type of measurement is used when a frame is built and helps to calculate lower head lug and down tube position, fork blade length in conjunction with other factors such as fork crown and brake reach/tyre clearance. I’ve also used Mavic SSC sprint rims with 21 mm Clement Seta tubs which are period correct and would have been the type of tyre/rim used when this frame was built.
I’ve measured loads of SBDU Ilkeston frames before based on a ‘stock’ set of measurements that existed around the start of the 1980s; but design and thinking does change and evolve over time – what used to be the cutting edge design in the late 70s may no longer be the current thinking of the mid 80s. So I’m keen to see how my 1984 Services des Courses frame measures up… what was the SBDU’s current thinking on design at that time.
The first thing to be measured were the angles – the head and seat angle.
Setting the gauge to zero on the top tube, both the head and seat angle are measured relative to that horizontal line.
- Head angle is 74.3 degrees
- Seat angle is 73.2 degrees
So the frame (for a 57 cm seat tube) is a little bit steeper on the head angle and a little bit ‘slacker’ on the seat tube based on the earlier known dimensions. Given the 0.1 tolerance on the gauge that I was using, that head angle could be 74.2 – 74.4 degrees.
Next came the tube lengths.
One issue with measuring the position of the bottom bracket in the way that the SBDU have done, from the ground up to the BB, is tyre size. It varies depending on the tyre being used. SBDU specified a BB height of 268 mm but don’t give the wheel/tyre radius or diameter used in that calculation. I actually got a measurement of 265 mm – that could be the tyres, the Seta tyres I’m using are quite low. It could also be that the SBDU slightly dropped the height in their general geometry design for a road frame. Most frame designs now specify a bottom bracket DROP rather than HEIGHT – this is a fixed measurement taken from the line of the wheel axles down to the centre of the BB – this measurement is fixed in frame design and can never be affected by tyre choice.
The head tube length and front centres match the spec while the top tube is slightly longer for a 57 cm frame.
Fork rake came out at 42 cm. It actually worked out at 42.34 mm but as I said, I’m not using anything more accurate than a workbench and digital calipers. My basic set up is like this.
Using a digital level to ensure the steerer is level with the surface of the table, a spirit level across the blades to check levels and a dummy axle in the dropouts to help locate the area to measure. This is the measurement to make…
What this all shows is that the SBDU had frame geometry sorted!
The TI-Raleigh team of the 70s and early 80s and then the Panasonic Raleigh team from 84, used design and geometry that only changed slightly over time – why change a design that clearly works well at the very top level of international racing.
Now that this frame is measured and recorded, the next step is to sort out those damaged gear lever bosses.