How do I properly torque a track cog lockring?
A torque specification is not just a torque-spanner setting but a physical property. That is, there are many ways to apply the correct torque.
In this case it means more or less: pull it as tight as you could. One can conclude this from the high torque value and wide torque range.
To illustrate this let's find the force F you need to apply to a tool to get the torque t.
The spanner you used as an example is 30 cm long. Since you need to grip it you cannot use its whole length for leverage. Let's calculate with l = 0.25 m.
t = F l
F = t / l
For the minimum torque 40 Nm we need a force of 160 N and for the maximum 65 Nm it is 260 N. That is the weight force of 16 kg and 26 kg, respectively.
The limit to over-torqing the lock ring is either your strength or pain in your hand as you begin to crush its bones on the narrow handle of the tool.
One more thing: with bike specific quality tools, especially from manufacturers who are long in the market, you can assume the tool was built to fit its purpose. That means also that it has just the right length and shape that a professional mechanic (who tends to be strong) intuitively uses it with the right torque.