Hi Alex,
let me see if I can find something in the documents…
…if not I’d need to take off the pedal and measure 
Sorry, no specification found…
From the “living object” 
That’s anyway a cup spring, made of stainless steel.
Inner Ø : 14,3 mm
Inner Ø : 27,8 mm
Material thickness 0,8 mm
Unloaded height ~ 1,6 mm
Please read here if you’re not familiar wih the function of cup springs
Re: Sideway movement of the rear wheel
Kind regards,
Chris