I was thinking is the spring on a coil shock, sprung or unsprung weight or 50/50?

Guess it’s not just the spring, the real question is, if the shock is sprung or unsprung weight or somewhere in between?

It’s about 50/50 but not quite that percentage from memory, would have to look through some notes to give you the full tech description and proportions.

So if you have a piggy back shock, theoretically you should mount the piggy back ‘frame end’ 😉

If it was 50/50 would the ratio change the more it is compressed?

yes

The answer will be in here somewhere probably, don’t have time to find it atm though 😉 http://www.tonyfoale.com/

Depends on where it is! The coil spring in strut suspension (like a fork or McPherson strut) is about 50% sprung mass. With inboard rod actuated springs like on an F1 car the spring is essentially 100% sprung mass, and MTB rear suspension is fairly similar to that.

Just think about what happens when the wheel hits a bump – does the centre of mass of the spring move in the vertical plane as the wheel is pushed upwards? The ratio between vertical wheel movement and vertical spring centre of mass movement tells you the sprung:unsprung ratio.