What’s the best practices with large maps in regards to physics?
How far off origo can you go before you need to recenter everything back to origin?
Are there any other issues I should start thinking about with physics in large maps?
This has probably been asked before, but I didn’t get any useful answers when searching for it…
Don’t try to unfold them in small cars. 
Stay within 10K units of the origin.
–Eric
Just replying to myself and for future reference, in case this hits a user search.
Found this thread: https://forum.unity3d.com/threads/wobbly-physics.486125/
Yes, seems like that is the short answer, +/- 10.000 units,
e.g. 20.000*20.000 map
At the time of Unity 5.0 betas I did a stress test:
There were 441 objects in a scene (houses), 121 colliders per each (box colliders and simple mesh colliders), so there were ~50000 colliders in total. Adding a new rigidbody to that scene in runtime was causing short (0.5-1 sec) but noticeable CPU spykes / FPS drop.
The solution I found was to bake the colliders of individual houses together, so that (441 * 121) box and simple mesh colliders turned into 441 complex mesh colliders.
The conclusion was: the number of individual colliders in the scene matters, the complexity of colliders - not so much.
@alexzzzz Thank you, that is very helpful.
From experience where 1 unit = 1 meter world scales, you should reset your origin before reaching 10,000 Units from origin. This is basically where numbers begin to crap out at a noticeable scale, given 1 unit = 1 meter.
The precision will start to show issues at this point, with a typical 3rd person or first person game.
edit: just noticed the other post mentioning it, sorry 
Yeah, 1u = 1m, always. Unless it’s a project with “special needs”.
Math, in this context, not being my strong suit. I don’t really understand how much of a relative divergence physics would have at 10.000 units.
So it’s good to have some general guidelines, that and combined with a few nights of failure (eg. testing). Should be sufficient to avoid most pitfalls.
I wonder how they deal with this in games like “Just Cause 3”, with a map size of ~640.000 meters… not that my ambitions is anywhere near this number.