So I'm going to machine up some RCA spacers shortly and I was curious if anyone knows what the max thickness is and still be able to still use the stock wheels.

I'm going to be taking a 8000KM road trip this summer and want to pack along a full-size spare rather than the dinky little space saver that the OP must have picked up at some point along the way.

I'd like to run 30mm spacers but I seem to recall something like 17-20mm being the max with the stock 16s..

Can anyone confirm this?

should be less, the stock 16s don't have much clearance down to the LBJ.

hmmm, wonder if i should grab a crappy generic 17/18 with a decent tire then...
I already have 17" snow tires on wheels.

a stock '01-04 LS430 17 should be easy to find.

I run an Axis 20" 5-spoke wheel as my spare, just keep a spacer in the car for it since i'm already running extended studs.

Started to look, for decent 17/18" LS430 wheels.

So my question now is, what is the maximum thickness that would work with most 17" wheels?

assuming there's 0 clearance (which there isn't, there's more) for a 16" wheel, a 17" wheel should have at minimum [0mm+ (0.5*25.4mm)]= 12.7mm of additional clearance.

That being said, I THINK you can get 15mm RCAs under stock 17s, though I can't remember where I read that so the information isn't 100% reliable.