If you absolutely, positively, cannot go beyond even a teensy-weensy bit beyond 30" at any point, it obvioulsy limits your minimum radius to what will fit. If you have the loco(s) already your best bet would probably be to set up a test loop (or just a 180-degree curve) with flex track and see what radius the locos will negotiate. Check it with cars attached, in forward and reverse, with cars on each end, etc. That will give you an idea what your minimum radius can be.
If it's small enough (say around 13"), you'll be able to build turnback curves at each end of of your space and you'll be able to have a continuous run.
If you can cheat just a little on the width in a couple of spots for turnback curves, you can go up to a larger radius, which would probably be better for appearance and reliability.
I saw a nifty little layout recently with small HO (standard gauge) locos happily running around 13" R curves with short cars, so it can be done -- but a lot will depend on how willing your Climax locos are to swing around those sharp turns with cars attached.
Byron Model RR Blog
QUOTE: Originally posted by ukraine
I'M new to this hobby and only have space for a shelf layout of 12' long and 30" deep. It will be a logging railroad using small cilmax loco's and my longest car is only 24"long. I don't really want to have a point to point scheme, I would prefer continous operation. Do I have enough space? any suggestions for minimum radius?