that's a good start, may be conservative in cities where the fire engines have tighter turning radius's. I suggest calling the fire department for that city your project is situated and ask for the outside radius turn at least. If you are running Autoturn, you may want to ask for the front wheel overhang, wheel base, rear wheel overhang, track width, body width and maximum steering angle. You can create a specific fire truck template with this information and proceed on modeling the turns. This is how I usually do the process.