1. Steerable. This is a misnomer, it is not steerable but rather pivots. Steerable implies it is somehow connected to the steering wheel. It is more like a caster on a shopping cart. If you have one of these, consider yourself lucky. Get loaded, put it down, forget about it. I have had them on my past several trucks and love them. I average about 200,000 miles on the tires. Incidentally, the steerable axles are typically lighter as the components do not have to be as heavy duty because it does not scrub like the non-steerable.
2. Non-steerable. This one will take some skill to get used too. You have to pick this one up to go around turns, tight on-ramps etc. My rule of thumb was if I had to take a turn slower than 25 mph I would pick it up. Otherwise you will scrub the heck outta the tires and in some situations the lift axle will force your truck to stay straight. We have all forgotten to pick it up one or twice and gone for that little spot in traffic only to find out your truck won't turn. Now the skill part, once you lift that axle up the brakes still work on it, but remember when you have to pick it up, when you are slowing down. That axle does not instantaneously fly up off the ground. It comes up kinda slow (different trucks different speeds) And as it is coming up, if you hit the brakes, it will lock up and flat spot your tires. Then you will have a square tire, that ain't no fun. So you have to learn how to time when to pick up your axle, meanwhile you are shifting gears, eating your lunch and talking on your cell phone watching traffic and turning. Loads of fun. I have found it very difficult for many drivers to keep a tire nice and round on a non-steerable. And once you get that flat spot, it will vibrate the truck until you replace the tires.
Now with all lift axles on straight trucks it is a good idea to pick that sucker up when you are off road, or you will absolutely get stuck. When you back up, pick it up. When you dump, pick it up. As a general rule, if you are not on a road, don't put it down.
Some states use the lift axle to meet federal bridge law, meaning you have to adjust the pressure to ensure you meet the formula. Other states Just mandate it to have so many pounds on it but don't care about the bridge law.
Now all states are different with their laws, where are you thinking about running and we might be able to provide some in site as to specific laws in your state.
As far as a 50 state legal truck that night have a need for a lift axle to meet interbridge, you can go off the chart for federal bridge law
http://www.hendrickson-intl.com/lite...ws/bridge3.asp
And if you have a hard time figuring that out, drop me a pm or post your pertinent info here and I can figure it up for you.