Advantages, Disadvantages, and Overview of the SOA

Advantages and Disadvantages:
The main purpose of SOA if mostly for 4 wheel driving purposes.  The biggest advantage of the SOA is additional ground clearance of your body and chassis from the ground.  The SOA also allows you to run much larger tires if you are interested in doing so, generally the 33" tires as a minimum required size but 35" tires are much more adequate for a SOA using stock-height springs.

The largest disadvantage is also the increased height of your vehicle.  It makes it tippier and because of the nature of physics, unless built intellengently it will require more thought when driving both on the street and off road.

For vehicles that see mostly mild trail driving and are daily drivers, we would recommend sticking with the simple 2.5" or 4" lift for your cruiser, they are more than adaquate to get your cruiser going up and down most obstacles and provide the best on-road handling and characteristics.

Fruits of the Labor: "Spaceghost" Mike Smyth's competition-built 
FJ40 running stock axles, 35" tires, and a Spring Over Axle conversion.

A SOA is basically removing your leaf springs from your axles in the stock configuration, and bolting them above the axles.  It naturally raises your rig about 6” if you are running stock-height springs, and more than that depending on how much arch you have in your springs. Though it’s a relatively simple conversion in theory, there are number of fabrication related modifications that you have to make to compensate for the additional lift.  Because your transmission and transfer case sit so much higher with a SOA, but your axles stays in the same location, you have to make adjustments in the steering, angles in which the differentials point, and some basic suspension changes.  You also have to deal with brakes, emergency brake setup (when applicable), and of course, modify your steering.

Safety: Because of these factors, there is always “that guy” who who we are worried about.  It’s probably the guy who says “this thing is only going to be a trail rig,” but fails to remember the truck will need be driven, even if occasionally, at 60 MPH to the trailhead, and will see some street time regardless of what he says to himself.  Because it will “be a trail rig” some corners are cut, the rig handles awfully, the springs are too soft without other compensations for them, and the truck is dangerous.  Time and time again, other than power steering conversions, the most commonly botched modification is a SOA conversion.

Therefore: USE COMMON SENSE - take measurements, remeasure, and re-measure again.  Do not be in a hurry to do things, and make sure you do it right, because it’s your life, and your 5,000+ lb missile riding on your axles and on your welds. Make every SOA conversion something that you can do 75 MPH with and have no fear or concerns about.  The SOA is a serious modification that should not be taken lightly.

Drivability and the General Nature of the SOA
If you take a look at a lot of the Ford 250’s and 350’s out there (and numerous other 4x4’s on the road today), you’ll notice many of them are SOA from the factory.  This means, despite Toyota’s original suspension engineering with Land Cruisers, the SOA setup is something that can be used on the road safely if engineered correctly. 

Someone once upon a time started messing around with Toyota axles and leaf springs and discovered a few good basic techniques for the SOA.  These have been widely discussed on the internet, on the LCML, and other various online forums to the point where just about everyone knows where to get certain parts, what to do, and how to do it right.

If your SOA is done right, you should have no problems driving your rig on the street at 75 mph, or as fast as your truck will let you.  A SOA that is done right can actually make your truck handle better than it did before.

Next page:
2. How Much Height and Which Springs to Use
Back to SOA Main Page