Originally most 6x6s used Balloon tires. These tires were vulcanized to a small center hub and acted as sort of a suspension giving a soft bouncy ride. With a solid frame mounted axle the tire and axle to some extent work as the suspension for the vehicle. Depending on tire construction and air pressure, when you hit an object, the tire will give way a certain amount and try to absorb the energy. If the object is large enough and/or the speed traveled is high enough you can overcome the ability of the tire to fully absorb the impact and the energy is transferred through the rim to the axle which will deflect and also lever itself against the frame a bit depending on its length. Now depending on how hard the impact is and at what speed it might occur, depends on weather the axle has the ability to withstand the impact and throw the vehicle in the air or bend, break and possibly bend the frame and rim. Here is an example of even the strongest axles currently available to the 6x6 community showing the worst case scenario.
Add to this torsional load due to the fact that the axle is driving the vehicle and the fact that the axle is also supporting the weight of the vehicle and it is easy to see why even high strength alloy axles start to be required with the demise of a readily available compliant tire like the old balloon tires originally used. I think it is easy to see why the ride for the 6x6 becomes so rough and the axles can fail on the older 6x6s when agricultural, implement and mud tires are used not to mention the torsional load from the larger lugs and torquier 4 stroke engines.
Now enter the springer. Which uses an independent suspension or IS for each wheel. Now you have essentially three drive components for each wheel. A drive flange back at the frame, axle shaft and wheel hub in the hub carrier. The hub carrier usually has an upper and lower a-frame attached to it with some sort of shock and spring arrangement that is connected to the lower a-frame and frame support. This IS arrangement sort of takes the load bearing and need to absorb and impact out of the equation for most of the axle components and only require it to take the demands of torsional load. Energy not absorbed by the tire is now transferred to the spring and shock. Sounds great right. Smooth ride no matter what tire right. Well there are some other considerations to take into account especially in wet adverse conditions. And here is were I ask the question of durability of the springer. This question has nothing to do with axle strength. If an inch and a quarter stock Honda Civic axle can take 500HP at the wheel in the cars I dyno at my shop I would think an axle in a 6x6 springer should pretty well handle the 8-40HP a 6x6 can transfer to its wheel.
Its all the other components. Strength of the A-frames, shock bushings and mounts, plus the cradle or exo-frame that supports everything. How about life of things like CV joints, boots and spherical rod ends and bearings. What happens when the suspension bottoms out? In things like buggies running in the desert or on sand dunes these components deal with one set of challenges. In woods, swamps, mud holes I would think that maybe the game would change. Seaweed, roots, small twigs muck all balled up around the axles. Every part of the suspension submerged in sandy grimy clay enriched muck. Running the machine back and forth across deep ruts just to try to make it in and out of a hole like Mike in this video which is sort of typical of many of the videos posted of group rides on this site.
Call me crazy to ask, but fitted with an aggressive mud tire would a springer be more capable than a Max IV like Mike the administrators or a RZR?
How long would the bearings, rod ends, bushings and CVs actually last in adverse conditions. I know the number of springers is few, but there sure is a lot of interest and fitted with a big mud tire? Do they have more potential than for just zipping around the desert fast with a softer ride. Is the ride that much better than an old balloon tire? Who knows?
Looking forward to discussion and education. Keith.