Yeah. I measured a 3.13" O.D. this weekend. A quick check using 40 ksi steel and .2" wall put it bending when the the majority say 80% of the vehicle weight was on one tire with some impact. Think fully loaded vehicle going down hill with one tire high. If the wall is a little thinner and the steel a little stronger.....that's the same range. I think that's a reasonable design starting point. It's 2x stronger than it needs to be for road use (a reasonable design point for Toyota in the beginning), but is bendable under extreme use (which is important validation because it does bend under extreme use). So far i have a basic idea that doubles, or triples the strength (depending on strengthening member used) all the way down the axle and doesn't obstruct stock mounts, or lose clearance. I'll keep working on it.
