New axle

[bdog]

That assumes the wheels have zero offset and the tires are perfectly centered with the hub face. That may be the case I don't really know if they are or not.

I would want more space than that. Tire flex, mud, etc could cause problems. I built a trailer one time that had about 1" between the tires and frame. I was pulling it through a muddy field and the mud packed between the tires and frame to the point where the trailer tires would not even turn. I was literally dragging the trailer through the field without the tires spinning. Luckily it was a really light trailer and no match for my 4WD 1 ton.

 

[Diamondpilot]

That is way too tight.

Chris

 

[schmism]

they are expensive but solves your "custom" axle issues

Timbren Axle-Less Trailer Suspension System - 4" Drop Spindle Only - 3,500 lbs Timbren Trailer Axles ASR3500S04

 

[farm boy00]

they are expensive but solves your "custom" axle issues

Timbren Axle-Less Trailer Suspension System - 4" Drop Spindle Only - 3,500 lbs Timbren Trailer Axles ASR3500S04

If you had money and was making a walking beam axle that would work great

 

[Stimw]

Easiest way to locate the spring seats is to lay out where they will go (make sure the axle is straight and not pre-bent, if it is bent the crown goes up). Weld the first one in place and then use a 8" torpedo level, set the welded one level and then line up the other with the level and weld.
I have replaced MANY semi trailer axles and this way is fool proof!
Just clamping with the U-bolts isn't accurate.