Assuming the same material and tolerance, I pick the right-hand detail.
Due to having a larger resistance arm against shimmying and lateral shock when the wheel falls into an unsymmetrical pot-hole or passes over random construction debris like broken cinderblocks, pieces of metal, pebbles, etc. remember direct loading stresses are secondary to lateral moments.
ease of inspection of the bearing and adding lubricant, and removal of a flat tire for repair or replacement.
To my understanding that is the main requirement to minimize as much as possible tear and wear, is to have only one of the two components loosely fit on the rotating shaft. So in principle, both solutions you are considering should be fine. To my mind, the main drivers for the choice come from other considerations.
To avoid confusion, I will hereafter refer to your solutions as the :
- the left which has interference fit on the structure of the wheelbarrow (the wheel is rotating)
- the right which has interference fit on the wheel (the structure of the wheelbarrow is rotating freely).
(To be honest, I don't have as much experience as kamran in wheelbarrows used in structural site so I might be wrong.) My experience is drawn from a very common solution in the bicycle industry. The critical loads on a bicycle and a wheelbarrow can be similar in nature (lateral load, shocks, vibrations). If anything, the demands on a bicycle are probably more demanding due to the higher rpms and vibrational loads. So, a common bicycle solution for this problem is the following:
As you can see, they are using the left option (i.e. the shaft is fixed on the bicycle frame, and the wheel is rotating around the shaft.
The main benefit of this is that you can have quicker disassembly and inspection. This option is actually your left option (a fixed shaft on the wheelbarrow and a rotating wheel).
However this is very much depended on how the wheel is mounted on the wheelbarrow ie. if its one of the following.
If you want to have with the interference fit on the wheel(right) then if you have :
type A (closed mounting), it will be difficult to assemble the wheel.
type B (open) (which is more convenient for assembly) then its difficult to achieve rotation (without extra components or changing cross-sections on the shaft).
So basically, I would recommend the left option provided its with type B mounting, mainly for serviceability and inspection purposes.
This would be easy to assemble away from the wheel barrow and then fit on the wheelbarrow.