Thanks for this input.
I was trying to understand
It is clear that if the same wheels are used on a gun, its limber, the forges and the ammunition wagons, if a wheels of a gun broke, the gun could be saved by disabling a forge or whatever.
Yet, such a decision for flexibility comes with a price if only have over-dimensioned wheels for certain pieces of equipment. My interest is the technical price, if you will (besides costing more money and some extra weight of the over-dimensioned wheel).
My original question was as to the effect on the artillery piece and its fire charateristics (say, loss of steadiness in "holding the line of fire" or loss of time in returning the piece to its position after firing or whatever).
Thinking about over-dimensioned wheels and weight, it could it be that on the carts, the weight meant it needed four horses rather than three.
I do not know. Thus, my question as to what caused them to change.
It may have to do with budgets.
With sufficient money to afford a supply of extras and timely mainenance, meant they may not have any need to change. This was my other point that the number of extra wheels avaiable (carried, not mounted) could be enough and the "maintenance" routine of replacing wheels with even some wear or risk of breaking might mean there is no need for such flexibility.
I suspect budget pressures emerged to help them along, so - in the end - it was a combination of factors. - R