To replace 21" demountable wooden wheels on a small drum 1925 car with 21" wire wheels from a 1926-7, do you need differnet hubs or anything else?

Yes, the wire wheel hubs are special with 5 bolts, while the wood hubs has six bolts. A small drum can be redrilled for the 5 bolt pattern and fit to a wire wheel rear hub. The original rear hubs can also be redrilled for wire wheel hub bolts. Redrilling the wood front hubs isn't recommended, they are not strong enough and hasn't got the right shape to support a wire wheel properly. New wire wheel hubs are available, but (cheaper) original ones can still be found occasionally.

But good wire wheel hubs seem, to me, to be more expensive than good wire wheels. You'll also need hub dust covers for the front. You might be able to find these at tractor supply houses. I think new dust covers from our Model T suppliers are around $9.50 each. You'll be able to use wood wheel inner and outer bearings, races and seals but also need wire wheel hubcaps.

Remember that the wire wheel rear hubs fit the large drum rear end. If you have small drums you will need to change the housings. You can put them on a small drum rear end but it will require modifications, involving a spacer plate, to the rear hubs.
Erik

You don't need to change housings. You can remove the studs and large drums and redrill small drums and reinstall them. Spot weld the studs to the drums and re-crimp the studs through the hub.

You must have liked the picture I sent you of the wires on my sedan! My car is equipped with most of the items you have been asking about in recent posts. It has taken a few years and lots of dollars but my heavy old sedan can hold its own on most tours and is a pleasure to drive. when you are back in Aus. you are most welcome to come and check out my car. It has the RM brakes, KC Warford and a Z Head.

Kenny is correct. As I mentioned, it can be done. When I put wire wheels on my 13 speedster I did as he described except one more step was required. I had to put a spacer in between the wheel and hub about "3/4 thick. This is because the wheel center is dished and the drum and RM brakes will not fit inside it. I built my own spacers but others have used wheel adapter plates available at parts stores with some modifications.
Fordially, Erik

It only takes one thing, $$$$. Dan