I shopping for spare rim for 1924 touring..
Tire size 30x3.5"
Is the rim 21"?
No. It is 23". 30" minus 3.5 x 2 (7") = 23
Steve is of course correct, but if you measure the outside diameter with a tape measure, you'll get 24" due to the edges on the rims that holds the tire:
You also need the correct MAKE of rim for your make wheels. Dan
Is the demountable rim the dealers sell the "Ford" type?
The picture above looks like it came from this site:
That rim is compatible with Hayes felloes that have an indentation or notch in the felloe at each of the lug locations to allow space for the extended "foot" of the lug.
My 1924 cut-off touring (now a pickup) came to me with Hayes wheels/felloes and four Hayes rims with lugs like the picture posted above.
It also came with two spare rims - one was a later Hayes rim with the same extended lug foot, but a more tapered shape to the lug. The other spare rim was a Ford rim, the lugs on it do not have the extended "foot".
Here are a couple of pics of Hayes felloes from elsewhere on the forum. Some have an indent for the lug foot, others have a notch.
Hope this helps.