The way I understand this is, the 14.9 is basically the same tire as the 11.25 but put on a wider rim and measured different. The original 8 rims work fine with a 14.9 tire, just may be a bit more round top on an 8 inch rim than on the later 13 inch rim.

I'm not sure if this picture attached properly but that ME Miller chart is exactly right.  I've been studying F&H wheels, rims, and early tires for several years now and have quite a bit of information on when and why the sizes changed.  Goodyear was the first company to figure out around '38-'39 that it was better to have a wider rim that allowed the sidewall of the tire to be straight rather than rounded.  The original tires from '32 to '39 were called balloon tires and they bulged out wider than the rim.  The widest rim in the early days was 8".  To go along with these wider rims after '39 the tire companies also redesigned their tire to have a straight sidewall and a thicker tread section.  All of these rims and tires were then called "wide base" and the old ballon tires and drop center rims were referred to as "conventional".

This was the biggest change in the tire numbering system.  So the 11.25 tire was really discontinued at a certain point and the 13-24 "wide base" tire was sold to replace.  The tire itself was changed.  The later change to the decimal system just better reflected the actual size of the tire width.  So 13-24 became 14.9-24.  Same tire, just a different label.  But neither of these were exactly like the early balloon tires.  Most tires changed during the 40's and later would be of this new wide base type so technically the 14.9 is correct.  Some people do prefer the 13.6 though.  Hope this helps.

11.2x24