Wow 31 looks and no answer! Here’s my no research guess: back in the old days, one company made 1/25 cars. For marketing reasons, another company came out with the 1/24 scale to advertise it as a bigger kit with more detail! The closeness of the size allowed them to be in similar sized boxes. Like I said, this is totally off the top of my head and not factually based at all.
There is another reason for the 1:24 scale. It is an architectural scale. Architects prefer scales that are in so many inches per foot, or even fractions of an inch per foot. 1:24 scale is half inch to foot (1:48 is quarter inch per foot, etc). There are architect’s scales available that have a number of these scales (usually six) on this triangular scale. All other things being equal, I prefer such an architect’s scale.
Interesting! I wonder also if it had anything to do with the pre-built promo models that the auto companies used to send out to dealers in the '50s and '60s to advertise the upcoming new model year.
I suspected the 1/24th may simply be a mathematical derivative of 1/48th but also wondered if the current die cast scale of 1/50th may have led to 1/25th for the same reason.
My take is that 1/24 scale is derived from 1/2inch = 1 foot and is primarily a US manufacturer’s scale. 1/25 scale is a partial decimal scale, 4 times 1/100 scale. Early on, the Japanese were tendig toward decimal or partial decimal scales, hence the 1/100 and 1/50 scale aircraft kits. They were pretty much overruled by the market in aircraft kits and went with the flow of 1/72 and 1/48.
…and the 1/25 may have migrated into the system thanks to the metric-speakers among us! (I know, I’m technically one of those - but after helping my father build or renovate everything from cabinets to houses since I was old enough to hold a tool I tend to think inches & feet when measuring anything!)
I recall the imported 1/50th scale Japanese aircraft models of the 1960s, but don’t recall any automobile kits.
I may do some old kit research to see if I can locate any early European or Japanese kits that may have prompted the US manufacturers to begin issuing 1/25th auto kits in the 1960s.