70's F1 tire size question

I bought a 1/12 Heller kit of Ligier JS11 (1979) recently, but disappointment is a little beyond my expectation, especially the tires which are not even round in shape. Instead of fixing the them, I bought a Tamiya WR1 (1977) at a bargain price for the tires (or even the wheels) as replacement. But to my surprise the size of the Tamiya tires are a bit smaller (both front & rear) than the Heller ones. Now, can anyone kind enough to tell me this is correct, the tire size of 79 is actually larger than that of 77?

I haven't done any scale measuring but I have two sets of aftermarket tires, one set from MFH for 1/12 M23 and one from another Japanese company for the 1/12 312T...and both sets are wider and a bit taller than Tamiya's tires.