Typical wheel diameter for a 70 Ton Class C Climax was 36" (30" Hub with 3" Tire).
It is reported that Climax reduced the tire on 70 Ton Class C to 2.5" (35" total) so that the calculated tractive effort would exceed that of the 70 Ton Shay. With 36" wheels the calculated tractive effort was slightly less than the 70 Ton Shay.
1551 now was 36" wheels.