I was moved over from 657's to 660's when it was discovered the Cal-Trans engineers made a big mistake in calculating cut and fill balance on CA. Hiway 46 West in the early 1970's. The primary grading contractor bought a fleet of 660's for a long haul to balance the dirt. The 660's came from Greene Construction and just finished the big California Coast Rincon job between Santa Barbara and Ventura. They were blowing out tires from overheating because of distance. The dual tires made the difference. 660’s are tall geared and haul ass when they get up to speed!

Great Photo . . .
Made a lot of trips on that road 1976 thru 1980.

Are them the same size tires as the original single tires. Are they each narrower for less heat buildup?

Definently not the same size as the std drive tyres (37.5 x 39) I suspect maybe a 24.00 x 49 size tyre like what was used on the first 777. I am sure the dual wheel option was a factory deal as i have seen a pic of at least a dozen early 660 or 666 tractors at decatur plant with just the inners on.

I have not seen a triple 6 up close for years but I thought they were much wider.