How to find the circumference of a race car tyre?

One last question for Y/A from me. 

I'm trying to learn how to calculate race car speeds from vehicle specifications. 

Vehicle speed = wheel speed x wheel circumference.
 πD = Wheel circumference

Unlike standard road car tyres, race car tyres provide an overall diameter instead of an aspect ratio.  

Front tyre size: 305/605/18 (mm/mm/in) (Tread width/Overall diameter/Rim diameter)
Rear tyre size: 335/710/18 (mm/mm/in)  (Tread width/Overall diameter/Rim diameter)

Is it just as simple as 'π x overall diameter' to find the circumference here? 

TIA, and good luck in the future all!