Take into account that the static friction supplies the centripetal force, then, you can write:

where,
m: mass of the truck = 1700 kg
v: speed of the truck = 20 m/s
r: turning radius = ?
Fr: maximum frictional force = 12,000 N
Solve the equation above for r, replace the values of the other parameters and simplify:

Hence, the turing radius of the car is approximately 56.67m