What is the biggest tire i can put on a 1972 Buick skylark?

You CAN put lots of sizes on it but as the OEM size is 185/70-14 you must stay with what works well. A 215/60-14 is a great fit for this car and is the biggest size I would install. Speedometer will still be accurate and it will actually improve handling and braking. Car will look great with this size if you are staying with the OEM wheels.