We can see that as the number of pounds of load the tire supports increases, the units of traction do not increase at the same linear rate. The dashed line represents an ideal linear increase in traction in relation to the increase in weight supported by the tire. That's not how it works. In reality, the solid line more closely represents the true picture. At 300 pounds of load, the units of traction are 2.4. If we double the load to 600 pounds, the units of traction only increase to 4.4 instead of double, which would be 4.8.