I have this locked down after my drive today. When Speed Limit is set to Absolute the value next to is is called Limit. When Speed Limit is set to Relative the value next to is is called Offset. When set to Absolute the min value of Limit is 20, so when the car hits 20 you get the 20mph warning. I adjusted this value to 20, 30, 40 and 50 and each time I hit those speeds the warning popped up. When I switched to Relative the warning went away completely.