Usually you have a crummy-but-good-enough encoder on the wheel in the form of a steel tone ring and a magnetic pickup. If you know the steering wheel angle and

Usually you have a crummy-but-good-enough encoder on the wheel in the form of a steel tone ring and a magnetic pickup. If you know the steering wheel angle and can observe the relative rotation rates between wheels, you can infer which tire is low. How do you determine that all of them are low? I guess you could compare against a GPS velocity?