The first thing to know about roadside testing is that, when you are stopped by police, you do not have to do the tests! You can refuse to perform these tests, and not be given a separate ticket for refusing to perform them.
Unfortunately, police officers are not required to tell you that you do not have to perform these "tests".
And, the current state of the law is that you do not have to be read your Miranda rights prior to performing the tests, even though the very tests that you do on the roadside are going to be used to try to convict you in court.
Since the State can convict you of DWI in two ways: (1) if your blood/breath alcohol concentration is greater than 0.08%, or (2) if your ability to drive a car is impaired due to drinking alcohol or taking certain drugs - it is very important to the reliability of the tests given to you just before your arrest.
When the breath/blood testing is suppressed or kept out of the trial due to errors in that testing, you still have to "beat" the field sobriety testing in order to be successful in your defense of the DWI charge.
The challenge against the testing is based on many things.
How did you get out of your car? If you didn't need to use the car for support as you walked to where the officer told you for the testing, you are better off than if you needed to use the car door to help you out of the car, or used the car for support as you walked along side of it.
Did the officer ask you if you had any injuries that would prevent you from doing the testing, or that would cause you any problems while doing the testing? Any injury to your back, legs, knees, or feet, could cause problems standing on one leg or walking a line, and as a result, even if you performed the testing, the validity or reliability of the testing is compromised.
Do you have balancing problems, middle ear problems, vertigo, or anything else that would cause you to have a problem with balancing while performing these tests?
Are you 50 pounds overweight? Are you over 65 years old? These are reasons that the officer should not do field testing on you.
If you are wearing two-inch heals or anything larger, you should be given the opportunity by the officer to take off your shoes.