need help, waiting online

I was issued a ticket for speeding and will go to the court tomorrow. The police told me i was at 31miles/hr on a 25 miles/hr local road. Actually I am pretty sure I was driving at around 25. The situation was that I just passed a stop sign and driving down a slope following another car. I drive on that road everyday, so I know the limit is 25. I kept pressing the brake to keep it under 30. But the police let the other car pass and stopped me. I feel it is unfair. What should I say to the judge to win the case? Please share your thoughts and experiences, thanks a million.