My question involves a traffic ticket from the state of: California, Contra Costa County

Hello, I searched through this forum but did not find any questions similar to mine. Any help would be greatly appreciated. Here is my situation;

Charge is Infraction 22350 cvc excessive speed.

I was traveling on a rural country road (mostly crops and fields of corn) with a posted speed limit of 50 mph. At one intersection, immediately after a stop sign, the speed limit changes from 50 to 40. It was completely dark out, there are no street lights and there were no other cars on the road. I never saw head lights of the officers patrol vehicle driving behind me, so he could have only pulled behind me from sitting in the dark with no lights on at the cross road where it turns to a 40 mph. He wrote on the ticket I was travelling at 58 mph. He did not use radar and again it was pitch dark out side. There was no way I could have reached 58 mph from the stop sign to the section at which he said I was speeding. When he turned his patrol lights on to pull me over, it was less than 1/4 mile after the speed change/stop sign, so he could not have been following me long enough to calculate my speed by distance with his car.

I feel I was driving safe and that I was not traveling at 58 mph. My question is, can or should I plead not guilty to this ticket by writing, then follow with the trial by declaration? I asked a "fight your ticket" service if I should try and they said if I file a declaration by mail the court will suspend my drivers license? I'm not sure if that is true, so if any one has advise, please post.

Thank you!