I need to determine speed of a vehicle based on length of skid marks

I have a project that requires the speed of a vehicle to be determined based on the length of the skid marks it has left. The markings were made on a dry surface, and the vehicle was a septic truck. Unfortunately, I'm not sure what condition the tires of the vehicle were in. I am looking for someone who can take this information and work out a way to accurately calculate the speed of the vehicle in question.