Auto Insurance Claims: Contesting Contributory Negligence, contributory negligence, car lengths

Question
First, thank you for your time.

I was recently involved in an auto accident.  I was going 60mph in the carpool lane (there was a passenger), when another car that was speeding lost control and spun out of control into my lane from an adjacent one.  He swerved erratically and then righted himself about two car lengths ahead of me.  I started to brake as soon as I saw him break the double lines into my lane, but even so he was less than 35 feet ahead of me, and I could not bring my vehicle to a full stop at such a short notice, at such a small distance.  I hit his car from behind, causing moderate damage to his vehicle but totaling my own.  

The police report lists the other driver as at fault(speeding caused hime to lose control), however his insurance company insists that I am 25% liable for the accident.  Their reasoning is that the driver claims he was swerving erratically for some time before losing control and breaking into my lane, and thus I should have seen him and should have driven more carefully.  From my perspective, this is bogus; as I understand it, he was several car lengths ahead of me in an adjacent lane, and his lane was crowded. How could I see him 100 feet ahead of me in full traffic, in another lane?  He did not come into my view until he broke into my lane.  His insurance company refuses to accept this logic, since there were no witnesses to the accident on the police report.  

They are offering me only 75% of the value of my vehicle.  I have liability coverage, so I can not claim the rest from my own insurance company.

Is their reasoning fair?  If not, what recourse do I have in recouping the total value of my vehicle?  I am in the state of California.

Thanks so much.

Answer
You can contest the insurance company's position by taking the case to small claims court. If you prevail there, you will get 100% of the value of your vehicle. Since you had a passenger, was he or she not a witness to the accident and would they not support your version of the events? Small claims court is the proper venue to resolve this issue. If the court's ruling is in your favor it will compel the liability carrier of the other party to pay your claim and back off the contributory negligence argument.