The crash happened shortly before 10:40 a.m. at the intersection of West Steele Lane and Range Avenue.
Gilbert Dorame, a 71-year-old Santa Rosa resident, was driving his Prius west on West Steele Lane while Dieckmann was riding his special-construction electric motorcycle east on Steele Lane.
Dorame appears to have turned left onto Range Avenue from Steele Lane and crossed into the motorcycle's path.
Dieckmann crashed into the right side of the Toyota and died at the scene, police said.
The intersection is controlled by a traffic signal that appears to have been operating properly at the time, police said.
The cause of the crash is still under investigation, but so far police are saying that alcohol or speed do not appear to have been factors.
Dieckmann was the founder of a Santa Rosa-based company called Electric Race Bikes.
KGO contributed to this report