Proper Scope for an Automobile Search?

Proper Scope for an Automobile Search?
John Lee was pulled over on Interstate 10 after a highway patrol officer observed her aggressively weaving from one lane to another. The officer had probable cause to search the vehicle for drugs. Accordingly, Lee opened the trunk, at which point the officer’s attention was drawn to the spare tire. To the officer, it looked as though the spare was the wrong one for the vehicle. In addition, there appeared to be a white, powdery substance on the rubber. Based on his knowledge that narcotics are smuggled in such a fashion, the officer pulled the spare out of the vehicle, slashed it open with a knife, and found drugs inside. The drugs were seized and Lee was arrested. In terms of scope, was this justified?
What would be a case law that supports this decision?