Investors & landlords

I've had up to 5 but does the number of cars matter if I only use them as rentals?  I don't drive them personally.  They are really only rentals that customers rent and drive.  I didn't think there was a way for me to deduct the federal .625 per mile mileage deduction if I (or an employee) was not doing any of the driving.  Am I wrong about that?