Informal staring out the window while at red lights survey over the past 2 weeks shows me that in my town over 95% of tires are some variation of a 5 rib. I think I saw a 6 rib on the back of a ‘Vette. I spotted 4 ribs on the back of a pickup and on the trailer of a semi . There were a couple of I don’t know what ribs on off road mud pickups. Motorcycles excluded. Other than those it made no difference in any of the sizing parameters (tall, short, narrow, wide, aspect ratio). So why is 5 the magic number?