5 Ribs

[userfriendly]

My take on 5 (or more) ribs is that they provide better lateral traction, or they don't slide sideways as easy as 3 or 4 rib tire designs do.

For getting out of my driveway at 3am after the plow filled it in with snow, I need straight line traction and the "traction control" turned off so I can spin the tires.

Once I'm on my way on un-sanded hard pack under a layer of fresh snow, I need a ribbed tire to keep me on the road.

 

[PandaBear]

I remember seeing a Michelin ad flyer claiming that their larger amount of void justify their use of thinner trend (as well as their rubber open up to larger void as it wear thinner).

I think the total width of all circumferential grove is what helps, regardless of 4 or 5 "ribs". If I remember right the first circumferential groves on each shoulder, if exist, is used as indicators of where patching is allowed.