How important is the tire rotation mark? If you are using a flip flop wheel on a SS/FG bike and you want to change from SS to FG does that mean the tire has to be taken off and turned around on the rim? The simple answer is yes but how many do it?

The less tread pattern/depth, the less important the rotation direction becomes. I'll try to get it "right" in the shop, but should I accidentally reverse it during a roadside repair, I'll leave it as-is until the next natural opportunity to reverse it occurs.

+1 There are some tires, like GP4000, with tread patterns so light that I don't know why they bother with direction arrow.

"I don't know why they bother with direction arrow."

My uneducated guess may be that it has less to do with the tread and more to do with the direction the internal fabric plies are laid/overlapped when the tire is manufactured.

That was kind of my thought too, but I'm currently working on a bike with Schwalbe Land Cruiser tires.
They have opposite pointing arrows for <F-R>

"They have opposite pointing arrows for <F-R>"

Well, that doesn't fit into either tread shape or internal construction categories. Esthetics?

Easy solution: buy a non-directional rear tire.

I "think" it's for rolling resistance or braking on the front and drive traction on the rear (in dirt).
I've seen similar on a "few" mountain bike tires.
I'd describe these Schwalbes as a "bike path" tire. Mainly pavement & some hard packed dirt.

Technically it's based on the tread shape since you want the front tire to have maximum traction when braking and the rear tire to have best traction for propulsion - therefore opposite directions. It makes a marginal difference in loose dirt/mud with tires that have substantial tread patterns - doubt it makes any difference with road tires or on pavement.

That is the case for motorcycle tires. I can't say for bike tires.

Yes, and I've never understood directional road tires as tread is of no use and, in fact, something of a detriment. I have seen dedicated front and rear road tires and I assume it has to do with rubber compound and durability differences.

The fabric in bike tires is diagonal, so it runs the same way whether the tire is going "forward" or "backward" -- OP, feel free to ignore the little arrows when flipping your wheel.

Unles the surface that you're riding on is deformable the tread has very little effect on traction. And since the contact patch is long and narrow there's little or no chance of hydroplaning, so no need for tread because of that concern. For road tires tread is a sales thing not a performance one. Andy.

IMO, tread only makes a difference on dirt, snow or mud using directional mtn bike tires. These have the knobs shaped to provide more bite on the back edge, and better release on the leading edge. Otherwise tread barely matters, though if you're OCD buying a non directional tire for use on your flip-flop wheel may help you sleep better.

I like that answer although I would be cautious in wet weather since it looks like treads are meant shed water to the sides and rear.

As a bicyclist, you can't build up water underneath the tires fast enough for the sipes to do a damned thing.

+100,

It isn't onlyu a question of speed, but the shape of the tires. Car tires have flat profiles that can act like skis and hydroplane on a film of water. Bicycle and motorcycle tires have crowned profiles and cut through water pushing it out to the side. Even on a motorcycle it requires tremendous speed to hydroplane.

I accidentally put my front Maxxis Overdrive tire on the wrong way (rotation); didn't noticed it until I took a corner which I usually take with moderate lean-in and nearly had the front tire slip from under me. Maybe it was a fluke, but after catching my breath, I noticed that the tire was on backwards.