Tire tread & rotational direction

Continental Explorer. Actual model fitted on my Scott.

For simplicity, you just fit tire to your wheel according to the direction as indicated on the sidewall. It meant to make your life easier after all. For those of you that want a better explanation, continue reading.

For passenger cars, tires can be bidirectional, inside/outside or rotational direction.
Bidirectional - your can never go wrong mounting the tire to the wheel.
Inside/outside - "Outside" is meant to be on the outer part of the wheel, i.e. the part where you see the tyre most of the time.
Rotational direction - it has the arrow that shows the direction of the tire when the car move forward. If mounted on the right side of the car (front or rear), the arrow indicator pointed to the your right side, if it on top most of the tire. (see photo below)

My focus is elaborate on rotational direction since that's the only concern for MTB'r.


Tyre fitted on wheel for right side of the car

On tarmac, rotational direction wasn't a major factor if you are driving in hot & sunny day. Rotational directional comes to its purpose when it's raining or you hit patch of water. The tread on rotational directional tire will "channel" out the water in between the tire and the tarmac away as to gain contact to the road. Without this, the tire will hydroplane (or aquaplane) and car will lost contact with the road renders braking, steering, and accelerating useless and disastrous. As such, mounting rotational direction tire wrongly will increase the risk of hydroplaning since instead of "channel" out the water, it "scoop" the water in!

Back to MTB, directional tyre for MTB is always on the opposite side for front and rear. This is for the reason that rear tire is the driving wheel and it need all the traction required to maintain its contact to the terrain in order to move forward. On the other hand, front tire is always on rolling and doesn't need that much of tread until you need to apply brake. Front tire works the same way like the rear tire in term of traction but in different rotational direction. That's another reason why rear brake has less stopping power that the front.