Probably I should know this but I don’t.
Truck tyres have an arrow on them, telling the tyre fitter which way round to put them on so that when the vehicle is moving forward, the tyre moves in the direction of the arrow.
Why is this, and what would be the consequences of mounting them the wrong way round so that the tyre rotated against the direction of the arrow?
some tyres have a single direction rotation tread pattern, hence the direction arrows, it is down to the water dispersion of the tyre
I did wonder that, but it even seems to be a feature on tyres where the tread pattern would appear to be identical the other way round.
some tyres are directional…and have the arrow,some tyres are not directional and can be fitted either way.
usually the directional tyres have offset tread patterns the non directional have straight grooves.
only thing to watch is a directional tyre fitted the wrong way will fail the mot.
Wrong way round will cause drag ! And supposedly not grip properly. Or so I’ve been told.
Post deleted.Trumped by Mr.Bridgestone 
I was told by a man from Michelin, that they are only directional for the first 20,000miles, then you can put them where you like
newmercman:
I was told by a man from Michelin, that they are only directional for the first 20,000miles, then you can put them where you like
13/32nd of their life apparently
Having watched a few hundred tyres been re-manufactured I was under the impression it was so the banding took hold and the joint was well sealed
Not so it seems
But I wouldn’t risk fitting them the wrong way on a MOTO GP bike or even my road bike.
Wheel Nut:
But I wouldn’t risk fitting them the wrong way on a MOTO GP bike or even my road bike.
I’ve fitted a few bike tyres and the one that caught me out years ago was the old Dunlop K82. Nothing special in a directional sense of the look of the tread pattern. Look for arrow on the sidewall and fit. Look again, and find there is an arrow on the other side pointing the opposite direction. Look closer still and find one arrow is for front rotation and the other for rear rotation. Dismount tyre and start again. DOH! 
Although the original tyres were fresh and still had hairs, they had to go as they were Pneumants!
They are directional because of how the layers of banding overlap
I’ve never had a problem with directional tyres when reversing. 
Funny enough the Michy slicks I currently use on my Blade are directional, the Bridgestones I used to use weren’t. Quite handy after spending a Wednesday afternoon at Mallory, 'cos being a skinflint I could turn them.
triple-tango:
They are directional because of how the layers of banding overlap
That was my understanding too, until I read that Bridgestone article.
Then I read this and decided that they do put arrows on for a reason.
Directional tyres
Directional tyres usually have a chevron or arrow pattern in the tread and are designed to work in only one direction of rotation.
Directional tyres disperse water that builds up in front of the tyre more effectively, reduce road noise, and improve directional stability.
They must rotate in the right direction and this will be clearly marked on the sidewall of the tyre.
If a directional tyre is fitted the wrong way round, the tyre won’t be dangerous, but you won’t gain any of the benefits of it’s design.
Incorrect fitting of both asymmetric and directional tyres is a reason for MOT failure.
Some high performance cars are fitted with directional and asymmetric tyres. These must be fitted the right way round on the wheel and on the correct side of the vehicle.
the maoster:
Funny enough the Michy slicks I currently use on my Blade are directional, the Bridgestones I used to use weren’t. Quite handy after spending a Wednesday afternoon at Mallory, 'cos being a skinflint I could turn them.
It seems to vary from make to make whether slicks are rotational.
The ones I’ve worked with over the years, Bridgestone were, as are Avons, but Dunlops aren’t. The Avons were run one way on the front and another on the rear, I was told this was because of the construction, so it was better for the front under braking and rear under acceleration.