If the triangle points forward, it is meant to channel out water better, to prevent aquaplaning, which becomes more of an issue with wider tyres.
Sheldon says aquaplaning isn't an issue for bicycles http://www.sheldonbrown.com/gloss_ho-z.html#hydroplaning
@mr_tom started
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Sheldon says aquaplaning isn't an issue for bicycles http://www.sheldonbrown.com/gloss_ho-z.html#hydroplaning