I had the same question when I got mine. The Prez is right. But unlike most tires on the market, the forward direction usually puts the manufacturers logo on the drive side of the bike. When you set these tires up like the Prez mentioned, this puts the logo on the non-drive side. When I was installing these at my local bike shop, the shop actually e-mailed Challenge to ask them what the correct direction was. Challenge's answer was -- You can mount them in either direction. Thus, looking around at local races. Most folks have both tires with the Chevrons pointing forward (including me), but I have seen some put the tread pattern pointing the other way on their rear tire to try and gain even better traction. My opinion -- if you think you need more traction from these Kick a$$ tires, then you might want to invest in a pair of Challenge Fango also.
There's only one direction for the Grifos
If you put them on backwards then expect to ride backwards.
Once you begin to lean the bike or corner your traction will decrease.
If you want to improve the traction of the Grifo's try sipping