Originally Posted by johnny99
If the cut is just in the rubber, you can usually fix it with shoe repair glue (e.g., Barge Cement or ShooGoo). If the cut damages the tire cords or casing, then the tire is probably too dangerous to repair.
This is good advice but I would like to add, you should move the tire to the back. I had a front tire fail on me once while going downhill. Fortunately I was only going 30. Flats on the rear usually don't cause a crash.