Yesterday, I was riding down a long steep hill on a wet day. I have a Cannondale Synapse road bike that's about 5 years old. I was tucked down on the drops for a good aerodynamic ride. I hit, I'm guessing about 40 mph, and the front wheel began to wobble and I couldn't control it. This has never happened with this bike on dry pavement. I always test the wheels before riding to make sure they are true and they were. It was somewhat terrifying because I was going pretty damn fast on pavement and felt I was going down. I grabbed the brake handle with my left index finger and slowed the bike down a bit and the wheel stopped wobbling and I regained control. But for a half a minute there, I was truly frightened. Anyone ever have this experience and what could have caused it? The tires are typical thin road bike tires and were inflated to about 120 lbs.