[Cyberdemon]

If you go on Tirerack they have plenty of stories and videos comparing the performance of summer tires to winter tires.

I have a few friends who are engineers at good year, and I know what you're asking for is "At 55 degrees you still have 85% of your grip" but it's not that simple.

Rubber is a dynamic compound - the temperature, tire pressure, compound of the rubber, and age of the rubber all play a factor in deciding how much grip you have.

A Goodyear F1 summer may not have the same grip as a Contactisport @ 65 degrees, etc.

The generalization is this:

Summer tires have their grip fall off drastically in the cold. At the same time, they are designed to have a ton of grip to begin with, so are you going to endanger yourself driving if you're not pushing the limit of the tire? No. Are you increasing your risk if you have to make a sudden lane change or abrupt stop? Yes. The summer compounds on a cold day are not ideal, and that's precisely where you run into issues.

I am in the same boat as you, and a few weeks ago after hurricane Sandy we got hit with a snow storm. I still had my summer (Goodyear Eagle F1's) on the car and I commute 30 miles a day to work. So I drove my car 30 miles in a good 3" of snow on summer tires with temps below freezing and it was surprisingly confident...much more so than my old Kuhmo MX's which were so bad in the cold I literally couldn't pull my car out of a parking spot in 1/2" of snow.

If it's a dry day, you're probably fine as long as you take it easy. But again, it's the emergencies that are going to be where you run into a potential problem. If your car used to stop in 140 feet and now it stops in 180 feet, that small delta could be the difference between safely stopping and hitting the back of a truck.