The issue with summer tires in sub 40 degree temperatures is extremely limited traction for the first 15 or so minutes of driving. If you had to make an extreme avoidance maneuver or slam on your brakes while the tires were still super cold and rock hard, you're going to have no grip and likely crash.
After 15 minutes of regular driving the tires get enough temperature in them to be able to drive normally, granted you won't have as much traction as you would in warmer weather. You must always keep this limitation in mind when you drive in cold weather with a summer tire.
Summers are perfectly manageable in winter provided you:
- Take it very easy during the warm-up period. This means easy acceleration, slowing down sufficiently for corners, and avoiding all hard cornering.
- Leave a safe distance between you and the car ahead of you so you have enough room to stop in an emergency. Cold summers WILL slide in an emergency stop.
- Avoid all ice/snow
