Originally Posted by porshah
Great information. Thanks dmppdx and ben@tirerack.
I was also curious as to what temperature Summer Performance Tires are not as effective. I don't plan on driving my M through snow, but do like to drive it through cold winter months, and was going to get a set of M+S rated tires.
The exact temperature will vary, and it is more of a spectrum than a specific cutoff temperature.
Here's a general breakdown based on my experience:
As you get into the 40s Farenheit the summer tires will become less effective than optimum, but still are ok to use.
Below 40 they start to lose more traction, and may feel a bit skittish in wet weather. I am doing this right now, and I leave a little extra safety margin if there is any moisture on the road. By this point the All-Season tires probably provide more grip.
Below freezing the loss of grip is even more noticeable, and if you get into any snow or freezing rain it can get quite scary.