In California, summer tires get the best traction and all-seasons are generally worse (many people mistakenly believe that all-seasons perform better than summer in the rain, I suppose because winter is the rainy season here).
I guess it depends on what part of California you're talking about but all-seasons will generally outperform equivalent grade summer tires in the rain if temperatures start falling below 50-55° or so. A summer tire's grip falls off precipitously [1] when temperatures reach 40-45° but the loss of grip in that "NorCal winter" kind of weather can reduce their performance below that of all seasons. Just because they haven't lost a dangerous amount of grip doesn't mean they haven't fallen behind the grip available to a tire with a more temperature insensitive compound.
Agreed, I should have specified that all-seasons are the safe option in some parts of California. My frame of reference is the warm climates of Silicon Valley and SoCal. Summer tires could even lose traction in one of the colder nights in a San Jose winter.
in theory, the difference between summers and all-seasons is the rubber compound used. all things being equal, the summer compound will perform better when it's hot outside. in reality, most people in the US just don't care and run all-seasons year round. people tend to only buy summer tires for performance-oriented vehicles, so the tires offered with summer compound tend to be aggressive tires with less tread. if you pick a summer tire at random, it may well be less capable than an all-season tire in the rain. the superior compound can't grip if it can't evacuate enough water from the contact patch.
I always swap my own tires in the summer/winter because it takes me less time to do it than to drive to the shop. TPMS, but it can be such a pain.
My previous car, 2010 VW I could switch from summer to winter wheels/tires and drive away. TPMS would figure it out just fine. Now I have a Subaru and am debating buying a $100 tool to reset them. It won't take long to pay for itself, but as it is now, the light is still on.
Worse, my Ram has positional sensors and I haven't seen any "cheap" tools. It happens to be the same set of wheels, but I rotated them and it expects different pressure in the front vs rear. The light is on and it yells at every start because the rear tires are underinflated. How hard can it be for a car to learn which tire is on which corner of the vehicle?
I have a tool to reset them myself, I think it was free from Tire Rack when I bought the tires. It's like a keyfob and pretty simple to use, you just hold down a button.
TPMS reset is usually holding a button and typically in your driver's manual for the vehicle. Found this out myself when my tires got replaced and they couldn't reset my TPMS sensors.
