Yosemite is a National Park so the rules are a little different. During winter months you need to have chains in your vehicle, regardless of it's capabilities. Rangers can, and do, ask to see them. While I was living in California I had a nature photography business that had me in the park 60 days a year. I've had to show my chains several times and have seen folks turned away because they didnt' have them. That said, there was only one time I saw it hit R3 and it was only for a few hours. You'll need to have them in the car but it's unlikely you'll need them.
Your best bet would be to pick some up from a store that allows returns and take them back when you're done with your trip.