Snowy or icy road conditions are common in the mountains of California, including Yosemite, from fall through spring. When these conditions exist, federal regulations (in Yosemite) and state law (outside Yosemite) require that you use chains or cables in order to reduce the chances of accidents. Chain requirements are strictly enforced.
When do I have to use chains?
You must have tire chains or cables in your possession when entering a designated chain control area, even if you're driving a four-wheel drive or rental vehicle. (Designation is by a sign that says, "CHAINS REQUIRED.") If you're driving a vehicle that doesn't allow tire chains, consider using YARTS to travel into Yosemite.
Conditions dictate when chains are required, therefore, it's not possible to predict if chains will be required ahead of time. We strongly recommend that you have chains when visiting Yosemite from November through March (chain requirements may be in place on occasion as early as September or as late as May); conditions can change rapidly and chains can become required at any time.
Within a designated chain control area, you must use chains or cables on your car's drive wheels when the chain control sign does not exempt your car. Even if your car is exempt, you must have chains or cables in your possession.