The biggest tire you can fit on a stock Ram 1500 without altering the body of the truck or making any specific modifications is a tire of 35 – inches. After that, the bigger the tire you choose, the more you’ll have to trim and add modifications such as fender rolling and wheel-well cutting.  Before you rush and choose the biggest wheel you can find, you need to be aware that bigger tires don’t always mean better performance and more practicality.