* Wheel Well Clearance: The 2005 Taurus wasn't designed for 20-inch wheels. The larger diameter would likely cause the tires to rub against the fenders, suspension components, or brake calipers.
* Tire Sidewall Height: To compensate for the larger wheel diameter, you'd need a very low-profile tire. This reduces sidewall height, making the ride extremely harsh and susceptible to damage from potholes and bumps.
* Offset and Bolt Pattern: Even if clearance wasn't an issue, you need to ensure the bolt pattern (number of lug nuts and their spacing) and offset (how far the wheel sits in or out from the hub) are compatible with your Taurus. Incorrect offset can cause handling problems or rubbing.
In short: While technically *possible* with extensive modifications (like fender rolling or potentially different suspension components), fitting 20-inch rims on a 2005 Ford Taurus SEL is highly improbable without significant issues and is generally not recommended. It's much safer and more practical to stick with wheel sizes recommended by the manufacturer. Check your owner's manual or a tire size chart for your specific vehicle model to see the recommended sizes.
