The Ford Focus ST represents a significant performance milestone for the compact hatchback segment, and one of the most immediate ways enthusiasts personalize and optimize this hot hatch is through its rim size. Selecting the correct wheel diameter and width is not merely an aesthetic choice; it fundamentally impacts handling, ride quality, and the overall driving dynamics of the vehicle. This guide provides a detailed look at the appropriate rim sizes for the Ford Focus ST, ensuring both style and performance are perfectly balanced.
Understanding the Factory Specifications
When considering modifications, it is essential to start with the factory specifications provided by Ford. The standard wheel fitment for the Ford Focus ST, particularly models from the third and fourth generations, is typically 18 inches in diameter. These OEM wheels are usually paired with tire sizes such as 245/35R18 or 225/40R18, depending on the specific year and market. Sticking close to these dimensions is the safest route for maintaining the vehicle's intended suspension geometry and speedometer accuracy.
Performance Benefits of Upgrading
Upgrading to a larger rim size, such as 19 or 20 inches, is a popular modification for the Focus ST because it allows for wider tires. A wider contact patch enhances grip during aggressive cornering and braking, translating to improved lap times and confidence-inspiring handling. However, this upgrade is a compromise; while grip increases, the unsprung weight of the wheel also grows, which can slightly hinder acceleration and ride comfort if not chosen carefully.
Recommended Rim Size Range
For most drivers looking to enhance the Focus ST without compromising daily usability, a rim size between 18 and 20 inches is generally the sweet spot. Staying within this range ensures that the tire sidewall can maintain sufficient height to absorb road imperfections. It is critical to calculate the overall tire diameter to avoid significant discrepancies from the stock setup, as this can confuse traction control systems and alter the vehicle's speedometer reading.
Width is Just as Important
While the diameter often grabs the most attention, the rim width is equally crucial to the performance equation. A wheel that is too narrow will cause the tire to bulge in the center, leading to overheating and uneven wear. Conversely, a wheel that is too wide will stretch the tire sidewalls, reducing the contact patch and making the car susceptible to damage from potholes. For the 19-inch upgrade, a width between 8.5 and 9.5 inches is ideal for achieving the perfect rubber footprint.
Considerations for Suspension and Brakes
Installing larger rims on the Ford Focus ST necessitates a review of the vehicle's suspension and braking components. Larger wheels require larger brake calipers to maintain the same stopping power and thermal efficiency. Furthermore, the suspension must have enough clearance to prevent the tires from rubbing during full lock or when navigating road imperfections. Failing to address these factors can lead to premature bearing failure or even safety hazards while driving.
