2013 Ford Focus St Tire Size – Unlocking Peak Performance And Safety

ByRobert Lozano

When it comes to your 2013 Ford Focus ST, understanding the correct tire size is fundamental for maintaining its spirited handling and ensuring your safety on every drive. This guide cuts through the confusion, providing you with the exact specifications and expert insights needed to make informed tire choices for your hot hatch. From stock setups to performance upgrades, we’ll cover everything you need to know to keep your ST gripping the road with confidence.

Driving a 2013 Ford Focus ST means you appreciate a car built for performance, and nothing impacts that performance more directly than your tires. The right rubber is crucial for everything from razor-sharp cornering to confident braking, transforming your daily commute or weekend spirited drive. But with so many options and technical terms, choosing the best tires for your ST can feel overwhelming.

This comprehensive guide is designed to empower you, whether you’re a seasoned DIYer or a new ST owner, with the knowledge to select, maintain, and even upgrade your tires safely and effectively. We’ll demystify tire specifications, explain how different choices affect your car’s dynamics, and provide practical advice to ensure your Focus ST always performs at its best. Get ready to gain the confidence to make the smart choices for your wheels.

Understanding the Stock 2013 Ford Focus ST Tire Size

The foundation of any tire discussion for your hot hatch begins with its factory specifications. Knowing the original equipment (OE) setup is crucial, as it’s what Ford engineers meticulously calibrated the suspension, steering, and braking systems around. Deviating too far without understanding the implications can compromise your ST’s renowned driving dynamics.

What is the Factory Tire Size for a 2013 Focus ST?

For the 2013 Ford Focus ST, the factory-equipped tire size is 235/40R18. This specific dimension was chosen to provide an optimal balance of grip, ride comfort, and handling precision right off the showroom floor. It’s a key component in what makes the ST such a joy to drive.

This designation breaks down into three important metrics:

  • 235: This number represents the tire’s width in millimeters, measured from sidewall to sidewall. A wider tire generally offers a larger contact patch with the road, leading to more grip.
  • 40: This is the aspect ratio, expressed as a percentage. It indicates the height of the tire’s sidewall as a percentage of its width. In this case, the sidewall height is 40% of 235mm. A lower aspect ratio typically means a shorter, stiffer sidewall, which translates to better handling response and less flex during hard cornering.
  • R18: This denotes the tire’s construction type and wheel diameter. ‘R’ stands for radial construction, which is standard for most modern passenger vehicle tires. ’18’ indicates that the tire is designed to fit an 18-inch diameter wheel.

The stock wheel size for the 2013 Focus ST is 18×8 inches, meaning an 18-inch diameter and 8-inch width. The bolt pattern is 5×108, and the offset is typically around +55 mm, though this can vary slightly with aftermarket options.

Why the Stock Size Matters for Your Focus ST

Sticking with or understanding the implications of the original 2013 Ford Focus ST tire size is important for several reasons. Ford’s engineers spent countless hours tuning the suspension and steering to work optimally with these specific dimensions.

Changing tire sizes without proper research can lead to:

  • Altered Handling Characteristics: A different aspect ratio or width can change how the car feels in corners, potentially introducing understeer or oversteer.
  • Speedometer Inaccuracy: A significant change in overall tire diameter will cause your speedometer to read incorrectly, impacting legal speeds and odometer readings.
  • Fender Rubbing: Larger diameter or wider tires might rub against your fender liners or suspension components, especially during turns or over bumps.
  • TPMS Issues: While not directly related to size, different tire pressures or incompatible sensors can cause your Tire Pressure Monitoring System (TPMS) to malfunction.

For most owners, especially those not seeking extreme performance modifications, maintaining the stock 235/40R18 size is a safe and effective choice that preserves the vehicle’s intended performance. However, there are valid reasons to explore other options, which we’ll discuss next.

Decoding Tire Specifications: Beyond the Basic Size

Beyond the fundamental 235/40R18, every tire sidewall is a wealth of information. Understanding these additional markings is vital for ensuring you select tires that are not only the correct size but also appropriate for your driving conditions and the performance capabilities of your 2013 Ford Focus ST.

Load Index and Speed Rating

These two numbers are often overlooked but are critically important for safety and performance.

Load Index

The load index is a numerical code that corresponds to the maximum weight each tire can support when properly inflated. For the 2013 Ford Focus ST, a typical load index is around 95W. The ’95’ indicates a load capacity of 1,521 pounds (690 kg) per tire.

Always ensure your replacement tires meet or exceed the vehicle’s original equipment load index. Underspecified tires can lead to premature wear, tire failure, and unsafe driving conditions, especially under heavy loads or during spirited driving.

Speed Rating

The speed rating is an alphabetical code indicating the maximum speed at which the tire can safely carry its rated load. For the Focus ST, the ‘W’ in 95W signifies a maximum speed of 168 mph (270 km/h).

While you might not drive at these speeds, a higher speed rating often correlates with better handling and heat dissipation capabilities, which are beneficial for a performance car like the ST. Never choose a tire with a lower speed rating than your vehicle’s original equipment, as this can compromise safety and handling at higher speeds.

Treadwear, Traction, and Temperature (UTQG Ratings)

The Uniform Tire Quality Grading (UTQG) system provides comparative ratings for tires based on government-mandmandated tests.

Treadwear

This rating indicates a tire’s expected wear rate relative to a control tire. A tire with a treadwear rating of 400 is expected to last twice as long as a tire with a rating of 200.

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For a performance car like the ST, you’ll often find a trade-off: higher performance tires tend to have lower treadwear ratings (e.g., 200-300), meaning they offer more grip but wear out faster. All-season tires typically have higher ratings (e.g., 400-600) for longevity.

Traction

Graded from AA, A, B, to C, this rating indicates a tire’s ability to stop on wet pavement under controlled conditions. AA is the highest rating, indicating superior wet traction.

For safety, especially if you drive in wet climates, prioritize a higher traction rating. Your 2013 Ford Focus ST needs excellent wet weather grip to maintain control.

Temperature

Graded A, B, or C, this rating indicates a tire’s resistance to heat generation and its ability to dissipate heat. ‘A’ is the highest rating, signifying better heat resistance.

Heat is the enemy of tires, especially during aggressive driving. A higher temperature rating is always preferable for performance vehicles to prevent heat-related degradation and potential failure.

Choosing the Right Tires for Your Driving Style

Selecting tires isn’t just about finding the right 2013 Ford Focus ST tire size; it’s about matching the tire’s characteristics to your specific driving habits, local climate, and performance expectations. Different tire types offer distinct advantages and disadvantages.

Summer Performance Tires

These are often the go-to choice for ST owners who prioritize maximum grip and handling in warm, dry conditions. They feature soft rubber compounds and aggressive tread patterns designed for optimal traction and responsiveness.

  • Pros: Superior dry grip, precise steering response, excellent braking performance in warm weather.
  • Cons: Poor performance in cold temperatures (below 45°F/7°C), no traction in snow or ice, faster wear rate.
  • Ideal For: Enthusiasts who live in warm climates or have a dedicated set of winter tires.

All-Season Tires

A popular choice for many drivers, all-season tires aim to provide a balance of performance across various conditions, from dry pavement to light snow. They offer a compromise between summer performance and winter capability.

  • Pros: Versatile, decent performance in most weather conditions, longer tread life, convenient (no seasonal changes).
  • Cons: Not as grippy as summer tires in warm weather, not as effective as winter tires in heavy snow or ice.
  • Ideal For: Daily drivers in moderate climates who need year-round performance without the hassle of tire swaps.

Winter Tires

If you live in a region with true winter conditions, dedicated winter tires are a safety essential. They are designed with specialized rubber compounds that remain flexible in cold temperatures and aggressive tread patterns to bite into snow and ice.

  • Pros: Excellent grip and braking in snow, ice, and cold conditions; significantly safer than all-season tires in winter.
  • Cons: Reduced performance and faster wear in warm weather, requires seasonal swapping and storage.
  • Ideal For: Drivers in regions with consistent snowfall, ice, or prolonged cold temperatures.

Pro Tip: For the best performance and safety, many ST owners choose a “two-set” approach: dedicated summer performance tires for the warmer months and a set of winter tires for cold weather. This ensures optimal grip and handling no matter the season.

Upgrading and Plus-Sizing Your 2013 Ford Focus ST Tire Size

While the stock 235/40R18 is excellent, some owners explore “plus-sizing” their tires and wheels for aesthetic reasons or to gain a slight performance edge. This involves increasing the wheel diameter while maintaining a similar overall tire diameter to avoid speedometer errors.

Common Plus-Sizing Options

The most common approach is to move to a larger wheel diameter, typically 19 inches, while adjusting the tire’s aspect ratio to keep the overall diameter close to stock.

For an 18-inch wheel, some owners might opt for a slightly wider tire on the stock 8-inch wheel, such as a 245/35R18. This provides a slightly larger contact patch but requires careful consideration of potential rubbing, especially with aggressive offsets or lowered suspensions.

If moving to a 19-inch wheel, a common compatible tire size would be 235/35R19 or 245/35R19. These sizes maintain a similar overall diameter to the stock 18-inch setup, minimizing speedometer error.

Key Considerations for Upgrades

Before making any changes to your 2013 Ford Focus ST tire size or wheel dimensions, consider these critical factors:

  • Overall Diameter: Aim to keep the new tire’s overall diameter within 3% of the stock diameter. This minimizes speedometer error and maintains proper gearing. Use an online tire size calculator to compare dimensions.
  • Wheel Width and Offset: If going wider, ensure your new wheels have the correct width and offset to prevent rubbing on fenders or suspension components. The stock wheels are 18×8″ with a +55mm offset. Many aftermarket wheels for the ST are 18×8.5″ or 18×9″ with offsets in the +40 to +45mm range to push the wheel out for a flush look.
  • Fender Clearance: Wider tires or lower offsets can cause the tires to rub against the fender liners or even the fenders themselves, especially when turning or over bumps. This is more pronounced if your ST is lowered.
  • Suspension Modifications: If you’ve lowered your ST, your clearance will be reduced, making tire and wheel fitment even more critical.
  • TPMS Compatibility: New wheels will require new TPMS sensors or a transfer of your existing ones. Ensure they are compatible with your vehicle.
  • Ride Quality: A lower aspect ratio tire (e.g., 35-series) will have a shorter sidewall, which generally results in a stiffer ride and less absorption of road imperfections.
  • Weight: Larger or wider wheels and tires can increase unsprung weight, potentially impacting acceleration, braking, and handling. Lighter aftermarket wheels can help mitigate this.

When to Call a Pro: If you’re unsure about specific wheel and tire fitment, especially with aftermarket components or suspension modifications, consult with a reputable wheel and tire shop. They have the expertise and tools to measure clearance and recommend suitable options safely.

Essential Tire Maintenance for Your Focus ST

Proper tire maintenance is paramount for safety, performance, and maximizing the life of your tires, regardless of whether you stick to the factory 2013 Ford Focus ST tire size or opt for an upgrade. Neglecting these simple steps can lead to premature wear, reduced grip, and even dangerous situations.

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Tire Pressure Checks

This is arguably the most important maintenance item. Correct tire pressure ensures even tread wear, optimal fuel economy, and consistent handling.

  • Frequency: Check tire pressure at least once a month, and always before long trips. Do this when the tires are “cold” (driven less than a mile).
  • Specification: Refer to the sticker on your driver’s side door jamb for the recommended tire pressure for your 2013 Ford Focus ST. It’s typically around 39 PSI (pounds per square inch) for all four tires, but always verify.
  • Tools: A good quality tire pressure gauge is a must-have in your glove box.

Under-inflated tires can lead to increased rolling resistance (worse fuel economy), excessive heat buildup (risk of blowouts), and wear on the outer edges of the tread. Over-inflated tires can result in a harsher ride, reduced grip, and wear in the center of the tread.

Tire Rotation

Rotating your tires regularly helps distribute wear evenly across all four tires, extending their lifespan.

  • Frequency: Follow your vehicle’s owner’s manual recommendation, typically every 5,000 to 7,500 miles, or with every oil change.
  • Pattern: For directional tires (common on performance cars like the ST), rotate them front-to-back only. For non-directional tires, a cross-pattern is often used. Consult your tire manufacturer’s guidelines.

Wheel Balancing

Even perfectly good tires can feel off if they’re not balanced correctly. Unbalanced tires can cause vibrations, premature wear, and steering issues.

  • When to Check: If you feel vibrations through the steering wheel or seat, especially at highway speeds, it’s time for a balance check. Always re-balance tires after they are mounted or rotated.
  • Process: A tire shop uses a balancing machine to add small weights to the wheel rim, counteracting any imbalances.

Wheel Alignment

Proper wheel alignment ensures your tires meet the road at the correct angle. Misalignment can cause rapid and uneven tire wear, pulling to one side, and compromised handling.

  • When to Check: After hitting a major pothole, curb, or any suspension work. Also, if you notice uneven tire wear or your steering wheel isn’t centered when driving straight.
  • Frequency: A general recommendation is to have your alignment checked annually or every 15,000 miles.

Tread Depth Checks

Tread depth is crucial for grip, especially in wet conditions. Worn tires significantly increase stopping distances.

  • Method: Use a tread depth gauge or the “penny test.” Insert a penny into a tread groove with Lincoln’s head upside down. If you can see the top of Lincoln’s head, your tread is below the legal minimum of 2/32 inch and needs replacement.
  • Replacement: Most experts recommend replacing tires when they reach 4/32 inch of tread depth, particularly if you drive in wet or snowy conditions.

Frequently Asked Questions About 2013 Ford Focus ST Tire Size

Navigating tire choices for a performance vehicle like the Focus ST can bring up several questions. Here are some common queries answered to help you make the best decisions.

Can I use a different tire size than the stock 235/40R18 without issues?

While you can, it requires careful consideration. Changing the overall tire diameter can affect your speedometer accuracy and potentially rub against your fenders or suspension. Going slightly wider (e.g., 245/35R18) on stock wheels might be possible, but always check clearance, especially if your car is lowered. It’s best to stay within a 3% overall diameter variance to minimize issues.

What speed rating do I need for my 2013 Ford Focus ST?

Your 2013 Focus ST originally came with a ‘W’ speed rating, which means the tires are rated for speeds up to 168 mph (270 km/h). You should always replace tires with at least the OE speed rating or higher to maintain the vehicle’s performance and safety characteristics. Using a lower speed rating is not recommended.

How often should I rotate the tires on my Focus ST?

It’s generally recommended to rotate your tires every 5,000 to 7,500 miles, or with every oil change. This helps ensure even wear across all four tires, extending their lifespan and maintaining consistent handling. Always follow the rotation pattern recommended by your tire manufacturer, especially if you have directional tires.

Will installing larger wheels and tires void my warranty?

Generally, simply changing wheels and tires won’t automatically void your entire vehicle warranty. However, if a problem arises that can be directly attributed to the aftermarket wheels or tires (e.g., suspension component failure due to incorrect offset or tire rubbing), the dealership may deny warranty coverage for that specific issue. Always consult with your dealership if you have concerns.

What are the signs that my tires need to be replaced?

Look for several key indicators: tread wear indicators (small bars within the tread grooves that become flush with the tread when it’s worn out), tread depth below 2/32 inch (legal limit) or 4/32 inch (recommended for wet safety), visible cracks or bulges in the sidewall, punctures that can’t be safely repaired, or tires that are more than 6-10 years old (even if they have good tread, rubber degrades over time).

Conclusion: Empowering Your ST’s Performance

Understanding the intricacies of your 2013 Ford Focus ST tire size and its related specifications is more than just technical knowledge – it’s about empowering you to make informed decisions that directly impact your car’s performance, safety, and longevity. From the precise handling of the stock 235/40R18 setup to the careful considerations for performance upgrades, every choice you make for your tires ripples through the entire driving experience.

Whether you’re sticking to the factory specifications or venturing into the world of aftermarket wheels and wider rubber, remember that meticulous maintenance is key. Regular pressure checks, rotations, and alignments are not just recommendations; they are essential steps to keep your ST gripping the road as it was designed to. By following the advice outlined here, you’re not just maintaining your tires; you’re investing in every exhilarating drive and every safe stop. Keep your Focus ST rolling strong, and enjoy the ride with confidence!

Robert Lozano
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