What is second number in motorcycle tires?

When it comes to motorcycle maintenance, understanding the motorcycle tire numbering system is essential for selecting the right tire that ensures safety, performance, and overall riding experience. Among the various numbers that appear on a motorcycle tire, the second number is particularly significant, representing the aspect ratio of the tire. This article will explain what the second number means, how to read it, and why it matters in terms of motorcycle performance and safety.

1. Introduction: The Importance of Motorcycle Tire Numbering

Motorcycle tires are not just round pieces of rubber; they are intricately designed to meet specific performance requirements. Understanding motorcycle tire specifications, including the numbers and letters imprinted on the tire sidewall, is crucial for riders who want to ensure their bikes are equipped with the most appropriate tires. The motorcycle tire numbering provides essential information such as tire width, aspect ratio, and rim diameter, each influencing how the tire performs under different conditions.

Among these, the second number in the tire's size designation often confuses riders. However, understanding what this number means can help in making informed decisions when it comes to tire selection, maintenance, and overall motorcycle safety.

2. Overview of the Motorcycle Tire Numbering System

The motorcycle tire numbering system is a standardized format that conveys crucial information about the tire's size and type. A typical motorcycle tire size might read as "120/70-17," where each number and letter provides specific details:

1. The first number (e.g., 120) represents the tire's width in millimeters.
2. The second number (e.g., 70) is the aspect ratio or profile of the tire.
3. The third number (e.g., 17) indicates the diameter of the wheel rim in inches.

The focus of this article is on the second number—the tire's aspect ratio.

3. What Does the Second Number Mean: Tire Aspect Ratio

3.1 What is Tire Aspect Ratio?

The aspect ratio of a motorcycle tire, indicated by the second number in the tire size, is the ratio of the tire's cross-sectional height to its width. This number is expressed as a percentage. For instance, if a tire is marked as "120/70-17," the "70" means that the tire's height is 70% of its width. A higher aspect ratio means the tire has a taller sidewall, while a lower aspect ratio indicates a shorter sidewall.

3.2 How to Interpret This Number

Understanding how to interpret the aspect ratio is critical for ensuring you select the right motorcycle tire specifications. Here is how you can read it:

• In a tire size marked "180/55-17," the first number, 180, refers to the width in millimeters. The second number, 55, is the aspect ratio, meaning the tire's height is 55% of its width. Thus, the sidewall height is 99 millimeters (55% of 180).
• A tire size of "120/90-18" would mean the tire width is 120 millimeters, and the height is 90% of that width, which equates to a taller sidewall compared to the "180/55-17" tire.

3.3 Impact of Different Aspect Ratios

The aspect ratio of a motorcycle tire significantly affects its performance, handling, and ride comfort:

• Lower Aspect Ratio (e.g., 50, 55): Tires with a lower aspect ratio have a shorter sidewall, providing a sportier feel with better cornering and handling capabilities. These tires are more responsive to steering inputs and offer better grip during high-speed riding. However, they may provide a stiffer ride and less comfort on rough roads.
• Higher Aspect Ratio (e.g., 70, 80, 90): Tires with a higher aspect ratio have a taller sidewall, which tends to offer a smoother and more comfortable ride by absorbing road imperfections better. However, these tires may not handle sharp turns as precisely as lower aspect ratio tires.

4. Explanation of Other Tire Numbering

Understanding the second number's significance is essential, but it is also important to grasp the meaning of the other numbers in a motorcycle tire size.

4.1 The First Number: Tire Width

The first number in a tire's size refers to the width of the tire in millimeters from sidewall to sidewall. For example, in a tire size of "180/55-17," "180" means the tire is 180 millimeters wide. A wider tire typically provides more traction and stability but can also affect fuel efficiency and handling.

4.2 The Third Number: Rim Diameter

The third number is the tire's internal diameter, which must match the diameter of the motorcycle's wheel rim. In "180/55-17," the "17" means the tire fits a 17-inch rim. Choosing the correct rim diameter is critical because a mismatch can cause safety issues and improper tire fitment.

5. The Importance of Choosing the Right Tire Aspect Ratio

Selecting the appropriate tire aspect ratio is crucial for optimizing motorcycle performance. Different bikes, such as sportbikes, cruisers, and touring motorcycles, have specific requirements when it comes to tire dimensions. A mismatched aspect ratio can result in improper handling, reduced safety, and poor ride quality.

• Sportbikes: Typically use low aspect ratio tires to enhance cornering ability and road grip.
• Cruisers and Touring Bikes: Often require higher aspect ratio tires to provide comfort over long distances and rough terrain.

6. Frequently Asked Questions

To further clarify the subject, let's explore some frequently asked questions about motorcycle tire aspect ratios:

• Q1: Can I use a tire with a different aspect ratio on my motorcycle? It depends. While some variations might fit, it can affect handling, safety, and performance. Always consult your motorcycle's manufacturer guidelines or speak with a professional.
• Q2: How does the aspect ratio affect fuel efficiency? Lower aspect ratio tires may provide better handling and cornering but can decrease fuel efficiency due to increased rolling resistance.
• Q3: Are higher aspect ratio tires better for off-road use? Yes, higher aspect ratio tires generally provide better shock absorption and comfort, making them more suitable for off-road or uneven surfaces.

7. Conclusion: Understanding Tire Numbers and Their Impact on Motorcycle Performance

Understanding the motorcycle tire numbering system is more than just knowing how wide or tall a tire is. The second number—the aspect ratio—plays a vital role in determining a tire's performance characteristics, handling, comfort, and safety. Riders must carefully consider these numbers when selecting motorcycle tires to ensure their choices align with their specific needs and the riding conditions they face. Proper understanding and selection of tires can significantly enhance the motorcycle's performance, safety, and overall riding experience.

By knowing what each number means, especially the aspect ratio, riders can make more informed decisions, ensuring they get the best possible performance and safety out of their motorcycles.