The tire size 90/90-21 on your motorcycle tire provides important information about its dimensions and specifications. Here’s what each part means:
Tire Size Breakdown
90: This number represents the tire’s width in millimeters. In this case, the tire is 90mm wide from sidewall to sidewall.
90: This second number indicates the tire’s aspect ratio or profile height. This means that the sidewall height is 90% of the tire’s width. So, the sidewall height would be 81mm (90% of 90mm).
21: This number specifies the wheel rim diameter in inches that the tire is designed to fit. So, this tire is meant for a 21-inch diameter wheel.
Additional Information
- The tire size 90/90-21 is a common size for front tires on adventure motorcycles and dirt bikes.
- This sizing system uses width/aspect ratio-rim diameter, which is the modern metric method of denoting motorcycle tire sizes.
- The lack of an “R” between the aspect ratio and rim diameter indicates this is likely a biased ply construction tire rather than a radial one.
- You may sometimes see “M/C” after the size, which simply denotes it’s a motorcycle tire.
Comparison to Other Sizes
- A 90/90-21 tire is slightly taller than an 80/90-21 tire, which would have the same width but a shorter sidewall height.
- It’s equivalent to older alphanumeric sizes like MJ90-21 used on some cruisers and custom bikes.
When replacing tires, it’s important to use the size recommended by your motorcycle manufacturer for safety and performance reasons.
The tire size provides critical information to ensure proper fitment and handling characteristics for your specific motorcycle model.
The 90/90-21 tire size can significantly influence your motorcycle’s performance in several ways:
Handling Characteristics
The 90/90-21 size, typically used as a front tire on adventure motorcycles and dirt bikes, affects the bike’s handling characteristics. This relatively narrow and tall tire profile contributes to the following:
- Sharper turning: The narrower width allows for quicker and more precise steering inputs, which is especially useful in off-road situations.
- Improved accuracy: This size is particularly good for riding on grass and other loose surfaces, providing better control and accuracy.
However, it’s worth noting that some riders find the 90/90 size can feel “sharp” at times, which might require some adjustment in riding style.
Stability and Traction
The 90/90-21 size balances various performance aspects:
- Straight-line stability: The 21-inch diameter contributes to better stability when riding in a straight line, which can be beneficial for highway riding.
- Off-road capability: This size is often chosen for its ability to handle diverse terrains, offering a good compromise between on-road and off-road performance.
Comparison to Other Sizes
When comparing the 90/90-21 to slightly wider options like the 90/100-21:
- The 90/90-21 offers more precise handling and better performance on loose surfaces.
- A 90/100-21 might provide a smoother ride, making the bike feel more planted, which some riders describe as a “steamroller” effect (in a positive way).
Performance Considerations
It’s important to note that tire size is just one-factor affecting motorcycle performance. Other considerations include:
- Tread pattern: This significantly impacts traction on different surfaces.
- Tire compound: Softer compounds generally offer better grip but wear faster.
- Tire pressure: Proper inflation is crucial for optimal performance and safety.
Remember that the ideal tire size depends on your specific motorcycle model, riding style, and the types of terrain you frequently encounter. Always follow the manufacturer’s recommendations for the best balance of performance and safety.
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