It is generally not recommended to replace a tire of size 120/80-18 (rear tire) with a larger tire size of 130/80-18 (Continental GT) on your Royal Enfield Classic 500 without any modifications. Here's why:
Fitment and Clearance: The tire sizes mentioned represent the width, aspect ratio, and rim diameter of the tire. A larger tire size could have a wider profile and increased overall diameter. Without modifications, there might not be enough clearance within the motorcycle's frame, swingarm, or fender to accommodate the larger tire size. It could lead to rubbing against other components, affecting the handling and safety of the motorcycle.
Speedometer and Odometer Accuracy: Installing a larger tire size can affect the accuracy of your speedometer and odometer. Since the larger tire has a larger circumference, it will cover more ground with each rotation, resulting in an inaccurate speed reading. Additionally, your odometer will not accurately measure the distance traveled.
Handling and Performance: Tires are a crucial component that contributes to the handling and performance of a motorcycle. Different tire sizes can impact the balance, stability, and handling characteristics of the motorcycle. Installing a tire with a larger size might alter the bike's dynamics, affecting its overall performance and safety.
If you are considering changing your motorcycle's tire size, it is highly recommended to consult with a professional mechanic or authorized dealer who has expertise in your specific motorcycle model. They can provide guidance on suitable tire options that are compatible with your Royal Enfield Classic 500, taking into account factors such as fitment, clearance, and performance.