When you get a flat tire, one of the first things you need to do is figure out what size inner tube you need. Here are a few ways to determine what size inner tube you need:
1. Check the sidewall of your tire. On most tires, there will be a series of numbers and letters that look something like this: 225/50R17 91V. The numbers in this example (225 and 50) represent the width and height of your tire in millimeters, respectively. The letter after the dash (R) indicates the type of tire construction, while 17 is the diameter of your wheel in inches. Finally, 91V is the load index and speed rating of your tire.
2. Once you have all those numbers figured out, refer to a chart to find out what size inner tube you need. You can find these charts online or in many bike shops.
3. If you're still unsure about what size inner tube to get, take your oldinner tube with you when you go to buy a new one so that you can compare them side by side.
4. Another option is to bring your wheel (with the tire still mounted on it)to a bike shop and ask an employee for help picking out the right size inner tube