This is a common question. Your tyre size should be written on the side of your tyre. There will be a series of numbers showing the diameter and width. It will look something like this: 700c x 29. Occasionally different cycle manufacturers will use a different scale. If you have any problems working out your tyre size, please call us on +86 199 7018 0785. Alternatively, you can email us a picture of the writing on your tyre to customerservice miya@lvbu.tech.