Where to get tiny tyres (~12 inch)
Tire/Rim sizes can be quite confusing. Often times, in American sizing , a wheel listed as a 12-1/2 for example is actually quite smaller than that. The 12-1/2 actually is a rough measurement of about how big it will be with a tire and the wheel is actually only about 8 inches. Another example would be a 24" rim.. which generally have an ISO/bead seat diameter of 507mm, which when converted to inches is actually only 19.96" not 24" as they are listed.

So to correctly find what tire you need, you will need to first find out the Bead seat diameter of the wheel. The easiest solution may to be to take it to a bike shop and have them look at it. 

Otherwise it may be helpful to read through these two Sheldon Brown pages, which fully explain how to find the ISO and what exactly it means. 


Image from SheldonBrown.com

More from Sheldon:

Rim Sizing

Tire Sizing

Reading through those links will tell you how to determine the BSD of the wheel and in turn tell you what size tire you need. It may be a Japanese or European size that i am not overly familiar with so i don't want to guess on your behalf, just thought it may help to provide some resources and data.

You should look for a number in a format XX-254 on the tire, where the XX would be the width in millimeters and the 254 is the ISO diameter in mm, for example 50-254 would a 14" tire that is approximately 2" wide.

If i were to guess though it will be a 14" tire, if it is a 14 x 1.5 it should have a marking of 38-254 somewhere. They have a ISO of 254mm which translates to 10" which looks to be about the size of the wheel in the image. Purely a guess though, i would take further measurements to be sure.