Hello Franck, There are actually 2 tire sizes that will work on the Custom Weta Road King trailer. They both have 4 lug nuts. The two sizes that work are: 4.80/4.00-8 and 4.80-12 and the tire size is not the only consideration. Tires have a speed rating. If you tow your Weta on the highway you want a high speed rated tire. Also Bias vs Radial tires. Recently experts have started recommending Radial Tires for trailer tires, but as recently as a couple years ago Bias were considered the best for trailer tires. If you are only replacing one tire be sure not to mix Bias and Radial on the same trailer. I have both sizes in stock but only in Bias which is the type that come with a Weta Trailer. The tires I have in stock are the same Kendra Load Star brand that come with the Road King custom Weta Trailers and are High Speed Rated for towing at Highway Speeds. I will be at Weta Fest and the Alter Cup and I have both size tires in my van as well as many other Weta spare parts. Please call if you have more questions. Rick Upson Sail 1422. Rick's Small Sailboats LLC, Weta Dealer for Florida and nearby Southeastern States. 954-579-1289 Cell