I thought you said hub size not tire size. Your hub size is not 26 mm, that's the inside diameter of the tire.
So it looks like you are trying to mount the new tires on your stock wheels, which would work out fine. But remember your original tires are glued on, so be careful when removing them. It usually helps to heat them using something such as a hair dryer.
Does your manual for the himoto not have any info on the tires? You may have to look up places online that sell the tires and try to find the information there. Likewise if you look at places that sell the HPI tires online then on of them should say in the specs or product description.