Hi
The tyre you have (26x1 3/8) is a Uk 26" these have a different radius to the Us 26" tyres :cry:
I`ve got the reverse problem i want to fit 26" Creme Fat Franks on my Sunbeam roadster and can`t
get them on,
Theres a good article on Sheldon Browns site about tyre dimensions.
Good luck...