Me Again's recommendation may be an option if you can't get the Sailun S637's now and you don't want to spend the money on the GY G614's....I would opt for the GY's if you don't mind spending the money for them if you need tires sooner than later..
The Sailun S637 tires being on back order hopefully won't be an omen of price increases or issues with being able to obtain them in the near future...We finally get a good G rated tire that can go head to head with GY G614's, and now they are on back order.....
Chris, what do you know about these tires?
Jim