I've read afew threads on here that using 17" radials on the 17.5" 3 piece split rim but with using a 16" tube ...
I missed those threads, or I have forgotten.
Best I can tell mismatching tire sizes to rim size is asking for serious trouble.
Also, I'm not aware of any 17.5" three piece rims. 17.5" as already pointed out will be single piece rims. Do you have any pictures or info if there is such a thing?
Grigg