
tyre shops always tell u 30psi...dunno why
I've ran 205/50/15, 195/50/15, 205/45/16 and 195/55/15 at different times and at every tyre shop I've been to in my life, the attendant says "about 30" when I ask. Typically I'd run about 34psi so the ride isn't too harsh, but the lowest profile I've ever used was 45/16, so your 40/17 might be different.
45psi is a tad high IMO.
On the sidewall has the maximum pressure the tyre can handle, keep it below that and you'll be fine.