tyre sizes

hi i need help in knowing what size of tyre i can out on my wheels. they ar 15' by 7, i want them a little streched by i wish to use it everyday. Any help will be great.

 Thanks

what offset are they? maximum tyre size to squeeze under the arches are 205's. 195's are are a popular choice and cheepest choice. depending on how your suspension is and what offset your wheels are, 195/50/15's are cheepest choice for 15" and keep the rolling radius pretty much correct.