Steve Gilbert

how can a 15 inch wheel be made to fit a 2009 hhr ss

Oldblue

2004 or 05 Malibu Max rims if you have the Standard SS brakes , if you have Brembos then no 15 inch rims will fit

2005HHRauto

You just need to use the HHR LS/LT caliper brackets & rotors, if you have the standard HHR SS brakes.
Easy-peasy as you don't have to disconnect the brake lines.

14-1163 & 14-1164 brackets on rockauto for $25 each
22705303 & 22705304 from GM for $65 each.

Centric rotors for $30 each

$120 total to run 15" wheels on the front with new rotors & reman brackets.
A lot cheaper if you go to the bone-yard or craigslist.....

And correct, you can't use 'Brembos' as they are way too big.