I have a 2005 MCSC and currently running 215/45/17 tires. They have been rubbing inside the rear wheel wells when I have someone in the back seat and hit a bump or a change in road surface. Other than banning people from the back seat does anyone know if sway bars or something else would allow me to run this size tire without the rub?

 

Rear sway bar will not help.

215/45-17 is 0.4" taller than stock 205/45-17. Taller means less clearance and more risk for rubbing under load or with any lowering.

Do you have stock wheels?
Do you have stock suspension?

Normally stock suspension does not allow the car to go down low enough to rub tires unless the load is very heavy like 400 lbs or the shock or spring is worn out or broken.

First check the suspension in the rear for any problems on the spring or shock- look for leaking oil or a broken spring (cracked, deformed).

Next you can adjust a little more negative camber in the rear lower control arm to give you a little clearance. Only about 1/2 degree is adjustable.
If you want more negative camber in the rear you will need to add Lower adjustable control arms ( a pair for the lower ones, you have a total of four arms in the rear).

If you have aftermarket wheels your offset is much less than stock like +38mm and puts the wheel and tire farther to the outside of the wheel well where it can rub the inner plastic wheel arch.

You can trim the inner plastic liner with a dremmel tool for more clearance.

If you remove the rear wheel and look at the plastic it is already worn away a little so get the dremmel and keep trimming until you get a few more mm of clearance and maybe along with a small rear camber adjustment you can get enough clearance.

 

Now to decide what the best solution is. THANKS!