I'm looking to increase the tire sidewall height from 215/50r17 to 215/55r17, can anybody comment if these will fit, thanks.
This is on a 2008 HHR LT with stock 17" rims.

 

Click on tools in the tool bar and click on tire rim calculator to check to make sure.
I run 16 inch rims so I can't confirm from experience.

 

Thanks Oldblue, the calculator gives me tire diameter of + .85" but does not indicate strut clearance or any other "rubbing" problem, hoping someone has this information. I've read in other post that I "believe" max tire diameter is 26.3", if anyone can confirm that it would really help also.

 

That is the max diameter I would go

 

Style and shape of different brands/types of tires can be a factor.(some are flatter treads.some have more of a "crown" )

As a rule, 26.3 is usually considered the max.

 

Here's a shot of mine with 26.1" tall tires. (your results may vary), & as FMG posted tire shape / brand / etc can be different.