I am looking at getting 20x9 rims and if I do I would like to get nitto nt555 tires on them. But I was wondering if the 245/30zr20 90w tires fit on a hhr ss

 

The height of that tire is 25.79", so in theory it will work. 26.3" being the max on a SS with stock rims.
Problem is, there's no way to tell since you didn't list the offset on the 20's.

Fwiw. 20's in that size will have very little sidewall. It's gonna ride rough as all get out.

 

And be prepared for rim damage on even small potholes and sharp driveway ridges.

 

What is the widest tire that will fit on a ss? Will 255s fit? And would 245/45zr20 ride better?

 

here is one with 255x40's on it.

 

Thanks I feel like if I were to get anything bigger than 255 it would stick outside the fender and look bad

 

I recommend keeping with the 18's. I have 245/40 18's and they don't have a ton of sidewall(If that's what you're going for), but enough to save me from potholes and such. SS Fan, at one point in time, had (correct me if I'm wrong here) 255/40 18 with little to no rubbing. As Fireman said, the max for the SS is about 26.3", 245/45/ 20 would put you at 28.7".

 

Gah, SS Fan, ya beat me to it... Caught me while I was typing...

 

How wide were his rims? Cause I am having a little trouble finding 255s for 7.5 rims which are stock right?

 

The ones in the pic he posted, Factory Pontiac Solstice wheels. 8in wide.