Can someone please let me know if the 235/45HR18 tires on sale at tirerack can fit on all 4 rims with no problem for the 6mt with 18's?

 

The size is ok and will fit fine on the rim. Also within about 1.4% of the original diameters.
One issue that sticks out is that the replacements are only 'H' speed rated which is well below the original 'W' rating.

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<font color=red>G</font color=red>S<font color=green>M</font color=green> <font color=black>Silverstone Coupe</font color=black>

 

but thats alright since I am just using it for the snow in the winter, no?

 

Should be fine for snows bro.

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<font color=red>G</font color=red>S<font color=green>M</font color=green> <font color=black>Silverstone Coupe</font color=black>