I have a 07 350zr. i bought 255 45 r18 tires for the rear and it feels like the side wall is breaking down to easy. i had a 4 wheel alignment after, and they told me the rear toe was out of spec so i had them align it straight. i have factory v2 rims. should i have gone with a 255 40 r18?? or did he align the tires wrong? idk if this is normal when you go from a 245 45 r18.

 

what tires?

 

What's tire pressure.. also the added sidewall will flex more.

 

Brand and type of tire might help. BTW it's Injen not "injin."

 

You mean all tires aren't the same??? What????

 

First problem is those skinny *** tires for the rear. Second issue is prolly the tire itself. Third, check the pressure.

 

Did you buy firestone indy wide oval 500?

 

they are Yokohama AVID ENVigor (W-Speed Rated).

 

the pressure was 33 lbs. now its 43 lbs like the front.

 

Are all tires the same brand and model? Correct stagger? Correct size? A popular thing is to drop the sidewall aspect by 5 all around. Some tires just have a mushy sidewall, may just have to get used to it.

 

regular street driving..35lbs all around

 

43 is quite high.

 

im a 31-33psi person myself, that is what i was taught the first day i owned a car so i have stuck with it, never heard above 40psi..... interesting

 

Lower the pressure to 35 or so psi, and put a couple miles on them. Those tires aren't that stiff, but I doubt you are rolling the sidewalls over. See if they still feel funny after 2-300 miles. I had a set of hankook V12's that did that to me, the rear of the car felt really loose until they wore in a bit.

 

What do you mean by "handling like crap"? explain this and what size are your fronts?

Read this post for reference regarding correct OEM sizing:

https://my350z.com/forum/4936171-post42.html

 

+1

43psi is really high. Lower the psi, drive around a bit, see if it changes anything.

 

Pix would help out if you have any.