stock fronts, new wider rears = unstable
 

So I got new rears 305 30 19 on stock sport rays. I bought the continental extreme contact dw xl. I kept my stock fronts for now tread is still good. I was going to change those to 265 35 19 up front next year. However I noticed it seems unstable or "floaty" at high speeds changing lanes or even at speed of around 85 and above in straight lines. Is this because I should have wider tires on the front since I Put wider on the back? Any info would really help me with this.

Perhaps the tires havnt been weighted correctly, do you have two different tires on the front and back? it very well could cause an off-balance feel

1. Wider tires are more susceptible to tramlining. If you don't know what this is do a search as it's been discussed many times here on the forum.

2. Mixing tire compounds front and rear can really screw with the handling of a car especially this one. Again, it's been discussed at length in other other threads on here.

Gomer got it, be sure to check your pressures, when mine get a few pounds low early winter I can feel it doing the same thing

Do wider tires on the rear affect tramlining too? I thought tramlining would only be affected by the width of the fronts.. but I am not too knowledgeable about this stuff.

Yes they can. Wider tires will also make a bad alignment show issues worse. Make sure your toe is in spec, as that will cause issues with pulling over painted lines or camber changes.

Also, how many miles are on your Z? Bad hubs can also cause this, as I have been chasing a bad hub issue for about 6 months now.

It only has 15k miles on it. thanks guys i will check front pressure. I might just buy the matching front tires in 265 as well instead of waiting until next year

I experienced this with my new rims. It's really normal id say as far as tramlining goes. My rims spec are 19x9.5f and 19x10.5r with hankook ventus and i got my alignment and I notice this with certain roads. Just gotta have your hand on 9 and 3. Their is a article on tire rack that explains it.

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A lot of people who have changed tires either on the front only or the rear only with different tires have reported handling issues. Your's is not the first.

I get tramlining with my fronts. Hardly ever with my rear 345's.