I was wondering why we run a smaller profile rear tire? Is that to compensate for the bubling of the tire?

 

because the profile of the tire is the percentage of the width. So with a 245/35/19 tire, the side wall is 35% of the 245mm width. When you go wider and stay at the same profile, you'll have a thicker sidewall in the rear, so you go with a smaller profile to compensate and keep the tires all the same height or close to it.
-GP-

 

Hmm cause I am confused now. I recently got new wheels and tires. I went with 18x8 in the front and 18x9 in the rear and for tires I went 225/45/18 in the front and 245/45/18 in the rear and I wanted to make sure that was all ok.

 

Actually, we usually run the same profile tires front and rear, so the rear tire ends up being taller than the front due to the extra width

 

you're fine.

the sidewall aspect ratio is 45%. so in your case:
45% of 225mm = 101.25mm sidewall in front
45% of 245mm = 110.25mm sidewall in rear

so rear sidewall is taller.

you can get a pretty good idea using the tire size calculator on www.tirerack.com

 

because i was feeling uneasy about giving you metric numbers... i'll even give you the conversion.

101.25 = 3.99"
110.25 = 4.34"

 

Yea when I was at the store getting the tires there was a note for my car that said that the difference in size from the front to rear tires cant be less than a half inch and more than three quarters of an inch if that makes sense. I called infiniti just to make sure and they confirmed it was ok. I noticed it when I dropped my car that my rear tire looked a little bigger than my front tire.

 

well your difference is less than 1/2", but you're still fine...

 

Actually, his difference is .7" overall. Sidewall height X 2 + wheel diameter = overall tire diameter. Soooo, he's between the required 1/2" to 3/4".

And, that's the OE tire size on the Coupes with 18" Performance wheel/tire package.......

-Jerome

 

Don't confuse the unloaded tire diameter with the compression that occurs with 900+ pounds on it................the true rolling circumference is all that counts.

 

holy crap... i can't believe i didn't see that. you're absolutely correct.

it's been a long day...