Raptor303

Hello,

I don't know very much about tires, so I apologize if I don't know the correct terminology or phrasing.

Anyways, I want to put a set of tires on the 350Z Track that are slightly off of the stock sizing. I believe the fronts are 225/40ZR18 and the backs are 245/40ZR18. The middle number is the "aspect ratio" I think, so this would mean the tires have a smaller side wall, correct? (About 1/2 inch smaller if my math was right). Now, I understand the ride will be rough, but I have also been told that changing the tire to a slightly undersized one will cause excessive wear and blow outs. Is this true?

Furthermore, I've been told that because the tire will be a different size it will hinder the ability of the VDC and ABS to operate properly. Now if this were the case, wouldn't it make upgrading to 19" wheels impossible? I'm very confused.

On top of this, I have been having trouble finding a set of snow tires that will fit the rear wheels. Some people have gotten a set of cheaper, smaller wheels, but again, wouldn't this mess up the ABS and VDC?

Thanks a lot!

Audito350Z

iTrader: (1)

Not to worry. We will try to help as much as we can.

The OEM sizes for the Performance and Track (and maybe the Touring with the 18" wheels) is 225/45-18 Front and 245/45-18 Rear. The "aspect ratio" is the 45 number in that list of numbers. In simple terms, it means the sidewall height of the tire is 45% of the width of the tread.

I'm guessing you are planning to go with a 40-series (aspect ratio) tire to replace to stock tires. They will be a lower diameter than the stock tires, which has effect in the final gearing and the speedo control, but not much else.

As long as you keep them properly inflated and you keep the car in alignment you won't have to worry about blowouts or excessive wear.

The ride probably won't be too rough. Remember, you are driving a sports car, so it will be rough no matter what!

There are numerous tire-size calculators listed on this forum. Try one of those to make sure you are maintaing the factory diameter. I think the consensus on the best upgrade in size is to go with 245/40-18 on the front and 265/40-18 on the rear.


Not true. These devices use sensors to tell them when the car is slipping sideways (the VDC) and when the wheels are locking under hard braking (the ABS). Tire size has little or no effect in those situations.

You could put a 24" wheel on the car if there were a tire that would match the stock rolling diameter. Stock rolling diameter is something like 26.5", so there's not a lot of tire selection in that size.


Nope... you can't "mess up" the ABS or the VDC (see above comments). You will probably have to buy 16" or 17" wheels for the car to handle snow tires. With a snow tire, you want it to be narrow and tall. The best way to do that is go with a smaller diameter wheel.

If you put a snow tire on the car, and you use a 16" wheel, your tire size will have a section width and aspect ratio that gives it the same rolling diameter of the stock tires. This means the tire will be narrow (section width) and tall (aspect ration, or sidewall height).

Again, one of the tire size calculators can tell you what size yuo will need when using an smaller diameter wheel for the snow.



OK.... hope all that helps.


PeteH

Raptor303

Whoa! Thanks a ton! You just cleared everything up for me.



OK, now I got it. As long as the actual diameter comes out to be the same, I should be safe.

Once again, thanks a lot!

Raptor303

One more question (sorry!): How close to the factory diameter should I look for? Is .3" larger too much of a discrepancy?

Thanks!

Audito350Z

iTrader: (1)

Glad I could help.

your best bet is to stay within 3% of the original rolling diameter


PeteH