Has anyone run a 225/40/18 & 245/40/18 tire instead of the 45 series our cars come with?

I want to know if there is any downsides to this?

 

The overall tire height is wrong.

 

What would be the negative effect of running something with a smaller series?

 

Your speedometer will be off.

 

Positives would be slightly quicker acceleration.

Cons, Speedo would read faster than you are going, they will look small on the car, ride will be rougher and have higher chance of damaging the wheels, the fronts will be even more stretched looking than they already are.

Chris

 

It changes the ride height and handling. Members do lower the 350Z but there is a proper way to do it.

 

Flipping things the other way around.

(F) 235/40/18 – 2.25% fast
(R) 255/45/18 – 1.3% fast

Would this be ok?

 

Read this thread, the first and most easy to access:

https://my350z.com/forum/wheels-and-tires/231823-03-track-model-wheel-question.html

Do a search and you will find many answers.

 

I have been for a while now.

Sometimes you just want to get a straight answer instead of searching through thread after thread.

Would there be any rubbing issues using a 255/45/18 in the back since everybody is using a 255/40/18?

 

I dont think there would be any rubbing issues, but you are missing the point. The 40 and 45 numbers are aspect ratios, which are exactly that, ratios...specifically the ration of sidewall height to tire width. Therefore, a 45 aspect ration on a 245 tire is not the same as a 45 ratio on a 255 tire.

Now, the Z has various traction control/stability systems depending on what model you have (ie track has VDC, base has none). These systems use the stagger (difference in overall wheel/tire diameter) to calculate when the tires are spinning and when you are losing grip. Whenever you make a change in tire size or wheel size (or both), you have to make sure you maintain as close to factory stagger as possible so as not to upset these systems.

So, the end goal is to keep the sidewall height given a set diameter wheel as close to stock as possible. This is where tire size calculators come in. You obviously understand this as you have listed the speedo errors below. The 255/45/18 size works fine, but in my experience, it tends to run a bit tall...actual tire sizes are unfortunately not very constant given a listed aspect ratio. Depending on the tire you choose, it could be right on, but I would stick with a 255/40/18 rear. I have run this setup on a Michelin Pilot Sport and Falken Azenis RT615, and I can tell you that the inflated tire diameter is extremely close to stock...a 255/45/18 in these same setups would have been taller than stock. I know some might disagree, but this is simply my experience.

Hope this helps.