Need Help With my Next Tire Setup..
 

O.K. I am trying to figure out what to expect with potential tire setups so that I can decide on which tire sizes I will go with next. The problem is that I have NO idea about tire setups and their effect on handling on our Z's. My goals are:

1. To have an aggressive street driven car that will see some autocross and track duty (just for fun).
2. Increase turn in/reduce understeer (or at least not increase it)
3. Maintain straight line acceleration

At the time I purchase my new tires, my setup will be as follows:

Stance Coilovers (these may change to APEXi)
Stillen Sway bars (probably set to the softest setting)
Wheels: F: 19x9.5 R: 19x10.5
Tires: Nitto Invo F: 245/40ZR19 R: 275/35ZR19

I am considering changing my tires to:

1. Bridgestone Potenza RE11's F: 245/40R19 R: 285/35R19
2. Bridgestone Potenza RE11's F: 255/35R19 R: 285/35R19

Which would be the best set up to achieve my goals? What type of results can I expect?

Thanks for the guidance all!

Definitely option 2: having a 255 tire up front will reduce understeer over mounting a 245 tire. That is my choice and it would fit well with your intent with what you are looking for out of a new set of tires.

I kept leaning that way. One reason I considered option 1 was due to the Nismo 370Z setup. Also, I had some concern over the added heft (245 vs 255) of the tire affecting my straight line speed. The RE11's are a heavier tire already, so I may feel that difference already, plus the fact that I would be going with a 255 vs 245.

Is this a valid concern, or will it be so minimal I would not notice?

The difference between a 245 and a 255mm tire, especially the same brand/model of tire, will be negligible at most. You definitely will not notice the difference, 1cm is a tiny difference out of 24/25cm.

Great. That is what I figured, but again, do not know too much about tire setups. Great info christian!

TireRack says the 255 tire is a pound lighter than the 245/40 - I guess extra sidewall weighs more than extra tread.

You don't think 255/35 aren't too off from circumfrence of factor specs? I was thinking 255/40 would match better. Or have you heard the 255/35 is better?... based on 285/35 circumfrence

The 275/35R19 RE-11 is exactly the same weight as the 245/40 RE050. The more tire you can put up front the better, it will reduce under steer and improve turn-in. Increasing negative front camber did wonders for my car with initial turn-in.

jrniehaus - I do not know... From what I can see the RE11 only have 255s in the 255/35/19.

Does anyone know? I never understood why the factory spec is 40 in front, 35 rear.

Can anyone help out here? Does this make a big difference?

Profile is relative to the width of the tire, i.e. it is the height of the sidewall expressed as a percentage of the width. Given that the Z has a staggered width but not a staggered diameter the profiles will be different.

More or less you can just ignore the profile and instead look at the tire diameter and revolutions per mile. The goal is to have these numbers as close as possible to each other and close to stock.

I think I understand what you are saying... I think you are saying a F: 255/35 and rear 285/35 would be better in the sense that running a 255 is better than running a 245 up front; and the 255/35 would be o.k. vs. a 245/40 front??

I think what confuses me is where you say the numbers should be as close together as possible (which means 35/35 should be fine), but then you say they should be close to stock.

The numbers to be close as possible are the overall tire diameter and revolutions per mile, not the aspect ratio (35).

So you have to use a tire calculator to figure these out from the width and aspect ratio. A 275/35 is a much better front match than 255/35.

I was referring to the diameter / revolutions numbers, not the profile number. Please ignore the profile value and look at the diameter instead.

Ahhh.. I see. I do not want to go that meaty up front.....

Given the 275/35 is a better match than 255/35, maybe I would be better just sticking to 245/40 up front, matching the Nismo set up. Or again, maybe it does not matter and I should stay with 255s...

If I go that route, will adding Stillen sways (softest setting to start with) increase understeer, reduce understeer, keep it neutral????

I am so confused....

O.K. I stepped away and thought about all this and see what you all are saying. This is what happens when you have no idea about something, try to understand it, and am sick on meds! I am thinking I will go with a close to Nismo setup with the 245/40 fronts and 285/35 rears.

I still ask this question, and maybe it should be under the suspension section:

Will a 245 F / 285 R with a sway bar kit adversly affect turn in/understeer, or cause the rear end to break loose easily?

I ask this as the Nismo Z upgraded sways increase the front by only 15% while the rear is increased 50%. As I understand, I can set the Stillen sways on the softest setting which would mean a 30% increase in stiffness in front, and about 37% towards the rear. What should I expect?