First, I did read about differing tire sizes wreaking havoc with VDC/TCS systems...

Mine is an 04 Touring running the 18" 5-spoke nickel plated Nissan wheels. Cars got 51k miles.

I had Bridgestone REO 40 225-4-18" on the front, and BF Goodrich G-Force pattern 2 in 255-40-18" in the rear. With that setup I have never had VDC stepping in during hard driving and the car has always behaved well at the limit, but now that has changed when I put a new set of Sumitomo's, in the exact same size as the old G-Forces, on the rear. The front Bridgestones are still on the front as they are not wore out yet. They have about 15k on them.
I simply can't drive the car hard around corners at all anynore with the new tires on back. The VDC steps in, yanking the front of the car inward, even though I feel no pushing of the front when driving it. Its kinda frightening, and I actually had an SUV Hero keep up with me around a corner because of this.

I don't understand the dynamics of whats going on; my first guess was the added grip of new back tires combined with the limited slip diff was overloading the grip of the front, but I just don't know. All I know is a motivated Tahoe driver can hang with me if so desired. Obviously thats not why we buy these cars. Thanks for the assistance.

 

...

 

1) Mismatched tires are never a good thing. What model of Sumis?

2) New tires have a slippery release agent on them, that transfers to lower traction on the street until the surface is scuffed off.

3) Tire shops make mistakes, verify the sizes, especially the rears.

4) 15K on ultra-high-performace tires can be "worn out". Numerous heat cycles harden the rubber making them slipperier than before.

 

just turn the vdc off

 

I don’t have much experience running all-square summer performance tires, but i do run all square winter. I do this so I can rotate my winter tires to extend their life (buying winter tires is not much fun). My car has VDC.

If I run all-square 225/50-17” (overall diameter (OD)=25.85”), I experience occasional unwanted engagement of VDC. I don’t have this problem if I run all-square 225/55-17” (OD=26.74”).

You are running nearly the same diameter front and rear:

• 225/45-18” (overall diameter=25.97”)
• 255/40-18” (overall diameter=26.03”)

And, the overall diameter is closer to the front size than the rear size, which caused the problem in my case.

Anytime you run the same or nearly the same overall diameter front and rear with VDC, you may have problems. Shorter than stock rears can exacerbate the problem.

You did not have the problem before with the same size tires, but now you have new tires with a different tread, and you report a problem. Any of the points Dave mentions could be the culprit.

I would check (and maybe experiment with changing) the pressures. Also drive the tires a little longer in case it’s just the new tire “grease” causing the problem.

The easy fix is mounting 255/45-18” tires.

--Spike

 

Good catch Spike. Assume he has the OEM fronts at 225/45 that could definitely be the problem. OP - keep in mind that tires vary in actual size despite the specs given. Your Sumis could be slightly shorter than the Goodrich tires were and that makes the problem more apparent than before so that's why you didn't see it with the old tires.

 

^^ For sure... I tried looking up the tires he reports mounting on the rear, but was not sure of the exact models (you also noticed that he didn’t specify that in his original post). Anyway, I did discover there is a variation in the overall diameter for the same sized tire between the manufacturers (BF Goodrich and Sumitomo). That by itself could be an explanation.

And, your comment: “Mismatched tires are never a good thing” is very relevant here since a differential tread grip would certainly cause a VDC interrupt in the case of mounting tires with the same overall diameter.

Something else… In my case with an all-square setup for my winter tire/wheels setup, I must be very vigilant maintaining the correct psi in every tire. If this value gets off even just a little (and it does), I will experience VDC issues. The same is true when a tire (or a set, fronts or rears) wears more than the others.

People who have Z’s equipped with VDC and decide they want the same overall diameter on front and rear tires certainly encounter more issues than owners who go with the stock overall diameters.

The OP’s simple fix is going with a 255/45-18” rear tire. But, I suspect that is not what he wants to hear.

--Spike

 

Spike, where'd you see that he was running 45's on the fronts? I would assume he is too, but from what I read he just said 225-4-18

Request for moar tire infoz plx

 

We're assuming it based on the fact that he said "Bridgestone RE040" which would have been the OEM tires and they would be 225/45/18.