Tire Question

[adren77]

I have 04 Coupe with 18" rims.

The stock tire sizes are 225/45/18 front / 245/45/18 rear. All rims should be 18x8 30mm offset.

Does anybody see a problem with me going 245/45/18 all around and rotating my wheels/tires for longer life?

[C-Kwik]

The VDC will read same diameter tires as slip and it will cut back throttle when you try to go and activate the ABS each time you brake. There must be a similar percentage difference in tire diameter from front to rear as stock to keep this from occuring. Unless you are willing to deactivate the VDC each time you get into the car.

[adren77]

I heard of this before, but I wasn't sure because...

on my 2004 6MT Sedan, I had 19" Coupe wheels and I was running 245/45/19 all around (but the wheels were staggered) and never had this happen.

Hmmm

[Tampa G35 Sedan 6MT]

I had all the same size on the sedan and no problems... I now have 225 40 19 front and 245 40 19 rear and still no problems..

I don't think the car reads slip from the front tires because it isn't an X

DJ

[Jacko3]

Yep! My mechanic said the same thing as well.

[leeG35]

The VDC will read same diameter tires as slip and it will cut back throttle when you try to go and activate the ABS each time you brake. There must be a similar percentage difference in tire diameter from front to rear as stock to keep this from occuring. Unless you are willing to deactivate the VDC each time you get into the car.

What is being calibrated when you get the "chirp" as you first drive off then? Is it only the ABS? Wouldn't the VDC use this information also? If the system calibrates itself each time you start the car and first drive off, I would think the tire sizes wouldn't matter because the computer should be smart enough to figure this out. I was under the impression the different tire widths front and back were for handeling issues. Doesn't smaller width front tires promote understeer. Which is the same as saying it prevents oversteer? Which in the case of the coupe makes the handling more neutral and prevent the car from swapping ends at the limit? You guys tell me, I'm just guessing. But I find it hard to believe the VDC unit is different for the coupe and sedan.

[C-Kwik]

I heard of this before, but I wasn't sure because...

on my 2004 6MT Sedan, I had 19" Coupe wheels and I was running 245/45/19 all around (but the wheels were staggered) and never had this happen.

Hmmm

The sedan comes with the same sized tires all around. The coupes have staggered diameters and widths. I'd imagine the VDC/ABS computer is calibrated accordingly.

What is being calibrated when you get the "chirp" as you first drive off then? Is it only the ABS? Wouldn't the VDC use this information also? If the system calibrates itself each time you start the car and first drive off, I would think the tire sizes wouldn't matter because the computer should be smart enough to figure this out. I was under the impression the different tire widths front and back were for handeling issues. Doesn't smaller width front tires promote understeer. Which is the same as saying it prevents oversteer? Which in the case of the coupe makes the handling more neutral and prevent the car from swapping ends at the limit? You guys tell me, I'm just guessing. But I find it hard to believe the VDC unit is different for the coupe and sedan.

To my knowledge, nothing is being calibrated when you start the car. Its simply an ABS self test that confirms that the ABS is working properly. This really isn't speculation. Its pretty well documented within the G35 and 350Z community. And its also something I've seen and experienced firsthand in my friend's 350Z. He bought a Tommy Kaira Z and the wheel/tire package caused this issue. He sold most of the Tommy Kaira stuff off, including the wheels and tires and put some 06 wheels and tires on and the problem went away.

As for the effects on handling balance, its more complicated than tire sizes alone, but if we assume the vehicle would exhibit neutral handling with equal size tires, then yes, a smaller width front tire would likely result in understeer. Any specific reasons for staggering the tires on the coupes is really something Infiniti knows for certain. Speculation would point out that they would try and induce a bit of understeer as it is generally safer than oversteer, perhaps even safer than neutral steer.

[mbarra]

Thanks for the explanation. As a coupe owner, I erred on the side of not wanting to mess with the suspension geometry using a non-staggered setup. But I think the VDC/ABS issue is more immediate.