I have a 2003 Nissan 350z Touring, and I know that if I'm running 18's, the factory size would be 40 aspect ratio, and if I was running 19's the closest factory size would be 35 aspect ratio

I have 19 inch g35 rays as my daily wheels (2 rear pairs, to make square instead of staggered so 19x8.5 front, and 19x8.5 rear) and 18 inch kansei tandems as my autocross/track wheels (18x9.5 front, 18x10.5 rear), and at the moment I need new front tires for the Rays, and I need a full set for my track set, and currently, this is what im running -

G35 Rays -
255/35/19 all around

Kansei Tandems -
265/40/18 front
285/40/18 rear

And I am wondering, is it possible to run a SLIGHTLY larger diameter tire setup? or is that going to screw with the ABS/Traction Control of the car? I do Touge, track, autocross, and daily it, so its pretty multipurpose, but the tire setup I would WANT to run is as follows -

G35 Rays -
255/40/19 all around

Kansei Tandems -
265/45/18 Front
285/45/18 Rear

Obviously I know it would mess with the speedo, so I would have to compensate for that when im on the road, but other than that would it be fine?

 

In theory, it is possible to use slightly larger diameter tires, but do so with the potential impact on ABS, traction control, and the overall handling of the car in mind.

 

Larger diameter tire/wheel packages also run into the problem on clearance with tires getting caught on the wheel wells when using sharp steering angles.

 

On the 18s....

1.4" is NOT "slightly larger".

Like suffer interference with fender liners under full suspension compression, spring/FUCA/LCA contact. Not guaranteed but that's a huge diameter upsizing.


On the 19" G wheels, the caveat here is running square in a VDC car. Doesn't ALWAYS create issues but do you like the odds when 8 of 10 VDC issues are from improper tire sizing? Mo' better to go with at least a 20mm size stagger, maybe 225/245 (like OE) possibly 245/265.