Blackskiies

Im looking at wheels and tyres.
I currently have 19's running 40 AR
Im set on sizing down to 18's, so can i run an AR of 35 or should i stay with 40?

MicVelo

Key is to keep tire diameter close to OEM to avoid speedo and traction/VDC errors. (Of course, if you have a base model without TCS/VDC, no big deal other than below.)

With 18s, the general rule is going with a 245 or 255/40 front and 275 or 285/40 rear - on wider than stock wheels of course - BUT...

If you elect to go 35 aspect (for ever so slight acceleration advantage through change in effective rear gear), either upsize the width to try and retain diameter OR make sure you go with the same aspect ratio FRONT & REAR, e.g. 255/35F and 275/35R as an example. This keeps the wheel speed sensors reporting the correct ratio of tire revolutions F&R, thereby keeping the traction control in check.

But aside from that, I'd go 40. Dropping the diameter of the tire will mess up the speedo readout (by about 3.5%, not a huge deal) but also shows the wheel gap more.

19s with 40 aspect ratio.... the tires have gotta be too tall. (Unless width is less than OE.) 19s should use 35 aspect to maintain height as above.

Blackskiies

Im looking at running a square setup 18x10.5 on 265/35/18. So you recommend me to go up to 265/40/18?
Also, for the tyres, im looking at Federal ss595. I want slightly stretched but i don't want it to the point of being dangerous, so can i do 265 on 10.5 or just 275?
I do care about not trippin out the ABS VDC TDC...

MicVelo

Note stock reference diameters:
225/45-18 25.97"
245/45-18 26.68"

Now consider your stated choice:
265/35-18 25.30" That's -0.67" F -1.38" R

Look at the 40 aspect alternative:
265/40-18 26.35" +0.38" F and -0.33" R

The latter is right in between so it probably works from a fit perspective BUT with 0% delta F-R, I'd be concerned about going into slip mode without enough difference. ECM may read the relative non-difference as rear wheel spin (wheel sensors read the rear tires to be spinning as fast as the usually small diameter fronts.)

You be the judge.

If you're going square, consider that many people run 275s on 10.5 square. (Which is a better size on 10.5 anyways.) You might want to watch out for the inner fender bolt if running that tall of a tire though; might need cutting down, a very common but solvable issue.

Blackskiies

It came with 19" infiniti wheels on 40AR tyres
so if i got with 40ar on 18 it wouldn't trip the car out cus 35 on 18 would be too big of a height diffrernce?

g356sp

willtheyfit.com is a great little visualizer / calculator

MicVelo

Not necessarily. My point is that the ECM is programmed to read different wheel speeds front to rear. When the tire revolutions match one another, that reads as one or the other end's tire or tires is spinning and the ECM then cuts power to (or brakes) the wheel that it detects (rightfully or wrongfully) is spinning.

IF you were to run the proper tires, say, the OEMs, 225/45 and 245/45-18, all would be normal because the tires are spinning at their normal (differing) rates front to rear.

If you maintained the front:rear revolution ratio by running, say 245/35 and 275/35-18, it would still work fine because the tires, while all are revolving faster than OE, the ratio between front and rear remains the same, about 3% faster front. So no VDC.

In other words, the car is programmed for staggered height tires (within 3% F to R), not the same height.

But square setups can be done - but you might have to 100% disable VDC, not just hitting the switch to turn it off because it doesn't turn it off 100%. There's threads on here that describe how to fully disable it. I don't recommend it but there may be compelling reasons to do so, like racing.

My recommendation is to run the staggered setup just to avoid hassles. What is your reason for wanting to run square anyhow?

By the way, VDC is the most finicky about this, NOT TCS. There might be minor issues with TCS but none as drastic as when VDC kicks in almost instantly whenever the car is moving above 10mph.

EDIT: just realized this is almost exactly what I said in post #2, above. Hahahaha.

Spike100

• Why do you want to run an all-square setup? Some owners do this to allow rotating their tires. Is that your reasoning?
• 265/40-18" fits well on a 18/10.5" wheel.
• Engaging ABS, VDC, TCS, others can be a problem unless you fully deactivate these systems (which isn't as simple as you might think).

Blackskiies

Im running a widebody kit so having a square setup will be easier when ordering tyres and also rotating them

Blackskiies

like you said, the problem is only present if the wheels are spinning/revolution ratio then shouldnt tyre width not be a problem?
i thought square and staggered is talking about having the same width of the tyres

terrasmak

iTrader: (8)

Blackskiies

225/40 19 F on 19x8 30et
245/40 19 R on 19x8.5 33et
the offsets were not measured by me, i just found them online. its the infiniti g35 19" oem rims
don't know how they found its way to be on a 350z but thats how it was when i bought it.

terrasmak

iTrader: (8)

Blackskiies

so going from 40ar on 19 down to 35ar to 18 wont trip the car system out?
the wheels mounted with tyres will be slightly smaller so the revolutions will be shorter for the new 35.on 18 setup.

Everything below the URL is basically a fact (i am assuming)
https://tiresize.com/calculator/
35ar on 18 has 789 revolutions a mile
oem 40ar on 19 has 755 revolutions a mile

So the cars spedometer reading will be higher than the actual reading

Blackskiies

Im fine with moving 1-2 miles slower than what the spedometer says, but will this difference cause the ABS VDC TDC... to trip

MicVelo

You're overthinking it. If you go from, say 245&275/40-18 to 245&275/35-18, the drop in height is close enough to the same for F&R that VDC is still happy as the ratio between F&R is the same.

Spike100

Are you referring to an all-square setup?