Wider Tires

[distinctperson]

So I got another IS (2014 this time), and they came with the dreaded run-flats on 19" 326 wheels. I'm planning on switching them with the Pilot Super Sport immediately. My question is, what is the widest size I could go to gain the most benefits (primarily grip, and secondarily aesthetics) without having to use wheel spacers or worry about rubbing against fenders (both of those create extra hassle for me when explaining to the tire shop, so I'd rather have neither involved).

By default, according to Tirerack, the sizes are 225/35 front and 255/30 rear. Would, perhaps, 245/35 and 275/30 work ? more? less?

Also, it seems that there is a variance of 30 of in-between front and rear. Is this by convention for a legitimate reason, or just a coincidence ?

Responses greatly appreciated!

[Constant.S]

Hey congrats on the iS, first of all the variance is due different width wheel, in front its 8j and rear it is 9j. Maximum you can push on these stock wheels (8j and 9j) are 235 front and 265 rear, same as i did, after that you are distorting the geometry of the tires. So basically the setup would be 235/35/19 and 265/30/19. (As far as "flushness" goes you will need spacers with either setup, i'd say 10mm to 12mm max on stock tire specification 255/30 or 8mm to 10mm with 265/30.)
I hope these made sense
I can upload a photo of my setup if you want, its not a 326 wheel but a 296 which have exactly the same offset and width as yours. I have mounted 265/30 Contisports 6 with 10mm spacers just on the rear for a more aggressive look and 235/35 on the front

Cheers

[Innovative AutoConcepts]

This is what I am currently running.

Front:19x8.5 ET35 235/35/19 +10mm Spacer
Rear: 19x9.5 ET25 265/30/19 + 5mm Spacer
Tires: Hankook Ventus V12 Evo2

[distinctperson]

Constant.S, I spoke with the tire shop owner and he told me your setup will work on mine. However, based on what Innovative AutoConcepts, it seems that I could also add +5mm spacer in the front. Would that work on the stock 326s with MPSS ? thanks!

[Constant.S]

Yeah, +5mm in the front would work no problem but i didnt add any spacers in front cause i didnt feel they were needed.

Here's how my setup looks like:

[distinctperson]

So I had the tires replaced with MPSS 235/265. The tire shop owner stated that he couldn't fit 10mm hubcentric spacers in the rear; he only managed to add 5mm (any ideas why he wasn't able to ?).

This certainly improved the look of the vehicle, however, I am having some issues with stability. At higher speeds, the vehicle is no longer as stable as it were prior to the switch. There is a particular wide stretch on the highway here that I used to take at 140-150mph without any issues, that I'm now struggling to control the vehicle at a mere 130mph. At lower speeds stability is unaffected, but that's a given.

Any ideas what's causing this ? Is it the combination of the rear spacers and wider tires that's affecting the geometry of the car such that this is an unavoidable cost, or are there some other settings that need to be adjusted to complement this change ?

[NoQuarter]

Readjust the camber maybe?

If you have stock wheel bolts could be why he couldn't do the 10mm spacer?

[distinctperson]

He already replaced the bolts with longer one to fit the spacer, so that's not the issue as I'm sure he has even longer ones.

I will ask the owner about adjusting the camber settings. Hope that's what's causing the instability

[mrkoven]

Originally Posted by Innovative AutoConcepts

This is what I am currently running.

Front:19x8.5 ET35 235/35/19 +10mm Spacer
Rear: 19x9.5 ET25 265/30/19 + 5mm Spacer
Tires: Hankook Ventus V12 Evo2

any pics of this? sounds flush. im looking to add spacers soon. i have h&r sport and same wheel+tire specs except my offsets are f30/r37. im thinking +5f and +10r. maybe +15r?

[NoQuarter]

Mine:

VMR V706 Wheels - Matte Gunmetal
Hankook Ventus V12 EVO 2 tires

Front: 19x8.5 ET35 +12.5
Rear: 19x9.5 ET35 +15

Stud Conversion: 75mm Black Bullet Nose Race Stud Kit 12×1.5

I don't have decent pics handy and the car is up in the air at the moment.
I am on stock suspension for the 35is

[mrkoven]

any difference between vrsf, bms, h&r spacers? same difference i assume, all good?

[cruisingdownthestreet]

what size tires look better on the z4? 18s, 19s or 20s?

[OakDan]

I have the 296 19" rims and I'd like to use the following tire sizes:

235/35
265/30

Do I need to use any spacers? It sounds like on the front they aren't needed but wasn't sure about the rear.

[Tangent]

Originally Posted by distinctperson

...There is a particular wide stretch on the highway here that I used to take at 140-150mph without any issues, that I'm now struggling to control the vehicle at a mere 130mph. ...

I hate to be that guy but given your history of getting into accidents I beg of you, start going to track days and cool it on the streets!

[Constant.S]

Originally Posted by OakDan

I have the 296 19" rims and I'd like to use the following tire sizes:

235/35
265/30

Do I need to use any spacers? It sounds like on the front they aren't needed but wasn't sure about the rear.

Look at my picture i posted on one of my comments above, i have the 296 (painted satin black) wheels with 235/265 setup. Just used 10mm spacers on the rear.