18" Tire Size: Any reason not to get 255/40s?

[Emertxe]

According to the wheel offset calculator, 255/40/18 is as close of a diameter as I can get to the stock 245/30/20s.

In order of what I care about, it would be:

1) not rubbing
2) odo/speedo accuracy
3) performance feel vs stock
4) looks

Is there a reason why I shouldn't go with these over the usual recommendation of 255/35/40? If the performance feel is largely different, I'd be willing to get 255/35. However, I don't track my car. I plan on keeping stock height, getting wheels that are 18x9.5 +45mm offset, and planning on getting Michelin PS4S summer tires.

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[TheCanadian]

255/40 R18 is 0.8% larger than OEM
245/40 R18 is 0.4% smaller than OEM, and the same sidewall width

Closest to stock is 245/40 R18

EDIT: With 9.5" wheels 255/40 is your best bet

 

[adw818]

255/40 will check all those boxes and look best at stock height. That’s what I went with for now, may lower it later and adjust tire size then.

 

[evlsmurf]

255/40 will check all those boxes and look best at stock height. That’s what I went with for now, may lower it later and adjust tire size then.

Even if you lower, wouldn't 255/40 still be fine? I've read mixed reviews about rubbing.

 

[adw818]

Even if you lower, wouldn't 255/40 still be fine? I've read mixed reviews about rubbing.

I’ve read the similar things as well. I went +45 offset so likely won’t be an issue with a more mild drop, which is what I would go for.

 

[JohnInATL]

I’ve run this size at stock height and lowered. Good comfort from an all season tire, but they did numb up the precise steering a bit which I think a 265/35 would change. But I feel the 255/40 looks best at stock height. Depends on your personal goals!

stock height:

Lowered on Tein springs:

 

[evlsmurf]

Iive in upstate NY, so I need a bit taller side wall due to our horrendous roads. I plan to run Firestone Firehawk Indy 500 on Superspeed RF06RR 18x9.5 +38. I do have Swift springs to install. I plan to wait on those to see how the car sits with the 18's on.

 

[JO3L]

From my research on this forum, most FK8 owners recommended 255/35 over 255/40. The extra bit of sidewall with the 40 series might help with a softer more compliant ride, but you lose some of the edginess and direct responsiveness you get with the 35 series. This is all generally speaking and of course I understand different tires feature different sidewall stiffness.

FWIW I run 255/35/18 Falken Azenis FK510 on my Si

 

[BoostedDreams]

According to the wheel offset calculator, 255/40/18 is as close of a diameter as I can get to the stock 245/30/20s.

In order of what I care about, it would be:

1) not rubbing
2) odo/speedo accuracy
3) performance feel vs stock
4) looks

Is there a reason why I shouldn't go with these over the usual recommendation of 255/35/40? If the performance feel is largely different, I'd be willing to get 255/35. However, I don't track my car. I plan on keeping stock height, getting wheels that are 18x9.5 +45mm offset, and planning on getting Michelin PS4S summer tires.

You could also do a 275/35/18 as it’s equally as close in diameter as the 255/40. -0.8% vs -+0.8% from the OEM size.

 

[Emertxe]

You could also do a 275/35/18 as it’s equally as close in diameter as the 255/40. -0.8% vs -+0.8% from the OEM size.

What's the pros/cons of going up to 275?

 

[BoostedDreams]

What's the pros/cons of going up to 275?

Just another option since you want to be as close to OE diameter as possible. No cons come to mind other than increased cost. Pros- more contact patch, better traction, better cornering arguably, and looks a lot better IMO.

 

[AlphaDigital]

What's the pros/cons of going up to 275?

More expensive tire and a heavier steering feel due to the increased contact patch with the pavement.

 

[Emertxe]

Just another option since you want to be as close to OE diameter as possible. No cons come to mind other than increased cost. Pros- more contact patch, better traction, better cornering arguably, and looks a lot better IMO.

Is there a risk of rubbing? I often ride with passengers and don't want to rub at all.

 

[BoostedDreams]

In my experience at stock height with a +45 offset there is no rubbing.

 

[RickyJeezus]

I went 275/35/18 on mine with stock suspension….wheels are +42 have no rub and am very happy with the look….pretty much your 255/40 or 275/35 are your best bet

Tires will also be the difference in feel, they probably matter as much as the size you go with

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