18" Rays forged on GTST

[Hudders]

18" Rays forged on GTST

I've just swopped the Rays Forged 18" wheels that was on my 350z with the 19" deep dish wheels on my GTST. The tyres on the front are 225/45/18 and the rears are 245/45/18.
The Rays were fine on the Z but rub badly on the GTST. 
The fronts seem to touch the wheel arch liners. Not sure about the back.

ET is 33 front, 30 rear iirc.

Are the tyre sizes wrong?

[GTSBoy]

Have you got any idea how wide each of the sets of wheels are and what the offsets for both sets are?  Hint....it's unlikely to be tyre sizes that are the problem, more a case of where the wheel is putting the tyre.

[Hudders]

The 19" wheels I took off were 9" front (ET30) and 9.5" rear (ET35)   235/35/19    245/35/19 

The Rays I put on were 8" front (ET33) and 8.5" rear (ET30)   225/45/18    245/45/18

i could take the front arch liners out but in the land of rain that's not really a good idea

[GTSBoy]

So, enter those numbers into an offset calculator and you will see what the effect of having an inch less width and almost the same offset does to the locations of the inside and outside edges of the wheel rims.

But here's a thing.  I can see from those numbers straight away that the Rays wheels should project inwards by ~10mm LESS than the bigger wheels.  So they should not be scraping anything because of offset differences.  BUT.  And here's the big but.....the 18" wheel&tyre combo is ~12mm larger in OD than the 19" combo.  So they will possibly rub just from being too tall.

FWIW, both of those wheel/tyre combos are too tall.  The correct OD for OEM wheel&tyre is ~642mm.  Your 19" combo is ~647mm, which is acceptable, but the 18" combo is ~660mm OD, which is just stupidly large.

[Hudders]

So should I reduce the tyrewall figure to 40 instead of 45's?

[GTSBoy]

You really want me to keep doing simple arithmetic for you?

[Hudders]

Only simple if you know what you're doing bud. I don't so that's why I'm asking the question to people who do. 

My apologies if if I'm asking the simplest questions. 

[GTSBoy]

In that case, google is for learning.

https://tiresize.com/tyre-size-calculator/

[Hudders]

Thanks. I can see that reducing  the tyrewall to 40 saves me almost an inch on the front and exactly an inch on the back.

Can I ask what the oem wheel diameters are? 

[GH05T]

where in the wheel arch are they touching? is it on the inside edge of the tire? take a photo.

[GTSBoy]

1 hour ago, Hudders said:

Thanks. I can see that reducing  the tyrewall to 40 saves me almost an inch on the front and exactly an inch on the back.

Can I ask what the oem wheel diameters are? 

R33 GTST is stock on a 16" wheel.  Should be a 205/55 tyre on that, which gives an OD of 632.5mm.  This is also true for R32 GTR's 225/50-16 OEm fit.  You can see why I said some of your other combos are stupidly large.  Oh, and I made an error in my previous reply saying that the stock diameter was 642.  I meant 632mm.

[Hudders]

Wow !!  I see what you mean.    

So if I changed the fronts to 225/40's  I'd only be 5mm larger than OEM.   The rears though, changed to 245/40's  would be 20mm larger.  

Do you think the rear arches could take that increase?  The car isn't lowered and is on standard suspension.

[GTSBoy]

The rears can probably take it.  They don't have to steer, just go up and down, so they generally have less problems with clearance.  I personally wouldn't do it.  The gearing change is bad for speedo accuracy.  Being a turbo car, you can probably happily live with the taller gearing.  Taller gears makes the turbo work harder in each gear, which I think is better.  It's worse if you're a drag racing weenie though.  They like short gears.

The biggest problem with staggered wheel fitments is what you're going to do about the spare.

[Hudders]

Ok, so if the 245/45 is too big and the 245/40 is not advisable, what size tyre would you suggest for my 18" rims on the rear?

[niZmO_Man]

Just change the tyres to 40 series (e.g. 245/40 for the rear).