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Too small tyres on rims

snortings

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Hey guys,

This question has probably been asked quite a lot but I just can't find a thread that answers my question exactly :)

I took ownership of a 2015 VFII SV6 in November and the previous owner said that it had staggered wheels, I thought great the back is wider than the front and that'll be sick. When I had a closer look at the car all of the tyres were 255/35R20, bit strange if the car has staggered wheels. The owner said the front rims are 20x8.5 and the rear is 20x10. I've noticed the back rims stick out past the actual tyre itself, which I assume means that I need to get a wider tyre? It just annoys me that the back itself stick out, and would especially get on my nerves if I got a flat tyre and the rims would run on the road!

So I've looked around the forum and seen stuff like certain sizes would rub on the guards and something about offset (which I have no clue about), but my question is what size tyre should I put on the back if the rim is 20x10?

This is how they are at the moment to clear up any confusion:
FRONT: 20x8.5 | 255/35R20
REAR: 20x10 | 255/35/R20

I've attached a photo of the rim sticking out on the rears.

Thanks :D
 

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panhead

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It would be easier if the photo showed the lip of the rim and its relationship with the edge of the guard so we can get an idea of the offset, in other words a photo that shows the whole rim, tyre and guard and how far the rim hangs in or out.


The first thing you’d want to do is keep the overall rolling diameter similar front and rear.


I’ve used Tempe Tyres' Tyre Calculator for this exercise and there are many other calculators on the web you could use and sometimes you'll find there are variations from calculator to calculator when it comes to the O/D.

Tempe Tyres say:

A 255/35R20 has an overall diameter of 687mm.

A 275/30R20 has an overall diameter of 673mm which is -14mm or -2.04% smaller than the 255.

A 285/30R20 has an overall diameter of 679mm which is -8mm or -1.16% smaller than the 255.


The 285/30 is the best tyre to match with the diameter of the 255/35 and the 285 is also the best fit for a 10 inch rim but looking at what can be seen in the photo the offset looks very aggressive which means it may rub.


Also is the car lowered?


https://www.tempetyres.com.au/tyre-size-calculator





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Adza75

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Before you do anything, have you actually confirmed the size of the rims? Either by measurement or checking what's stamped on them?
 

snortings

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It would be easier if the photo showed the lip of the rim and its relationship with the edge of the guard so we can get an idea of the offset, in other words a photo that shows the whole rim, tyre and guard and how far the rim hangs in or out.

The first thing you’d want to do is keep the overall rolling diameter similar front and rear.

I’ve used Tempe Tyres' Tyre Calculator for this exercise and there are many other calculators on the web you could use and sometimes you'll find there are variations from calculator to calculator when it comes to the O/D.

Tempe Tyres say:
A 255/35R20 has an overall diameter of 687mm.
A 275/30R20 has an overall diameter of 673mm which is -14mm or -2.04% smaller than the 255.
A 285/30R20 has an overall diameter of 679mm which is -8mm or -1.16% smaller than the 255.

The 285/30 is the best tyre to match with the diameter of the 255/35 and the 285 is also the best fit for a 10 inch rim but looking at what can be seen in the photo the offset looks very aggressive which means it may rub.

Also is the car lowered?

https://www.tempetyres.com.au/tyre-size-calculator
Sorry about the photos. I'll retake the photo tomorrow as you've suggested with the better angle, hopefully it'll provide more insight :) As far as I know (pretty certain) the car is not lowered, looks like the normal setup. Read my quote below, I've linked to the actual wheels that has some info on them :)

Before you do anything, have you actually confirmed the size of the rims? Either by measurement or checking what's stamped on them?
Yeah I know the rims are what I said they are because I've searched them up and you can get the 20" rims in two sizes: 8.5" or 10". I've put a link below to the rims that I've found online, it has a bit of information on there that might help (offset etc) :) Though I do find it a bit confusing... it says 90mm lip on 9.5" but it never gives the option for 20x9.5, only 20x8.5 and 20x10. I know these are black, but they're the same but silver.

https://www.jaxtyres.com.au/wheels/brands/king-wheels/malice-satin-black
 

[paradox]

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these are the standard tyre sizes for factory staggered (8.5″ front & 9.0″ rear)
https://www.ebay.com.au/itm/HSV-HOL...-19-20-INCH-WHEELS-RIMS-GENUINE-/263210193790

you can also look at here for recommended widths, im sure there are other places, this was just the first one i googled
https://www.tyresizecalculator.com/charts/tire-width-for-a-wheel-rim-size-chart

then use panheads calculator to get the right profile,
but i agree with panhead id think you would want a 285 if the offset on your wheels is sufficient
 

BlackVXGTS

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For comparison, Gen-F2 GTS has 20” x 8.5” (Front) with 255/35 R20 tyres & 20” x 9.5” (Rear) with 275/35 R20 tyres.

Gen-F2 GTSR has 20” x 9” (front) with 255/35 R20 or 265/35 R20 tyres & 20” x 10” (rear) with 275/35 R20 or 295/30 R20 tyres.
 
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abuch47

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Hey @BlackVXGTS don't suppose you know the price for a set of the 30th anni GTS rims from HSV do ya?
 

panhead

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From the photos I’m sure the rims are a +50 offset and not a +38 as shown in your link in post #4.

Plus the rim in the link is for a Ford (PCD 5/114.3) and not a Holden (PCD 5/120) and from a quick search the Holden 10 inch Malice only comes with a P50 offset.

Which is a good thing as it’s a safe offset if you ever want to lower the car.

The car is obviously still in 4x4 mode so a wider tyre like a 275 shouldn’t be a problem, it depends on how much your suspension travels when you have passengers in the rear seat as to whether a 285 would rub.

Rolling the guards would get rid of the 285 rubbing problem and it would also mean you could lower the car if you ever chose to.




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