Tyre sizes and emergency use of back wheel on front

Wheels, Tyres, Suspension, Chassis, Issues and Fixes
ouzel
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Post by ouzel »

Hi All,
I have 19" wheels on my Macan S (2015). The rear has 255/50R19 tyres and the front tyres are marked 235/55R19. I have the opportunity of a rear spare spare wheel with 255/50R19. In an emergency (e.g. puncture) could I put that wheel on the front to get to a garange ?
Apologies for my ignorance in these things.
Ta.

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Nuclear Nick
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Post by Nuclear Nick »

ouzel wrote: Tue Jan 19, 2021 11:48 am Hi All,
I have 19" wheels on my Macan S (2015). The rear has 255/50R19 tyres and the front tyres are marked 235/55R19. I have the opportunity of a rear spare spare wheel with 255/50R19. In an emergency (e.g. puncture) could I put that wheel on the front to get to a garange ?
Apologies for my ignorance in these things.
Ta.
I wouldn’t advise that. You might get contact with the inner rim or tyre on or near full lock or with suspension movement. That could be dangerous and expensive. I don’t know where you are but certainly in the UK it would be classed as a modification, not approved by the manufacturer, and as a result your insurance would be invalid. It would almost certainly be illegal too.
Nick

Defender 90 V8

991.2 C2 GTS

Macan Turbo - sold

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ouzel
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Post by ouzel »

Thanks Nick,

I suppose the low profile spare is a lot narrower tyre, so fits front and rear fine in an emergency.

-chris
On-Track
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Post by On-Track »

It's not just the tyre tread width you have to think about. The front wheels are 8J and the rear 9J. So at full lock, there's a risk of the wheel rim fouling the wheel arch but also because of the wider wheel the tyre width will be greater at the widest point of the sidewall. I fully support everything Nick said.
Peter

Current: 2020 Carmine Red GTS http://www.porsche-code.com/PMST9ZI9
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SAC1
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Post by SAC1 »

ouzel wrote: Tue Jan 19, 2021 11:48 am Hi All,
I have 19" wheels on my Macan S (2015). The rear has 255/50R19 tyres and the front tyres are marked 235/55R19. I have the opportunity of a rear spare spare wheel with 255/50R19. In an emergency (e.g. puncture) could I put that wheel on the front to get to a garange ?
Apologies for my ignorance in these things.
Ta.
No. Don't do it.
Steve

2020 GTS in Sapphire Blue
(sold) 2017 SD in Rhodium Silver
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Kleynie
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Post by Kleynie »

Surely it depends on the offset of the wheels? My front wheels have 265 tyres and I assume at least 9J, so why wouldn’t a 255 on a 9J work if the offset is correct for the front?
June 2017 Macan GTS in Carmine red with 21” gloss black sport classics, GTS leather package, Air, PASM, PDLS+, pano roof, Sports Chrono, 18 way seats, BOSE, surround view, heated seats front and rear, carbon side blades and carbon interior package.
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SAC1
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Post by SAC1 »

^^^ You will not be able to store it under the boot floor - too big. It will take up a 1/4 of the boot space and unstrapped will slide around too.
Steve

2020 GTS in Sapphire Blue
(sold) 2017 SD in Rhodium Silver
On-Track
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Post by On-Track »

Kleynie wrote: Tue Jan 19, 2021 7:51 pm Surely it depends on the offset of the wheels? My front wheels have 265 tyres and I assume at least 9J, so why wouldn’t a 255 on a 9J work if the offset is correct for the front?
From Macan Brochure:wheel sizes for Macan and Macan S

Wheels Front: 8 J × 18 ET 21, Rear: 9 J × 18 ET 21
Tyres Front: 235/60 R 18, Rear: 255/55

The wheel widths and offsets don't change for the larger wheel sizes.
Peter

Current: 2020 Carmine Red GTS http://www.porsche-code.com/PMST9ZI9
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Kleynie
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Post by Kleynie »

On-Track wrote: Wed Jan 20, 2021 10:45 am
Kleynie wrote: Tue Jan 19, 2021 7:51 pm Surely it depends on the offset of the wheels? My front wheels have 265 tyres and I assume at least 9J, so why wouldn’t a 255 on a 9J work if the offset is correct for the front?
From Macan Brochure:wheel sizes for Macan and Macan S

Wheels Front: 8 J × 18 ET 21, Rear: 9 J × 18 ET 21
Tyres Front: 235/60 R 18, Rear: 255/55

The wheel widths and offsets don't change for the larger wheel sizes.
Yes they do, my rears are 10J ET19 and my fronts are 9J ET26 (21" Turbo wheels), hence my thinking that a 9J width is fine on the front if the offset is correct.
June 2017 Macan GTS in Carmine red with 21” gloss black sport classics, GTS leather package, Air, PASM, PDLS+, pano roof, Sports Chrono, 18 way seats, BOSE, surround view, heated seats front and rear, carbon side blades and carbon interior package.
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Kleynie
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Post by Kleynie »

A bit more digging, I have found that the 18" rears are 9J ET 21 (as Peter said), so in my opinion the rears will fit on the front as the offset is only 5mm different (further away from the suspension) than the 21" standard 9J front wheels, and the tyres are narrower by 10mm so that will compensate for the offset difference.
June 2017 Macan GTS in Carmine red with 21” gloss black sport classics, GTS leather package, Air, PASM, PDLS+, pano roof, Sports Chrono, 18 way seats, BOSE, surround view, heated seats front and rear, carbon side blades and carbon interior package.
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