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Discussion Starter #1
Hi, after much deliberation, I am putting a set of 18" Ethos bi colour alloys on my new T6 4 motion, these are from the VW Amarok range, fitted with 255/55R18 tyres, as recommended. Does anyone have any technical reasons why this shouldn't be done, thanks Holly.
 

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It'll look like a moon buggy.

You may get some wheelarch scuffing.

The speedo error will be significant - my speedo (on 255/45R18s) reads pretty accurately at 60 but your's will be 7.5% out so when your speedo says 60 you'll be doing 65mph.

You're gearing will be taller so acceleration in gear will be reduced. This tends to impact fuel consumption negatively as the engine's working point will be away from the best efficiency point.
 

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Discussion Starter #3
Original fitment wheel/tyre size is 215/65R 17, rolling circumference of 2145.24mm, new wheels/tyres 255/55R18, rolling circumference of 2224.85mm,
the resulting difference in rolling circumference is 79.62mm or 3.71%.
This means @ 70 mph it will actually be travelling at 72.6 mph, not quite the 7.5% you quote.
As moon buggy comment most 18" wheels on a Transporter would have a 255/45R18, bear in mind the profile(45 or 55) is calculated from a percentage of the width (eg 45 % of 255) the difference in both aesthetics and use is negligable.
Thanks for the un researched advice,
Holly.
 

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Holly. Everyone said my tyres wouldnt fit and would will scuff etc. They fit perfect, im well happy with the ride.


 

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It'll look like a moon buggy.

You may get some wheelarch scuffing.

The speedo error will be significant - my speedo (on 255/45R18s) reads pretty accurately at 60 but your's will be 7.5% out so when your speedo says 60 you'll be doing 65mph.

You're gearing will be taller so acceleration in gear will be reduced. This tends to impact fuel consumption negatively as the engine's working point will be away from the best efficiency point.
It'll look like a moon buggy...Wake up and smell the coffee! I:
 

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Discussion Starter #7
Thanks Cupra,
the official line from VW technical via my VW dealership (Cordwallis) is that this set up was all ok, although I would have to sign a disclaimer because of weight T32, but this doesn't impact as the Amarok is 3500gvw. I get that the profile is a little bigger (although moon buggy, harsh) but this Van is to be used for a fair bit of towing on light off road terrain, and difference on acceleration etc its a 204 ps, 450nm torque so doubt it will matter.
thanks Holly.
 

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Original fitment wheel/tyre size is 215/65R 17, rolling circumference of 2145.24mm, new wheels/tyres 255/55R18, rolling circumference of 2224.85mm,
the resulting difference in rolling circumference is 79.62mm or 3.71%.
This means @ 70 mph it will actually be travelling at 72.6 mph, not quite the 7.5% you quote.
As moon buggy comment most 18" wheels on a Transporter would have a 255/45R18, bear in mind the profile(45 or 55) is calculated from a percentage of the width (eg 45 % of 255) the difference in both aesthetics and use is negligable.
Thanks for the un researched advice,
Holly.
Sorry to disappoint but stock tyre sizes are either 215/65R16C, 215/60R17C, 235/55R17, 235/50R18 or 255/45R18

Your 255/55R18 will be between 6.8 and 7.5% larger than those.

Edited to add that 205/65R16C is also a factory spec tyre but it's rarely seen. It does appear on my vans tyre pressure plate. The Amorak tyres will over gear by 9.6% compared to those.

I cant comment on your vans speedo but I can calibrate mine against the GPS speed on my nav and the VW speedo only over-reads by 1 or 2 mph up to 70mph so you will probably be able to underead significantly and many people on here have speculated that oversize wheels with higher inertia have lead to worse fuel economy and even linked it to failing drive splines on the gearbox. Not enough study has been done to truly verify this and I'm not going to start running a driveline torsional dynamic model of it as it'll take too long and what would it prove when the easiest thing to do is just not modify the setup in the first place.

I have a colleague who drives a van on on 255/55R19 tyres and sat next to mine it is raised by 70mm as I can fit 40mm lowering springs and he cant. It's a big jump. You wont be that bad but it'll still be significant. The tyre's alone as you say will have 25.5mm taller sidewalls so you will lift the van and move the centre of gravity the wrong way. This will have detrimental effects on the handling. Edited to add - a 255/55 pascar tyre will have a 140mm sidewall. This is 11mm taller than any other factory pascar tyre (tallest being 235/55R17). This additional sidewall flex will lead to the van being slightly less stable. So in summary, van is higher off the ground and sidewalls are more flexy - not a combo I'd want if I was towing.

None of the above is a serious safety concern but each aspect is compromised from factory spec.

Sorry if the moon buggy comment offended you.
 

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Thanks Cupra,
the official line from VW technical via my VW dealership (Cordwallis) is that this set up was all ok, although I would have to sign a disclaimer because of weight T32, but this doesn't impact as the Amarok is 3500gvw. I get that the profile is a little bigger (although moon buggy, harsh) but this Van is to be used for a fair bit of towing on light off road terrain, and difference on acceleration etc its a 204 ps, 450nm torque so doubt it will matter.
thanks Holly.
Dont forget the spare wheel has to be the same. T:
 

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Just realised you have a T6 so I went and doubled checked that the tyre sizes haven't changed - and they haven't.

If you have a factory tow bar or prep then your van have built in ESP with trailer stabilisation. You'll significantly change the dynamics of the system with your extra ride height and tyre flex so I am going to now say that this just sounds like a bad idea now but that is an opinion not a fact. I do know that if I changed the tyres or ride height on the back of my Caterham it did change the handling bias significantly.

Could you not sell the tyres and buy the right size?
 

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Just realised you have a T6 so I went and doubled checked that the tyre sizes haven't changed - and they haven't.

If you have a factory tow bar or prep then your van have built in ESP with trailer stabilisation. You'll significantly change the dynamics of the system with your extra ride height and tyre flex so I am going to now say that this just sounds like a bad idea now but that is an opinion not a fact. I do know that if I changed the tyres or ride height on the back of my Caterham it did change the handling bias significantly.

Could you not sell the tyres and buy the right size?
Messed my dynamics up big time...for the better or the worse??

 

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Sweet. No complaints about that!

If we're having a bling wheel and tyre moment I'll contribute... but I've given up modding cars so this is a stocker...

 

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Sweet. No complaints about that!

If we're having a bling wheel and tyre moment I'll contribute... but I've given up modding cars this this is a stocker...

For some reason I can see some pics on here but not all. Sorry cant see your bling??
 

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Discussion Starter #18
The tyre size that this Van comes with from factory is 215/65/17, no choices on a T32.
The difference in ride height and rolling circumference between these and 255/55/18 is negligible.
When you calculate the difference between 255/45/18 & 255/55/18 it is greater.

It is only that VW technical are telling me to put these tyre sizes on that I am considering this.
Tyres have not been bought yet, wheels have.

I do take on board what your saying, and will continue researching this and welcome any more advice,

thanks
Holly
 

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Hmm, my bad, sorry. Your right there's something weird going on with only that model and it's not shown in the price list, but now I dont understand why the T32 Sportline has 255/45R18s? You could go either way but really you want a 255/50R18 to keep the same size but they dont really exist... The 215/65R17 is an outlier in terms of size compared to every other model...including the old T32.

If VW themselves sell the Sportline T32 with 255/45s then I'm still more biased to stick with that.
 

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Hmm, my bad, sorry. Your right there's something weird going on with only that model and it's not shown in the price list, but now I dont understand why the T32 Sportline has 255/45R18s? You could go either way but really you want a 255/50R18 to keep the same size but they dont really exist... The 215/65R17 is an outlier in terms of size compared to every other model...including the old T32.

If VW themselves sell the Sportline T32 with 255/45s then I'm still more biased to stick with that.
I think the tyre size on the T32 being different is to do with the load ratings. T32 (at least on my 2009 model) needs a minimum of load rating 103.
 
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