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Discussion Starter · #1 ·
Hmm. After a bit of "spirited" driving, managing to use full throttle and some not so smooth roads, causing the rear suspension to pretty much fully compress, I noticed, accompanied by a not so good noise, that the outer edge of the rear tyres on the XKR catch on the outer edge of the wheel arches, or more specifically, on the wheel arch extensions. It's marking the outer edge of the brand new MP4S 295/30R20 tyres I just had fitted. It has staggered Vulcan wheels and the old tyres (Pirellis) were the same size, but I didn't manage any "spirited" driving since owing the car, until today. Suggestions?
 

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The wall of the 4S is quite ‘upright’ if that makes sense.

I can’t remember how the Pirelli wall was but maybe that angle is enough to make it sit better in the arch?

I know the M0 version of the 4S has a slightly angled wall.

Generic 4S

IMG_6153.jpg


Mercedes Spec (ChrisSB’s car)

IMG_6152.jpg
 

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Discussion Starter · #3 ·
That could be it. The wheels are very proud in the arch and look to fit further out than in Chris's XFR. I'm wondering if I can fit some sort of suspension bump stop to limit the suspension on full compression? Will need to get it on the ramp and have a look. Away from home for a few days, hence the spirited drive over the North York Moors roads (A169 in particular). First time I've actually used full throttle in anger, superb! Except when it started to go brrrrrrrrrrr, brrrrrrrrr over dips in the road with full open throttle.
 

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From memory the stock XKR (X150) rear wheels have an offset of +45 while stock XFR rear wheels (such as Nevis) have an offset of (an utterly yuge) +66.
So 21 mm extra "poke" for the XKR wheels, combine that with 5 mm extra poke of 295 vs 285 and that's 26 mm more poke than a stock XFR, no wonder you have rubbing at times!
Obviously several possible solutions:
Fit smaller tyres eg 285 instead of 295
Fit different wheels with less offset
Fit smaller wheels and tyres (eg 19") if you can find such wheels which fit over the 380 mm front brake calipers.
None of those three options are optimal but option 2 seems the best bet albeit expensive.
But the upside if you don't mind extra expense on top is to go with after-market two piece lightweight forged wheels, lots of reports on the Yank forum across F-Type, XKR and XFR of the massive handling and ride improvements in doing so.
 

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Discussion Starter · #5 ·
I can't justify new wheels, plus I like the Vulcans. The current wheels are also the correct ones for the car, and the car should be fitted with 295s as it has the speedpack option. The tyre pressure chart sticker on the door states only 255 for front and 295 for rear. So it must be the design of the "generic" MP4S's. I don't know if the Pirellis's that were previously fitted did this, I'd presume not as there were no score marks on the tyres, but I'd not driven the car with those tyres in the fashion, nor on the roads I did today. I also can't justify changing the tyres again, these are brand new, even for MO spec ones on the 'hope' that they have a different sidewall configuration which will clear the wheel arch. I do suspect this is a positive option though. What if they don't? Another £500 on tyres to no affect. I don't think I really have much in the way of options though, but I'll explore the possibility of additional or larger bump stops. I likely only need to stop the suspension compressing the last 5mm or so. All depends on how the existing stops work, but likely internal to the shocker? And if the shocker rod is accessible to add an additional external to it.

Powerflex bump stops
 

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My Aftermarket MPS4s very occasionally catch the nearside rear arch. This is since fitting 20mm rear spacers. From closer inspection, the tyre is just catching the arch liner slightly as it appears to have deformed / sagged with age. When I have time I'm going to get my hot air gun out and see if I can reshape that area.
 

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Discussion Starter · #7 ·
The XKR does have very 'sticky-outy' rear wheels, they certainly fill the arches, much more so than my XF-S, but that's not an R I s'pose, the rears on that aren't as wide. I fitted 20mm spacers to the front on the XKR, in my view it needed it to make the arches, front and rear, look balanced. There's no spacers on the rear of the XKR, if I could just move the offset in by 5mm, there'd be no issues.
 

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Is the XK-R supposed to have 295s on the rear? Seems strange that a standard wheel and tyre combo would catch the bodywork. Assuming the suspension is also the standard set-up?
 

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Discussion Starter · #9 ·
As far as I'm aware, cars sold with the factory option Speed Pack were fitted with 255 tyres on the front, 295 on the rear, rather than 285 rears for non-Speed Pack cars. Of course, I don't know what's happened to the car between factory manufacture and my ownership. I don't think the current Vulcan wheels were sold with my car from the factory, but were fitted some time recently, prior to my ownership. I'm unsure of the name of the wheels it was fitted with, but they had bolts around the rims to emulate the look of split rims. I can look up the name once home tomorrow. I think the Vulcans were fitted to later vehicles, but the suspension would have been the same.
 

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By the sounds of it, were they Kalimnos?

If so the staggered set up is for 285 on the rear.

IMG_6413.jpg
 

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Discussion Starter · #11 ·
Kalimnos, that's them. But Speed Pack cars were fitted with 295's from the factory? I do think fitting 285s may well fix the issue though.
 

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A plate check on this press car for tyres shows 285 as the correct tyre size.

Was it not the XKR-S that has 295 rears?

IMG_6414.jpg
 

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Discussion Starter · #13 ·
If that’s the case, it’d explain the catching, the XK-RS has different suspension components, as far as I understand.
 

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Cos I’m bored and got nothing better to do at the moment, I found a brochure online.

For the speed pack, it’s either Kasuga as standard or Kalimnos if you spec the black pack in addition to speed pack. Both of these are have 285 rears.

The vulcans are standard on the dynamic pack and XKR-S but do have 295 rears, so you have the correct size tyres on there (for the wheels) at least!

 

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Discussion Starter · #15 ·
Mine is Speed Pack and Black Pack, I suspected it should have had Kalimnos but the previous owner fitted the Vulcans. I can only presume these were ex XKR-S, hence the 295s. So looks like to cure I’ll need to swap to smaller 285s. Anyone want a pretty much brand new pair of MP4Ss 295 wide?
 

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Mine is Speed Pack and Black Pack, I suspected it should have had Kalimnos but the previous owner fitted the Vulcans. I can only presume these were ex XKR-S, hence the 295s. So looks like to cure I’ll need to swap to smaller 285s. Anyone want a pretty much brand new pair of MP4Ss 295 wide?
Yep, I reckon you should be on the Kalimnos. Vulcans can be off a dynamic pack XKR too. Too many packs!

I’m ok for rears at the moment but out of interest how much would you want for them?
 

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Discussion Starter · #17 ·
If I was to change the tyres to 285s, then I'd put the pretty much much brand new (save for a tiny scratch here and there to the outer top edge) up for sale. Not sure on the price, 3/5ths of new, or thereabouts, a tad over half price? The hardest is getting them to whoever may want them, a courier likely won't take them due to size, else delivery is going to be expensive?

The picture below shows the issue, perhaps the angle accentuates the amount the wheel fills the arch.

187155
 

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Discussion Starter · #18 ·
Hmm, seems there's no stock of Michelin 285/30R20 MPS4S MO1 tyres anywhere :mad:
 

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Hmm, seems there's no stock of Michelin 285/30R20 MPS4S MO1 tyres anywhere :mad:
The non M0 won’t give you an issue with the 285s. Blackcircles have them when I checked yesterday.
 
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