Development Tyres for XKR

[JimMann]

When the X150 was being developed by Jaguar Cars, the tyre of choice for the car was the Dunlop Sport Maxx, which for the X150 were:

Fronts: 255/35/20Y
Rears: 285/30/20Y

These tyres were fitted as original equipment (OE) and had the additional designation of "J" specification for Jaguar on the sidewall scripts. I believe that there were other manufacturers specific designations such as "M" for Mercedes and "B" for BMW and, believe it or not, the tread patterns were all slightly different - as designed during the development phases.

As folks on here will probably know, I am of the opinion that tyres are a safety critical consumable item and tend to advocate changing the tyres at 5 years old, irrespective of tread remaining. This has been okay to date, but looking around the various supplier websites, I was finding that the rears were being advised with J specification, but not the fronts when looking at the Dunlop Sport Maxx tyres. It transpires that Dunlop, now a part of Good Year I believe, have ceased production of the J specification tyres, so where do we now go for suitable replacement tyres?

Within the Dunlop range, the Dunlop "official" home page offers the Sport Maxx RT 2, in the correct size variations, but without the J, meaning it is now a generic fitment tyre from Dunlop.

Looking at the Pirelli "official" home page, their offering shows they have a range of Pirelli P Zero and Pirelli P Zero (PZ4), some with Jaguar JRS markings, whilst others simply have Jaguar J markings, but in context they don't have the same consistent marking for both the fronts and rears.

The "Perfect Fit" tab is shown for the Pirelli P Zero, but it shows Jaguar JRS for the fronts and Jaguar J for the rears - does anyone know the difference between the JRS and simply J designations?

So a decision on my part in the near future is required, but what to go for? Watch this space.

Jim Mann

[mike020150]

Hi Jim,

I agree that the tyre companies don't make it easy to choose the right tyre. When I put my XKR's reg number into its site, Pirelli even lists an incorrect size for its rear tyres!
FWIW my interpretation of the J versus JRS designations is that the J tyres seem to fit a wider range of Jaguar models, whereas the JRS listings that I have seen, appear to be slightly more specialised. E.g. the tyres fitted to the X150 XKR were usually J rated but the XKR-S (and XKR Dynamic models) were fitted with slightly grippier (often noisier and less fuel efficient) JRS homologated versions. However, I wouldn't be surprised to find the difference is more prosaic! Mike.

[P700DEE]

Tyre technology moves on. It is true that manufacturers work with tyre suppliers to produce tyres specific to their models. It also allows the tyre supplier to charge a premium for those tyres and supply a J mark. The X150 was launched in 2006 so tyre development was probably completed by late 2005. That's best part of twenty years ago! I personally feel that general development of tyres means that even premium budget tyres probably out perform the original Dunlops as designed for the car. I'm certainly not going to pay a premium for something designed 20+ years ago over the best of today. Get the right sizes of tyre and buy modern technology I think that's best for my Jaguar.

[M100TWO]

I would fit Michelin Pilot4S that appears to be the best there is I won’t fit anything else on the XKR

John

[JimMann]

So the consideration moves on. Given the Club's historic partnership with Pirelli, I contacted the good folks at the PPC at Burton to ask about obtaining the correct JRS / J spec tyres when I don't have a PPC in Scotland, never mind nearby.

The PPC did respond very promptly, advising that they would be happy to supply suitable tyres to my local garage for them to fit, great I thought. Then the caveat came through. Whilst stocks of the front JRS spec tyres were plentiful, the rears in J spec were out of stock and with no current projections in the production schedule! What's going on with tyre production?

So I could have Pirelli fronts and Dunlop rears in the correct manufacturers J specifications - not going to happen.

I understand the comments already posted about personal favourites in tyre brands and selecting modern alternatives in the appropriate sizes over the development tyres from 20 years back, but I am not ready to give up as yet and I would NEVER stint on tyres by selecting anything other than a major premium branded tyre.

Watch this space.

Jim Mann

[JimMann]

So the conclusion has arrived.

After a serious amount of deliberation, I elected to conduct a detailed inspection of my 5-year old front tyres on the XKR. I removed the front wheels and cleaned up both wheel and tyres. Tread depth was even across the full width of the tyre and was recorded at 7mm, so approximately 1 mm of tread wear after 15,400 miles - remarkable. Both carcases were inspected and there were no cuts, cracks or deterioration found - car is always garaged so not left sitting under UV exposure for any length of time. The decision therefore was to retain my fronts and replace my rears.

Replacement rears, Dunlop SP Sport Maxx in J spec were ordered for fitting by my local garage, and duly installed. All 4 wheels were balanced and everything is feeling good.

Ahead of fitting the replacement rears, both wheels were removed and fully cleaned, including the removal of all existing balance weights. Same with the fronts ahead of being rebalanced. The new balance has required very few weights to be installed, which is a significant improvement over the previous new fitment, where 1 tyre required over 130g to obtain the balance correction.

Given the wear regime, the front tyres should easily last for the life of the new rears, but by that point they would be 10-years old and my OCD would surely be increasingly concerned. With that in mind, I will be inspecting the ageing fronts on a regular basis for some peace of mind. In addition, if I do have a problem with a front tyre I am resigned to being back to square one of this exercise and looking for a matching set of 4 tyres, again irrespective of the wear. Hopefully by that point the tyre manufacturers will once again be producing tyres to suit the car.

As an aside, on inspecting the rears removed from the car, the tread depth was "barely" above the wear bars, so around 2mm, albeit with even wear across the entire width. So, front wear in 15,400 miles was around 1mm, whilst the rears over the same distance had worn the full 6mm.

Case closed.

Jim Mann

[BrianG]

"Replacement rears, Dunlop SP Sport Maxx in J spec were ordered for fitting by my local garage....."
Jim,
I have been happily running Dunlop Sport Max tyres on my X356 XJ8 for some years since they first came out. I tend to buy these online from companies such as Black Circles etc. or at a reasonable price for supply and fit by a local tyre company (£600 for all four) but I have never seen "J Spec" versions offered anywhere, so presumably these were special order and you paid top whack for these via your local garage?

[JimMann]

Hi Brian, the J (for Jaguar) spec are not special order, but they were one of the original development tyres for the X150 model. Not sure that your X356 XJ8 would have sat on the same tyres as the X150, but nonetheless there would have been a "Development tyre" for the X356 at the time. See the first post in this thread for the section / sizes of the tyres for the X150 and compare them with your own. The cost of the J spec tyres in not that outrageous as far as I am concerned, the most recent rear replacements (today) were just under £250 each, fully fitted and balanced.

The Dunlop SP Sport Maxx in J spec is what I have had on the XKR (X150) since new and have always been quite happy / content with the performance of the tyres, in consideration of noise and grip, both dry and wet. Although with some +500 BHP to put down, it is always possible to spin the rear wheels if one happens to be too lead footed, irrespective of the weather.

The challenge for SP Sport Maxx users going forward would appear to be that Dunlop (Good Year) are no longer producing the standard, or J spec, versions, with the offering being for Sport Maxx RT2, which I will be investigating the differences in going forward.

Jim Mann

[BrianG]

Jim,
I was not suggesting that the Dunlop Maxx were "development" tyres for the X356 but I prefer them to the original fit Pirelli P-Zeroes (mine are 255/40 R19), which I could never find in J-Spec and dislike P-Zeroes anyway for a variety of reasons. I have seen other makes of tyre stating J Spec, hence my curiosity as to availability of the Dunlops in J-spec.

I may have confused the situation by assuming that your SP Dunlop J-spec Sport Maxx was the same tyre that I have used for some years, which started as Sport Maxx RT and became the Sport Maxx RT2.

You may be interested to know that in my modest car I find it gives superb cornering grip in the wet but does not wear that well as the RT2 is now a softer compound, wear being about 3.5mm after 19,000 miles.

[JimMann]

Hi Brian, tyres can be a very personal thing, depending on the enthusiasm of the person specifying them for their vehicle. I have seen some horrendous examples of inappropriate tyres on Jaguars. Uneven wear, chunks peeling out of the sidewalls - and that was on the sidewall I could see never mind the inside area. As a friend of mine says often - "don't try and run your Jaguar on Ford money, it simply is not worth it in the long run."

Many years ago when the Good Year Eagles F1 were a standard fitment on the sporty machines of the day (Scirocco GTi) I actually arranged a visit by the tyre manufacturer to come to Aberdeen and look at the wear on my front tyres. Completely even wear, but down to the bars in less than 6,000 miles. Explanation: these are very soft compound tyres!

Interesting what you say about the Sport Maxx RT2 being a softer compound. As reported above, my J spec Dunlop's are also quite a soft compound, completely shot after just 15k miles, on the rears at least.

Jim Mann