Hi
Pirelli have made the 235/60R15 P600 that fitted many of the XJS again.
https://www.longstonetyres.co.uk/classic-car-tyres/jaguar/xjs.html
These tyres are available through the distributors of Pirelli Collezione range.
https://www.pirelli.com/tyres/en-ww/car/collection
There is a perception that fitting a 225/60R15 tyre is an acceptable alternative. However there are several issues
It is a bit thinner.
It is the wrong diameter.
It is a modern carcass design.
Bit Thinner
This isn't so much of a problem. Earlier XJs's fitted 205 section tyres and 215 on the V12. When they sacrificed the ride a little and moved onto a 16" wheels they went down to a 225 section again, so the width thin isn't too much of a problem.
Wrong Diameter
Actually if you were going to be critical of an XJS, possibly the fuel consumption would be a valid starting point. having a smaller circumference tyre will only make that worse.
The speedo will be a bit out of wack.
The car will be lower, moving your exhaust pipe closer to speed bumps etc. Do you want your XJS lower?
A little bit less side wall height will give a slightly harsher ride.
If you want to go looking into diameters, the listed diameters i have for their OE tyres are 205/70R15 P5 675mm, 215/70R15 P5 685mm and then the 235/60WR15 P600 lists a diameter of 689mm
Modern Carcass design
This is the truly critical thing.
Jag didn't just guess that the 235/60R15 P600 was a good tyre for that car. It was chosen because Jaguar thought the tread pattern was pretty. Pirelli and Jaguar have a long history of working together to subtly tune the tyre to suit a car. They were OE because they work best on that car. Its not just guess work. When Jaguar moved to the 16" wheels they would have subtly tuned the chassis set up to suit the new wheel and tyre combination. these developments compliment each other.
The geometry and suspension of modern cars is different now to when the XJS was built. Yes the modern tyre carcass gives better performance on a modern cars chassis set up because they are designed to compliment that enviroment. But they do not suit an old chassis design. Modern cars have more caster, more negative camber and stiffer springs. The handling draw backs of these features are overcome by modern cleverer power steering and computer controlled suspension.
I realise that a lot of XJS owners will have bought their cars in the glory days in that period where they were cheap as chips. Lets face it they got outrageously cheap. At one point i would assume they were probably be the most car you could buy for the least money. However what you pay for a tyre isn't relative to what you paid for the car. specially something like an XJS. It was an epic car that ended up being too cheap. What you pay for a tyre is related to the quality, specification and unfortunately a big contributor is batch size. A 235/60R15 tyre only really fits a few years of XJS and the rear of a Delorean that i know about, and that makes the cost mout up a bit. the 235/60WR15 P600 is not expensive for what it is, but i cannot argue that it does add up to a large credit card bill. But one of the reasons an XJS got so cheap in the first place is because they are expensive to run.
I know its not what people want to hear. but the good news is that for people who really do want their late 1980s - mid 1990s XJS to handle at its best and choose their tyres based on what is best, they can at least get the right thing.
