Hi Philip
Bristol 411 | Longstone Tyres
Bristol 412 | Longstone Tyres
I would suggest that the P4000 is a good tyre for the late Series 3 XJ12 ( I had one with those tyres on it) However i think the ride will be a bit harsh for your car. I think they are a late 80's tyre and i believe they had to soften the Jaguars suspension to cater with the P4000 tyres.
If you have the 215/70R15 P4000, i would suggest they will be very old.
If you look on this page
Aston Martin DB5 there is some pictures of a green DB5. one picture of it wearing 215/70VR15 P4000 and a picture of the same car with the 205VR15 Cinturato CN12 so you can see the difference in diameter.
One of the things you get when you fit a car with a low profile tyre like a 215/70VR15 compared to a full profile tyre like a 205VR15 is you minimize the amount of movement in the side wall so the steering will feel tighter.
the draw back with modern tyres like the P4000 is the foot print will be dramatically wider than the car is designed to deal with so you may find it picks up the unevenness of the road and tracks on our horrible rutted motorways.
The
205VR15 Pirelli Cinturato ™ are ideally suited to modern roads. more importantly i would suggest that they are more suited to your car than anything else available. They have a V speed rating. we fit them on a wide range of things from Series 1 Rolls Royce Silver Shadow to the back wheels of a Ferrari 250GTO.
The P4000 is a good tyre but not for your car. the Cinturato will be much better as it is suited to your car. they are a period carcass which will suit your geometry but a modern compounds so they will grip in the wet.
The other alternative tyres are also listed on the 2 web pages at the top of my post. I don't think the price of the 205VR15 Cinturato is ridiculous. It is a high performance tyre made in small batches by one of the worlds best tyre manufacturer, all these things don't come cheap.