In 1977 Jaguar asked Pirelli to help them have the, consistently best tyre possible for their XJ6, XJ12 and XJS luxury cars. Through the Jaguar community, we have had the following words from one of the Jaguar engineers of the time who was involved in the testing of the Pirelli P5 on the Jaguar XJ12 in September 1978. The Pirelli P5 was homologated by Jaguar in 1979 for these cars and then later for the Jaguar XJ40.
Jaguar XJ6 Tyre Testing
"I was involved in every aspect of the original Pirelli P5 project in 1978. The steel braced Dunlop’s of the era especially the XJ-S D1 and to a lesser degree, the XJ12 tyres suffered from imbalance and out of roundness, from new. It got so bad the US importers refused to take cars on Dunlop tyres, Michelin XWX were approved temporarily for the US market.
Reluctantly Jaguar who had Very close contacts with Dunlop worked with Pirelli and developed the P5 205/70/15 tyre. never as good comfort wise as Dunlop’s , they were 100 % reliable !! , and did look a tad narrower than the equivalent Dunlop!!
All the Pirelli testing was done in southern Italy Sept 1978 using an XJ12, seen here jacked up having its tyre temps measured, Norman Dewis looking on, and Guy in white shirt is Andy Hallam from Pirelli who went on to head up Pirelli Motorsport and even higher posts!!
I included, the car jacked up is XJ12 MDU 129P, that I drove down to Nardo Italy with Norman Dewis, you can see him standing with his blue overalls rolled down, it was 30+ Celsius!!
The car ran for 20 minutes at every speed from 30 to 150 mph, in 10 mph increments and at every load condition and every tyre pressure option, Jaguar had 5 tyre pressure options in the handbook during the 70,s!! each tyre submitted by Pirelli to assess took a whole 12 hour day to drive through the options. After each speed, the car would pit stop, be jacked up and the tyre thread temps over 3 points measured for each wheel, Pirelli did all this. Watching in the white shirt is Andy Hallam, who went on to head up Pirelli Motorsport.
This routine went on for over a week. Once “we” had decided on the best tyre, ( we also did handling tests at another part of the test venue )it then ran for 2000 miles round the Nardo 8.5 mile banked track at 120 mph, and 50 miles at 145-150 mph flat out.
We then drove to the Stelvio pass in the alps to do brake testing! The white XJ12 went to Vitzola, Milan to Pirelli’s Test track to do wet grip tests with another Jaguar Test Engineer.
Orginal Equipment Jaguar XJ12 Tyres
Again, Pirelli are again making the Pirelli P5 for Jaguars Luxury cars in the following sizes: