[concours] (concours) Tires

David:

For what it’s worth, here are some comments I received from Dunlop Research &
Development Department in 1981 in response to a question I had asked about
tires for a 3.8 S I own.

  1. "The 185-15 SP41 tire was specifically developed for use on Jaguar
    automobiles, and official Jaguar approval was given in 1964.
  2. To the best of our knowledge, supplies of this tire to Jaguar commenced
    during 1964. We know that 1963 models fitted 6.40-15 RS5 and 1965 models,
    including S-types, had converted to 185-15 SP41. The change-over appears to
    have taken place during Jaguar’s 1964 production run. Unfortunately, we are
    unable to ascertain precise dates, and I doubt that even Jaguar Cars could
    give you more specific information since it is likely that for a period of
    two or three months they would have received both RS5 and SP41 tires
    concurrently.
  3. The Aspect Ratio of the RS5 is approximately 87 percent and that of the
    SP41 about 81 percent."

Along these same lines, a Service Bulletin dated June, 1964 that I received
from Jaguar in 1981 and titled Introduction of Dunlop SP.41 Tyres states
that “Commencing at the above chassis numbers, Dunlop SP.41 tyres are fitted
as standard except for white-wall tyres which will continue in the RS5 type
for the time being.” For the LH drive 3.4 ‘S’ cars, the chassis number
listed is 1B 25084 and for the LH drive 3.8 ‘S’, 1B 75382. Recommended
pressures are listed for normal motoring up to 100 MPH and for high speeds up
to maximum.

Alan Wiedie