Does anyone know offhand the rolling radius of the original Dunlop
640-15 tires supplied on the 3.8 E-Type? Guess I could look it up
in Porter’s book, it must be there somewhere…
Tom–
Tom Demergian (Madison, Wisconsin USA) 1962 FHC, 1949 MG TC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from TomDemergian sent Thu 1 Mar 2007:
Tom,
Revs/mile for a 6.40-15 is 777. That’s the figure to use when
buying tires. You can calculate an equivalent radius from that for
a guess at car height, 13.0 inches.
I have a 1973 Pirelli pocket guide with lots of good information
like that…
With Michelin XVS 185-15 radials, my wheel center is 12.5’’ from the
ground.
Tires are flexible and centrifugal expansion comes into play at
speed, ‘‘rolling radius’’ is not necessarily the same as sitting
radius, and simple geometry is not of that much use. Measuring the
revs/mile and actual sitting ride height are the best ways…
Jerry–
Jerry Mouton '64 FHC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from TomDemergian sent Thu 1 Mar 2007:
In Jaguar’s ‘‘Driver’s Handbook’’ for the E-type, there are
tables of engine RPM versus speed, from which you can
calculate the tire revs/mi (related by the rear end ratio).
From my S1 4.2 Handbook for the 3.54 rear: 2775 rpm at 60
mph, which translates to 784 rev/mi; and 1398 rpm at 30 mph,
which translates to 790 rev/mi. It’s ambiguous if that’s for
the 6.40x15 or 185x15 size since this was when Jaguar was
transitioning from the former to the latter. Anyway, with
the rev/mi figure in hand, you can go to a website like tirerack.com and compare to their posted numbers for rev/mi
for a variety of ‘‘modern’’ tires to get comparable radius
tires. I’m assuming that’s why your asking…–
The original message included these comments:
Does anyone know offhand the rolling radius of the original Dunlop
640-15 tires supplied on the 3.8 E-Type? Guess I could look it up
–
Mike - Ol’ Gurrl (1966 E-type OTS)
Aiken, SC, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
In reply to a message from Ray Livingston sent Fri 2 Mar 2007:
Ray,
According to Pirelli, 6.40-15 bias ply is 777 revs/mile, 185-15
radial is 788 revs/mile. So the radials were actually a little
lower profile than the bias tires. Didn’t see any with 666!
Jerry–
Jerry Mouton '64 FHC
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–