I currently have P205/75R15 tires on my XJ40, front and
back, but the front tires are pretty worn.
I have two P205/70R15 tires from my Chrysler Fifth Avenue
(of blessed memory) that are in good shape. I’d like to junk
the front tires on the XJ40, move the rear tires to the
front, and run the P205/70R15s in the back.
Assuming I don’t do any diagonal tire rotation that would
mix the sizes from side to side, am I OK making this change?
Based on my neophyte’s knowledge of tire sizing, the new
P205/70R15 rear tires have
(75% - 70%) x 205 mm = 10.25 mm = 0.40 inch
less sidewall height than the current P205/75R15.
I figure that putting them in back is less likely to throw
off the XJ40 steering that was designed for the 0.4 inch
higher sidewall.
The nice thing about this setup is that the rear tires are
studded, and I’m going into the Sierra Nevada winter right now.
Thanks in advance to any tire mavens that chime in with some
information on whether I can do this with impunity or not.–
1988 and 1989 XJ40s
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In reply to a message from John Benson sent Tue 13 Oct 2009:
No-one will say that it is OK, for fear of being sued if anything
goes wrong. I say that if anything goes wrong it won’t be because
of mixed tires that are so close.
By the way, my 1990 has P207/70R15. Are the '88 and '89
different? 75-series was pretty old-fashioned, even then.
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In reply to a message from AJME sent Tue 13 Oct 2009:
So true. No-one will say anything that can possibly be a cause for
legal action. I would say more but this is not the forum…–
The original message included these comments:
No-one will say that it is OK, for fear of being sued if anything
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In reply to a message from Alan4d sent Tue 13 Oct 2009:
Well, now I’m not american, so I guess I will be safe giving advice
here…
I would do it without hesitation, if the tire load index is high
enough.
I believe the 205/75R15 is the original size. Mine is from '92, and
I seem to remember that that is the size of the spare tire. At
least in Europe, you will not be able to find that size anymore. It
is simply not produced anymore
My winter tires are 215/65R15 and summer 225/60R16
I would be more worried about driving a car with winter tires rear
and summer tires in the front…–
BR Leo Jensen - Denmark - XJ40 3.2 1992
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In reply to a message from John Benson sent Tue 13 Oct 2009:
I believe the specification for the early XJ40s is 205/70R15,
not the 75 aspect ratio you’re running. I think you’re decision to
put the better tires on the rear is a good idea, because you have
the horsepower in the power steering to help control the car in the
case of a tire failure up front. I’ve had tires come apart at
highway speeds and it’s not a lot of fun when it’s a rear tire.
I run 215/70R15 tires all the way around on all three of my
XJ40s. I have a pair of Green Diamond 205/70R15 winter tires with
embedded carbide bits in the tread (www.greendiamondtires.com) that
I put on one of the daily drivers for the winter. I haven’t had
any driveability issues with the mis-match in sizes with the
slightly smaller tires are mounted in the back. But my Maryland
winters aren’t as severe as Sierra Nevada winters.
If you have doubts, mount them and find an empty parking lot (a
high school on a weekend, maybe) and really exercise the car about
to see whether the car performs satisfactorily for you. If you
find any driveability issues, don’t run the mismatched sizes.–
The original message included these comments:
I currently have P205/75R15 tires on my XJ40, front and
back, but the front tires are pretty worn.
I have two P205/70R15 tires from my Chrysler Fifth Avenue
(of blessed memory) that are in good shape. I’d like to junk
the front tires on the XJ40, move the rear tires to the
front, and run the P205/70R15s in the back.
The nice thing about this setup is that the rear tires are
studded, and I’m going into the Sierra Nevada winter right now.
Thanks in advance to any tire mavens that chime in with some
information on whether I can do this with impunity or not.
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In reply to a message from Jaguarpete sent Wed 14 Oct 2009:
I go back to a time that in November, you went to the local
garage to get your snow tires installed. Never ever did
anyone get snow tires on the front.
There may be a difference in handling with different tires
on the back but an adult with reasonable common sense should
respect the difference and drive accordingly.
Do you need to take those studded tires off by a certain
date. I think my State has some rule on it, not sure so
don’t quote me.–
The original message included these comments:
any driveability issues with the mis-match in sizes with the
slightly smaller tires are mounted in the back. But my Maryland
winters aren’t as severe as Sierra Nevada winters.
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In reply to a message from John S sent Wed 14 Oct 2009:
I think most States have problems with steel studded tires. That’s
why I bought the Green Diamond tires in the first place. I have
them mounted on spare Jaguar rims that I got from my local DIY
salvage yard for $30 each. That’s also where I buy my tires (for
$15 each).–
The original message included these comments:
Do you need to take those studded tires off by a certain
date. I think my State has some rule on it, not sure so
don’t quote me.
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In reply to a message from AJME sent Tue 13 Oct 2009:
Re mixing 75% sidewalls with 70% sidewalls:
My bad, my Jag has 205/70R15’s and the studded tires I want
to put in back are 205/75R15’s: I had it backwards.
The sense of the forum seems to be that the mismatch won’t
be too bad.
I just checked the maintenance handbook and the
manufacterer’s spec is Pirelli P5 205/70 VR 15 Cinturato.–
1988 and 1989 XJ40s
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