Help interpreting weird Goodyear tire size?

I have a 99 Dodge Durango and need to replace the tires, but the Goodyears
on the vehicle now are marked "31x10.5R15LT". Evidently this is an optional
tire size, the standard for this model being 235/75R15.

I understand the latter nomenclature; 235mm width, 75% of that for sidewall
height, and 15" rim. But what does 31x10.5 mean, and what's the equivalent
tire specified in the more usual way? Goodyear and a few others sell some
tires marked this way, but the selection is small, and I'd like to be able
to cross reference it.

Thanks,
J

31 inches tall, 10.5 inches cross section.
"JHD" > wrote in message
.. .
>I have a 99 Dodge Durango and need to replace the tires, but the Goodyears
>on the vehicle now are marked "31x10.5R15LT". Evidently this is an
>optional tire size, the standard for this model being 235/75R15.
>
> I understand the latter nomenclature; 235mm width, 75% of that for
> sidewall height, and 15" rim. But what does 31x10.5 mean, and what's the
> equivalent tire specified in the more usual way? Goodyear and a few
> others sell some tires marked this way, but the selection is small, and
> I'd like to be able to cross reference it.
>
> Thanks,
> J
>
>



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Those tire sizes are the 'old' way of measuring them.

The 31" is the unloaded height of the tire on the stock rim a 10.5" wide
tire is supposed to fit on according to the chart at Goodyear. Likely a
7" or maybe an 8" wide rim.

The 10.5" is the width of the tire at the fattest part of the sidewall
again on the proper rim size.

Just a note, the sidewall width does not normally correspond exactly to
the 'tread' width. I 'think' the 31x10.5 Goodyears have 'about' a
10.25" wide tread.

I 'know' my 33x9.5's have a 7.5" tread with the 9.5" sidewall width and
the last pair of 31x10.5's I had measured 10.25" at the tread but they
were MudKings, not Goodyears. Every maker is slightly different.

Our 235/75R15 BFG's measure 8.5" on the tread.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
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JHD wrote:
>
> I have a 99 Dodge Durango and need to replace the tires, but the Goodyears
> on the vehicle now are marked "31x10.5R15LT". Evidently this is an optional
> tire size, the standard for this model being 235/75R15.
>
> I understand the latter nomenclature; 235mm width, 75% of that for sidewall
> height, and 15" rim. But what does 31x10.5 mean, and what's the equivalent
> tire specified in the more usual way? Goodyear and a few others sell some
> tires marked this way, but the selection is small, and I'd like to be able
> to cross reference it.
>
> Thanks,
> J

"JHD" > wrote in message
.. .
> I have a 99 Dodge Durango and need to replace the tires, but the
Goodyears
> on the vehicle now are marked "31x10.5R15LT". Evidently this is an
optional
> tire size, the standard for this model being 235/75R15.
>
> I understand the latter nomenclature; 235mm width, 75% of that for
sidewall
> height, and 15" rim. But what does 31x10.5 mean, and what's the
equivalent
> tire specified in the more usual way? Goodyear and a few others sell
some
> tires marked this way, but the selection is small, and I'd like to be
able
> to cross reference it.
>
> Thanks,
> J
>
>

Those are Light Truck tires. 31 inches in diameter, 10.5 width at the
sidewalls, R = Radial 15 inch rim width, Light Truck

If those are what was on that vehicle from the factory (check the door
tag to be sure) then you almost have to buy that size. Metric sizing
would be close to 325/75/15 and those are not real common.




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"Steve W." wrote

> > on the vehicle now are marked "31x10.5R15LT".
>
> Those are Light Truck tires. 31 inches in diameter, 10.5 width at the
> sidewalls, R = Radial 15 inch rim width, Light Truck
>
> If those are what was on that vehicle from the factory (check the door
> tag to be sure) then you almost have to buy that size. Metric sizing
> would be close to 325/75/15 and those are not real common.

Really? In my metric system, 10.5 inches is 266.7mm.
That would be about a 265/75-15, or 255/80-15.