...Carlisle ST175/80D13 [b]SPORT TRAIL (radial) tire on a 1989 Scamp 16. Recently I purchased a couple of the above listed radial tires at a Tractor Supply Company (used to be Farm & Fleet) store, and have found them to be 7 3/8" wide (inflated) while the original tires on my Scamp 16 are Carlisle ST175/80D13 [b]USA TRAIL bias ply tires that measure 6 3/4" wide(inflated)...
The Sport Trails
would be ST175/80[b]R13 (not "D"), if they are radials... and the Carlisle catalog I recently downloaded shows the Sport Trail
only as a bias (diagonal=D) ply tire. Are the Sport Trail
tires really radials, Karl?
Carlisle does make [b]radial trailer tires; the models in the 2007 catalog are Ultra Sport
(low profile, not Karl's tires), Radial Trail
, and Radial ST
. I suppose it's possible that the "Sport Trail" name could be moulded into the sidewall of a Radial Trail
tire, but I would hope that the construction letter in the size spec ("R" or "D") and other informational text on the tire sidwall would be correct, regardless of the marketing text.
The [b]section width of a tire depends significantly on the wheel width, which is why the tire specifications list a "measuring rim width" (the width of wheel used for the reference tire width measurement, as well as a range of acceptable rim widths. Were the Sport Trail
and USA Trail
tires measured on the same rims? In both cases, the "measuring rim width" is 4.50", and the allowable range is 4-1/2" to 5-1/2".
Tires also bulge at the bottom where they are "squashed" by load. My guess is that the widths were not measured down there, but if they were, the measured width would be changed due to the amount of load on the tires, as well as their construction.
According to the [b]specifications in the 2007 Carlisle catalog, the section width of an ST175/80D13 Sport Trail
is 6.6" (for load range B ) or 6.8" (for load range C ): that shows that there is a significant variation within the same nominal size, and that the measured width of 7.375" is too wide (so they must be on a wide wheel, or something else is strange). The same catalog shows the same size of USA Trail
to be 6.65" wide (LR B ) or 6.67" wide (LR C )... essentially the same as the spec for the Sport Trail
, and about the same as measured by Karl (6.75").
The Carlisle Radial Trail
ST175/80R13 (load range C ) tire shows a section width of 6.97" on a 5.00" measuring rim (with the same allowed rim width range); my guess is that the difference (from the bias ply models) is almost entirely due to the wider rim.