my mistake, i got confused. the D / E load rating has to do with the total rating of the tire, not the actual total of plies. so, as it would seem, an E (10 ply equivalent) load rated tire has a higher load and PSI capacity than a D (8 ply load equivalent), it comes down to the material used rather than the total number of plies.
The load range or ply rating branded on a tire's sidewall helps identify how much load the tire is designed to carry at its industry specified pressure. Passenger tires feature named load ranges while light truck tires use load ranges that ascend in alphabetical order (letters further along in the alphabet identify stronger tires that can withstand higher inflation pressures and carry heavier loads). Before load ranges were adopted, ply ratings and/or the actual number of carcass plies were used to identify the relative strength with higher numeric ratings or plies identifying tires featuring stronger, heavier duty constructions.
Today's load range/ply ratings do not count the actual number of body ply layers used to make up the tire's internal structure, but indicate an equivalent strength compared to early bias ply tires. Most radial passenger tires have one or two body plies, and light truck tires, even those with heavy-duty ratings (10-, 12- or 14-ply rated), actually have only two or three fabric plies, or one steel body ply.
In all cases, when changing tire sizes or converting from one type of size to another, it is important to confirm that the Load Index in the tire's Service Description of the new tire is equal to or greater than the Load Index of the original tire and/or that the new tire’s rated load capacity is sufficient to carry the vehicle's Gross Axle Weight Ratings.
Passenger Tires
Since most P-Metric passenger tires are manufactured in the Standard Load Ranges, they will have nothing branded on their sidewalls or may be branded Standard Load and identified by an SL in their descriptions, as in P235/75R-15 SL.
Extra Load P-Metric tires will be branded Extra Load, and identified by an XL in their descriptions, as in P235/75R-15 XL.
Light Load P-Metric tires will be branded Light Load, and identified by an LL in their descriptions, as in P285/35R-19 LL.
NOTE: Only P-Metric sized tires with 45-series aspect ratios or lower may be manufactured in a Light Load configuration. Light Load tires are designed to carry less weight than Standard Load tires and have been developed for specific applications (typically when relatively large tire sizes are used as Original Equipment (O.E.) on relatively small cars or for Track & Competition DOT tires used for racing applications).
P-Metric Passenger Vehicle Tires Load Ranges Abbreviated Max Load Pressure
Light Load LL 35 psi (240 kPa)*
Standard Load Nothing or SL 35 psi (240 kPa)*
Extra Load XL 41 psi (280 kPa)*
*In an effort to internationally harmonize load ratings and ranges, recently introduced and future LL, SL and XL P-Metric sizes will use ISO/Euro-metric maximum load pressures of 36 or 42 psi
Standard Euro-Metric tires will have nothing branded on their sidewalls, while Extra Load/Reinforced Euro-Metric tires will be branded as such and identified by an XL or RF in their descriptions, as in 305/50R20 XL or 305/50R20 RF.
Euro-Metric Passenger Vehicle Tires Load Ranges Abbreviated Max Load Pressure
Standard Load Nothing or SL 36 psi (250 kPa)**
Extra Load RF or XL 42 psi (290 kPa)**
**Reinforced and Extra Load nomenclature may be used interchangeably to designate heavy-duty tires
Light Truck Tires
Since light truck tires are often available in multiple load ranges, the appropriate load range is identified immediately following the size's rim diameter in Tire Rack's descriptions.
LT-Metric, LT-Flotation and LT-Numeric tires are branded with their load range (Load Range E or LRE) or their ply rating (10 Ply Rated) on their sidewalls and list their appropriate load range letter in their descriptions as LT245/75R-16 E, 7.50R-15 D or 31x10.50R-15 C.
LT-Metric, LT-Flotation and LT-Numeric Light Truck Tires Load Range Ply Rating Abbreviated Max Load Pressure
B 4 B 35 psi (240 kPa)***
C 6 C 50 psi (350 kPa)***
D 8 D 65 psi (450 kPa)***
E 10 E 80 psi (550 kPa)***
F 12 F 95 psi (650 kPa)***
***Selected large LT sizes are designed with reduced maximum load pressures
Special Trailer Service Tires
Special Trailer Service tires are often available in multiple load ranges. The appropriate load range is identified immediately following the size's rim diameter in Tire Rack's descriptions.
ST-Metric sized special trailer service tires will be branded with their load range (Load Range D or LRD) on their sidewalls and list their appropriate load range letter in their descriptions as ST205/75R15 LRD.
ST-Metric Trailer Service Tires Load Range Ply Rating Markings Max Load Pressure
B 4 B 35 psi (240 kPa)
C 6 C 50 psi (350 kPa)
D 8 D 65 psi (450 kPa)
E 10 E 80 psi (550 kPa)
