My source was memory from reading these forums for a while. But here is an explanation of load rating and a chart showing max load at 41 psi from Tire Rack with an explanation that it is actually 42 psi.
Actually it does "square" with Franks chart. The other pertinent information is that for use of a P tire on a trailer DOT requires that the maximum load rating is 10% less that what is stamped on the tire. That gives you 1965
lbs for trailer use. (This is one of the statements that aggravates Frank)
And note that it says max load 2183 and max pressure 50 psi. But it does not say 2183 at 50 psi. I think that statement is actually true, but it also carries 2183 at any pressure down to 42 psi. Like I said, I run mine at 48-50 because I only found the lower pressure numbers recently and saw no reason to change what works good.
I think the E2 means the tire was registered in France.
I do not know about the Defender yet. I have been running the LTX 15" tires for 8 years now. The first set was a true LT tire (load range C). The second the p-XL tires. I hope the Defenders are as good. 8 trouble free years of smooth pulling and a good ride for the trailer. I will get new tires next spring and probably the Defenders.
From the Tire Rack site:
"The load range/ply rating branded on a tire's sidewall identifies 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 casing 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.
"The load range/ply rating branded on a tire's sidewall identifies how much load the tire is designed to carry at its industry specified pressure."
Since most P-metric passenger tires are manufactured in the standard load range, 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.
P-Metric Passenger Vehicle Tires
Load Ranges Abbreviated Maximum 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-Mc Passenger Vehicle Tires
Load Ranges Abbreviated Maximum Load Pressure
Standard Load Nothing or SL 36 psi (250 kPa)
Reinforced or 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-sized tires featuring section widths of 305mm/12.50" or wider have their maximum loads and cold tire pressures rated at reduced maximum load pressures.
LT-Metric, LT-Flotation and LT-Numeric Light Truck Tires
Load Range Ply Rating Abbreviated Maximum 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
Euro-Metric Commercial Vehicle/Van Tires
Load Index Maximum Load Pounds Maximum Load Pressure
116/114 2,705/2,600 69 psi (475 kPa)
118/116 2,910/2,755 75 psi (525 kPa)
121/120 3,195/3,085 83 psi (575 kPa)
Euro-metric commercial vehicle/van tire dimensions end in a C (signifying commercial), such as 225/75R16C. Differences in load capacities and maximum pressure are identified by their load index and the maximum load/pressure for single/dual applications branded on their sidewall. The example provided above is for single/dual applications of a 225/75R16C size tire.
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 Maximum 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)
Diameter Comparison of Light Truck
Dual Tires for Light Truck Use
Light Truck Fitment Formula
Load Reduction of Euro- &
P-Metric Tires on Light Trucks "