I'm going to shorten this for clarity:
Quote:
Originally Posted by Concrete
.........
you have lots of information in your post but not much on this opinion
what are the issues with this?
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Here's a comparison of the load curves for the "same size" P metric to LT metric. (excerpted from 2005 TRA Yearbook)
Pressure......P245/75R16...........LT245/75R16
...(psi).....Max Load (pounds)....Max Load (pounds)
...30...........1914....................... ---
...35...........2065 (SL)................ 1700
...40........... --- ....................... 1865
...45........... --- ....................... 2030
...50........... --- ....................... 2205 (C)
...55........... --- ....................... 2335
...60........... --- ....................... 2480
...65........... --- ....................... 2623 (D)
...70........... --- ....................... 2765
...75........... --- ....................... 2900
...80........... --- ....................... 3042 (E)
Notes:
1) The letters in the parantheses are the load range and are placed next to the maximum load (and corresponding pressure) for that load range.
Put another way: An LT245/75R16 LR C has a max load of 2205 # and it occurs at 50 psi - and 50 psi is the max usable pressure.
2) I've applied the 10% load reduction for "P metric tires used in LT application" to make the comparison "apples to apples".
3) The "---" in the table means the yearbook doesn't have an entry for that pressure - meaning the table either doesn't go that high for P metric or that low for LT metric. I take that to mean those pressure are not usable.
There are some notes under the published load tables that allow higher pressures than listed in the table above. Because of the way the governmental regulations read, this note is usually what governs what gets imprinted on the sidewall - and as I said in the previous post, there is not 100% agreement within the tire industry about passenger car tires.
What you should get out of this comparison is that for the same load, the LT metric tire requires a higher pressure, but the maximum load carrying capacity is higher for an LT metric tire (at a higher pressure).
From all this, I conclude that P metric and LT metric tires are not interchangeable.