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Old 12-18-2012, 06:36 PM   #15
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"It sounds like those tires are exactly the same tire under the lable."

That is sorta what I am thinking. Maybe the testing and the rating of the tires is different. maybe the C tire is already rated down because of the 10% de rating for P tires on trucks and SUV's that they are being marketed for.

I am interested if anybody thinks a tire that has 50 psi max inflation stamped on it will carry a higher load at 41 lbs than it will at 50?
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Old 12-19-2012, 06:12 AM   #16
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Originally Posted by ROBERT CROSS View Post
Our LTX's are @.....or more accurately at....
Bob
You must be careful here. P type tires are done differently than LT and ST tires.

For P type tires it is common to indicate a maximum inflation pressure that is different than the pressure where the max load occurs. Mis-understanding this is very common.

For LT and ST tires it is the usual practice to indicate the pressure where the max load occurs.

I hope this clears this up.
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Old 12-19-2012, 06:20 AM   #17
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Originally Posted by Bill M. View Post
"It sounds like those tires are exactly the same tire under the lable."

That is sorta what I am thinking. Maybe the testing and the rating of the tires is different. maybe the C tire is already rated down because of the 10% de rating for P tires on trucks and SUV's that they are being marketed for.

I am interested if anybody thinks a tire that has 50 psi max inflation stamped on it will carry a higher load at 41 lbs than it will at 50?
Sorry guys, but this has gotten all sideways.

P metric Standard Load (SL) tires are rated for a maximum load carrying capacity at 35 psi. Extra Load (XL) P metric tires are rated for a maximum load at 41 psi.

When P metric tires are used in a Light Truck application, they have to be derated by a factor of 1.1. They aren't derated if used in a passenger car application.

LT and ST type Load Range C tires are rated for maximum load at 50 psi. For LR D it's 65 psi. etc.

Where the confusion comes in is that P metric tires are commonly marked with a higher maximum inflation pressure than the pressure where the max load occurs.

So - There will be differences between XL and LR C tires. In particular the pressure where the max load occurs.

And to help with things, you might want to read up on tires on my website:

http://www.barrystiretech.com/
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Old 12-19-2012, 07:56 AM   #18
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If one goes to the Michelin website:

michelinman.com/tire-selector/category/suv-crossover/ltx-m-s2/tire-details#techspec_table

and look at the first tire which is the P235/75R15 XL tire, you will see that the factory specs the tire at 1,985 pounds @ 50 psi. That is the derated load capacity per 49 CFR 571.110 s4.222 while the sidewall rates the tire at 2,183 pounds and maximum pressure of 50 psi. I would believe the factory data sheet before a retail outlet.

The reference CapriRacer points to is a generic, no brand or tire model specification. I believe the tire manufacturer knows their product better and they have the liability of living up to that specification.

Running at 41 psi would not be appropriate for my tires in my application.
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Old 12-19-2012, 08:12 AM   #19
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Measure temperatures across the tire profile with an IR thermometer and adjust pressure to get an even temperature at the sides and the middle. The idea pressure is a function of the load on the tire. I run about 25 psi in the rear tires on my Ranger truck because it has nothing in the bed. If I ran 35 psi the tires would wear out in the center and I would have no traction especially in the rain. I run the fronts at about 35 psi which is the max for that tire.

No a tire won't carry more load at 41 psi than at 50. It is possible to overheat the center of a tire by overinflating it.

If you are at the max pressure and the tires are running hot on the edges then they are overloaded.

Perry
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Old 12-19-2012, 10:30 AM   #20
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Originally Posted by switz View Post
If one goes to the Michelin website:

michelinman.com/tire-selector/category/suv-crossover/ltx-m-s2/tire-details#techspec_table

and look at the first tire which is the P235/75R15 XL tire, you will see that the factory specs the tire at 1,985 pounds @ 50 psi. That is the derated load capacity per 49 CFR 571.110 s4.222 while the sidewall rates the tire at 2,183 pounds and maximum pressure of 50 psi. I would believe the factory data sheet before a retail outlet.

The reference CapriRacer points to is a generic, no brand or tire model specification. I believe the tire manufacturer knows their product better and they have the liability of living up to that specification.

Running at 41 psi would not be appropriate for my tires in my application.
2 thoughts: I have no problem with your using 50 psi in your P metric tire. That's OK according to all the rules I am aware of.

I just want folks to be aware that there is a difference between P metric and LT metric tires and they have to adjust things accordingly.

BTW, the "generic" specifcation is an industry standard used by Michelin, Goodyear, Bridgestone, and everyone else I know of. It is unfortunate that Michelin has made the chart the way they did. It is inaccurate.

So just to prove my point, email Michelin and ask them what the load carrying capacity is for their P235/75R15 XL at 41 psi.
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Old 12-19-2012, 12:25 PM   #21
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Goodrich has the same 1985 pounds @ 50 psi on their webpage as in the Michelin webpage.
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Old 12-19-2012, 02:33 PM   #22
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Is there a difference or benefit to running a P rated tire at 41psi vs a LT tire at 50psi, as long as you don't exceed the weight limit of the tire at that particular PSI?

Also is there a benefit to inflating a P rated tire beyond 41psi?
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Old 12-19-2012, 06:00 PM   #23
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I doubt Michelin's webpage is in error if the actual tire has a 50psi side wall maximum pressure and a stated load of 2183 pounds. The foot note in the tire rack page picks two pressures for discussion, not the maximum pressure nor the maximum load capacity.
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Old 12-19-2012, 06:05 PM   #24
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Michelin does not provide pressure = weight capacity table for this tire. I put maximum pressure for maximum load just you do on the GYM ST tires or the 16" LT tires Airstream sells. I would not use 41 psi and expect tire to carry full load.
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Old 12-19-2012, 06:32 PM   #25
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I tow with Michelin P 235 R 75 XL tires on my 6300 gvw 2004 25 Safari. I inflate to 50 lbs. I am on my 3rd year with about 7500 miles.
I tow fast, about 70 mph, hot, one long road trip in 100+ weather and around curves and down steep downgrades in the mountains. I make lock to lock U turns and don't baby the tires in any way whatsoever.
Zero problems and no visible tire wear. The ride is so much smoother than the E rated ST tires I used to use.
If there is a practical difference between these tires and C rated LT tires of the same size, it escapes me.
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Old 12-21-2012, 07:03 AM   #26
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Originally Posted by switz View Post
Michelin does not provide pressure = weight capacity table for this tire......
How about asking for one? Or make it simple, ask them what the load carrying capacity is at 41 psi.
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Old 12-21-2012, 12:00 PM   #27
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On our 2008 Tundra, when the OEM tires wore out, I replaced the P (passenger) tires with E-rated LT tires, in the same size. You can really tell the difference in ride and handling at the same inflation pressure.

I used to run the P tires at 44 psi, which was the maximum printed on the sidewalls. When first installed, I ran the LT tires at 45 psi; and there was much less squishing around in the turns. The P tires made our pickup ride like a boat, actually like a really soft-sprung luxury sedan (like a Cadillac); and the LT tires hold a straight line better and don't feel squishy.

I now run the LT tires at 55/65 psi (front/rear) when towing, as those P tires always looked under-inflated.

Obviously, there is a big difference between P and LT tires; and this comparison probably does not accurately reflect the difference between C and XL tires. However, please note that we now have LT tires on our Bambi.
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Old 12-21-2012, 12:28 PM   #28
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The more air pressure you put in any tire, the more weight it will handle and the more stable it will be on the road. The tire rated for more pressure in a given size will carry more weight, at that max pressure.

If you air an "E" rated tire to the pressure of a "C" rated tire, it will carry no more weight than a "C" rated tire, and if you don't believe me, check the charts.

I don't know how it could be any more simple.
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