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Old 02-03-2016, 07:04 PM   #183
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Somewhere someone said (maybe Andy) that max load capacity is reached at 44 psi. The 50 is for mounting or something else.
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Old 02-04-2016, 06:24 AM   #184
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Originally Posted by interstateflyer View Post
I have the same tires on my 2014 23D. The side walls say 50 PSI for 2185 max load. I'm wondering why Andy suggests 44 PSI.
Question: Does the tire say: Max Load 2185 pounds at 50 psi?

Or does it say: Max Load 2195 pounds, Max pressure 50 psi.

Notice the difference. One states a relationship and the other states 2 maxes with no relationship implied.

Here's the scoop: In every other type of tire, the way it is expressed is the first way - a relationship. But in passenger car tires it is generally stated the second way: 2 maxes, no relationship.

Why? It has to do with speed capability. Because Europe has roads where there aren't any speed limits, the tires are inflated differently. That is a tire's speed capability is increased if more inflation pressure is used.

For example, when a passenger car tire is tested for an S speed rating it is inflated to 35; for an H rating, it is inflated to 44 psi; and for V or higher, it is inflated to 51 psi.

So the max pressure reflects this.

- BUT -

Load carrying capacity is done differently. For a Standard Load Passenger car tire, it maxes out at 35 psi.

So an S speed rated tire could say: "Max Load XXXX @ 35 psi" or it might say "Max Load XXXX, Max Pressure 35 psi".

But a V speed rated tire will only say: "Max Load XXXX, Max Pressure 51 psi".

HOWEVER, you will find some tires that do not follow the rule: S or T speed rating = 35 psi max / H = 44 psi max / V and higher = 51 psi max. ....... either by stating a higher pressure or by indicating a relationship. I consider these to be errors on the part of the manufacturer. They aren't serious errors, just minor and inconsequential ones - although it does lead to confusion (as we have seen).

OK, how does that apply to this situation?

Well ......... The tire being discussed is an Extra Load (as opposed to a Standard Load), and it reaches its maximum load carrying capacity at 41 psi. And following the same logic, it is labeled as a 50 psi max pressure (+ 9 psi more than the rated pressure) - and don't forget that it is possible for tire manufacturer to commit the same error in the way they state this.

Clear as mud, right?
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Old 02-04-2016, 06:33 AM   #185
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Interesting!
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Old 02-04-2016, 07:52 AM   #186
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So Capri - does that mean for this tire the max load is achieved at 41psi but speed would be restricted unless inflated to 50psi?

I apologize for not following the logic....thanks!
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Old 02-04-2016, 08:21 AM   #187
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Originally Posted by SteveSueMac View Post
So Capri - does that mean for this tire the max load is achieved at 41psi but speed would be restricted unless inflated to 50psi?

I apologize for not following the logic....thanks!
I would highly recommend you fully inflate the tires to 50 psi if you wish to run them at 118MPH, Steve
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Old 02-04-2016, 09:35 AM   #188
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Seems to me you would want the higher inflation so there is less sidewall flexing (creating heat) at high speeds and the tire sidewall would hold up better in tight, low speed turns.
My opinion would be to run the max pressure.
I did this for my sister's F150. It has P rated factory tires. We pumped them up to max sidewall pressure (44 psi) and it drove straight as an arrow when hooked to the trailer. With the standard door placard pressure the truck wallowed and squished all over the road.
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Old 02-04-2016, 09:45 AM   #189
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Originally Posted by crispyboy View Post
Seems to me you would want the higher inflation so there is less sidewall flexing (creating heat) at high speeds and the tire sidewall would hold up better in tight, low speed turns.
My opinion would be to run the max pressure.
I did this for my sister's F150. It has P rated factory tires. We pumped them up to max sidewall pressure (44 psi) and it drove straight as an arrow when hooked to the trailer. With the standard door placard pressure the truck wallowed and squished all over the road.
When the P rated tires wear out, move to LT tires and you'll see an even bigger benefit. At least that was my experience.
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Old 02-04-2016, 09:50 AM   #190
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Andy told me years ago (October 2012) that this Michelin LTX (P) 235/75R15 XL tire is similar to a Load C (if I remember correctly) and has it's maximum load capacity around 41 psi and going to 50 psi stiffens the sidewalls to help when making turns and twisting the tires on the rims.

I know the load from the CAT scales on the axles of our 2015 23D ready to camp and the four tires are carrying less than 1,500 pounds each on average. Next week I will set up my individual wheel scales to get actual loads per tire location and an actual tongue weight reference when not attached to the car.

He also suggested taking the tire pressures on my 2007 Mercedes ML320 CDI diesel from the door label pressures (front 32 psi and rear 39 psi) to 44 psi front and rear to stiffen the sidewalls when towing. The maximum side wall pressure is 51 psi on the Michelin car tires.
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Old 02-04-2016, 10:41 AM   #191
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Quote:
Originally Posted by CapriRacer View Post
Question: Does the tire say: Max Load 2185 pounds at 50 psi?

Or does it say: Max Load 2195 pounds, Max pressure 50 psi.

Notice the difference. One states a relationship and the other states 2 maxes with no relationship implied.

Here's the scoop: In every other type of tire, the way it is expressed is the first way - a relationship. But in passenger car tires it is generally stated the second way: 2 maxes, no relationship.

Why? It has to do with speed capability. Because Europe has roads where there aren't any speed limits, the tires are inflated differently. That is a tire's speed capability is increased if more inflation pressure is used.




For example, when a passenger car tire is tested for an S speed rating it is inflated to 35; for an H rating, it is inflated to 44 psi; and for V or higher, it is inflated to 51 psi.

So the max pressure reflects this.

- BUT -

Load carrying capacity is done differently. For a Standard Load Passenger car tire, it maxes out at 35 psi.

So an S speed rated tire could say: "Max Load XXXX @ 35 psi" or it might say "Max Load XXXX, Max Pressure 35 psi".

But a V speed rated tire will only say: "Max Load XXXX, Max Pressure 51 psi".

HOWEVER, you will find some tires that do not follow the rule: S or T speed rating = 35 psi max / H = 44 psi max / V and higher = 51 psi max. ....... either by stating a higher pressure or by indicating a relationship. I consider these to be errors on the part of the manufacturer. They aren't serious errors, just minor and inconsequential ones - although it does lead to confusion (as we have seen).

OK, how does that apply to this situation?

Well ......... The tire being discussed is an Extra Load (as opposed to a Standard Load), and it reaches its maximum load carrying capacity at 41 psi. And following the same logic, it is labeled as a 50 psi max pressure (+ 9 psi more than the rated pressure) - and don't forget that it is possible for tire manufacturer to commit the same error in the way they state this.

Clear as mud, right?
Max Load 2185 pounds at 50 psi.
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Old 02-04-2016, 11:28 AM   #192
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I think the statement "max load at 50 psi " Is true and accurate. What is also true is that they will carry the same max load at 44 psi. So on a trailer what are the pros and cons to running at 50 versus 44 psi?
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Old 02-04-2016, 11:53 AM   #193
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If you're going to say something authoritative (especially on my thread as the OP for this thread), it would be super helpful to include a link that proves the point. I don't mean to be a pain, but just saying "Max Load 2185 pounds at 50 PSI" doesn't prove anything. Show us the money via a link to a truly authoritative source.

Thanks!
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Old 02-04-2016, 12:43 PM   #194
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A point on pressure that I learned here-
The pressure that the Michelin LTX M/S2 P235/75R15XL 108T carries its rated load is 41 PSI. The maximum pressure is 50 PSI. There is no load capacity increase above 41 PSI.
Tire Tech Information - Tire Specs Explained: Maximum Load
For the people too >redacted< or don't have time to read the thread from the beginning.
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Old 02-04-2016, 12:47 PM   #195
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I don't believe there are any cons to inflating these tires to the maximum sidewall pressure of 50 PSI when used in trailer service. Tireman 9 has written many times that tandem axle trailers tires should always be inflated to the maximum sidewall inflation pressure to lessen the effects of interply shear.
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Old 02-04-2016, 02:53 PM   #196
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Originally Posted by Rocinante View Post
If you're going to say something authoritative (especially on my thread as the OP for this thread), it would be super helpful to include a link that proves the point. I don't mean to be a pain, but just saying "Max Load 2185 pounds at 50 PSI" doesn't prove anything. Show us the money via a link to a truly authoritative source.

Thanks!
I'll try to take a photo of the tire with the printing "Max Load 2185 pounds at 50 PSI". I assume that the tire is the ultimate authority. All the rest of this is speculation based on theory.
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