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CapriRacer · 02-05-2016, 06:09 AM

And on a side note:

I think it is best if everyone weighs their trailer - tire by tire if at all possible.

I also think everyone should pay attention to pressure buildup. No more than 10%!

When I was actively racing, part of my "Before Leaving" checklist was to do tire pressures on the tow vehicle, the race car, and the trailer. If I stopped along the way, I did a quick check of the tow vehicle and the trailer. I think everyone should have a checklist and tire pressures ought to be on it!

SteveSueMac · 02-05-2016, 06:19 AM

So what then - if anything - happens to factors other than load when at 42-50 PSI?

**Action** · 02-05-2016, 01:39 PM

My guess would be it is limited to tire wear & fuel economy.

>>>>>>>>Action

xrvr · 02-06-2016, 05:35 AM

Seems this is getting confusing, wasn't this thread about the new defender tire!

Lance M · 02-06-2016, 06:57 AM

Quote:

Originally Posted by avionstream

Seems this is getting confusing, wasn't this thread about the new defender tire!

Yes, but the new Defender is also an Extra Load (XL) tire, so this discussion of pressure is relevant.

CapriRacer · 02-06-2016, 07:06 AM

Quote:

Originally Posted by SteveSueMac

So what then - if anything - happens to factors other than load when at 42-50 PSI?

If by "factors" you mean "performance properties", then:

a) The tire will tend to wear in the center more, but trailers hardly wear tires at all, so this shouldn't be a concern.

b) The tire will have a higher spring rate, which means more impact force will be transmitted through the suspension.

c) The tire will tend to more follow the ruts and grooves in the road.

d) The tire will tend to be more resistant to cross winds.

e) The tire will run cooler - which I don't think is such a big deal unless the heat generation was a problem to begin with

f) The tire will have more speed capability - and that translates into more resistance to failure.

I think that about covers it.

Edit: I forgot to say that fuel economy will be better, but only marginally so.

Quote:

Originally Posted by avionstream

Seems this is getting confusing, wasn't this thread about the new defender tire!

It was (is?), and this part is discussing what it means when a P type tire states a load and inflation pressure on the sidewall - and the Michelin Defender is such a tire - especially considering this tire is being used to replace an ST tire, where things are stated differently.

SteveSueMac · 02-06-2016, 09:10 AM

Thanks. Very helpful. I see you didn't mention anything about "interplay shear" we hear a lot about with double (or triple) axle trailers. In your view - does max pressure (50 psi in this case) offer an advantage there?

I may try mine at 45 PSI this season and see what differences that makes.

Thanks again!

Bajaexplorer · 02-06-2016, 11:36 AM

[QUOTE=CapriRacer;1745307]False, but not for the reason you think. On an SUV, the tire has to be derated by a factor of 1.1, so the max load would be 1985#.

But to try to answer the question as you intended: In one sense it is true. The tire will support that load at 41 through 50 psi.

Yes.

No, but to be clear, if you use a pressure lower than 41 psi, the max load is lower, but between 41 psi and 50 psi, the max load is 2183# (or 1985# depending on what vehicle it is on).

Greetings,,

I have been reading this thread from the begining, over and over and I have to admit that the longest this thread goes the more confused It gets. I thought it has been mentioned before in a previous posting that this thread was exclusively about the performance of these tires on a trailer, air presuure, loads, derating the max load , and so on. But here, quote, " the max load is 2183# (or 1985# depending on what vehicle is on)
So this tire gets derated on a SUV use? or a trailer use?, please explain

**Action** · 02-06-2016, 11:43 AM

Quote:

Originally Posted by Flyingsilver

So this tire gets derated on a SUV use? or a trailer use?, please explain

Tires not designed for the application should be derated as they are being used on a different application than what was designed.

A passenger tire (The size starts with a P) is designed for a passenger car or some light truck. If the user installs on a non-passenger car the rating was not created for that application. derate it

LT is for light truck application

ST is for trailer application

The tire in question is a P tire.

This is the issue with off topic threads and long threads. Instead of creating a new thread posts are made that are related to the main topic just not the thread topic. In this case the thread topic is Michelin Defender LTX M/S 235/75-15 109T XL. However the answer was made to the tire pictured in post 135. That picture is of a P rated tire, which on a SUV is an application of a tire to a vehicle it was not designed for. A LT tire is designed for a SUV. A "P" tire is not designed for a SUV or light truck application.

>>>>>>>>>Action

**Rocinante** · 02-06-2016, 11:48 AM

Meaning it's load capacity should be de-rated by 10%. I'm pretty sure we've already established that at least 3 times in this FrankenThread I started .

There's really little more to say on this topic until the tires are available, hopefully in March. Thanks for playing, everybody!

DoublTrouble · 02-06-2016, 12:04 PM

Roc On!

CapriRacer · 02-07-2016, 05:36 AM

Quote:

Originally Posted by Flyingsilver

Greetings,,

I have been reading this thread from the beginning, over and over and I have to admit that the longer this thread goes the more confusing it gets. I thought it has been mentioned before in a previous posting that this thread was exclusively about the performance of these tires on a trailer, air pressure, loads, derating the max load , and so on. But here, quote, " the max load is 2183# (or 1985# depending on what vehicle is on)
So this tire gets derated on a SUV use? or a trailer use?, please explain

P type tires are load derated by a factor of 1.1 when used in certain types of service - trucks, vans, (although the popular interpretation doesn't include minivans), multipurpose vehicles (which includes SUV's, but doesn't seem to include crossovers!), and trailers.

If a P type tire is used in passenger car service, it is NOT derated.

LT type tires include the factor in the calculations - as does ST tires. It only applies to P type tires.

Why? I've tried to get to the source and have traced it back as far as 1968 - about the time the US federal regulations on tires began. I do not think this has anything to do with the federal regulations, only that whatever thinking was taking place occurred in the same timeframe and was adopted as a regulation. But I can only find the rule, not the justification behind the rule.

My best guess is that the types of vehicles mentioned tend to have stiffer suspensions, and to be driven on ...... ah, let's call it less smooth roads, than passenger cars. Both of those are factors when determining the load carrying capacity of a tire.

Quote:

Originally Posted by SteveSueMac

Thanks. Very helpful. I see you didn't mention anything about "interply shear" we hear a lot about with double (or triple) axle trailers. In your view - does max pressure (50 psi in this case) offer an advantage there?

I may try mine at 45 PSI this season and see what differences that makes.

Thanks again!

Interply shear is covered by my comment on failures.

A word of caution: When talking about fatigue type tire failures - and tread separations are the most common type - there are very few ways to determine that any particular thing makes things better or worse. Ya' see, we can't actually measure how much fatigue life is left in a tire. We can draw the inference that operating temperature is an indication - and I'm sure that the change in rubber properties is a factor here! If we measure the load on a tire, we can draw an inference there as well.

However, there are some early warning signs that we all should be on the alert for:

a) Bulges: Bulges are a sign of things within a tire failing.

b) Cracks: Cracks are a sign of either too much stress or deterioration of the rubber - both of which are bad things.

switz · 02-07-2016, 09:42 AM

Derating of the "P" tire falls under this regulation:

49 CFR 571.110

Tire selection and rims and motor home/recreation vehicle trailer load carrying capacity information for motor vehicles with a GVWR of 4,536 kilograms (10,000 pounds) or less.

S4.2.2.1

Except as provided in S4.2.2.2, the sum of the maximum load ratings of the tires fitted to an axle shall not be less than the GAWR of the axle system as specified on the vehicle's certification label required by 49 CFR part 567. If the certification label shows more than one GAWR for the axle system, the sum shall be not less than the GAWR corresponding to the size designation of the tires fitted to the axle.

S4.2.2.2

When passenger car tires are installed on an MPV, truck, bus, or trailer, each tire's load rating is reduced by dividing it by 1.10 before determining, under S4.2.2.1, the sum of the maximum load ratings of the tires fitted to an axle.

S4.2.2.3

(a) For vehicles, except trailers with no designated seating positions, equipped with passenger car tires, the vehicle normal load on the tire shall be no greater than 94 percent of the derated load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

(b) For vehicles, except trailers with no designated seating positions, equipped with LT tires, the vehicle normal load on the tire shall be no greater than 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure for that tire.

Lance M · 02-07-2016, 10:00 AM

switz,
I'm not a lawyer, but I don't think this CFR applies to me when I select tires for my travel trailer. I believe this is for vehicle manufacturers. I'm not saying this is something I wouldn't/shouldn't do as a good practice, I just don't believe this code applies to me when I'm making tire decisions.

CapriRacer · 02-08-2016, 06:18 AM

Quote:

Originally Posted by Top

switz,
I'm not a lawyer, but I don't think this CFR applies to me when I select tires for my travel trailer. I believe this is for vehicle manufacturers. I'm not saying this is something I wouldn't/shouldn't do as a good practice, I just don't believe this code applies to me when I'm making tire decisions.

Top,

This derating appears in the tire standards as well - meaning it is part of the Physics of Tires, and not just a regulator admonition.

Lance M · 02-08-2016, 06:43 AM

I have no issue with following the tire standards from the tire manufacturers. Please post that information from the tire standards book. The CFR that is often copied and pasted here is a regulation that pertains to tire selection and sizing for vehicle manufacturers.

CapriRacer · 02-09-2016, 06:05 AM

Quote:

Originally Posted by Top

I have no issue with following the tire standards from the tire manufacturers. Please post that information from the tire standards book. The CFR that is often copied and pasted here is a regulation that pertains to tire selection and sizing for vehicle manufacturers.

Unfortunately, I would have to scan a page from the Tire and Rim Association Yearbook, and my printer/scanner isn't seem to want to communicate with my computer.

Sorry.

**Rocinante** · 02-09-2016, 09:31 AM

Why not just let all those who care on this thread buy their own copy?

http://us-tra.org/publications.html

Tireman9 · 02-09-2016, 12:11 PM

Quote:

Originally Posted by SteveSueMac

Is that a single or double axle? If single - the Michelin you're talking about has to be de-rated 10% for use on a trailer so it basically carries 1985# per tire. If a single axle, you have 3970# of load carrying capacity though most would suggest you want to leave about 10% "headroom" meaning your trailer (if single axle) shouldn't weigh more than about 3600# loaded for camping. If a double axle, you'd have 7840# of carrying capacity or with some headroom, 7200# loaded for camping.

Given that and the weight of your trailer, you should be able to decide whether those Michelins will work for you or not. As an FYI - my double axle 27FB weighs in at about 6000# on the scales and I use the Michelin 15" tires. I'll be starting my 4th year of camping this spring - only trouble was when I scuffed them on a curb and replaced them out of an abundance of caution (with very few miles on them and an assurance they'd be ok...).

Good luck!

Single or double axle is not the determining factor. It is the type vehicle i.e. not being a standard passenger car.

Station Wagons, SUV, P/U, Trailers all require "P" type tires to be de-rated i.e. Load/1.10 which is considered -10% by many.

Tireman9 · 02-09-2016, 12:19 PM

Quote:

Originally Posted by Bill M.

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?

You can find the answer if you Google

"Interply Shear RV tire)

or

Pro 50 will decrease likelyhood of tread separation and improve fuel economy
Con 50 may increase likelyhood of impact damage but this is not a condition I see very often of tires that are 70, 75, 80 or 85 series aspect ratio