Michelin run psi

[DeltaRon]

Thanks everyone. Consensus was 65 - 80, huh. Guess I’ll just stay at 75.

[mikeinca]

Originally Posted by uncle_bob

Hi

All tire pressure numbers are for a cold tire. What happens as they heat up is not what the pressure spec is about. Checking pressure on a hot tire is not going to do much good.

The main logic for running below max pressure is that the tread wear is more even and the braking will be a bit better (more road contact). I'm not sure how many of us will wear out the new Michelin LT tires based on treads. Normal end of life for trailer tires is time ( 5 to 7 years) rather than tread or mileage.

The math:

Tires are rated for 50-60,000 miles. Warranty is for 6 years. 60,000 / 6 = 10K miles per year. That's a lot of trailer miles for most of us ....


Bob

For the most part, I agree completely. I'd only add that while tire pressures should almost always be set and adjusted when cold, there are exceptions. Track tires, for example, are designed to perform best in a specified pressure range and depending on track and ambient temperatures, adjustments should be made even when the tires are hot.

Our trailer tires obviously don't require the same kind of pressure management as track tires do, but ambient conditions can still have an affect on pressure which can in turn affect ride quality and wear as well as the other performance parameters you mentioned. If one is experiencing PSI readings in the mid-90's on the road, like I was, it might be useful to adjust the cold pressure baseline reading next time so that when the tires are hot they are in a more acceptable range. Just a thought....

[thewarden]

I run 62-64 in my 16" LTX tires on a 27 International loaded up. I have run this pressure for several thousand miles now and am quite happy with the ride, handling etc. I initially ran the max 80 psi and that made for a rough ride in the trailer as evidenced by the seat cushions, throw pillows and the sink cover found scattered all over the trailer floor. Now it is rare to find anything moved after several hours of travel.

[uncle_bob]

Originally Posted by mikeinca

For the most part, I agree completely. I'd only add that while tire pressures should almost always be set and adjusted when cold, there are exceptions. Track tires, for example, are designed to perform best in a specified pressure range and depending on track and ambient temperatures, adjustments should be made even when the tires are hot.

Our trailer tires obviously don't require the same kind of pressure management as track tires do, but ambient conditions can still have an affect on pressure which can in turn affect ride quality and wear as well as the other performance parameters you mentioned. If one is experiencing PSI readings in the mid-90's on the road, like I was, it might be useful to adjust the cold pressure baseline reading next time so that when the tires are hot they are in a more acceptable range. Just a thought....

Hi

Given that the tires likely will "do ok" anywhere from 60 to 80 PSI (cold) fiddling the hot pressure down from a "result of starting at 80 PSI cold" number likely will not cause them to self destruct. The sort of issues here are cumulative rather than immediate. You would have to run for a few tens of thousand miles to really know if fiddling a hot temperature did you any good ....

Bob

[HHPJ]

65psi. When warmed up after a few miles, they run at about 70psi according to the Tire pressure monitoring system.

[CapriRacer]

Originally Posted by mikeinca

........ The Michelin LTX M/S tire pressures were set to 78 PSI (cold) before we left, which was close to the Airstream spec of 80 PSI.

On the road with ambient temperature in the mid to high 80's and at about 5000' elevation, I was somewhat surprised to find that pressure spiked at 92-94 PSI across all 4 tires, which concerned me a little. …….

As it should. That's almost a 20% pressure buildup.

Originally Posted by mikeinca

........ I readjusted the cold pressure to 72 PSI and during the return trip I saw hot pressure readings in the mid 80's, which seemed more appropriate. ….

No, No! Wrong direction! That's still almost a 20% pressure buildup.

Rule of thumb. Tires don't like to see more than a 10% pressure buildup. That pressure buildup is coming from the heat generated from within the tire (AKA hysteresis = rolling resistance.) Heat is the tire killer.

If you see more than 15%, then something is terribly wrong and you need to take immediate action. The easiest thing is to slow down. That reduces the RATE at which heat is being generated.

Please note: This rule of thumb does NOT include pressure build up due to ambient temperature change (about 3% for every 10°F). Hopefully that is the problem here!

The fix is a tire with larger load carrying capacity = higher starting pressure, higher load range, larger size. Ultimately that may mean you need to weigh your trailer - fully loaded and each wheel position - or at least account for side to side and front to rear weight variation.

So the next time you take the trailer out, note the outside temperature, then factor that into the equation. Let us know what happens.

Afterthought: You may want to verify the TPMS is giving you accurate readings by using a regular pressure gauge.

[mikeinca]

Originally Posted by CapriRacer

No, No! Wrong direction! That's still almost a 20% pressure buildup.

Rule of thumb. Tires don't like to see more than a 10% pressure buildup. That pressure buildup is coming from the heat generated from within the tire (AKA hysteresis = rolling resistance.) Heat is the tire killer.

If you see more than 15%, then something is terribly wrong and you need to take immediate action. The easiest thing is to slow down. That reduces the RATE at which heat is being generated.

Please note: This rule of thumb does NOT include pressure build up due to ambient temperature change (about 3% for every 10°F). Hopefully that is the problem here!

The fix is a tire with larger load carrying capacity = higher starting pressure, higher load range, larger size. Ultimately that may mean you need to weigh your trailer - fully loaded and each wheel position - or at least account for side to side and front to rear weight variation.

So the next time you take the trailer out, note the outside temperature, then factor that into the equation. Let us know what happens.

Afterthought: You may want to verify the TPMS is giving you accurate readings by using a regular pressure gauge.

Thanks for your feedback. A couple of things, though.

First, let's get the math squared away. With PSI adjusted to 72 (cold) and climbing to 84 hot, that's an increase of 16.6%, not 20%. Second, cold PSI was set at an ambient temp of about 50 degrees with midday temps climbing close to 90 degrees. At about 1 PSI of increase per 10 degrees F, that works out to 4 PSI due to ambient temperature changes alone. The net increase due to road heat buildup is then only 8 PSI, or about 11%; very close to the 10% figure you state as a rule of thumb.

The other variable is the change in altitude. At the beginning of my trip the setting of 78 PSI (cold) was made at sea level and my PSI readings in the low 90's were observed at 5000 feet. This change in elevation alone contributed about 3 PSI to the pressure change. BTW and FWIW, I typically drive at the legal trailer limit here in CA (55mph) and almost never go over 60. Also, the TPMS seems to track closely with my Longacre digital tire gauge.

I didn't intend to get into the weeds with a bunch of numbers. My original point was simply that since factors like ambient temperature and elevation, as well as road speed and load can affect tire pressure, that maybe choosing a single cold tire pressure setting for all conditions might not be the best way to go. That point was driven home for me by getting real time PSI readings for my trailer tires from the TPMS. Anyway, just my $.02. YMMV.

[paiceman]

Originally Posted by mikeinca

Thanks for your feedback. A couple of things, though.

First, let's get the math squared away. With PSI adjusted to 72 (cold) and climbing to 84 hot, that's an increase of 16.6%, not 20%. Second, cold PSI was set at an ambient temp of about 50 degrees with midday temps climbing close to 90 degrees. At about 1 PSI of increase per 10 degrees F, that works out to 4 PSI due to ambient temperature changes alone. The net increase due to road heat buildup is then only 8 PSI, or about 11%; very close to the 10% figure you state as a rule of thumb.

The other variable is the change in altitude. At the beginning of my trip the setting of 78 PSI (cold) was made at sea level and my PSI readings in the low 90's were observed at 5000 feet. This change in elevation alone contributed about 3 PSI to the pressure change. BTW and FWIW, I typically drive at the legal trailer limit here in CA (55mph) and almost never do over 60. Also, the TPMS seems to track closely with my Longacre digital tire gauge.

I didn't intend to get into the weeds with a bunch of numbers. My original point was simply that since factors like ambient temperatures and elevation, as well as road speed and load can affect tire pressure, that maybe choosing a single cold tire pressure setting for all conditions might not be the best way to go. That point was driven home for me by getting real time PSI readings for my trailer tires from the TPMS. Anyway, just my $.02.

Out west the side in the sun on ours runs at about 4 degrees higher than the shade side

[mikeinca]

Originally Posted by paiceman

Out west the side in the sun on ours runs at about 4 degrees higher than the shade side

Roger that. Black tires readily absorb heat from the sun, which I why I always try to have all 4 tires in the shade when setting pressure, even on a cool morning.

[CapriRacer]

Originally Posted by mikeinca

Thanks for your feedback. A couple of things, though.

First, let's get the math squared away. With PSI adjusted to 72 (cold) and climbing to 84 hot, that's an increase of 16.6%, not 20%. Second, cold PSI was set at an ambient temp of about 50 degrees with midday temps climbing close to 90 degrees. At about 1 PSI of increase per 10 degrees F, that works out to 4 PSI due to ambient temperature changes alone. The net increase due to road heat buildup is then only 8 PSI, or about 11%; very close to the 10% figure you state as a rule of thumb.

The other variable is the change in altitude. At the beginning of my trip the setting of 78 PSI (cold) was made at sea level and my PSI readings in the low 90's were observed at 5000 feet. This change in elevation alone contributed about 3 PSI to the pressure change. BTW and FWIW, I typically drive at the legal trailer limit here in CA (55mph) and almost never go over 60. Also, the TPMS seems to track closely with my Longacre digital tire gauge.

I didn't intend to get into the weeds with a bunch of numbers. My original point was simply that since factors like ambient temperature and elevation, as well as road speed and load can affect tire pressure, that maybe choosing a single cold tire pressure setting for all conditions might not be the best way to go. That point was driven home for me by getting real time PSI readings for my trailer tires from the TPMS. Anyway, just my $.02. YMMV.

Thanks for the clarification.

What concerned me was not only how much pressure build up you were getting, but that this was a 2018. I was looking to see if newly made trailers were better tire size-wise. Older trailers had marginally sized tires (sometimes worse!) and that was contributing to the tire failure rate.

Good to know that the numbers are within bounds.

[Ted S.]

I ran at 80 at TV and trailer and it was a rough ride. Drag it all over the country and was shocked at how rough it was. Got a few popped rivets. Lowered to 60 to 70 depending on axle load as determined by CAT scale and it was 1000% better.

Those who claim a smooth ride at 80, how do you know? My rough ride was in the truck, I could only assume it was rough in the trailer as well because nobody ever rode in it to be sure.

My pressure gain has been considerable. Big changes due to temperature and elevation. Once you get some experience with trailer tires you can understand what happened with Tom Brady’s footballs.

[tjdonahoe]

Originally Posted by DeltaRon

Just wondering what most of you run with (psi) on your Michelins. We’re towing 2018 Classic 33 with Silverado 2500 HD Duramax. Been using 75 psi but getting some rough riding to trailer.

13 31’ Classic....7800 on axles...16” michelins.....70 lbs...all’s well

[uncle_bob]

Hi

The outside temperature is one thing that contributes to the tire temperature. The temperature of the pavement is another thing.... black pavement is just like a black tire in full sun ...

Lots of variables.

Bob

[turk123]

OK Uncle Bob

You may laugh at me but I'm gonna ask it anyway.

Does the temperature of the tire affect the elasticity of the rubber? Does the rubber get softer and more pliable as temps go up and even though the pressure is higher, is it relatively "softer" than a cold tire? The higher pressure may counteract this, but is the tire actually softer than a cold tire at the same temperature?

Told you it was gonna be a whopper!

[BigSxyWhtGuy]

I’d like to add the earths rotational velocity in parallel with the moons gravitational pull of the particular season you are in (assuming you’re in the northern hemisphere), don’t forget to account for the direction the geese are migrating. It matters.....

lol [emoji23] it’s just another troll tread.

[turk123]

Originally Posted by BigSxyWhtGuy

I’d like to add the earths rotational velocity in parallel with the moons gravitational pull of the particular season you are in (assuming you’re in the northern hemisphere), don’t forget to account for the direction the geese are migrating. It matters.....

lol [emoji23] it’s just another troll tread.

Well here is the answer, i think?

The full name of Tg is glass-rubber transition temperature which means, as you know, the temperature interval below which a polymer becomes glassy in behavior & above which the polymer becomes flexible or elastic. For example, atactic PMMA plastic has an average Tg =105 oC which indicates that at room or ambient temperatures it will act like glass & it does and that is why it is called Plexiglas & is used for the airplanes' & buses' windows.
As for rubbers, there is a case which needs explanation: As you know, for a given strain, the stress increases linearly with temperature. Alternatively, if we fix the stress (e.g. by suspending a mass from a piece of rubber), then the extension should decrease as we increase the temperature. This is a well known property of rubber which the rubber elasticity theory correctly predicts. This behavior is the opposite of what we observe for normal materials: Typically, heating something up causes it to expand.
So rubber is soft & flexible within a limit above Tg but when temperature is raised, it becomes rigid.
The rubbers used in tires of vehicles are mainly natural rubber or styrene-butadiene copolymer (SBR) with the first is yellowish in color while the second is almost colorless. Additives for these 2 polymers, in manufacture of tires, are a must & one of the major additives is carbon black "colors tires" in > 20% amount.

[BigSxyWhtGuy]

Originally Posted by turk123

Well here is the answer, i think?

The full name of Tg is glass-rubber transition temperature which means, as you know, the temperature interval below which a polymer becomes glassy in behavior & above which the polymer becomes flexible or elastic. For example, atactic PMMA plastic has an average Tg =105 oC which indicates that at room or ambient temperatures it will act like glass & it does and that is why it is called Plexiglas & is used for the airplanes' & buses' windows.
As for rubbers, there is a case which needs explanation: As you know, for a given strain, the stress increases linearly with temperature. Alternatively, if we fix the stress (e.g. by suspending a mass from a piece of rubber), then the extension should decrease as we increase the temperature. This is a well known property of rubber which the rubber elasticity theory correctly predicts. This behavior is the opposite of what we observe for normal materials: Typically, heating something up causes it to expand.
So rubber is soft & flexible within a limit above Tg but when temperature is raised, it becomes rigid.
The rubbers used in tires of vehicles are mainly natural rubber or styrene-butadiene copolymer (SBR) with the first is yellowish in color while the second is almost colorless. Additives for these 2 polymers, in manufacture of tires, are a must & one of the major additives is carbon black "colors tires" in > 20% amount.

So, are the geese migrating north or south?

[uncle_bob]

Hi

If the tire does go "soft" when it gets hot, the next thing you will notice is a loud bang as it explodes on you .....

If you take a saw to a tire, there is a lot more than rubber in there. Most of the "other stuff" (like steel belts) is there to add strength. It also keeps things from going weird over temperature.

Bob

[turk123]

Originally Posted by uncle_bob

Hi

If the tire does go "soft" when it gets hot, the next thing you will notice is a loud bang as it explodes on you .....

If you take a saw to a tire, there is a lot more than rubber in there. Most of the "other stuff" (like steel belts) is there to add strength. It also keeps things from going weird over temperature.

Bob

Well, the interesting thing is as rubber gets warmer it actually gets harder! It seems as if a race car goes out with soft tires, they warm them up and they actually get harder. Not what the race announcer says. Contrary to what I thought.

[truxpin]

This thread caught my eye. I'm always interested in the "theory" of tire pressures & what people think is good/bad/acceptable risk.....
As always, the varying answers and reasoning behind them is always good reading but I got lost later in the thread when the discussion turned to the molecular breakdown of rubber and it's underlying principals.
So, let's get back to tire pressures. I've always been told to pressure your tires up to the tire specs located on the sidewall (assuming we have the correct tire on the rim ) Variance from the manufacturer dictated pressure could easily cause "issues" with the performance of said tire due to their specific design properties. Right? I'm confused.....
I've also always been told that trying to adjust ride quality by adjusting recommended tire pressure is a recipe for disaster. Right? It's just what I've been told.

I've recently had to replace rubber on my triple axle and decided on some nice 12 ply's. Was shocked to see the recommended pressure is 90 PSI !! While this makes me a bit nervous, it IS what the manufacturer states.