Tire pressure

[slowmover]

Originally Posted by Tireman9

Goodyear chose to publish the same Load & Inflation numbers for both the marathon and the Endurance.

While there are construction features that can be included in tires to make them more tolerant of abuse (overload, underinflation and cornering forces) IMO I do not know what features could be applied to an ST tire to achieve the higher load capacity and the very high speed rating.

If Gy engineers have some magic to allow tires with "ST" on the sidewall to support +10% to +20% more load than an identical size LT tire, why don't they put the magic rubber in their top line LT and Passenger tires to increase their load capacity?

Ha! Great!!

(Recommended your RV tire safety blog to a couple in a Moho I met today, Tireman 9, at Cummins Southern Plains in Amarillo. And, related to latest post there, it was a "thing" in 1980s - 90s to have tire covers for AS-type trailers made from awning material as a sheet with bound edges. Held on with snaps. Plenty of space from tire to sheet to act as insulator).

.

[Mollysdad]

Originally Posted by slowmover

For best tires Need individual tire loads:

Need to weigh trailer with and without WD applied (Three Pass Method) to set up hitch.

Second step with trailer is (WD applied) to do an axle split (ask Cat Scale operator for assistance).

Final step would be split with but port or starboard tires only on scale.

Okay, that makes sense. "But". I did that at a MH rally once where a company put down four thin scales (like 1" x 12" x12"). You paid $25 and they had you drive up on the scales, then mailed you the results.
That's how I concluded that for my RV Michelins (23") I needed 95 PSI, and I did after that.

So where's the Good Year chart for Marathons or Endurance tires doing the same?

If I followed GY's chart, I'd be running 30 PSI, not 65 PSI.

If GY recommends max tire pressure, then why do people visit the Cat scale? (other than to set up the hitch, and hitch makers don't recommend that.)

[Adventure.AS]

Originally Posted by Mollysdad

...
If GY recommends max tire pressure, then why do people visit the Cat scale? (other than to set up the hitch, and hitch makers don't recommend that.)

Where does GY recommend max tire pressure? On the sidewall they recommend not going over the max tire pressure (which indirectly states the max weight for the tire.) There is no reason to run max tire pressure unless the loaded weight dictates it. Max tire pressure on a trailer of your weight will be very hard on your TT with consequences such as popped rivets.

[slowmover]

Originally Posted by Mollysdad

Okay, that makes sense. "But". I did that at a MH rally once where a company put down four thin scales (like 1" x 12" x12"). You paid $25 and they had you drive up on the scales, then mailed you the results.
That's how I concluded that for my RV Michelins (23") I needed 95 PSI, and I did after that.

So where's the Good Year chart for Marathons or Endurance tires doing the same?

If I followed GY's chart, I'd be running 30 PSI, not 65 PSI.

If GY recommends max tire pressure, then why do people visit the Cat scale? (other than to set up the hitch, and hitch makers don't recommend that.)

The problem (please read Rogers applicable blog posts) is that with a trailer, tires are subject to forces NOT found on a Moho or TV.

For a vehicle that steers itself, the rear tires follow pretty closely the track of the Steer Axle tires.

A trailer is almost dragged sideways in every instance of turning. The greater the angle, the worse for the trailer tires. The trailer does not track the TV at all like the rear TV tires follow the Steer.

It's by no means impossible to tear the tires off of a trailer. I've done it (from a spread-axle 48' flatbed with a 35,000-lb steel coil aboard; wunnerful Chicago), and it's crippling. The wheel may also be ruined, and the axle bearings are now a big question mark.

Thus, the cheaper the tire (rating and/or manufacturer) the greater the need for full inflation. The trailer tire needs to pivot with very low sidewall stress.

Yes, there are those with premium tires not respecting this rule. I'd say that tire brand and rating need be "best".

Also, the lighter the trailer, the better the outcome of lower pressure may be. Same for avoiding high heat climates and high speeds.

Is the tire (non ST) a good Load rating match? (85% load maximum)?

One can say, well, "experiment" . . . I know I'm not willing. Not in this instance. The cost of trailer repairs is astronomical, and the high risk of being on the side of the highway to get the spare installed make it a double NO in my book.

Popped rivets? First, get a suitable TV such as car or SUV. Second, get a tapered bar hitch (Dual Cam). Set the hitch lash up accurately (and TV tire pressure).

Another way of "seeing" it is this: the trailer is always hungry to get around the towing vehicle. Do we want to increase its tendency to resist steering input to stay in alignment? Not only does it move side to side (unless one has a VLP hitch), now we are introducing a wobble at the beginning and end of every re-alignment of the combined vehicle.

I dial in steering degree to lane change AND now I have to wait longer for the trailer to respond. Duration of that input is thereby lengthened, and the same for ending that input. I may even have to introduce counter steering force to stop the trailers movement altogether.

It's much more apparent on a big truck when tire pressure is too low (and not the only cause; dead shock absorbers mean the load is affecting steering), but let's remember that as good as these trailers are, they still are tall, long and can be top heavy.

Plus the choice of live Axle trucks as TV (with deadened crude steering) mask this information to the driver. So much so that by the time it's felt in a one ton, the trailer is going over with the truck. The small stuff isn't felt.

Low tire pressure gives poor steering response and roadholding. The tire really heats up fast.

I've joked about the cliche one ton yanking a 25' along on one axle. That makes it even worse yet again.

Etc

So think of full pressure as something one needn't worry about when it's used. For a given rig on ST tires especially.

.

[DaveP]

We always run our "E" rated tire at the recommended pressure - 80 PSI.

[Adventure.AS]

Originally Posted by DaveP

We always run our "E" rated tire at the recommended pressure - 80 PSI.

Who’s recommendation? Airstream doesn’t recommend 80psi. The OP states his trailer weighs 7,000 lbs. According to the AS manual the tires should be inflated to carry this load (or 4 times the weight of the heaviest loaded tire.)

In my 2017 International manual it is recommended that: “Air pressure should be checked based on the load on each individual tire. Cold Inflation Pressure should be adjusted to handle the maximum tire load, and all tires on the axle should carry the same inflation pressure.”

[Turbine]

Some thoughts from the cheap seats:

First the known stuff, compliments of a stint in the research and product development lab department of an industrial rubber products manufacturer early in my engineering career: heat is what kills composite rubber structures, especially at laminate interfaces. Heat also degrades durability properties in rubber, whether natural or synthetic. In tires, UNDER-inflation and its resulting deformation, along with velocity is a significant source of heat and has the potential to destroy the structure in relatively short order. Beyond the range of operating pressure designed into the structure, the most serious influence of OVER-inflation is a reduction in safety factor, which is a function of the constituent material properties, not the environment it is operating in. So if safety is the #1 criteria (as it should be), a minimum required pressure should be the beginning point of the discussion.

As noted in previous posts to this thread, the tire mfrs have published their tables that quantify what combination of minimum pressure and load correlate to a tolerated amount of deformation-induced heat that does not compromise the minimum specified safety factor for the product/tire model and size under discussion. So the table can tell us what minimum pressure is necessary to be safe at a given load, or what maximum (up to) load can safely be carried at any given pressure.

This thread has a fabulous discussion on ascertaining how much load your TT tires are experiencing during their service life. Keep in mind it is always OK to bump up the calculated tire load, knowing there is more danger in exposure to under-inflation than over-inflation.

So what are the ramifications of a tire pressure above the minimum required for safety, but not beyond the specified maximum? Again, I think the various posts are really great at addressing the topic. Higher pressures reduce rolling resistance, which means less effort to pull that TT down the road, which equates to lower costs of TV (better mileage AND less wear and tear on the drive train--at up to $15K to rebuild a modern automatic transmission, it is no small expense to be avoided especially if you spend time in the mountains!). Too, depending on tire design and rubber composition, a tire inflated too much will have a smaller footprint resulting in accelerated wear at the center of the tire that requires replacement sooner than if the tire tread had worn evenly. Also, that smaller footprint can significantly degrade directional stability (that is not a happy thought in rain, snow, or panic stop conditions). And of course a tire is usually 'harder' at loaded higher pressure and can transmit larger amounts of road vibration(s) to the TT. Having said all that, it seems everyone has had their own personal experiences and drawn their own conclusions. I think all the comments here in the thread are valid, when considering the circumstances under which they occurred.

So let me offer my experience in this matter.

I too faced this dilemma when first acquiring our AS. It is an older model, so the data plate was talking about bias ply tires. The situation was somewhat aggravated by having off brand (Maxxis) ST tires rather than the typical GY or Marathon. So it took a bit of digging to get an official loading chart from the mfr. This was important; there are HUGE variations for the same designation of tire amongst the different brands! It was easy enough to run our TV and AS across some DOT scales and get the load readings. Beyond measuring the tire load, I also now know how close (or far) I am from the rated capacity of the tire at its highest allowable pressure. Always good to know in a pinch/emergency.

In my particular case, according to the tire mfr chart and the scale weights I should inflate to not less than 40 psi. I filled them to 45 psi, just because I could. Doing visual inspections regularly, in less than 4K miles I began to notice more wear on the edges than the middle of the tread indicative of under-inflation. I pumped up and maintained 55 psi with no appreciable difference in how it "felt" towing. After about 10K at 55 psi the tread pattern had evened out, indicating a bit of over-inflation in terms of tread wear. So I'm now settled in to 50-52 psi. I have uniform tire wear (i.e. most efficient tire consumption) and maximum available longitudinal stability, at the expense of probably giving up some mpg gains available at a higher pressure. If I quit driving in the mountains and diesel went back to $4+/gallon I might be tempted to re-evaluate. If I change brand when it is time to put new tires on the TT I will replicate the process (except for establishing tire load on the scales - that hasn't changed) and pay attention to any explicit written instructions from the tire mfr.

Contrary to what others have reported about other brands encouraging inflation to the maximum allowed, in my instance there was no such statement from the mfr of my tires. Just demonstrates how different each brand is designed to perform even though visually they appear identical.

Finally, a suggestion: get into the habit of feeling the tires (and axle hubs) for temperature every time you stop for the day, or fuel, or a construction zone. After a short time you will become familiar with "normal" and be able to instantly know by touch when something is not right. This technique allows you to plan the time and place the machine becomes unserviceable, instead of the TT becoming disabled when it wants to (most often under very inconvenient and expensive conditions).

[xrvr]

Originally Posted by slowmover

The problem (please read Rogers applicable blog posts) is that with a trailer, tires are subject to forces NOT found on a Moho or TV.

For a vehicle that steers itself, the rear tires follow pretty closely the track of the Steer Axle tires.

A trailer is almost dragged sideways in every instance of turning. The greater the angle, the worse for the trailer tires. The trailer does not track the TV at all like the rear TV tires follow the Steer.

It's by no means impossible to tear the tires off of a trailer. I've done it (from a spread-axle 48' flatbed with a 35,000-lb steel coil aboard; wunnerful Chicago), and it's crippling. The wheel may also be ruined, and the axle bearings are now a big question mark.

Thus, the cheaper the tire (rating and/or manufacturer) the greater the need for full inflation. The trailer tire needs to pivot with very low sidewall stress.

Yes, there are those with premium tires not respecting this rule. I'd say that tire brand and rating need be "best".

Also, the lighter the trailer, the better the outcome of lower pressure may be. Same for avoiding high heat climates and high speeds.

Is the tire (non ST) a good Load rating match? (85% load maximum)?

One can say, well, "experiment" . . . I know I'm not willing. Not in this instance. The cost of trailer repairs is astronomical, and the high risk of being on the side of the highway to get the spare installed make it a double NO in my book.

Popped rivets? First, get a suitable TV such as car or SUV. Second, get a tapered bar hitch (Dual Cam). Set the hitch lash up accurately (and TV tire pressure).

Another way of "seeing" it is this: the trailer is always hungry to get around the towing vehicle. Do we want to increase its tendency to resist steering input to stay in alignment? Not only does it move side to side (unless one has a VLP hitch), now we are introducing a wobble at the beginning and end of every re-alignment of the combined vehicle.

I dial in steering degree to lane change AND now I have to wait longer for the trailer to respond. Duration of that input is thereby lengthened, and the same for ending that input. I may even have to introduce counter steering force to stop the trailers movement altogether.

It's much more apparent on a big truck when tire pressure is too low (and not the only cause; dead shock absorbers mean the load is affecting steering), but let's remember that as good as these trailers are, they still are tall, long and can be top heavy.

Plus the choice of live Axle trucks as TV (with deadened crude steering) mask this information to the driver. So much so that by the time it's felt in a one ton, the trailer is going over with the truck. The small stuff isn't felt.

Low tire pressure gives poor steering response and roadholding. The tire really heats up fast.

I've joked about the cliche one ton yanking a 25' along on one axle. That makes it even worse yet again.

Etc

So think of full pressure as something one needn't worry about when it's used. For a given rig on ST tires especially.

.

Your comments are excellent! Much better than when you insist upon attacking another poster. Keep your info non personal and you'll get a much better auduence. I agree with you99% if the tme. Keep up the good work.

[ROBERT CROSS]

I use n2, it's slightly less dense than air so I can run higher pressures with less chance of failure. not





Bob

[CapriRacer]

A couple of clean up items:

* - Those tire load tables: Those are the same regardless of the tire manufacturer - because they originate from the applicable tire standardizing organization (in the case of ST's it's the US based Tire and Rim Association) and the tire manufacturers republish them if they so desire.

* - Those tire load tables are MINIMUMS! They tell you the MINIMUM inflation pressure to use to carry a given load. (or if you look at it the other way, they tell you the maximum load a given pressure is supposed to carry.)

* - The biggest problem in the past for tires on travel trailers is that the trailers were designed with minimal tires. The tires had very little reserve capacity (or in some cases negative). One of the lessons from the Ford / Firestone situation a few years back was that tires need to have some reserve (unused) capacity. That's just good engineering!

Further, some ST tires had (have?) a 65 mph speed limitation and that was not communicated to the operator of the trailer. The combination of load and speed resulted in many tire failures.

* - Tire wear is relatively insensitive to inflation pressure. Other factors are much more important (like alignment!) While you will find many warnings that improper inflation pressure will cause uneven wear, this is more about getting people interested in keep enough pressure in the tire to carry the load (to prevent failures).

So don't use the tire load tables AS IS. Add more pressure than the minimum. - and don't forget to account for side to side and front to rear weight variation.

In theory, that was what the vehicle tire placard was supposed to do, but since we know that the trailer manufacturers haven't always done a good job of tire size selection, we have to be diligent ourselves.

[Tireman9]

Originally Posted by slowmover

Ha! Great!!

(Recommended your RV tire safety blog to a couple in a Moho I met today, Tireman 9, at Cummins Southern Plains in Amarillo. And, related to latest post there, it was a "thing" in 1980s - 90s to have tire covers for AS-type trailers made from awning material as a sheet with bound edges. Held on with snaps. Plenty of space from tire to sheet to act as insulator).

.

Thanks, Glad you found the info in my blog useful. Have you read the posts on tire covers & shades? Some brand new info posted just last week.

[Tireman9]

Originally Posted by rmkrum

And pressure in excess of that needed to carry the load will lead to excess wear in the centre of the tread...

That idea applied to bias tires. radials do not respond the same and tread wear has a wide range before you can get excess center wear especially in trailer application.

[Tireman9]

Originally Posted by Mollysdad

Okay, that makes sense. "But". I did that at a MH rally once where a company put down four thin scales (like 1" x 12" x12"). You paid $25 and they had you drive up on the scales, then mailed you the results.
That's how I concluded that for my RV Michelins (23") I needed 95 PSI, and I did after that.

So where's the Good Year chart for Marathons or Endurance tires doing the same?

If I followed GY's chart, I'd be running 30 PSI, not 65 PSI.

If GY recommends max tire pressure, then why do people visit the Cat scale? (other than to set up the hitch, and hitch makers don't recommend that.)

The published load / inflation charts for ST tires from Goodyear have the same numbers as for MAXXIS and other ST type tires.
Just pay attention to the size and Load Range.
I have published the GY Endurance info on my blog if you can't find elseware.

[slowmover]

Originally Posted by Tireman9

Thanks, Glad you found the info in my blog useful. Have you read the posts on tire covers & shades? Some brand new info posted just last week.

It's why I posted about the use of awning material.

[Tireman9]

Originally Posted by Adventure.AS

Where does GY recommend max tire pressure? On the sidewall they recommend not going over the max tire pressure (which indirectly states the max weight for the tire.) There is no reason to run max tire pressure unless the loaded weight dictates it. Max tire pressure on a trailer of your weight will be very hard on your TT with consequences such as popped rivets.

Suggest you Google " Interply Shear tires" and learn the facts on why inflating tires in trailer application to the tire sidewall max is a good policy.

[slowmover]

Originally Posted by avionstream

Your comments are excellent! Much better than when you insist upon attacking another poster. Keep your info non personal and you'll get a much better auduence. I agree with you99% if the tme. Keep up the good work.

Don't nominate me for sainthood just yet. It's the post you quoted -- but on another subject where ignorance likes to chime in -- that's otherwise the same sort: Find authority and work from experience. Numbers.

Peddling claims contrary to what can be measured ("my magic one ton"; my little pony) are what get the rocks airborne.

It's in making the case for the assertions.

.

[Tireman9]

Originally Posted by CapriRacer

A couple of clean up items:

* - Those tire load tables: Those are the same regardless of the tire manufacturer - because they originate from the applicable tire standardizing organization (in the case of ST's it's the US based Tire and Rim Association) and the tire manufacturers republish them if they so desire.

* - Those tire load tables are MINIMUMS! They tell you the MINIMUM inflation pressure to use to carry a given load. (or if you look at it the other way, they tell you the maximum load a given pressure is supposed to carry.)

* - The biggest problem in the past for tires on travel trailers is that the trailers were designed with minimal tires. The tires had very little reserve capacity (or in some cases negative). One of the lessons from the Ford / Firestone situation a few years back was that tires need to have some reserve (unused) capacity. That's just good engineering!

Further, some ST tires had (have?) a 65 mph speed limitation and that was not communicated to the operator of the trailer. The combination of load and speed resulted in many tire failures.

* - Tire wear is relatively insensitive to inflation pressure. Other factors are much more important (like alignment!) While you will find many warnings that improper inflation pressure will cause uneven wear, this is more about getting people interested in keep enough pressure in the tire to carry the load (to prevent failures).

So don't use the tire load tables AS IS. Add more pressure than the minimum. - and don't forget to account for side to side and front to rear weight variation.

In theory, that was what the vehicle tire placard was supposed to do, but since we know that the trailer manufacturers haven't always done a good job of tire size selection, we have to be diligent ourselves.

Well said. But what else would I expect from a tire engineer and fellow racer.

[xrvr]

Marhofer Chevy in Stow Ohio?

[WhereStream]

Originally Posted by Tireman9

Suggest you Google " Interply Shear tires" and learn the facts on why inflating tires in trailer application to the tire sidewall max is a good policy.

I read the Interply Shear explainer (via link up earlier in this thread). Does it apply to single-axle trailers ... is shear an issue for those pulling Bambi's?

[Adventure.AS]

Originally Posted by Tireman9

Suggest you Google " Interply Shear tires" and learn the facts on why inflating tires in trailer application to the tire sidewall max is a good policy.

I read your article and understand what you are saying, but you don't explain why, in your opinion, a higher tire inflation pressure will alleviate the 'interplay shear' forces. The forces are still there. Are you suggesting that is better in the long run for the tire with a stiffer sidewall to be skidding rather than deforming when cornering?