Observations after swapping out the China bombs

[BigH]

Originally Posted by Tireman9

I would be very interested in the engineering and dynamic stress analysis you used to decide that the physics of tire scrub doesn't apply to your RV.

Are you serious?

If you would have come back with some reasonable (lol) response about the manufacturer's chart being full of some kind of BS rather than the snarky jab I quoted about what analysis I preformed and had some good info about how my switching from a load D tire to an E while using a tire pressure from the manufacturer's chart that puts their tire well above the weight limit of the original tire (and rim) I replaced, while also extending them well above the weight of my trailer...if anything in your post would have explained how my changes made my travels less safe you may have been able to get my attention.

For a guy who portrays himself as an expert and comes back with the response I quoted, you clearly do not intend to be helpful...no mater, some times you sound knowledgeable, other times not so much...this time the later prevails strongly and if you do have more to say on this subject I'm not sure I could apply much, if any, credence.

[Tireman9]

Interply Shear is the recognized force that is in all radial tires that is acting on the belt package trying to tear the belts apart.
These forces are not an "On-Off" switch but just get larger as the tire load and deflection increase.

The unique nature of multi-axle trailer suspension results in significantly higher shear forces (+24%) even with identical inflation and vertical load if the tires were on a motorized vehicle like a pick-up.

With 4 or 6 tires on a trailer, it is impossible for them all to rotate around a centerline that goes through the center of a turn. Most of the tires are simply dragged around the turn with the significant increase in the shear forces primarily due to the increased Slip Angle. This is seen in the video from Keystone RV I posted in my blog on Interply Shear.

There is nothing that a user can do to eliminate this overload of shear force BUT by increasing the inflation the slip angle will be lowered. This would lower but not eliminate the extra shear forces the tire has to tolerate. Also lowering the vertical load would also lower but not eliminate the interply shear.

Lower Interply Shear would result in more miles being driver before a belt separation might occur.

The load inflation tables are not BS but are based on straight-ahead travel and simple vertical loading. The numbers represent the maximum load for a given inflation level or the minimum inflation level for a given load for straight ahead operation. There is nothing wrong with running lower load or higher inflation levels than what is shown in the table.

The reason multi-axle trailers see shorter tire life than seen in motor vehicles is simply that the Interply Shear forces they are being subjected to are higher.

Going up in Load Range simply allows the user to run higher inflations which can result in a decrease in the shear forces. Going from 65 psi to 70 is good but not as good as going from 65 to 80psi in the same tire with the same loads.

I apologize for sounding snarky. I misunderstood your comment about nothing more needs to be addressed as implying that my suggestion to consider the Interply Shear forces was not called for or not based on engineering facts.

[Tireman9]

Originally Posted by marc.williams

After inspecting the inside sidewall of the never used TSC China bomb spare I bought in 2015; I found an extensive dry rot patch hidden from view that I missed when installing it in haste when the Vail OEM blew 6 hrs from home. The tire’s date code indicated it was 3 yrs old off the shelf from TSC in 2015. I had it inflated to 50 psi and covered until I needed it. I needed to replace it along with the 2 OEM Vail still on the other side. I have had it with China tires and my neighbor who works for Goodyear got me 35% off some Endurance tires so I replaced all four. So far so good.

Any chance you have a picture of the inside of the suspect tire? I have seen examples where a tire was classified as "defective" due to the appearance of "cracks" on the innerliner. However, the compound used in the innerliner in almost all tires is very resistant to ozone cracking. What was discovered was that the bladder used in the curing of the tire was approaching the end of its life and it had surface cracks. These cracks had transferred an impression onto the innerliner of the tire which initially looked identical to ozone cracking.

[Slow Moon]

Originally Posted by Tireman9

Interply Shear is the recognized force that is in all radial tires that is acting on the belt package trying to tear the belts apart.
These forces are not an "On-Off" switch but just get larger as the tire load and deflection increase.

The unique nature of multi-axle trailer suspension results in significantly higher shear forces (+24%) even with identical inflation and vertical load if the tires were on a motorized vehicle like a pick-up.

With 4 or 6 tires on a trailer, it is impossible for them all to rotate around a centerline that goes through the center of a turn. Most of the tires are simply dragged around the turn with the significant increase in the shear forces primarily due to the increased Slip Angle. This is seen in the video from Keystone RV I posted in my blog on Interply Shear.

There is nothing that a user can do to eliminate this overload of shear force BUT by increasing the inflation the slip angle will be lowered. This would lower but not eliminate the extra shear forces the tire has to tolerate. Also lowering the vertical load would also lower but not eliminate the interply shear.

Lower Interply Shear would result in more miles being driver before a belt separation might occur.

The load inflation tables are not BS but are based on straight-ahead travel and simple vertical loading. The numbers represent the maximum load for a given inflation level or the minimum inflation level for a given load for straight ahead operation. There is nothing wrong with running lower load or higher inflation levels than what is shown in the table.

The reason multi-axle trailers see shorter tire life than seen in motor vehicles is simply that the Interply Shear forces they are being subjected to are higher.

Going up in Load Range simply allows the user to run higher inflations which can result in a decrease in the shear forces. Going from 65 psi to 70 is good but not as good as going from 65 to 80psi in the same tire with the same loads.

I apologize for sounding snarky. I misunderstood your comment about nothing more needs to be addressed as implying that my suggestion to consider the Interply Shear forces was not called for or not based on engineering facts.

Many thanks to you, Tireman9.

Although what you have said is based on impeccable logic and extremely important, it is often misunderstood based on mistaken belief that Load Inflation Tables imply a maximum or optimum PSI for a given load. To be sure I understand the essence, in the 5 numbered points below, I have attempted to sum up what you said to help myself and others get to the right conclusion. Please correct any mistakes

1—Interply Shear is the greatest destructive force on multi-axle radial tires. No matter the inflation PSI, Interply Shear ALWAYS hurts our tires and ALWAYS hurts more at lower PSI because lower PSI ALWAYS increases deflection and Shear Force.

2—Multi-axle trailer tires are subject to far higher Shear Force than Motor Vehicles at ANY given inflation and vertical load because of the way tires are dragged around.

3—Reducing Shear Force increases tire life/reliability, and the ONLY thing we can do to reduce Shear Force is increase inflation PSI to reduce deflection and slip angle. This HELPS, but Shear Force always continues trying to tear our belts apart, and destructive forces always increase as PSI is reduced.

4—Inflating to Max Sidewall PSI does no harm—Load inflation tables neither discourage Max Sidewall Inflation nor imply harm in doing so. It is wrong to think that they do.

5—Going up in Load Range allows higher PSI and decreases in the Shear Forces. Going from 65 to 70 PSI is good but going to 80 PSI is BETTER because it decreases deflection and Shear Force.

[Tireman9]

Originally Posted by Slow Moon

Many thanks to you, Tireman9.

Although what you have said is based on impeccable logic and extremely important, it is often misunderstood based on mistaken belief that Load Inflation Tables imply a maximum or optimum PSI for a given load. To be sure I understand the essence, in the 5 numbered points below, I have attempted to sum up what you said to help myself and others get to the right conclusion. Please correct any mistakes

1—Interply Shear is the greatest destructive force on multi-axle radial tires. No matter the inflation PSI, Interply Shear ALWAYS hurts our tires and ALMOST ALWAYS hurts more at lower PSI because lower PSI ALWAYS increases deflection and Shear Force, EXCEPT when extreme low inflation can lead to sidewall flex failure in just a few miles.

2—Multi-axle trailer tires are subject to far higher Shear Force than Motor Vehicles at ANY given inflation and vertical load because of the way tires are dragged around.

3—Reducing Shear Force increases tire life/reliability, and the ONLY thing we can do to reduce Shear Force is increase inflation PSI to reduce deflection and slip angle. This HELPS, but Shear Force always continues trying to tear our belts apart, and destructive forces always increase as PSI is reduced.

4—Inflating to Max Sidewall PSI does no harm—Load inflation tables neither discourage Max Sidewall Inflation nor imply harm in doing so. It is wrong to think that they do.

5—Going up in Load Range allows higher PSI and decreases in the Shear Forces. Going from 65 to 70 PSI is good but going to 80 PSI is BETTER because it decreases deflection and Shear Force.

Good summary. Minor addition in red

[Oaklevel]

I do wish to thank Tireman9 for all the great information that you provide. I do need to check out your blog.

I do have a question that I have not found an answer to. When did ST tires come on the market ? My early campers 1980s came with "P" tires.

I suspect ST and other tires made overseas are for numerous reasons. One being cost / keeping prices down. Second being much of our manufacturing capacities are aging. The two tire plants in our area are aging with numerous accidents. I hate to say this but I have learned a lot about tire building through investigating serious accidents at both plants.

[Tireman9]

Originally Posted by Oaklevel

I do wish to thank Tireman9 for all the great information that you provide. I do need to check out your blog.

I do have a question that I have not found an answer to. When did ST tires come on the market ? My early campers 1980s came with "P" tires.

I suspect ST and other tires made overseas are for numerous reasons. One being cost / keeping prices down. Second being much of our manufacturing capacities are aging. The two tire plants in our area are aging with numerous accidents. I hate to say this but I have learned a lot about tire building through investigating serious accidents at both plants.

The oldest ref in Tire & Rim standards book in my library is 1975 and it has St type tires. These would of course probably have been bias tire construction.


RE overseas production. Radial tire construction is significantly more expensive and complex than bias. Quality and uniformity requirements are tougher to meet with bias construction so as the market moved from bias to radial St tires were last to be "upgraded". In some cases, today's ST tires still have to meet 1975 regulatory requirements while P and LT had their durability standards significantly improved in 2002 timeframe.


Yes, the cost is a major consideration. IMO the main reason for ST tire requirements not being updated in 2002 was the RV industry had a lobby that didn't want to see tire prices go up.

[Oaklevel]

Thanks for the info.!

I was curious as my 1980s Fleetwood Terry campers came with "P" rated tires . I personally did not see the STs until the 1990's but that does not mean much even though I own several trailers.

[Shadowchaser]

This is what it took to return my peace of mind.

Max pressure 110# but I run them at 85# for a softer ride.

[Larry-NC]

Originally Posted by Slow Moon

Many thanks to you, Tireman9.
1—Interply Shear is the greatest destructive force on multi-axle radial tires. No matter the inflation PSI, Interply Shear ALWAYS hurts our tires and ALWAYS hurts more at lower PSI because lower PSI ALWAYS increases deflection and Shear Force.

2—Multi-axle trailer tires are subject to far higher Shear Force than Motor Vehicles at ANY given inflation and vertical load because of the way tires are dragged around.

3—Reducing Shear Force increases tire life/reliability, and the ONLY thing we can do to reduce Shear Force is increase inflation PSI to reduce deflection and slip angle. This HELPS, but Shear Force always continues trying to tear our belts apart, and destructive forces always increase as PSI is reduced.

4—Inflating to Max Sidewall PSI does no harm—Load inflation tables neither discourage Max Sidewall Inflation nor imply harm in doing so. It is wrong to think that they do.

5—Going up in Load Range allows higher PSI and decreases in the Shear Forces. Going from 65 to 70 PSI is good but going to 80 PSI is BETTER because it decreases deflection and Shear Force.

And from a subsequent post:
The oldest ref in Tire & Rim standards book in my library is 1975 and it has St type tires. These would of course probably have been bias tire construction.

I'm old enough (73) to remember bias-ply tires and when radial tires were first offered. I had cars that were built for bias-ply tires and when both were available, I bought bias-ply tires until I could no longer get them. I had two reasons for this:

1. I figured (possibly incorrectly) that the vehicle was designed for bias-ply tires and wouldn't handle safely with radial tires.
2. The early radial tires had a terrible reputation for delamination, even when new. The tire companies countered by changing the tire rotation recommendation to require a 4-tire rotation (excluding the spare) keeping the tires on the same side. That is, never changing the rotation direction of the tire. Their theory was that changing rotation direction encouraged delamination failures. I was a little wary of this.

It wasn't until the late 1970s when I finally had to buy radial tires. By then the delamination problems were greatly reduced. I had a 1969 Dodge Custom Sportsman full-size stretched van. This was the snub-nose, cab-over version with a steel I-beam axle with kingpins, mounted on leaf springs. The engine was a heavy, cast-iron 318 V-8, mounted directly over the axle. The steering column went almost straight down (steering wheel almost flat, like a bus), and it was a BEAR to steer. I really had to haul the wheel around while rolling (never standing still), and my (late) wife could barely drive it.

But when I was finally forced to switch to radial tires, it was like driving a different car. I couldn't believe how easily it steered. I wonder why it makes such a difference.

Another aspect of the difference seems to be tire pressure. You (Tireman9) recommend pressures at/near the maximum tire rating for radial tires. I had worn out bias ply tires that had been run overinflated and only wore in the center of the tread, and tires that had been run underinflated and wore at the edges of the tread. Do radial tires somehow keep the same footprint (or close to it) as long as they aren't grossly underinflated? Or is it possible that running max inflation reduces flexing enough to discourage separation failure and uneven tread wear is just an unfortunate consequence?

Which leads me to my final questions:

1. Can you still get bias-ply trailer tires?
2. Would they be better on multi-axle rigs?
3. Would they be less vulnerable to separation?
4. Would it be important to manage inflation pressure to maximize tread wear?

Larry

[Tireman9]

Originally Posted by Larry-NC

I'm old enough (73) to remember bias-ply tires and when radial tires were first offered. I had cars that were built for bias-ply tires and when both were available, I bought bias-ply tires until I could no longer get them. I had two reasons for this:

1. I figured (possibly incorrectly) that the vehicle was designed for bias-ply tires and wouldn't handle safely with radial tires.
2. The early radial tires had a terrible reputation for delamination, even when new. The tire companies countered by changing the tire rotation recommendation to require a 4-tire rotation (excluding the spare) keeping the tires on the same side. That is, never changing the rotation direction of the tire. Their theory was that changing rotation direction encouraged delamination failures. I was a little wary of this.

It wasn't until the late 1970s when I finally had to buy radial tires. By then the delamination problems were greatly reduced. I had a 1969 Dodge Custom Sportsman full-size stretched van. This was the snub-nose, cab-over version with a steel I-beam axle with kingpins, mounted on leaf springs. The engine was a heavy, cast-iron 318 V-8, mounted directly over the axle. The steering column went almost straight down (steering wheel almost flat, like a bus), and it was a BEAR to steer. I really had to haul the wheel around while rolling (never standing still), and my (late) wife could barely drive it.

But when I was finally forced to switch to radial tires, it was like driving a different car. I couldn't believe how easily it steered. I wonder why it makes such a difference.

Another aspect of the difference seems to be tire pressure. You (Tireman9) recommend pressures at/near the maximum tire rating for radial tires. I had worn out bias ply tires that had been run overinflated and only wore in the center of the tread, and tires that had been run underinflated and wore at the edges of the tread. Do radial tires somehow keep the same footprint (or close to it) as long as they aren't grossly underinflated? Or is it possible that running max inflation reduces flexing enough to discourage separation failure and uneven tread wear is just an unfortunate consequence?

Which leads me to my final questions:

1. Can you still get bias-ply trailer tires?
2. Would they be better on multi-axle rigs?
3. Would they be less vulnerable to separation?
4. Would it be important to manage inflation pressure to maximize tread wear?

Larry

1. Can you still get bias-ply trailer tires? Yes but the selection list is very short and none in some sizes
2. Would they be better on multi-axle rigs? I would go with radials
3. Would they be less vulnerable to separation? Yes Bias cannot have belt separation (no belts) but they can have a body ply separation
4. Would it be important to manage inflation pressure to maximize tread wear? Yes. Bias tread wear more sensitive to inflation

The other thing to remember is that radial tire materials and construction are significantly advanced from bias technology which might still be stuck in the 70's