Are Our Tires REALLY that sensitive?

[10forty2]

I know I will roust the ire of many a tire aficionado, as well as those who will claim expert knowledge from years of traveling and RV'ing and quasi-engineering or actual engineering status/certification....I assure you I mean nothing personal towards anyone and I don't mean to walk on the waters of your knowledge because I have and will benefit immensely from it..... BUT with that said....

Are our tires really that sensitive? I mean, these things cost $400-$1K each and we talk about and treat them like they are made of glass or fine crystal. I certainly understand the need to ensure safety by checking certain parameters, but honestly? I must admit, after 2 tire failures within 2 months of each other, I'm a bit paranoid, myself. The first was just an old tire that I failed to verify its age when I bought the coach...my fault. The second was a new tire but turned out to be a factory defect....it happens from time to time with anything a human-being manufactures.

But can it really be so critical that the pressure stay within 1-psi of the recommended "weight table?" Do we need to have professional scales in our basement bins so we can weigh each wheel every time before we pull out so we know exactly what pressure the tire should have? And if we do, should we have two identical sets of scales so that we can leave one in the basement bin where the other one stays so we know exactly how much it weighs? Should I calculate how much weight I will gain over the course of my vacation depending on how well I eat so I know how much to compensate the air pressure? Do I have to become a meteorologist so I can predict the temperature of the places I travel so I can ensure that I have the proper pressure for the weight that I measured in that climate?

I admit it... I'm a Class A Newbie, but it just can't be this complicated...can it?

Your discussions please....:?

[Tireman9]

Jim, My point was that when the pressure has dropped 20% from the inflation needed to carry the load you are doing damage to the tire.
Given that when driving the tire pressure will be 5% to 10% higher than your set pressure. You should be able to set the TPM warning at as little as 5% below the set pressure and never get a warning when running unless there is in fact an air leak.

[JimM68]

Tireman9 wrote:

JimM68 wrote:
There is a lot of discussion on this. And that is good, losing a tire in a violent manner is a scary and expensive thing.

I'm a technician, not an engineer. I gave up long ago wondering "WHY?" I want to know "what broke?" "how to fix it?" and hopefully on a very good day, "how to prevent it from happening again.

I've had 2 motorhomes over 7 years, and during that time I've lost 3 tires.

Today, I run a good tpms. I weighed my rig, checked my weight tables for my tires, and set my pressures at 5 lbs above minimum for the weight. I set the alarm on my tpms to 75% of my cold tire pressure. When / if the tpms alarmgoes off, I stop.

The last time I bought tires, I had them install solid metal valvestems, pointed out in all cases. My TST flow thru sensors screw right on the inner duals. The outer duals have 3" solid extensions then the (non flothru) sensors. and the fronts have non flo thru sensor screwed right onto the stems. This eliminated my previous problem of leaking extensions.

And now I just forget about my tires. Every spring coming out of storage, I check and adjust the air pressure, and the rest of the season I ignore them. Unless the TPMS alarm goes off.

Minor but important point. If your "cold" inflation is the MINIMUM needed to carry the known actual load they you might want to bump up the warning point on your TPMS. A tire that has lost 20% of it's required inflation is considered to be "flat" and driving on it will do irreversible internal structural damage. This damage might not make itself known for weeks or possibly many months but you will definately have shortened the tire life.

I am watching the TPMS CONSTANTLY as part of my gauge scan. I see the actual number for each tire at least once every 6 minutes. If the alarm goes off, my DW gets a bit out of shape.
when my TPMS alarms, it is plain and simply time to get off the road now.

[Tireman9]

frankdamp wrote:
One of the big mistakes people make is to look at the max pressure molded into the sidewall and then use that as their inflation guide. Way too high and putting you at a much higher risk of a blow-out.

My approach is to buy good quality tires (we got Toyos), weigh the rig so you can figure out the individual axle weights when you're loaded for travelling, then inflate cold tires to the pressure the manufacturers' chart tells you. TPMS will give you a heart attack if you monitor what the pressure is while going 70 on the freeway in Arizona in the summer. Check it only when the rig has been sitting overnight and don't sweat it too much.

It really takes a lot of abuse to blow a tire. I worked in Boeing's landing gear group for a while, and we investigated an in-flight tire burst on a 727. It blew when the airplane was at about 12,000 ft, climbing out of Baltimore (I think). It punched an 18" diameter hole in the wheel-well pressure bulkhead and only a couple of USPS mailbags jamming in the hole prevented a disaster.

It turned out the airplane had taxied two miles with a dragging brake, then accelerated for take-off at close to maximum weight, needing about 150 mph for lift-off. After the gear was retracted, the heat build-up caused the failure, which was actually an explosion of gases that had been released from the tire compounds. The failure of the tire bead suggested an explosion pressure of about 12,000 psi. That's why airlines use nitrogen.

The "abuse" possible with an RV pales into insignificance. IMO, as long as you're within 15% of the pressure your weight calls for, don't sweat it. Being slightly under-inflated, based on a weigh-bridge check, is a lot better than being at the pressure shown on the tire's sidewall.

BTW, even after 47 years in the US, I still have trouble not spelling it "TYRE"! Fortunately spell checker alerts me.

Sorry but "blowouts" or Run Low Sidewall Flex like This are normally the result of air loss. Tires can tolerate much higher inflation than the number on the sidewall. many times the wheel is the weakest link.

TPM is primarily a LOW Pressure warning device. The temperature is too distracting for the average user IMO.

Interesting item on the airplane tire. I note that there was an actual investigation and not the knee-jerk "It was a retread so that's why it failed". Brake heat can also revert or un-vulcanize rummer so it turns into silly putty and the tire structure can then simply unwrap from the beads. Probably the tire did not actually see 12,000 psi as the wheel might have failed at that pressure. When the structure of the tire is compromised all bets are off on what will happen first. If you look at the posts on my blog on "blowouts" you will see examples of melted polyester which is similar to what can happen in Nylon bias airplane tires with too much heat.

Sorry but I do not agree that being 15% low on pressure us worse than running the pressure molded on the tire sidewall.

Tyre is fine by me 😉

[Tireman9]

Raymon wrote:
To Bikeboy57,

You stated "Moisture is the enemy of the steel belts." How does the steel belts become exposed to moisture when the belts are vulcanized between layers of rubber? In my opinion the steel belts only become exposed to moisture due to tire wear. If the belts become exposed they will rust which is not good. Also, steel belts exposed to brine created from applying salt to the roads during winter, not only rust, but corrode very quickly.

You also stated "Driving the tire and getting it up to temperature dissipates the moisture,..." What moisture are you referring to?

Ray

Rubber is not a 100% barrier to moisture. While the steel belts are covered in rubber and even brass plated to help rubber adhere to the belt material as rubber does not chemically bond to rubber. There is still microscopic locations for moisture to start attacking the steel.

[Tireman9]

JimM68 wrote:
There is a lot of discussion on this. And that is good, losing a tire in a violent manner is a scary and expensive thing.

I'm a technician, not an engineer. I gave up long ago wondering "WHY?" I want to know "what broke?" "how to fix it?" and hopefully on a very good day, "how to prevent it from happening again.

I've had 2 motorhomes over 7 years, and during that time I've lost 3 tires.

Today, I run a good tpms. I weighed my rig, checked my weight tables for my tires, and set my pressures at 5 lbs above minimum for the weight. I set the alarm on my tpms to 75% of my cold tire pressure. When / if the tpms alarmgoes off, I stop.

The last time I bought tires, I had them install solid metal valvestems, pointed out in all cases. My TST flow thru sensors screw right on the inner duals. The outer duals have 3" solid extensions then the (non flothru) sensors. and the fronts have non flo thru sensor screwed right onto the stems. This eliminated my previous problem of leaking extensions.

And now I just forget about my tires. Every spring coming out of storage, I check and adjust the air pressure, and the rest of the season I ignore them. Unless the TPMS alarm goes off.

Minor but important point. If your "cold" inflation is the MINIMUM needed to carry the known actual load they you might want to bump up the warning point on your TPMS. A tire that has lost 20% of it's required inflation is considered to be "flat" and driving on it will do irreversible internal structural damage. This damage might not make itself known for weeks or possibly many months but you will definately have shortened the tire life.

[Tireman9]

Effy wrote:

mike brez wrote:
I weighed my rig once loaded up how it will travel. Inflated tires 5lbs over what inflation chart says for my weights. Check them every time before we leave. Have a tire pressure monitor system of some sort. At home when we park we park on rubber mud flaps.we don't cover our tires but is most likely a good idea.

Never understood the 5-10 PSi over the chart thing I see on here all the time. Why? If the chart says at x weight adjust to Y PSI, why would you go over? 10 miles down the road once they heat up now you are way outside the parameters specifically outlined in the chart. I don't get it. Over inflated tires can be just as bad as under-inflated. Why wouldn't you go by the chart?

Lets stick to discussing the "cold" inflation. If your cold inflation is correct for your actual tire load and you aren't exceeding the speed rating for your tires (normally 75 for Motorhomes with TBR or LT type tires or 65 for ST type tires on trailers) the tire will function within design limits when hot.
The Load / Infl tables provide the MINIMUM recommended cold inflation needed to carry the load. Cars basically come with a 12% to 20% extra margin over the minimum. SUVs usually have a 5 to 10% margin. SUVs with a 1% margin can have problems as this margin goes negative with 4 people inside, but that's a separate issue.

I and others know that a majority of RV have one or more tire in overload condition and that's why we strongly recommend getting your RV on a scale. We also know that unlike cars RVs can have significant side to side imbalance and that's why we suggest getting corner weights so you are not misleading yourself into thinking you have the needed minimum inflation when in reality one or more of your tires is probably overloaded.

Once you know the actual load on each end of each axle the proper MINIMUM inflation is selected from the tables and all tires on an axle should have the same inflation. Now the above does not give you the same margin you have in your car. In fact it may give you no margin at all.

Now if you want to avoid a lot of unnecessary hassle I suggest you add a 10% margin to your minimum inflation. That way you probably can go months without the need to add air. Of course running a TPM is extra insurance that something unusual hasn't happened such as a slow air leak. The other advantage of TPMS is that after a few weeks use you will become familiar with the normal range of pressures for your RV and you will soon learn that you don't have to worry about minor inflation changes and don't need to be adjusting your inflation every travel day. I don't adjust my tires every travel day. In fact on a 7 week trip from Ohio to Oregon to Canada and back I only added 5 psi to one tire one time as it had slowly dropped down to only 1% above the minimum it needed to carry its load and the temperature had dropped by 60°F one morning.

[Tireman9]

mabynack wrote:
I feel the same way. My truck tires last 5 years before the tread wears out. Two of my FW tires had catastrophic failures within 100 miles and they were less than two years old and had less than 10,000 miles on them. I've had issues with tires in the past, so I check the pressures every morning before I start off. I run 65 mph or less on the highway. The last one blew out about a hundred miles into the trip and the sun was just coming up, so overheating and under-inflation weren't an issue.

I would like to go on a trip, but don't dare leave the driveway unless I have new tires on my FW.

Not sure how you know that under-inflation wasn't the cause of the last "Run Low Flex Break" (correct term for blowout).

I have over 20 posts with label "blowout" on my tire blog. These are posted in an attempt to educate people in the variety of real reasons tires fail suddenly. If you read only one then I suggest THIS one as the owner in this case said he checked the air just 50 miles before the failure but sadly for him the physical evidence is incontrovertible...The tire was run while the tire was still leaking air.

[Gjac]

frankdamp wrote:
One of the big mistakes people make is to look at the max pressure molded into the sidewall and then use that as their inflation guide. Way too high and putting you at a much higher risk of a blow-out.

My approach is to buy good quality tires (we got Toyos), weigh the rig so you can figure out the individual axle weights when you're loaded for travelling, then inflate cold tires to the pressure the manufacturers' chart tells you. TPMS will give you a heart attack if you monitor what the pressure is while going 70 on the freeway in Arizona in the summer. Check it only when the rig has been sitting overnight and don't sweat it too much.

It really takes a lot of abuse to blow a tire. I worked in Boeing's landing gear group for a while, and we investigated an in-flight tire burst on a 727. It blew when the airplane was at about 12,000 ft, climbing out of Baltimore (I think). It punched an 18" diameter hole in the wheel-well pressure bulkhead and only a couple of USPS mailbags jamming in the hole prevented a disaster.

It turned out the airplane had taxied two miles with a dragging brake, then accelerated for take-off at close to maximum weight, needing about 150 mph for lift-off. After the gear was retracted, the heat build-up caused the failure, which was actually an explosion of gases that had been released from the tire compounds. The failure of the tire bead suggested an explosion pressure of about 12,000 psi. That's why airlines use nitrogen.

The "abuse" possible with an RV pales into insignificance. IMO, as long as you're within 15% of the pressure your weight calls for, don't sweat it. Being slightly under-inflated, based on a weigh-bridge check, is a lot better than being at the pressure shown on the tire's sidewall.

BTW, even after 47 years in the US, I still have trouble not spelling it "TYRE"! Fortunately spell checker alerts me.

Very interesting post Frank, but why would inflating the tires to the max sidewall pressure be more prone for a blowout then under inflation?

[Bikeboy57]

Raymon wrote:
To Bikeboy57,

You stated "Moisture is the enemy of the steel belts." How does the steel belts become exposed to moisture when the belts are vulcanized between layers of rubber? In my opinion the steel belts only become exposed to moisture due to tire wear. If the belts become exposed they will rust which is not good. Also, steel belts exposed to brine created from applying salt to the roads during winter, not only rust, but corrode very quickly.

You also stated "Driving the tire and getting it up to temperature dissipates the moisture,..." What moisture are you referring to?

Ray

Ray, good questions. We are not talking about cups of water in the tires. We are talking trace amounts of moisture in the air and in the rubber in the tires. You know compressed air contains moisture, but the source of the moisture that I was referring is that the rubber actually allows parts per million transfer of water through the rubber. Given enough time a spot on a tire sitting on wet ground will allow trace water to penetrate to the steel belts. Driving the tire heats the rubber. The heat helps to "evaporate" the moisture from the rubber.

Can I quantify this? No. Is it the major factor one should be concerned about? No. Should you listen to snake oil salesmen and fill your tires with Nitrogen to avoid the moisture in compressed air? No.

Certainly the mechanism you described of worn to the belts would result in extremely quick degradation of the belts.

The best thing one can do to preserve tires is to drive them.

[frankdamp]

One of the big mistakes people make is to look at the max pressure molded into the sidewall and then use that as their inflation guide. Way too high and putting you at a much higher risk of a blow-out.

My approach is to buy good quality tires (we got Toyos), weigh the rig so you can figure out the individual axle weights when you're loaded for travelling, then inflate cold tires to the pressure the manufacturers' chart tells you. TPMS will give you a heart attack if you monitor what the pressure is while going 70 on the freeway in Arizona in the summer. Check it only when the rig has been sitting overnight and don't sweat it too much.

It really takes a lot of abuse to blow a tire. I worked in Boeing's landing gear group for a while, and we investigated an in-flight tire burst on a 727. It blew when the airplane was at about 12,000 ft, climbing out of Baltimore (I think). It punched an 18" diameter hole in the wheel-well pressure bulkhead and only a couple of USPS mailbags jamming in the hole prevented a disaster.

It turned out the airplane had taxied two miles with a dragging brake, then accelerated for take-off at close to maximum weight, needing about 150 mph for lift-off. After the gear was retracted, the heat build-up caused the failure, which was actually an explosion of gases that had been released from the tire compounds. The failure of the tire bead suggested an explosion pressure of about 12,000 psi. That's why airlines use nitrogen.

The "abuse" possible with an RV pales into insignificance. IMO, as long as you're within 15% of the pressure your weight calls for, don't sweat it. Being slightly under-inflated, based on a weigh-bridge check, is a lot better than being at the pressure shown on the tire's sidewall.

BTW, even after 47 years in the US, I still have trouble not spelling it "TYRE"! Fortunately spell checker alerts me.

[rgatijnet1]

JimM68 wrote:

rgatijnet1 wrote:

JimM68 wrote:
I set the alarm on my tpms to 75% of my cold tire pressure. When / if the tpms alarmgoes off, I stop.

Are you saying that when your tires which would have a 100psi cold tire pressure leak down to 75psi, you stop? In other words 25 psi below the minimum cold tire pressure.
You're kidding, right? :h

I am not kidding. My tires do not lose any air, not ever, unless a failure is in progress. I do of course monitor the TPMS always. The air pressure on these tires fluctuates a LOT. Depending on outside air temp, and if the tires are hot or cold, pressure changes are crazy.

In this bus, with the new sumitomo's I put on a few years ago, I only have needed to put air in the tires in the spring coming out of storage. I credit that to getting rid of the extenders, they've been known to leak...lol. just a bit. sometimes...

I'm not running around chasing my air pressures. 110 / 95 cold tires at 70 ish ambient is good. All the fluctuations, I don't chase them.

I understand what you are saying but it just does not make sense to me. IF you got a small leak from a nail, by the time your TPMS let you know about the problem at 25% below minimum, and if it was on a dual tire, the weight would have been shifted to the other dual for a lot of miles, which would probably permanently damage that tire as well. Seems to me that a 10% range of tire pressure would be sufficient to let you know that you had a problem and still be able to stop in time to protect the other tire.

[cwdavis]

I'm a bit surprised no one has mentioned Roger Marble's RV tire safety website in this thread. RM worked for 40 years developing tires in the industry and offers a wealth of information about tires and tire safety on his website. He also offers seminars at RV rallies (or, he at least did at the FMCA convention in Perry last year.

Here's the link: http://www.rvtiresafety.com/

[JimM68]

rgatijnet1 wrote:

JimM68 wrote:
I set the alarm on my tpms to 75% of my cold tire pressure. When / if the tpms alarmgoes off, I stop.

Are you saying that when your tires which would have a 100psi cold tire pressure leak down to 75psi, you stop? In other words 25 psi below the minimum cold tire pressure.
You're kidding, right? :h

I am not kidding. My tires do not lose any air, not ever, unless a failure is in progress. I do of course monitor the TPMS always. The air pressure on these tires fluctuates a LOT. Depending on outside air temp, and if the tires are hot or cold, pressure changes are crazy.

In this bus, with the new sumitomo's I put on a few years ago, I only have needed to put air in the tires in the spring coming out of storage. I credit that to getting rid of the extenders, they've been known to leak...lol. just a bit. sometimes...

I'm not running around chasing my air pressures. 110 / 95 cold tires at 70 ish ambient is good. All the fluctuations, I don't chase them.

[VinCee]

Tropical, that happened at a local Goodyear store several years back. Tech was airing up a tire on a mid size truck and was crouched down square in front of the tire. It blew and he died instantly. From that news story, and hitting close to home (1/2 mile away), since I always stand or crouch down off to the right side of the tire I'm filling. Doesn't matter if its a bicycle tire at 85lbs psi or my RV tire at 95 to 100lbs.