Run-Flat Tires: Self-Sealing, Self-Supporting, Auxiliary supported

Run-Flat Tires: Self-Sealing, Self-Supporting, Auxiliary supported

For many many years tires have played a very important role in determining how well a vehicle performs. Whether we’re talking about high performance, comfort or overall safety, tires are a major part of the equation.  Tires are constantly subjected to the worst and most extreme parts of driving, extreme temperatures, varying road surfaces, potholes and other debris and constant load changes. Tire manufacturers have worked hard over the years to provide the public with tires that could perform well and also deal with things like punctures and other holes or loss of air. It wasn’t until the invention of the Run-Flat tire that this was actually achieved. And the inflated performance of these Run-Flat tires has gotten remarkably better over the years.

Ill bet you never thought about this…..Tires don’t carry the load of our vehicles!!!! Then what does? The air in the tires is what carries the load. The amount of load that a tire is allowed to carry is determined by three main factors. 1) The size of the air chamber between the tire and wheel. 2) How much air pressure the tire can hold based on its construction. 3) The air pressure in the tire.

So let’s look at the different methods used to support tires should they have a blowout or other form of flat.

Self-Sealing

These tires are designed the same as standard tires with one exception. They have an extra liner in the tread area on the inside of the tire that is coated with a puncture sealant. Any object that punctures the treat area, up to about 3/16 of an inch is instantly and permanently sealed.  The sealant will seal around whatever punctured the tire i.e. nail, screw etc. And then, if the object is removed it will fill and seal the hole. Because these tires work so quickly and permanently, most drivers never know it happened.

Self-Supporting

Self-supporting tires are capable of supporting the weight of a vehicle even after the tire has lost all air pressure. This is achieved by adding heat-resistant cords in the sidewall construction as well as special beads that secure themselves to the wheel. These tires do such a good job of masking a tire that has lost all air pressure, it is recommended that they only be used if your vehicle has a TPMS (Tire Pressure Monitoring System). If these tires lose all air pressure they are typically rated to last for around 50 miles at speeds around 50mph.

Auxiliary Supported System

These systems are not quite as widely used in the general public, in large part due to their cost. These systems require special wheels and therefor normal tires will not fit. One of the best examples of an auxiliary System is Michelin’s PAX system.

These auxiliary systems are more common on military and protection vehicles. For example, the presidential limousine has an auxiliary run-flat system.

Smart Tire Care

Help your tires last longer. 

We all hate buying tires. They tend to be expensive and most people just assume all tires are the same so just put something round and black on the car, fill it with air and move on. This couldn't be further from the reality of the importance of tires, but that's not what this post is about. 

If you don't like spending money on tires, then it's best to make the ones you have last as long as possible. Here are a couple ways to make that happen.

• Check your tire pressure every 3,000 miles to keep your vehicle driving smoothly and evenly. This also helps promote propper wear and as a side benefit, your vehicle will use gas more efficiently.
• Tires should be inflated when COOL to the vehicle manufacturer's recommendations printed on the vehicle door placard or in your vehicle's owner's manual, NOT the maximum limit stamped on a tire sidewall. 
• Rotate your tires every 6,000—8,000 miles to help equalize treadwear.
• Get your wheel alignment checked as specified in your vehicle's owner's manual, or as soon as you feel the wheel "pull" to one side or the other. Also, pay special attention to this after you run off the shoulder of the road or hit something hard like a pothole. 
• Visually check your tires for irregularities in treadwear as these could indicate problems with alignment, inflation or an internal tire failure like tread seperation. 

If your not sure about any of these or would feel more comfortable if a professional took a look, stop in at Ian Stowell's Tire and Battery any time Monday through Satuday between 9am and 5pm and we will be glad to check your tire presssure and inspect your tires at no charge. 

TIRES - More important than you may realize.

In this post let’s talk about where the “rubber meets the road”. This area is known as the "contact patch". In order to discuss the contact patch, we will also be talking about weight transfer, how the vehicles weight moves around as we drive. See, once your feet leave mother earth and sit in the seat of a vehicle, the only thing keeping you stuck to the road are your tires.

Tires are way more complex than most people give them credit for, but we’re not going to get into the construction of the tire, but rather the function of the tire on the surface of the road. As well as how you as a driver effect that function.

An average tire has a contact patch about the size of the palm of your hand. Another way to consider the contact patch size is to take a standard size sheet of paper and fold it in half and then half again. The rectangle shape you now have is about the size of the average contact patch. So as you are driving down the road, the only thing keeping you connected to the surface of the road, is a patch of rubber that totals to be about the size of a sheet of paper! Yea, keep thinking about that for too long and it just might scare you away from driving all together.

Now let’s add to the fact that this relatively small contact patch is almost constantly changing in size. 

When we brake, accelerate and turn the steering wheel left and right, we are constantly moving the vehicles mass around and thereby changing the size of the contact patch on the road surface.

Here's the deal;

Cars move on three basic axis, Vertical, transverse and longitudinal. (Fig. 1)

The vertical axis is the axis the vehicle rotates on if its spinning, also called the “yaw” axis. The transverse axis comes in to play when braking and/or accelerating. And lastly, the longitudinal axis is what the car moves on when cornering.


Fig. 1



Let's say we are starting with a vehicle that has equal weight distribution across both axles. This is to say that half of the vehicles weight is supported by the front axle, and the other half by the rear axle. This set up provides four equal contact patches on the road. (Fig. 2)


Fig.2



As long as the vehicle is either sitting still or driving in a straight line at a constant speed, the four contact patches will remain equal. But lets say that we press the brake pedal or simply decelerate. When we do this the weight of the vehicle shifts to the front. You know, when the smelly little pine tree hanging from the rear-view mirror swings toward the windshield. This 'shift of weight' to the front applies more weight to the front axle therefore making the front contact patches a little bigger. Much in the same way that if you had a beach ball sitting on the ground it would have a certain portion of the ball touching the ground, but if you sat on it, more of the ball would be touching the ground. Same concept.

But, because a vehicle moves the way that it does on these axis, the weight that was added to the front, came from the rear. This means the rear axle now has less weight on it therefore the rear contact patches become a bit smaller. (Fig. 3)


Fig. 3




Obviously the above figure is an exaduration, but I think you get the point. 

With the above being true, then obviously when we accelerate in a vehicle just the opposite happens. Weight moves to the rear axel and increases the rear contact patch and the weight came from the front and reduced the contact patch size on the front tires.

Likewise the same happens when you turn the steering wheel except it’s a left to right thing rather than a front to rear.

So this is how the “vehicle dynamics" effects the contact patch.

There is a way of looking at the contact patch called the “friction circle”. It’s a simple way of looking at a tires grip on the surface.

I’m all about simplicity, so I will explain this as simply as I know how. Well, simple is actually the ONLY way I know how to explain it, so its more about my ability than yours.

The circle below will represent the “limit” of the tires contact patch on a dry road. (Fig. 4) This means that if you go outside of that black circle, the tire starts to slip at a high rate. So if accelerating, it means wheel spin. If cornering it means the tire is sliding sideways. And if braking it means you have locked the tires and it’s skidding. Or nowadays, you've activated the ABS.


Fig. 4





Now, If its raining and the road is wet, the “limit” becomes smaller because the surface is more slippery. (the blue line Fig. 5)



Fig. 5




And of course if you were driving on snow or ice, that circle would be even smaller yet.


So lets say that we are driving on a dry asphalt surface and we end up in a moment where we have to break pretty hard. Maybe we weren't paying attention and we were caught by surprise by a stopped vehicle in front of us. So we apply the brakes hard. (Fig. 6)


Fig. 6




As you can see I added the directional forces that are applied to the contact patch. Yes, I do know my right from my left. Again I am showing forces applied. So for example, when you turn the wheel to the right, the force on the contact patch pushes left.

You can see that in figure six we are braking hard so it pushes the tire close to the limit of its ability, but still inside of the tires capability. All is good, no skidding. No ABS. No lock up.

Now let’s say that we realize that we are closing in on the car in front of us too fast and we are not going to be able to stop before making impact. This means we are going to have to swerve to avoid. We find an opening to the left and we turn the wheel. (Fig. 7)


Fig. 7




Again, you can see that the red line shows that the forces to the left are still within the limits of the tires grip., therefore we successfully avoid the incident without any loss of traction right? …………..WRONG!


When you vector the two lines, they meet OUTSIDE of the limit of grip. This is because you are utilizing both forces on the tire at the same time. (Fig. 8)


Fig. 8





So, as I said, you see that when you vector the lines, the two points meet OUTSIDE of the tires limit of grip and now you have a tire that has lost traction. A tire can only do 100% of one thing. This means you can use the brakes all the way to the limit or you can accelerate to the limit and you can corner to the limit. But of you are braking at the limit and then you try to corner at the limit, the tire is not going to be able to handle both of those inputs at 100% and it will lose traction.

Does this mean that we were not able to avoid the incident? Not necessarily, it simply means that the tire is sliding and now you have to "manage" it. You have to get the tire to function back within its limits. You can do this by reducing your braking or reducing the steering input or both. And, provided you have the time to do this, you could still avoid the incident.

Also, these days we now have vehicles with systems that can recognize when you have gotten yourself beyond the tires limit and they can assist you in getting the vehicle on your intended path. Some of these systems are known as; traction control, stability control and ABS. In the situation in this example, the systems would have come into play. (Fig. 9)



Fig. 9




The yellow line shows that the systems would operate to keep you near the limit to try and maximize both of the requests you have made, within the tires ability. Provided you have ABS, all you really need to do is stay on the brake and steer the vehicle, the systems will do the rest.


So that’s a quick and dirty way of showing you how inputs to the vehicles control systems affect the contact patch. In a more complicated but realistic picture you would see that a real contact patch is not a circle, it’s more of an oval type shape. (Fig. 10) below is a picture taken by a camera mounted under a glass plate as a vehicle drove over the plate. This shows an actual contact patch. The patch and its size will also vary dependent on tire pressure.



Fig. 10




The reality is, the example I have discussed, no matter how detailed (or simplified) is only for one specific moment in time. Its what the tire is capable of at that moment, at that time, on that specific piece of asphalt, at that speed, with that steering angle. As the vehicle moves, the tire (contact patch) is constantly changing the surface that it is in contact with. Maybe it started out on a perfectly clean dry spot of asphalt, but then transitioned to a spot that had a little sand or oil on it. Whatever the case may be, its an ever changing scenario.

A lot of race cars have data acquisition on them and its really cool to look at data and look at the plot points from the G-meter. They use these meters to show where the car can be faster and where it had more or less grip. It can also show the driver where he can gain time/speed by utilizing the vehicle a bit more to its limits in some areas. And where he/she may be losing time/speed due to going beyond the tires grip level in some places. It’s a cool science, and although you may not be into racing and you feel you may never take a tire to it’s "limit of grip". The reality is, the tire has no idea if it has gotten to its limit or gone beyond its limit because its on a race track and the driver is trying to get the most out of his/her contact patch in an effort to go fast, or if its on a highway trying to avoid a head on collision with another vehicle. All the tire knows is that it has been taken to or beyond it’s limit and it will react accordingly. It’s now up to you as a driver to manage the rest.


What?......................you mean they didn’t explain that to you in Driver’s Ed?..................... I’m shocked!


Now give you're sixteen year old the keys and send him/her on there way. Scary isn't it? It's no wonder the leading cause of death for teens is auto accidents.

Summer, summer, summer-time!

Hopefully we've haerd the last of winter this year, but time will tell. We've has some pretty heavy snow and ice in March in the past.

As winter ends and summer approaches, be sure to prep your vehicle for summer driving. Here are some things to consider.

• Air Conditioning

  A marginally operating system will fail in hot weather. Have the system examined by a qualified technician. Also, newer model vehicles may have a cabin air filter that cleans the air entering the heating and air conditioning system. Check your owner's manual for location and replacement interval. 

• Cooling System

  The greatest cause of summer breakdowns is overheating. The cooling system should be completely flushed and refilled about every 24 months. The level, condition, and concentration of the coolant should be checked periodically. (A 50/50 mix of antifreeze and water is usually recommended.) DIYers, never remove the radiator cap until the engine has thoroughly cooled! The tightness and condition of drive belts, clamps, and hoses should be checked by a pro.

• Oil

  Change your oil and oil filter as specified in your manual. Typically around every 3-5 thousand miles. Change more often if you make frequent short jaunts, extended trips with lots of luggage, or tow a trailer.

• Engine Performance

  Replace other filters (air, fuel, PCV, etc.) as recommended by manufacturer. (see owners manual. If you dont have an owners manual, look it up online. most owners manuals are available for free online now.) Change these additional items more often if you regulary drive in dusty conditions like dirt roads or long dirt driveways. 

• Windshield Wipers

  A dirty windshield causes eye fatigue and can pose a safety hazard. Replace worn blades and get plenty of windshield washer solvent.

• Lights

  Inspect all lights and bulbs; replace burned out bulbs; periodically clean dirt and insects from all lenses. To prevent scratching, never use a dry rag to wipe lenses. Most lenses these days are a form of plastic and can scratch pretty easily.

• Tires

  Have your tires rotated about every 5,000 miles. Check tire pressures once a month; check them while they're cold before driving for any distance. Don't forget to check your spare as well and be sure the jack is in good condition. Examine tires for tread life, uneven wearing, and cupping; check the sidewalls for cuts and nicks. An alignment is warranted if there's uneven tread wear or if your vehicle pulls to one side.

• Brakes

  Brakes should be inspected as recommended in your manual, or sooner if you notice pulsations, grabbing, noises, or longer stopping distance. Minor brake problems should be corrected promptly.

• Battery

  Batteries can fail any time of year. The only accurate way to detect a weak battery is with professional equipment. Routine care: Scrape away corrosion from posts and cable connections; clean all surfaces; re-tighten all connections. If battery caps are removable, check the fluid level monthly.Avoid contact with corrosive deposits and battery acid. Wear eye protection and rubber gloves.

• Emergencies

  Carry some basic tools such as a multi tip screwdriver and bits, adjustable wrench and a pair of pliers. Also include a first aid kit, flares, and a flashlight.
  Come by or schedule an appointment and we can handle any of the above summertime prep work for you. 

Tire Pressure Monitoring Systems

As some of you may know, new cars now come standard with Tire Pressure Monitoring Systems (TPMS) or (TPM). These systems work my a pressure sensitive device in your wheel that communicates with your vehicles computer.

A lot of people think their tire-pressure monitoring system in their new car makes sure that their tires are adequately inflated. This is not true. A TPMS is not required to issue a warning until the tires pressure is 25 percent below the vehicle manufacturer's recommendation. And according to AAA, that's "well below the pressure required for safe driving." And the Rubber Manufacturers Association (RMA) says that 25 percent below the recommended pressure is "barely adequate to carry the vehicle's maximum load." TPM systems are intended as a last-minute warning before imminent tire failure is possible, not as a monitor to make sure your tires are properly inflated. 

If your TPMS does recognize that one of your tires is below spec, you should see a symbol like this somewhere on your vehicles instrument display. 

To make sure that your tires stay at their optimum operating pressure. Be sure to check the pressure regularly.  Buy a quality tire gauge and set your tire pressure to at least the vehicle manufacturer's recommendation, which is found on the driver's door jamb. I'd rather you set your tires 3 or even 5 psi high rather than 1 low. Tire-pressure gauges can be inaccurate, and tires leak as much as 1 psi per month. Higher pressure improves hydroplaning resistance and, if you're like many folks, you may not bother to check your tires again for six months.

I only need two tires, where should I put them?

For years the common belief was that any time you put just two new tires on your vehicle, they should be mounted on the drive wheels. So if you had a rear wheel drive they went on the rear and a front wheel drive got them put on the front. Well this has changed. And for years now the tire industry has been trying to get the message out there that this old way of thinking is incorrect.

So where do we mount the tires with the best tread? On the rear! Always! It doesn't matter if it's front, rear, all, or four wheel drive. The new tires go on the rear and the less tread tires go on the front.

Why is this? Let's say you have a front wheel drive car. You put your two new tires on the front and leave the rears to be the more worn tires. When driving in the rain the front tires will cut through the water just fine. However, the rears will not perform at the same level and you can drive yourself into a rear tire aquaplane or hydroplane. This can get the back of the car sliding around, especially if it happens in a corner. A rear tire slide is more difficult for the average driver to control or in some cases even recognize.

If we keep the better tires on the rear, then the front tires will always be the limiting factor. If the front tires aquaplane it is easy to recognize (the steering feels light all of a sudden). And it's easier for a driver to control, simply ease off the accelerator and keep the steering wheel pointed where you want to go.

If you think I'm wrong, here's a video from 2009 that was put together by Michelin. I've driven these two seperate setups on their skid pad and I assure you, it is correct and true.



New Tires - Front vs. Rear

All-season vs. Winter

Do we really need winter tires here in the south?

Aren't my "all-season" tires made for use in all seasons?

The answer may suprise you.

First, are all-season tires really made to operate in all seasons? Yes and no. All-season tires are designed to operate in a variety of conditions, wet, damp, dry and in most cases light snow. However, the issue is not the tread. The issue is the compound of the rubber. And herein lies the biggest difference in winter tires and all-season tires.

A winter tire is designed to operate in temperatures below 45° F.  By "operate" I mean that even in the very cold temperatures, the rubber of a winter tire will stay malleable. It can still flex and move to grip the surface as best possible. As well as discharge packed snow. An all-season tire, when in temperatures that are regularly below 45°F, will become very hard. The rubber compound is not meant for these cold temps. So when exposed to them, it does as most things do in the cold, it gets hard. And what does hard rubber do very well on ice and snow? Well, how does a rubber hockey puck perform on ice?  Exactly.

So this brings into question, Should we run winter tires here in the south. The answer would be, it depends on where in the south. If you live in Asheville or up in higher elevations, yes, you should invest in a set of winter tires. If you live in a climate like Greenville, Spartanbug, Charlotte etc. then no, it's not necessary. However, what I would recommend is to make sure that your tires, at a minimum, have the M+S marking on the sidewall. This means that the tire has been approved for use in mud and snow by the RMA (rubber manufacturers association). This means the tires should perform well in light snow. However, I wouldn't want to be out driving on them in a big snowstorm.

Another thing you can look for, and a lot of times you'll find this on light truck and SUV tires, is a symbol of mountains with a snowflake in it.

This symbol means that the tire has been approved for severe snow by the RMA. 

If you live in an area like Charleston thenI would say no, not necessary. 

Another thing to consider. If you have a performance vehicle, or a vehicle with performance tires on it. I would definitely recommend you do not attempt to drive it in the snow. 

I regularly hear people complain about how terrible their Mustang or Camaro or other sports type vehicle drives in the snow. The majority of the problem is not the vehicle, but rather the tires. 

When your feet leave Mother Earth and you sit in your vehicle, the only thing that keeps you connected with the road are your tires. THEY ARE IMPORTANT! I don't care how much horsepower your car makes. Or how great of an upgraded brake system you've installed or whether you have a front - rear - or all wheel drive. If your tires aren't making good contact with the surface they are riding on.......all of the above is pointless.  

If you're not sure if you have the right tires on your vehicle, stop in and see us. It won't cost you a thing for us to let you know whether or not you're riding on what you should be.