A Guide to the use of BFGoodrich Comp T/A R1 Tires

Jim Fogarty & BF Goodrich Team T/A

Copyright (c) by Jim Fogarty, and Team T/A

Mechanics of the Aysmmetric Construction

BFGoodrich Comp T/A R1 Tires are built with both asymmetric tread design and asymmetric construction. Asymmetric means the outboard half of the tire is different from the inboard half of the tire. The asymmetric tread design is obvious because it can be seen by the naked eye; the asymmetric carcass construction is, however, hidden inside the tire.

The Asymmetric Construction is a unique BFGoodrich tire construction to help maximize the tire's contact patch while cornering.

First, you must understand what happens when the car is cornering. While the car is cornering, there is a lateral weight transfer away from the center of the corner. Because the center of gravity of the car is some distance above the ground, weight is removed from the inside tires and added to the outside tires. This weight transfer causes the outside springs to compress and the inside springs to extend, thus causing "body roll." The outside tires are more heavily loaded. Because of body roll, the tires tend to go towards a more positive camber state, and the size of the contact patches have decreased.

Remember, the car's only link to the road is the four contact patches of rubber, and their actions determine how the car handles.

One way race teams compensate for the decreased contact patch is to dial in more negative camber. A problem many drivers have in stock classes is that their cars do not have the suspension adjustments that will allow them to make these modifications. So, that is why the asymmetric construction was developed -- to increase the size of the contact patch by giving the tires a pseudo camber effect without any adjustments to the car.

The Comp T/A R1 Tire is built with more stiffeners in the inside sidewall than the outside sidewall. This creates a differential between sidewall spring rates. The inside sidewall has a greater spring rate ("stiffer") than the outside sidewall. During cornering, the tire rolls onto the outside shoulder creating an uneven load across the tread. Instead of lifting the inside of the tire and rolling onto the outside as normal tires do, the outside of the tire is more compliant, therefore, not rolling, but giving, and the inside of the tire being more rigid, stays firm. This makes the load more evenly distributed across the tread, effectively giving a larger contact patch.

To Shave, or not to Shave...

One of the first decisions you have to make when you get a new set of tires is whether or not you need to get them shaved. You need to decide when they are NEW because once the tires have been on the ground, you are not going to be able to get them shaved. This is due to the small particles of sand and gravel that get embedded in the tread rubber when you run the tires on the road or track. These particles will grind up the cutting edges of shaving equipment. So, most people with shaving equipment guard that equipment against tires that have been on the ground.

Let's talk a little about why we shave tires. The reason is heat. The tread rubber on tires in general -- and racing tires in particular - is hysteric by design. This means that it generates heat when it is flexed.

Heat is a double-edged sword when it comes to tires --

A certain amount of heat is necessary to produce good grip.

Excessive heat will cause the tire to lose grip; it can cause the tire to wear exceptionally fast; and, in extreme misapplication cases can cause separation in a tire.

The key is to allow the tire to generate enough heat for good grip, but not so much as to be detrimental to its performance.

Think about a spot on a tire -- let's say a tread block. As it rolls through the contact patch, it becomes distorted and is flexed. This flexing generates heat. If the car happens to be in a long sweeping corner when the ambient temperature is high and the track is very hot, it can generate a lot of heat. But then, as that tread block rolls out of contact and into the air stream rushing by and around the tire, it begins to dissipate the heat. In other words, it begins to cool off. The' tire goes through this heat generation/dissipation cycle with each revolution. If the rate at which the tire dissipates heat is more or less constant, then the faster you go, the more heat that is generated. This is because the tire is generating heat faster than the tire can dissipate heat. This is where a problem could arise.

How does shaving tread rubber off the tire affect heat generation? It actually affects it in two ways. Remember -- work equals energy and energy can be translated into heat.

Shaving then, is a useful tool for controlling the amount of heat your tires generate. The key is to allow the tires to generate enough heat to work effectively, but not so much that performance is hurt.

All tires have an optimum operating temperature range. To get the most out of them, you need to operate in that range. In the case of Comp T/A R1s, that optimum temperature range is from 160 to 230 degrees F. for the 230 Series.

Next question - How much do you need to shave off of the tires? Obviously, this will depend on how you plan to use them. Tire wear must naturally be considered before deciding on what is right for you. Experience is the best teacher. If you don't have the experience, talk to someone who does. Call Team T/A if you have questions.

Taking Tire Temperatures

Why take tire temperatures? Getting accurate tire temperatures is important to getting the most out of your tires. The term accurate, however, is a relative term. It is far more important to be able to get repeatable readings than it is for the actual temperatures to be accurate to the nth percentile of a degree.

What you want to know is the temperature profile across the tread more than anything else. The actual magnitude of the readings are only important in being confident that you are in the proper temperature range. How, when, and where you take your tire temperatures is amore important than whether or not your pyrometer reads 2 degrees high or 2 degrees low. As long as you keep using that same pyrometer, your readings should be comparable.

By the way, if you want to check the accuracy of your pyrometer, stick the probe into boiling water. It should read somewhere near 212 degrees F. (100 degrees C.).

A lot of people constantly debate whether you should use a probe-type pyrometer or an infrared-type pyrometer. In truth, if you use either one properly, it doesn't matter much. Both types have their good points and bad points. The key here is to understand your pyrometer's strengths and weaknesses, and be consistent in how you use it.

One good thing about infrared pyrometers is that they can be used quickly. If you want to bring your car in during a practice session and get a quick look at temperatures and get the car back out into the session, this is o ne way of doing that. One bad thing about these pyrometers, though, is that you have to BE QUICK to use them.

The way they work is you hold them some distance from the surface of the tread and pull a trigger. The distance you hold it from the tread surface is somewhat important to getting consistent readings. When you pull the trigger, the pyrometer takes a snap shot of the area it sees in its measurement window. The size of that area is dependent on how far away you hold the pyrometer. Next, the pyrometer calculates the average temperature it sees in that area and displays that number for you. Some of the things to watch out for when using this type of pyrometer are time, ambient air temperature, and wind. Since you are getting surface temperatures, time is very important. Surface temperatures can change rapidly, especially if there is any breeze or if the ambient air temperature is cool.

The best way to be consistent with this type of pyrometer is to get to the tire as soon as you can, get your readings quickly, making sure to be consistent in how far above the surface you hold the pyrometer. Then move on to the next tire and do the same thing. You should establish a set procedure to use every time you get tire temperatures. If the course you run is predominantly right-hand turns, you should probably be most concerned with the left front tire, and then the left rear. But you should work out what works best for you.

Probe-type pyrometers make it a little easier to be consistent. The metal probe penetrates the surface to measure internal temperatures of the tread. Internal temperatures do not change as quickly as surface temperatures, but they do change. So, you should still pay attention to time.

Another point about this type of pyrometer is that you don't have to worry about how far away to hold it. You do, however, have to learn to be consistent in how you read these pyrometers. Since they are taking actual temperatures instea d of giving you one average number, the number is constantly changing. You have to judge which number to use. This can be very important if you have more than one person taking your temperatures in your practice sessions.

Typically, when you first insert the probe, the temperature reading will jump to some number higher than the true reading. This is due to the friction of inserting the probe. The number will quickly start dropping back, however. As the numbers drop towards the true reading, the pace that the numbers are changing will slow down. All of this happens in just five or ten seconds or so. The total change in temperatures may be 10 degrees, 20 degrees, or even 30 degrees. You need to establish a method of determining which number you want to use as that reading is falling. Most people pick the number where the reading first seems to be stabilizing, or changing less rapidly. Some people wait until the readings seem to be stabilizing and then round off to the nearest 5 degrees. Whatever method you decide on, be consistent. And train all of the people who take temperatures for you to do it the same way every time. Then you will be able to compare results from one session to another, and from one day to another and be confident that differences you see are due to factors outside your measurement methods -- like car setup or weather changes.

So, now you know a little about pyrometers and how to use them. But where you take the readings on the tire is important too. On the Comp T/A R1, we typically look at three temperatures across the tread. We look at the outside shoulder, the tread center, and in the inboard shoulder regions.

We do not take the shoulder temperatures all the way out on the edge of the tread, however. Instead, we move a little in towards the center from the edge on both the outer shoulder and inner shoulder areas. On the outer shoulder, you will most typically find that the hottest area is about 1" or so in from the edge of the tread. If you are familiar with the round tread wear indicator holes that we put on the outer part of the tread surface, the area you want to measure temperatures is roughly between those two indicator holes. With practice, you will get to know where the hot area is on your tire. That is where you want to measure the outer shoulder temperature. On the inboard side, just probe the very center of any tread block in the rib closest to the edge of the tire to maximize the use of your R1s.

By looking at the temperature profile across the tread surface of your tire, you are really looking at how much work each part of the tire is doing. If your outer shoulder is hotter than the center of the tire, for example, that means that the outer shoulder is doing more work than the center of the tire. Another way to look at it is that the outer shoulder is carrying more of the load out there under hard cornering conditions. And, if the center of the trSead is hotter than the outer shoulder, then it is carrying more of the load than the outer shoulder. You want to balance the amount of work each part of the tire is doing to maximize the use of your R1s.

Let's just for the moment, ignore the fact that it is the inflation pressure that actually carries all of the load on the tire. Just for the sake of illustration, let's think of the tire as having three different load carrying regions across the tread. Each region has its own spring rate, or stiffness.

This spring rate determines how much load that region will carry in relation to the other regions. The sidewall regions each get some support from the internal construction of the tire. The center region, however, gets nearly all of its support from the internal air pressure of the tire. (There are really a LOT more dynamics going on here. But, for the sake of simplicity, let's just consider these.) So, let's go back to our first example where the outer shoulder was hotter than the tread center. In this case, the center region isn't holding up its share of the load. So, you may want to increase the spring rate in that region by increasing the air pressure in the tire.

In our second example, the tread center was hotter. In that case, you may want to decrease the spring rate in that region by decreasing the air pressure.

Ideally, you would want to end up with identical temperatures in all three regions of the tread. This would mean that all three regions are doing equal amounts of work, and you are, therefore, getting the most out of your tire's capabilities. In many cases, however, the inboard region will be significantly cooler than the other two regions. In stock-type cars, this is usually indicative of not enough negative camber to compensate for the vehicle's body roll. Conversely, if your inboard shoulder temperatures are hottest, then you may be running too much negative c amber. If you are allowed to change your suspension settings to compensate for this, great! If not, you may just have to learn to live with it.

Now, what temperatures are you looking to find? For the 230 Series Comp T/A R1, we have already stated that we like to see temperatures between 160 degrees and 230 degrees F. This tire will perform well even below that temperature range. But, the compound really starts working well when it's above 160 degrees. If you are seeing temperatures above 230 degrees F., you are probably overheating your tires. When temperatures are in the 250 degrees range, you may have to worry about the tires losing grip or even blistering if they aren't shaved. And, when temperatures approach 300 degrees, you may have to start worrying about separations in the tire itself. This is not a good situation to get yourself into. So, keep things cool, or at least in the proper range for what you're doing.

Common Sense Application for Taking Tire Temperature

Since we have just given you the technical side of taking tire temperatures with pyrometers, it is now time to discuss the common sense applications of the data. On the next page, you will find a chart which can be used to record temperatures and pressures.

First, in order to be meaningful, it is important that pyrometer readings be taken immediately after the car comes off the track under full competition conditions. If you have just completed a "cool down" lap, the pyrometer readings you get will not reflect the true heat profile under full competition conditions. You need to have someone ready and waiting to take your readings under full competition conditions. It is, therefore, best to do your pyrometer work during practice and perhaps qualifying if time allows.

The second thing you need to know is that you are looking for linear pyrometer readings. By this, we mean a progressive heat reading across the tire's tread face with no outstanding irregular peak. To explain further, a pyrometer reading of 220 degrees outboard, 210 degrees center and 200 degrees inboard is considered linear. A pyrometer reading of 200 degrees outboard, 230 degrees center and 190 degrees inboard is not linear. It has an irregular peak in the center of the tread, a condition that may call for a reduction in air pressure as the center measurement is out of line with the shoulders. Conversely, a reading of 240 degrees outboard, 200 degrees center and 220 degrees inboard would seem to indicate that more air is needed in the tire once again because the center reading is out of line with the shoulders.

The third thing you need to understand is that a pyrometer is merely a tool -- it is not an answer in-and-of itself. The interpretation of heat measurements in a tire is also directly related to what the car has just done prior to entering the pits. Consider: At Mid Ohio, immediately before the pit entrance, the car has just gone through the carousel. Since the carousel i/s a rather steady state right-hand sweeper, the left side of the car would be loaded while the right side of the car is unloaded. It would be a reasonable expectation then to witness high outboard temperatures on the left side tires and high inboard temperatures on the right side tires.

Conversely, at Road America, the working pits are about one-half mile from the last right-hand, 90 degrees turn. By the time the car comes to rest in the working pit area, the tires will have had time to share the heat across the tread face and not be truly reflective of the heat generated in any one corner of the race track. Does this mean that you should adjust suspension settings and tire pressure? Perhaps, but not necessarily.

The important thing to understand is that while the suspension settings and tire pressures may have been exactly the same, the configuration of the track will have a bearing on the pyrometer readings taken in the pits.

Dealing with Pressures

By now, you can read your pyrometer and take your tire temperatures. So, how do you use that information? Well, getting the information is only the first step. Now, you have to learn to interpret that information. Understanding what the information means is every bit as important as getting good, reliable information. Although we are talking about Comp T/A R1's here, some of the general theories can be applied to other radials tires as well.

Let's say that you are sending your driver out on R1s for the first time. The driver has never driven on them before. What pressures do you use?

Well, a good place to start would be to talk to someone with some experience with the tires. Either Team T/A personnel or another driver who runs a car similar to yours on BFG's can give you a recommended starting point - we call this "peer pressure." Then, send the driver out with instructions to take it easy at first. Learn how the tires feel, how they react. Spend some time getting to know them. When the driver feels that they know what the tires and the car are doing, bring them in and take a look at the tire temperatures.

Now, here is the most important point in the process of finding the right setup. Always, always, always, talk to the driver to see how the car felt before making any decisions or changes. If the driver tells you that the car was pushing coming out of that last corner before coming into the pits, then he has given you additional information to consider when interpreting your temperatures.

If the driver says, "The car is too loose! I had the tail hung out in every corner!," then you've got to consider that. Remember, you can look at all of the tire temperatures, and all of the hot and cold pressures in the world. With experience, you may even be able to predict from all of that data how the car is handling. But why go to all that time and effort when the driver can tell you what the car is really doing? You may have to pry the right information out of your driver, but ~it's in there. Use it!

If the car is really pushing, it may show up in the front tire temperature profile as really hot outer shoulder temperatures. If the car is loose, the rear tire temperatures may be high. Try and relate what the driver says is happening to what you see in the tire temperatures. Until the driver is comfortable and confident with the handling of the car, you really can't find the right pressures. That's because the driver may be changing their driving style to compensate for the balance of the car. Different styles will require different air pressures. Get the driver comfortable so the preferred driving style is used. Then tune the inflations to get the most grip and quickest lap times.

Okay, now you are ready for some general rules for adjusting the balance of the car using inflation pressures. Comp T/A R1s work a little different, (okay - backwards), from most radials due to the asymmetric construction. Generally, (for an R1) if you want more grip at one end of the car, LOWER the inflation pressure at that end. If you are already as low as you feel you should go at that end, then raise the pressure at the other end. By changing the differential in pressures front-to-rear, you can dramatically change the handling of the car. If the car pushes - or understeers - lower the front, or raise the rear pressures. If the car is loose - or oversteers - lower the rear, or raise the front pressures.

Proceed cautiously. We recommend making changes of a couple psi at a time, and only at one end of the car at a time. We also don't recommend going below 20 psi, or over 44 psi. That is a very wide range to play in. If you are going to drive on the street, adjust your pressures to the vehicle manufacturer's recommendations.

Heat Cycles

Heat cycling, or scrubbing tires, is a very useful thing to know about. But it is not something that many people understand or use properly.

A tire will perform differently when it is new, compared to how it will perform after it has been through a heat cycle. This is not necessarily a bad thing. In fact, in a lot of cases, it is a very good thing indeed. In the case of R1s, a heat cycle will make the tire wear much longer, and be more consistent in its performance. By this I mean that the tire will not change as much during a race or practice session if it has been heat cycled. There will be a slight drop in performance during a session - slightly less grip -with new or non heat-cycled tires, though.

Let's look at what a heat cycle is and what it does to the tire. We will concentrate on the tread compound, but there are similar benefits for the other compounds in the tire that actually hold everything together.

To understand what happens in a heat cycle, let's talk about the molecules that make up the compound. For those of you who don't remember your high school chemistry classes, the molecules that make up polymers are long chains of aitoms. To visualize this, think of a bunch of rubber bands. Imagine that they have all been cut with a pair of scissors so that they are not closed loops anymore. Now, throw a bunch of them into a box and shake it up. Those represent the polymer molecules.

In addition to being highly intermingled, polymer molecules are connected, or attracted, to each other by a variety of chemical networks. For simplicity, we will refer to all of these networks as chemical bonds. These bonds, or attractions, are what are important. During the manufacturing process, these bonds form in a more-or-less disorganized way. Some of the bonds are very short and strong. Some of them are very long and weak. The rest of them vary between the two.

Now, when you take that tire and run it, things start to happen. The molecules get stretched and compressed. This first causes the weaker bonds that connect these molecules to break. When the bonds break, heat is generated. As the heat builds and the flexing continues, more bonds break, more heat is generated, stronger bonds break, more heat is generated, and so on... Remember that these bonds are what connect the molecules to each other. They give the compound its strength. When this strength is reduced, the compound can't grip the road surface as well. It rubs off instead of holding together. The result is less grip, more slip on the road surface, and more heat generated. You can see that it can become a self-perpetuating kind of thing. How fast this all occurs determines how fast the tires tend to lose grip.

So then, what happens in a heat cycle that can improve this pretty bleak situation? Well, actually, the situation described above is the first step in the heat cycle process. You want to break all of those "uneven" bonds. What happens next is where the real magic of alchemy comes into play.

After these bonds have broken, and this heat has been generated, and the tires are finally allowed to be set aside and relax, the bonds tend to REFORM! But now they reform to a much more uniform manner! This means that they are more consistent in strength. Therefore, the compound becomes more resistant to losing its strength the next time the tires are run. That doesn't mean that you can't make the tires give up anymore. If you exceed the limits of the compound - both mechanical and thermal - the bonds will still break. But they will be more resistant to it because they are working together now as equals - in parallel - instead of individually - in series. And, given the time to relax again, they will reform again in the same uniform manner.

Here is the most important thing to learn and remember about this process. These bonds MUST be given ENOUGH TIME to do their magical reformation. In the case of the R1, the tires must be allowed to relax for an absolute minimum of 24 hrs. after that initial "break in." We sometimes tell people to wait up to 48 hrs. to be sure. But, we really haven't seen any additional advantage to waiting any longer than that. If you don't give the tires enough time to reform those bonds, then you are going out on tires with a weakened compound and their performance will show it. Understanding how this works, and how to use it to your advantage, is important to getting the most from your tires.

Let's talk now about the number of heat cycles you can expect out of a tire. We've heard people talk about Brand-X or Brand-Y or Brand-Z only being good for X number of heat cycles. We really have not seen this with the Comp T/A R1. You should be able to expect the same performance level from the tire after 20 heat cycles as you get after 1 - assuming, of course, that tread wear isn't an issue. Additional heat cycles beyond the first don't make the tire "harder." The tire can and will change over time just due to "aging." But thact is due to other influences like ultraviolet light, ozone, etc. And that time period, with proper care, should be at least a couple of years.

So, to recap, heat cycling will improve the consistency and longevity of your R1s. The first heat cycle is the most critical. Subsequent heat cycles do not cause any detriment to the performance of the tire. It is still possible to overheat heat-cycled tires. Assuming you don't do any other permanent damage to them and give them the minimum of 24 hrs. to relax afterwards, they should be fine for later use.

Tire Pressures

The following questions and table are to help guide you toward determining approximate air pressures.

The air pressures given are a CONSERVATIVE STARTING POINT. They are on the high side for cold starting pressures. This allows the driver to safeguard his/her tires while adjusting air pressures to fine-tune the handling of the car.

The questions on make/model and weight distribution is to give you a little more information on the car in case you need to make any "educated" decisions.

QUESTIONS TO ASK:

  1. Make/Model of Car?
  2. Weight of car?
  3. Front Wheel or Rear Wheel Drive?
  4. Weight Distribution from front to rear?

                STARTING AIR PRESSURE (COLD TIRE)
                     
               FRONT WHEEL DRIVE  REAR WHEEL DRIVE
VEHICLE WEIGHT        F/R              F/R                 

     0 - 2000        28/25            28/25
  2001 - 2500        34/27            32/30
  2501 - 3000        38/28            34/32
  3001 - 3500        40/30            36/34
  3501 - 4000        42/32            40/36

COMP T/A R1 GUIDE TO HIGH PERFORMANCE HANDLING

   ADJUSTMENTS        DECREASE UNDERSTEER    DECREASE OVERSTEER

Front Tire Pressure         Lower                 Higher
Rear Tire Pressure          Higher                Lower

Front Tire Section          Larger                Smaller
Rear Tire Section           Smaller               Larger

Front Wheel Camber       More Negative         More Positive
Rear Wheel Camber        More Positive         More Negative


Front Wheel Toe          Toward Toe-Out        Toward Toe-In
Rear Wheel Toe           Toward Toe-In         Toward Toe-Out

Front Wheel Caster       More Positive         More Negative

Front Springs               Soften               Stiffen
Rear Springs                Stiffen              Soften

Front Anti-sway Bar     Soften (Thinner)     Stiffen (Thicken)
Rear Anti-sway Bar      Stiffen (Thicker)    Soften (Thinner)

Weight Distribution      More Rearward         More Forward

Tire Pressures in the Rain

Increase tire pressures 6-10 psi from what you would normally run in dry conditions. This is for both autocross and road race. Reason Hydroplaning occurs when a wedge of water develops between the tire and road surface. This wedge can actually lift the tire off the road and eliminate traction. Increasing the pressure rounds the profile of the tire by decreasing the deflection of the tire. This results in a smaller contact patch - narrower and shorter. It also helps keep the grooves in the tread open so they can channel the water out from under the tire.

Tire Rotation

Can I rotate the Comp T/A R1? "YES!"

Front to rear, left to right, crisscross, any way is fine. You must keep in mind, though, that the R1 tire can ONLY be mounted with the DOT CODE ON THE INSIDE. As long as the DOT code remains on the inside, tires can be rotated at will.



HAVE FUN OUT THERE !!!!


Copyright (c) by Jim Fogarty, and Team T/A