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Old 03-06-2009, 01:42 PM   #1
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Care and Feeding of your Comp T/A R1's

Found this article while browsing teh intra-webz!

Thought i'd share -

Originally Posted by Jim Fogarty

This file contains some general advise on how to use and care for your Comp T/A R1's. Specifically, it contains some general explanations about things such as shaving tires, taking tire temperatures, finding proper inflation pressures, and heat cycling tires. All of these things are important to getting the most out of your tires.

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 get them shaved. This is due to the small particles of sand and gravel that gets 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 hysteretic 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. However, excessive heat is the single most damaging thing to tires. Excessive heat will cause the tire to lose grip. It can cause the tires to wear exceptionally fast. And in extreme cases can cause separations in the tires. So 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 gets flexed. This generates heat. If the car happens to be in a hard corner on a hot race track, 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 gives up, (or dissipates), some of that heat. The tire goes through this heat generation/dissipation cycle with each revolution. Let's assume that heat is dissipated from rubber at a more or less constant rate. Then the faster you go, the more heat you generate. This is because the amount of time the tire is dissipating heat in each cycle is shorter when the tire is turning faster. If the tire generates heat faster than it can dissipate heat, you can see where there could be a problem.

Now, how does shaving tread rubber off of a tire affect all of this? Well it actually affects it in two ways. First, by reducing the thickness of the rubber, you reduce how much the rubber flexes. This means less heat is generated. Secondly, the reduced thickness of the rubber also allows it to dissipate the heat faster. So by shaving rubber off the tire, the tire runs cooler. 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 R1's, that optimum temperature range is from 90 to 150 deg. F. for the 226 (autocross) series, and from 160 to 270 deg. F. for the 230 series. If your tires are running hotter than these ranges, you need to shave your tires. If your operating

temperatures are below or within these ranges, then you don't need to shave your tires.

Next question is how much do you need to shave off of the tires? Obviously this will depend on how you plan to use them. Typically for most road race use, we take about 2/32" off. This reduces the tread skid depth from the 6/32" that the Comp T/A R1 is molded to, down to 4/32". On more abusive tracks, and in hot weather, we may take as much as 4/32" off, leaving only 2/32". 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:

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 temps is more 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 much matter. Both types have their good points and bad points. The key here is to understand your pyrometers strengths and weaknesses, and be consistent in how you use it.

One good thing about infrared pyrometers is that they are quick to use. If you want to bring your car in during a practice session and get a quick look at temps and get the car back out into the session, this is one 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 temps 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 that you use every time you get tire temps. 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 are a little easier to be consistent with. The metal probe penetrates the surface to measure internal temperatures of the tread. Internal temperatures do not change as quickly as surface temps, 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 temps instead 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 temps 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 temp may be 10, 20, 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. What ever method you decide on, be consistent. And train all of the people who take temps 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 do 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 on the tire you take the readings 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 the inboard shoulder regions. We do not take the shoulder temps 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 temps in is roughly between those two indicator holes. With practice, you will get to know where the hot area is on your tires. That is where you want to measure the outer shoulder temp. On the inboard side, just probe the very center of any tread block in the rib closest to the edge of
the tire.

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 tread 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.

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 simplicities sake, lets 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 would 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 would 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 tires 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 vehicles body roll. Conversely, if your inboard shoulder temps are hottest, then you may be running too much negative camber. 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 226 (autocross only) series tire, we like to see temperatures no higher than 130 to 150 degrees F. For the 230 (road race & autocross) series, we like to see temperatures between 160 and about 270 degrees F. This tire will perform well even below that temperature range. But the compound really starts working well when it's above 160. The 230 will generate more grip in that range than the 226 will at its optimum temp. Softer doesn't always mean grippier. If you are seeing temps above 270 degrees F., you are probably overheating your tires. When I see temps in the 290 range, I start to worry about the tires "Going Off", or even blistering if they aren't shaved. And when I see temps up in the 300's, I 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.

Dealing With Pressures:

By now, you can read your pyrometer, and can take your tire temps. 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 radial tires as well. Let's say that you are sending your driver out for the first time on R1's. They have never driven on them before. What pressures do you send them out on? Well, a good place to start would be to talk to someone with some experience with the tires. Either Team T/A or another driver, (who you can believe <g>), who runs a car similar to yours on BFG's can give you a recommended starting point. 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 is doing, bring them in and take a look at the tire temps.

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 like a pig coming out of that last corner before coming into the pits, then you have to know about that so that you can consider that in interpreting your temps.

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. And 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 temps. If the car is loose, the rear tire temps may be high. Try and relate what the driver says is happening, to what you see in the tire temps. 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 that they can use their preferred driving style. 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 R1's work a little different, (okay, backwards), from most radials due to the asymmetric construction. Generally, 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, lower the front, or raise the rear pressures. If the car is loose, 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 55 psi. That is a very wide range to play in. Generally, most people will end end up with front pressures in the low to mid 30's. Rear pressures will depend on the vehicle. Remember, these pressures are for competition use only. If you are going to drive on the

street, adjust your pressures to the vehicle manufacturers 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 the R1's, 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 , (lose grip), with 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 atoms. To kind of 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, these 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 we are concerned with here. 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, more heat generated, and more tread wear. You can see that it can become a self perpetuating kind of thing. How fast this all occurs determines how fast the tires "Go Off".

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. Because 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 in 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 relax for an absolute minimum of 24 hrs after that initial "break in". I will 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 though, 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. I've heard people talk about Brand-X, or Brand-Y, or Brand-Z tires 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 that 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 help improve the consistency and longevity of your R1's. 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. But, assuming you don't do any other permanent damage to them, give them the minimum of 24 hrs. to relax afterwards and they should be fine for later use.

I hope that this information helps you in understanding how to get the most out of your Comp T/A R1's. If you have any questions, Team T/A is available by phone or at many events. Feel free to ask. If they don't have the answer for you, they will try everything possible to get it for you. That is what being a part of a team is all about. Have fun out there.

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Old 03-06-2009, 03:40 PM   #2
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