Am I Using the Right Tire?

[Dietzsch_Racing25]

No matter what type of racing you do, tires play a big role in the overall handling of the car. Tires act as part of the suspension and absorb many of the irregularities that your typical dirt track has to offer. They are the only means to transfer the power from the engine to the track and are relied on to keep the car traveling in the direction it is pointed. In addition, they offer the easiest way to tune the handling of the car via pressure and circumference changes.

I run the Street Stock class at both Perris Auto Speedway and Victorville Auto Raceway. The tire rules for both tracks restrict us to 8-inch or narrower DOT approved passenger car tires mounted on 8” wide wheels. “Soaking” (softening) or grooving the tires is not allowed. In my opinion, these simple but restrictive rules are what help make the Street Stock class as cost-conscious and competitive as it is. The tires used in this class are relatively inexpensive (compared to racing tires), last a long time, and have limited traction.

I had been using the Kelly Charger tire since I started racing at Perris Speedway a few years ago, and it had served me well. At the beginning of the 2009 season, I received the sad news that the tire I'd been using religiously, the Charger, had been discontinued by Kelly. The time had come for me to pick a new tire. I asked around to find out what everyone else was using, and I got a lot of different answers. Everyone had an opinion, but most were very subjective.

Terry Warp, owner of Rubidoux Tire (where I buy my “race” tires), suggested an alternate tire; one that I had never heard of. It was called the Mastercraft Avenger. Terry had raced at Perris in the past and had won a main event or two in his day, so I figured I’d give his suggestion a try. I used the tire last year and was happy with it, however I decided that this off season I would attempt to find a more objective way to determine which tire I would use for the 2010 season. I needed to arm myself with information in order to do that.


The Tire Sidewall

I figured I would start with the markings on the tire’s sidewall. I already knew what most of the nomenclature meant from buying street tires for my daily driver. What I didn’t know was whether or not this information could help me pick a good tire for the dirt. There is a lot of writing on the sidewall and a lot of fine print as well. Let’s go through all of these markings, starting with the obvious ones.

Kelly: The manufacturer of the tire.
Charger: The model of the tire.


The nomenclature above contains the tire's size as well as speed and load rating.

P245/60R15 101S P: Identifies the tire type. The P (if shown) stands for PMetric and identifies the tire as a passenger tire. An LT identifies the tire as a light truck tire. As the picture above illustrates, the P is not always shown.

P245/60R15 101S 245: Identifies the section width of the tire in millimeters (25.4 mm = 1 inch.). This is the measurement of the tire from sidewall to sidewall. The actual dimension varies depending on the width of the rim the tire is mounted on. This is not a measurement of tread width. The tread width will always be smaller than the section width but can also vary from manufacturer to manufacturer.

P245/60R15 101S 60: The Aspect Ratio of the tire. It is expressed as a percentage of the section width. This number compares the tire’s section height with the tire's section width. An aspect ratio of 60 means that the tire's section height is 60% of the tire's section width.

P245/60R15 101S R: Indicates the construction used within the tire’s casing. R stands for radial construction. B means belted bias and D stands for diagonal bias construction.

P245/60R15 101S 15: The last dimension listed in the tire size is the diameter of the wheel measured in inches.

P245/60R15 101S 101: The Load Index indicates how much weight the tire can support when properly inflated. Load Index numbers range from 70 - 110 for passenger tires with each numeric value corresponding to a certain carrying capacity. A higher Load Index indicates a higher load capacity. A Load Index of 101 equates to a load capacity of 1819 lb. This number is not shown on all tires, but the load rating (in kg and lb) is printed on the sidewall of the tire in small print near the bead.

P245/60R15 101S S: The Speed Rating is represented by letters ranging from A to Z. Each letter corresponds to a maximum speed a tire can sustain (e.g. S is equivalent to a max speed of 112 mph for one hour). Previously, the speed rating was shown in between the Aspect Ratio and tire construction (e.g. 245/60SR15) but is now supposed to be shown only after the load index. The manufacturer is not required to show the speed rating on the tire.


The Z speed rating indicates the tire is capable at speeds in excess of 149 mph, but it does not indicate by how much. W and Y ratings were added to better describe the limits of a tire.

The "M+S" or "M/S" indicates that the tire meets the RMA (Rubber Manufacturers Association) specifications for use in “severe snow conditions”. It says that the tire has some mud and snow capability, and most radial tires have this marking. It does not mean that the tire is a snow tire.

The DOT serial number can be easy to overlook but the date code contained in these markings can be quite useful.

The DOT Serial Number

DOT PJOP 3NLR 2005 DOT: This symbol certifies the tire manufacturer’s compliance with U.S. Department of Transportation (DOT) tire safety standards. DOT approval is required for all tires used on the street.

DOT PJOP 3NLR 2005 : The next two blocks of letter/numbers specify the Manufacturer’s Plant Identification Code, the Tire Size Code, and the Tire Type Code.

DOT PJOP 3NLR 2005 2005: The last block of digits is the date code. It signifies the week and year the manufacturer made the tire. The last two digits signify the year of manufacture (05 indicates 2005). The first two digits signify the week of manufacture (20 means the 20th week of the year). Based on the Date Code (2005), the tire above was manufactured in the 4th week of May in 2005.


The Treadwear, Traction, and Temperature Grades can be located in various places on a tire. Kelly located them right above their name.

Tread Wear, Traction, and Temperature
The DOT National Highway Traffic Safety Administration's (NHTSA) Uniform Tire Quality Grade (UTQG) Standards were originally designed to provide consumers with useful information about a tire’s tread wear, wet traction, and temperature handling capabilities. The testing is performed by the tire manufacturer or an independent testing company (hired by the manufacturer), and the manufacturer assigns the grades that will be advertised on the side of the tire based on the test results.

Treadwear Grades
UTQG Treadwear Grades are based on actual road use. The tire being tested is run on a vehicle alongside other vehicles running other “test” tires and standardized “course monitoring tires”. The convoy runs 400 mile test loops for 7,200 miles. The wear of the test tire and the course monitoring tire are measured periodically as well as at the end of the test. The tire manufacturer then assigns a Treadwear Grade to the test tire based on the observed wear compared to that of the course monitoring tire. A grade of 100 would indicate that the test tire tread would last as long as the course monitoring tire, a grade of 400 would indicate the tread would last four times as long, and a grade of 600 would indicate six times as long.

The Treadwear Grade is a somewhat subjective number. The tire manufacturer must extrapolate the theoretical tread life of both their test tire and the course monitoring tire from the 7,200 miles of data (a street tire’s life can be three to ten times longer than the test). This data can be processed using different methods which may result in varying grades. In addition, the course monitoring tire is updated periodically and detailed information about the tire itself is not readily available (at least I couldn’t find any information on it) on UTQG’s website. Since the Treadwear Grades are assigned by the manufacturers using differing methods, comparing Treadwear Grades within a manufacturer may give you a good indication of which tire has longer tread life. However, attempting to compare grades between different manufacturers is likely to be much less useful.

Traction Grades
UTQG Traction Grades are based on a tire's straight line coefficient of friction as the tire skids across specified wet test surfaces. The Traction Grade is determined by installing test tires on an axle of a skid trailer. The skid trailer is pulled behind a truck at a constant 40 mph over wet asphalt and concrete. Its brakes are then locked, and the axle sensors measure the tire's coefficient of friction (braking g forces) as it slides.


The Traction Grade indicates the kinetic (sliding) coefficient of friction for a tire on wet surfaces.

Temperature (Resistance) Grades
The UTQG Temperature Grade indicates the extent to which heat is generated/dissipated by a tire. If the tire is unable to dissipate heat effectively or if the tire is damaged because of heat buildup, its ability to run at high speeds is reduced. This grade is established by measuring a loaded tire's ability to operate at high speeds without failure by running a test tire against a large diameter high-speed laboratory test wheel.


Every tire sold in the United States must be capable of earning a "C" rating which indicates the ability to withstand 85 mph speeds.

Other Markings

Load Rating - The load rating of the tire is printed near its bead. The load rating corresponds exactly with the load rating that is sometimes displayed near the tire size (which, I assume is why it is optional).

Pressure Rating - The pressure rating is shown just below or next to the load rating. It is a maximum pressure rating, not a recommended pressure rating (don’t laugh; I have seen it done). Most of the tires I’ve looked at had a max pressure rating of 44 psig, but it varies by tire manufacturer and model. I have a tire that has a pressure rating of 35 psig, which is something to consider if you are trying to stretch a tire by airing it up.

Tire Construction - The tire construction is also shown in small print on the side of the tire. For the tires I am considering, it typically reads something like: Tread - 2 ply polyester + 2 ply steel, Sidewall - 2 ply polyester. All the tires I looked at had the same construction with one exception. That particular tire had 2 additional plies of nylon under the tread.

Of course there is the CYA warning on the side of the tire threatening severe damage and bodily injury if the tire is under-inflated, over-inflated, or mounted on the wrong size wheel.

How is All This Information Helpful?

Like I said, there is a lot of information on the sidewall of a tire. Some of the information is actually quite useful, some not so much. Let’s start with the tire size marking. Track rules require a passenger tire, so I need to look for a “P” and avoid an “LT”. Also, using the tire size markings I can approximate the circumference and tread width of a tire.


Using these formulas will give you good estimates of circumference and tread width in inches. Just plug in the numbers directly from the side of the tire. Actual dimensions will vary from manufacturer to manufacturer and from tire to tire.

A DOT approved tire is required by both tracks. The DOT symbol should appear on every tire that you buy at a tire store, but it doesn’t hurt to confirm it.

The Manufacturer’s Plant Identification Code, Tire Size Code, and Tire Type Code are probably important to the manufacturer for tracking purposes, but I don’t have much use for them.

On the other hand, the Date Code can be very useful. Tires don’t last forever. Rubber can degrade over time when exposed to heat and sunlight. I have several tires that will celebrate their fifth birthday early in 2010. They have been relegated to spares but do periodically see some track time. In addition to baldness (it's hell getting old), I know to pay close attention to other visible signs of aging, like cracking on the side wall and around the tread blocks. Even if there is still tread left the time may come to put these tires out to pasture. The Date Code can be especially helpful when buying used tires. When stored properly, a tire (and rubber in general) has a very long shelf life. Used tires have not been stored properly. They have been sitting on hot pavement and baking in the sun for thousands of miles. If a tire is too old I may decide not to buy it even if the tread looks okay.

I think the Treadwear Grade might be useful. Here is my theory (and it is JUST a theory): If I am lucky, a typical track tire may get driven 500 or 600 miles over the course of several seasons if the tire is not damaged first. Therefore, I am not overly concerned about tread life. What I am concerned about is the grip of the tire on the track. A tire with a high Treadwear Grade indicates that the tread should wear slowly and therefore last longer. According to my theory (and again, it is JUST a theory), a tire with a long lasting tread would require harder (higher durometer) rubber. Conversely, a tire with a low Treadwear Grade could be constructed of softer tackier rubber (or perhaps just cheaper lower quality rubber). To me, a lower Treadwear Grade indicates that I may get more grip from the tire.

The Traction Grade seems more straight forward. No theories required here. A better rating is given for better traction on wet pavement. Now I know I’m not racing on asphalt or cement, but a higher coefficient of friction is a good thing no matter what surface I am racing on. All the tires I’ve looked at had a Traction Grade of “A”. I doubt that I could find a tire in a size I need with an “AA” rating for a reasonable price, but I will keep my eyes open.


With a maximum speed of around 85 mph at Perris Auto Speedway, the Temperature Grade and Speed Rating don’t factor in when deciding which tire to buy for the track. Photo courtesy of Vane Ledgerwood.

The Temperature Grade is a rating that I probably don’t need to consider when picking my racing tire. Even a “C” rated tire can withstand speeds of 85 mph. I don’t get much past 85 mph at the end of straight on Perris' 1/2 mile dirt oval, and I am lucky to hit 75 mph at Victorville (which is advertised as a 3/8 mile dirt oval). A majority of the tires I have looked at have a Temperature Grade of “B”.

The Speed Rating doesn’t seem to be very helpful either. As I indicated earlier, I am rarely doing 85 mph. An “S” rated tire (a very meager rating) can handle 112 mph. I don’t really need a speed rated tire.

The same goes for the Load Rating. The lowest Load Rating I have noticed is 1764 lb (most are higher). That is more than half the total weight of my car. Even with some load transfer during cornering I am not approaching this limit, and it means that any tire that I might consider is more than capable of handling the loads it will see on the track. I guess it’s nice to have piece of mind though.


The outside tires are working pretty hard entering turn three at Victorville Auto Raceway. Photo courtesy of Vane Ledgerwood.

The Bottom Line

So what is the bottom line? After comparing sidewall information from several tires, Terry at Rubidoux Tire seems to have steered me in the right direction. It seems that the Mastercraft Avenger that he suggested last year is an upgrade over my trusty Kelly Charger. It is no more expensive than the Kelly, and the tread pattern looks a little more aggressive. The Treadwear Grade is lower (400 vs 500), and both the Load and Speed Rating are higher. For now, the Mastercraft Avenger will continue to be my tire of choice, but the search goes on. There may be a better tire out there for my car, and if there is I will find it!

[Nerd49]

Just a couple side notes from "rice burner" research.
For street stock size tires CD's tread width formula works but on the smaller ones the -2 is too much. I've observed tread width to be 80-85% of section width. The 185/60-14 I run on my Corolla are about 6" of tread. 185/ 25.4 X 0.80 = 5.82 , CD's formula 185/25.4 -2 = 5.28 About 1/2" difference. Now for street stock size tires 245/ 25.4 X 0.80 = 7.71 , CD's formula 245/ 25.4 -2 = 7.64. About 1/16" difference. So for you big car guys keep it simple, use CD's formula it's easier to -2 than figure out 80%. But for all us rice burners, use the 80-85%.

To clarify CD's Circumference formula, you need to take the answer you get from (section width X Aspect ratio)/ 404.3 and add it to the answer you get from (3.14 X wheel dia.). Don't just type in (section width x aspect ratio/ 404.3 + 3.14 x wheel dia.) on your calculator. It'll give you very odd result!

If you want an "idiot's, just type it in the calculator and hit equals" version use:
Section width X Aspect ratio / 1270 + wheel diameter X 3.14 = Circumference
Example: 185 X 60 / 1270 + 14 X 3.14 = 71.4

[09 FS ump national champ]

hi just to through this out there my name is bill may i have won 9 track championships in street stock, factory stock,and enduros all on dirt. this year i also won the ump factory stock national and reginal championship . i found a tire in the mid 90s that i run. at first i was getting them form police take offs till they went to 16 in. tires they are goodyear eagle rsa 235 & 225 70 15 they have a treadwear rating of 260 and traction rating of AA they are the best street tire i have found for dirt.some of the guys i race with run copper cobras and the avenger that you talk about and i have seen the tread come out of some of them tires but never any problems with the rsa,s.the good year tires cost a little more but the last a whole season if not popped.if you have a chance to try them im sure you will like them very much.

[Dietzsch_Racing25]

Nerd49, You are absolutely right. The tire width formula is totally inaccurate for smaller tires. I have a set of 185/60R14s at the house and they measure over 6 1/4" wide. The equation seems to be pretty good for section widths between 225 and 275 on 15" wheels (at least the ones at my house). However, I wouldn't use it for the smaller tires (I never considered that sport compact drivers might try to use this).

FS UMP champ, I will be looking for the Eagle RSA. Thanks for the tip!

CD

[Nerd49]

Originally Posted by Dietzsch_Racing25

(I never considered that sport compact drivers might try to use this).

CD

VAR is one of the few tracks that let the Sport Compacts alter the car. Most require 4 same sized tires on same offset wheels. Air pressure and sidewall size are about the only way to alter spring rate legally. Also, there's usually not a choice for the diff gear on a FWD so tire diameter becomes very important for altering final drive. So your article is not a bad read for savy SC drivers.

I'm pretty sure these are the Goodyears UMP champ was talking about.

Tire Specs for Goodyear Eagle RS-A

Looks like lots of edges to the tread with good "mud channels". Tread depth looks about average so the 260 rating most likely means soft compound.
Some tires have a low # on the treadwear because they have a shallow tread depth. (Again, an observation from "rice burner" research.) Drifter/ tuner tires tend to be shallow tread depth and a harder compound but will still have a low treadwear # since they don't have that far to go before they're "worn out" by DOT standards.

[Rowdy Burns]

I will not make the assumption that you already think that you know all there is to know about tires. But several companies - such as Hoosier and American Racer makes tires that says that they are street legal. BARELY!

IN order to use a street tire on the track, you want to find a tire that has a very low number on the sidewall for treadwear , you also want one with a low traction number - but with a lot of tread. One tire that worked well on the street but not so hot in the dirt that I used for years was the Cooper Cobra. Here is the tire I would use - Bridgestone Blizzak WS-50
http://www.tirerack.com/tires/tires....=Blizzak+WS-50

Any track that told me that they were going to save me money by making me run street tires is only kidding themselves. Most dirt tracks in Pennsylvania allows their street stock racers to use new / used Late Model Tires.

Rules just gets in the way of racing.

Take for example the Late Model Tire, you have teams in my area that spends days grooving and siping tires just for one race. The first time they run over something and get a flat - they take the tire off the rim and they throw it on a junk pile. I come over and offer them $20 a tire. I take it home and put a patch in it and maybe a implement tube and I have a $125 Late Model Tire that has already been grooved and Siped and I only have about 1/2 a hour to a hour of work in it.

Unless you have a tire shop that is just giving you passenger car tires, there is no way that you can tell me that you can buy a brand new car tire for $20!

The problem with racecars and racetracks is that everyone is out for themselves. If everyone refused to race unless they changed the rules - the track would be forced to change the rules and allow you to use Late Model Tires. But because there is always that one person that dreams of the night when no one shows up and they can make a couple of laps and win a feature, you will always have some idiot that is willing to race on anything with anything.

Then you have the cry babies who already have this big pile of tires and they don't want the rules to change because they are afraid that if the rules were changed - they wouldn't know what they were doing and they would probably no do so good on the track. Then you have the people who has already found a way to cheat up the tires they are running and so they don't want the rules changed either.

I have seen just about every stupid rule in the book right down to track tires and branded tires. Nothing works when it comes to cheating.

In a bad economy - you are better off to get rid of all of those rules and run whatcha brung.

Until the days comes when the tracks learn to make their money off the front gate and not off the back - you will always have racers who spends $1000 to make $200 on the track.

[Dietzsch_Racing25]

Hola Rowdy,

I certainly do not know everything there is to know about tires. I hope the article doesn't indicate that I think I do.

One driver ran the DOT approved Hoosiers a couple years ago. The improvement over normal street tires was dramatic. The tires were banned after 2 races.

I did a search for the Blizzak tire. Although the price seems reasonable it isn't available in the sizes I need and isn't available in CA (not much need for snow tires here).

I have do disagree with you on the cost effectiveness of race vs street tires. Lets compare apples to apples...

A new street tire costs me around $75-80 compared to a new LM tire costs $125 (I used your description and price, I don't know what they are called and what they cost). So a new street tire is much less expensive than a new LM tire.

A used streed tire cost $20-30 bucks. Lets compare that to your used LM tire. $20 for the tire, $12 for the inner tube, $3 for the patch. So a used street tire is about the same price as a used LM tire.

The real cost saving of street tires is that they essentially don't wear out (You can't say the same thing for LM tires). I have never discarded a street tire (that I used for racing) because it wore out. Unless you damage the tire it will, for all intents and purposes, last forever. So replacing worn out tires is significantly less expensive with street tires.

Since street tires offer signifcantly less traction than LM tires. Corner speeds are much slower with street tires. IMO this means that the benefits of a high dollar/high hp motor are minimized. It also means that I can stick with stock suspension components that I can buy at Kragen or Autozone without the fear of a failure. I can save alot of money there as well.

I am not a big fan of a "track tire" but I am in favor of a simple but restrictive tire rule.

Your last comment about tracks relying on the back gate and racers losing money is true for every track and racer in CA (there may be an exception somewhere). I wish it wasn't.

JMO, CD

[Nerd49]

I have to agree with Curtis, street tires are the cheaper alternative here in So. California. We don't have a big late model following here so "take offs" just aren't available. Last year our track combined the Sport compacts with the Mini stocks so racing tires were now legal for my 240sx. Due to my gear ratio, I figured out I needed P265/60-15 Hoosiers. When I priced them they were $150 delivered here to California. About twice the price of street tires, but in order to compete with the Pintos I really had no choice. I happened to get lucky and "uncle" Ralph had some about 4 year old leftovers that he gave me. So yeah, FREE, was a whole lot cheaper than street tires for now, but at some point I'll have to shell out the bucks for new ones. The "fast" Pintos had to buy new tires during the season. My "backup" SC is still running the same set of street tires I put on it 3 seasons ago. Brand new with tubes, they were $60 a tire so that's only $20/ tire/ season. Pretty cheap in my book.

And, I'll agree with the street tires helping keep the cost of everything down. If you can't hook up the HP there's no incentive to build crazy motors. A nice strong dependable motor will do just fine. If it blows up during the season most guys either have another one or can afford to rebuild. Helps keep the car counts up. I prefer to watch a full field of cars "racing" one another instead of a handful just going fast in a circle.

[Rowdy Burns]

You can buy tires - street tire from Tire Rack - Your performance experts for tires and wheels

Now think about it like this. A big time dirt late model driver might only use his tires one night and then he either throws them away, gives them away or sells them for pennies on the dollar.

The dirt late model tire - is bigger - 11 inches wide and anywhere from 88 to 92 inches - 28.5 - 29 inches tall on average depending on which design and manufacturer.

If you use 10 inch wide wheels, the weigh more then the 8 inch wide wheel and if you add a bead lock, you add even more weight.

On a 1/3 mile to 3/8 mile track - which most dirt tracks average that size - you do not need a lot of motor to get around the track. You need a good handling car and have all your ducks in a row.

Several years ago - someone sent me a story of a old truck driver down in Georgia who raced street stocks. His car was a old Impala and he ran a old junkyard motor. He would get laughed at when he showed up at a track because his car was real rough looking. One track promoter when asked - where should I park, told him that the junkyard was down the road about 3 miles. On that particular night, they told him that his car was too slow to run at their track, but they would let him start the race in the back and as long as he did not hold anyone up = they would allow him to race. There was a big pileup on lap 10 and guess who came through it without a scratch.
He went on to win the race. Same held true one night when he wrecked his dirt track car and showed up with his paved track car. The track owners and all the racers in the pits told him that you can't race a paved track car on dirt. He went on that night to win the race.

It isn't what type of car you own or how many horsepower it has under the hood, it is all in how you drive it. The Late Model tires is not going to make the cars that much faster, but it will make it cheaper for you and the late model drivers to race. They can make a couple of dollars by having a market to sell their used tires and you can save money by buying used tires.

The experience using the late model tires will HELP you when you decide to move up to a higher division such as the Late Model Class. The Street Stock division is only designed to be a support class, someplace where you can learn something before you move up = not someplace to spend your whole life - like some people at some tracks in Pennsylvania where once they win a couple of races = they spend the rest of their life trying to be the king of one local track.