Drives: 13' 1LE
Join Date: Apr
Im in the same boat, same cam LOL! Im like 80% set on 26" tires. I think its the best for car under hp, but it depends on gearing. Since our gearing sucks, 26inch is the way to go, I think. Too bad they do not make the 27 tire anymore
What size you want to run on what rim?
13' 1LE, TSP /Tick / PR, UDP, SW LT 2'' & HFC, stock NPP & H pipe, VR-DRX CAI, air scoop, Goertz1 manifold, mm BBK, 26" Toyo DRs, Forgestars R17x10 & F18x8, rear seat delete, remote Pat G tune Autocal, limiter, Spec Mini Twin. 91oct.
@, ft / @, ft DA+ RWHP SAE
FED TFS cc & LLSR [email protected] N/A HP still climbing.
In the last issue, we wrote about how to stuff larger tires inside your ride. While that article focused on filling up existing wheel wells with larger rubber, it also brought this question to the table:
How big is too big when it comes to tires?
Decades ago, in a conversation with the late Bill Jenkins, the Grump succinctly stated that many racers “over-gear” their cars and many racers use too much tire. Jenkins went on to say that you should only use as much tire as necessary. Otherwise, you’re carrying excess baggage (the weight of the tire carcass) around for nothing.
So was the Grump right when it comes to tires? Absolutely. Keeping in mind we’re moving from little tires — maybe a P or P drag radial to something much larger like a 14X32 slick — well share our reasoning.
One common assumption is that the wider the tire you put on the car, the better the traction. We spoke to pro chassis builder Jerry Bickel about the topic, and we can assure you this is not necessarily the case. Bickel notes that tires grip the pavement by way of “the force of friction”.
“The force of friction is equal to the coefficient of friction times the force perpendicular, Bickel said. Different surfaces have different amounts of friction. For example, smooth glass is very slippery while rubber grips very well. The coefficient of friction for metal on metal may be but rubber on concrete may be or higher.
Fair enough, but what is perpendicular force? Its the weight applied straight down to an object. If you increase the perpendicular force, the force of friction will increase proportionately. If the race car is working properly, you’ll transfer a big chunk of weight to the rear tires. For the moment, however, let’s concentrate on a specific weight. The Bickel drawing below shows a ounce brick. The perpendicular force of the brick is 40 ounces, no matter which side of the brick you place against the table.
For the sake of comparison, let’s assume the brick has a coefficient of friction when it is “dragged” across the table. Since the brick is constructed of a consistent material, the coefficient of friction is the same, no matter how the brick is rotated and no matter which side is exposed to the table.
When the coefficient of friction is multiplied by the perpendicular force, you come up with the total force of friction: X 40 = 16 ounces
As you can see, there’s nothing in the formula that takes surface area into consideration. The reason is if you place the brick on the table with any side down, then the force of friction will still remain the same. Bickel points out that if you pull a brick across a table with an ounce pull scale, no matter what side of the brick you place the table, the pull in ounces will remain the same.
Given the above, it stands to reason that narrow tires should have exactly the same traction as wide tires. That may be true, but much of it depends upon some important characteristics of the rubber compound found in the slick.
The coefficient of friction for rubber varies with the compound. Soft rubber has a low durometer reading and has a high coefficient of friction. Hard rubber has a high durometer reading and most often has a lower coefficient of friction. Because of this, it would seem logical that a very soft tire compound would provide your car with the most grip, but the reality is you may actually lose traction if the tire is too soft. This is because of the inability of softer compounds to resist high shearing forces.
Likely everyone reading this is familiar with the black tracks that are laid down by drag race slicks on the racing surface. Bickel points out that “burning rubber” doesn’t accurately describe what is happening during a run. Unless the tires spin violently, the tire tread will not become hot enough to burn. More often, the rubber tracks that remain on the pavement are a result of the shearing effect of the tire tread against the pavement. Thats why (where legal), cars perform a burnout and carefully reverse in order to line up in the tire tracks.
If the rubber shears off the tread too easily, the tires spin. The car doesnt hook and of course, it can’t make a clean pass. The truth is, slicks with a hard compound will not shear as easily as soft ones, but they will have lower coefficient of friction. To increase the shear resistance of a soft rubber compound, a large tire to pavement contract area (footprint) is required. There are two ways to increase tire footprint: Lower the tire air pressure or choose a bigger tire.
It’s also no secret that drag slicks are designed to operate with low ( PSI) operating pressure. Lower tire pressures such as this will flatten the contact area, which in turn, increases the size of the tire footprint. The larger footprint resists shearing forces, which in turn allows the car to hook and of course, have a lower foot time.
Tires that are wider or have a larger diameter create a bigger footprint, but many people tend to forget the second part. Taller tires will in fact place more tire area (front to back) on the racing surface.
When you’re choosing slicks, it’s important to balance the tire size with the compound softness. Bickel offers a good rule of thumb to follow when picking tire widths and compounds:
“Bigger tires do not automatically provide better grip — if you change to a larger tire, you must also select a softer compound to assure better traction”.
Bickel also points out that you should never select a bigger tire just because it looks like it will work better. Large tires have more inertia and require more power to accelerate. That’s why Jenkins told us years ago that we should only use as large a tire as necessary in order to get the job done.
When you’re doing your drag slick research, it’s a good idea to double-check the race rules for specific tire size limitations. You might be surprised to see that tire dimensions can be restricted. It’s also a good plan to snoop around and check out what other folks with similar combinations are running (at least those in your class). You should also contact the tire manufacture and get their input into the sizing and compounds recommended for your particular application. Most of the factory reps are really dialed in to what is currently the hot setup and will know exactly what you need.
The tire manufacturers have a wheel rim width recommendation range for each size drag slick. They usually allow for a inch tolerance.
“Rim width is related to drag slick inflation pressure, Bickel said. The wider the rim, the more tire pressure you can run while maintaining the same footprint area. A higher inflation pressure can help prevent tire shake. Drag slick circumference (rollout) is also affected by rim width. Wider rims relax the tire and result in a smaller rollout measurement. Narrow rims pinch the tire beads together and create a greater rollout measurement.
According to Bickel, a drag slick works best when the circumference remains relatively round and the tread is flat (not arched or dished) across the tread. Violent chassis setup can cause the tire sidewalls to compress too far and fold up the center of the tread. This results in poor traction and slower ETs.
As you can see, picking a tire isn’t exactly based upon bigger is better. There are tons of variables, and in many cases, a car might actually perform better with a smaller tire.
Author: Wayne Scraba Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4, tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.
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How to Select a Tire - Tire Talkin'
Which Tire Is Best For You? We Offer Some Clues
Like cams, carbs, and chassis settings, selecting the right "shoes" for your machine can make the difference between winning and being an also-ran. More than once we've heard the phrase, "Tires win races." Okay, fine. But which tire is best? That is an age-old racing question. Maybe we can help.
We talked to representatives from Firestone, BFGoodyear Hoosier, Mickey Thompson, and Goodrich to find out how they help match up their customers' racing machines with the best tire for their combination. Our goal is to lay out their advice in a format that will at least get you into the ballpark when selecting the rubber for your ride, focusing on helping you select the right size, compound, and type of tire for your vehicle.
Although it doesn't sound easy at first, once you set about selection in a methodical manner, the right one for you is not hard to find. The goal is to select a tire that allows your car to hook the same every time, preferably without tire spin, leading to consistent foot times on every pass.
First, you need to decide how you intend to use the tires. If you drive your car to the track, are you going to change to performance tires, or do you intend to drive to and from the track on them? Using the same tires to drive home on definitely limits your choices. BFGoodrich makes a number of sizes of their Comp T/A Drag Radial, a tire that is an honest-to-goodness street tire, although the tread will wear out relatively quickly. However, the same things that make them a good street tire-sidewall stiffness, for example-limit their effectiveness on the track for cars with any kind of serious torque.
BFGoodrich doesn't make "slick" slicks, but the company does make a wide variety of D.O.T.-type racing tires that hook up just as good as a regular slick. Its line of Comp T/A Drag Radials comes in so many sizes-we counted that the D.O.T. racer won't have a problem choosing which "feet" to wear on the drag strip.
Downloading info from BFGoodrich's web site, www.eurotire.com/goodrich, we found tires that ranged from an overall diameter of inches and a tread width of inches to its biggest, a incher that had a tread width of 12 inches. The tires are especially attractive to the guy who wants to put a pair of good-hooking tires on his car without having to go through the hassle of installing tire screws in the rims, because according to BFGoodrich's literature, none are needed. Sizes range from P/60R14 to P/35R Each tire in Goodrich's racing catalog is "R," for radial, rated.
Are there any tire restrictions in the class you will enter? Obviously, a drag slick is unwelcome in Trophy or DOT tire class. Feron Lubbers of Hoosier pointed out that those racers might want to consider a Quick Time Pro tire. They come with a medium soft D05 compound, identical construction to their slicks, they have a couple of grooves in them, and they qualify as a DOT tire.
M/T ET Street tires are basically the same as an M/T ET Drag slick also, but are DOT-legal. Classes with a inch tire limit make choices a little easier. Just pick your favorite brand.
Sometimes the width number doesn't always correspond with tread width, like tires with a "W" suffix on the part number. Several years ago, fellow racer Chuck Conaway gave us some well-worn 6-inch Firestone "W" slicks that actually measured 8 inches wide. To deal with that, some organizations like Hot Rod, PHR, NMCA, and NSCA supply a go/no-go gauge. If the tire's too wide, you don't pass tech. Simple.
Another limiting factor may be the wheels you have. The tire reps said to keep the tread width within plus or minus 1 inch of the rim width, but a look at Goodyear's Web page shows they actually allow a little bit more tolerance. The Hoosier catalog actually recommended an inch wheel for their inch slicks, but also said the inch wheel was fine.
How big are your wheelwells? Sometimes your car is the limitation. Novas are notorious for not allowing anything wider than 9 inches, although I have seen 28 x 10 Goodyears under the stock wheelwells of one. And I've even seen leaf springs trimmed to clear the tire, a practice that doesn't sound too safe, but appeared to function.
What is your rearend gear ratio? Mickey Thompson representative Jerry Francis said they recommend most cars with a three-series gear ratio like a use a inch-tall tire. If your machine uses a four-series gear, go up to 28 inches. Past that, you need to do some talking with the representative, but definitely go with a taller diameter, which gives a bigger footprint.
Francis also noted that any tire can be overpowered. "If you put a inch slick under a heavy car with a gear and a big nitrous kit, you will see tire spin," he says. Although some of the inch tire guys hit the eight-second range in the quarter mile, you can safely bet money they spin just a bit. Francis noted that in the smaller tires, generally up to inches tall, compound selection is not even an issue. He said there is usually only one choice, a medium-soft compound.
Goodyear calls their medium-soft a D3, Firestone says theirs is the F9 series, Hoosier's is D05, and Mickey Thompson L8. These compounds work well with many combinations, our tire men say. Obviously, when one gets into faster cars, compound selection becomes more crucial. Firestone representative and Super Stock racer Mike Crutchfield says that one of their rules of thumb for selecting compounds is, if your race car is under 2, pounds, use a soft compound, and anything over should use a medium compound.
Firestone's main compounds are F9, a medium-soft compound, and F30, a soft compound. Hoosier makes a D05 (medium-soft), and a D07 (soft). Goodyear's most popular compounds are D3 (medium), and D5 (soft). Mickey Thompson's medium compound is L8. All the manufacturers also offer other compounds designed for specific applications. Goodyear rep Eric Rang pointed out that Goodyear offers nine different compounds, each having a specific application, in this order, from softest to hardest: D-1, D-2, D, D-9, D-6, D-5, D-7, D-3 and D If your car can run either soft or medium compound tires, ask yourself which is more important to you: Better hook and shorter life, or longer life with possibly a little less hook?
If medium compound is all your setup needs, then save your money and buy medium compound tires. Crutchfield also pointed out that one manufacturer's medium-soft is not exactly the same as another manufacturer's medium-soft compound. The only way to find out what is best for your combination is to try them out. We learned the hard way that soft compound tires don't work on our 3,pound Camaro. Several years ago, we bought some Hoosier 28 x 10 x 15 slicks, and had problems with the tread ripping apart. After talking to Hoosier rep Feron Lubbers, I found out why. The compound was their C07 compound, which was simply too soft for our heavy second combination. The tire now comes with D05 compound, their medium-soft compound.
Stiff sidewalls are another item to consider. And sometimes, those "race track" deals from a fellow acquaintance aren't so good after all. Our friend, Brian O'Hern, who races an alcohol Footbrake car, found a great deal on a set of 14 x 32 Mickeys that had a grand total of two passes on them. What he didn't know at the time was that they were stiff sidewall tires. Stiff sidewall tires are made for cars where a quick reaction time is necessary, such as in the Pro Tree "Super" classes: Super Gas, Super Comp, Super Street, Quick Rod, Super Rod, and Hot Rod. The tire works for them because it doesn't wad up as much. They also work better on heavy, high-horsepower cars.
The downside for O'Hern was the tires didn't hook as consistently with his second car as well as his old wrinkle walls. However, another racing friend, Laura Brunson, tried a pair of soft sidewall 14 x 32s on her second, 3,pound Trans Am. It didn't take long before they realized that what worked fine on a 2,pound machine was not so good on theirs. The car wagged its tail on the top end of the track, and when they put enough air in (13 pounds) to make it stable, the outer edges never touched the ground. They are much happier now with a set of stiff sidewall Mickeys.
Crutchfield also said that you might not want to over-tire a car if you are looking to make it go as fast as possible. For example, a hp Stocker shouldn't need a tire more than 10 inches wide. Anything more actually slows or even bogs the car down, due to increased rolling resistance. But he did give us another quick rule of thumb, also echoed by Lubbers of Hoosier: If you want to decrease your rpm through the traps by rpm, just get a tire with one more inch of circumference-the distance around the outside of the tread. If your tire is already 91 inches around, typical of a inch-tall tire, a inch circumference tire, like a 30 incher, will lower rpms through the traps by about rpm.
Lubbers also noted that for bracket racing, you want the biggest tire possible. The term "wider is better" applies here. Drag Racing School professor Frank Hawley said it well here a couple of years ago: "Stuff the biggest, stupidest tire you can fit under the fender wells." What you give up in speed can be gained back in consistency.
So what about those used slicks you see for sale behind someone's trailer? Sometimes they are a bargain. For example, the owner might have bought the wrong tires. However, before you plunk down that hard-earned cash, ask yourself, "Do those tires really only have 15 passes on them? Is the compound still any good?" All reps said the heat from hard burnouts decreases the life of the compound. The tires can have check holes left, but the compound won't be as good as it should be.
Ask, "Were they stored properly?" Crutchfield said the shelf life of a slick is a couple of years if stored properly, away from excess heat or temperature changes of more than 20 to 30 degrees and away from any electric motors. Know what you are getting when you buy a used set of Comp or Super Stock tires. Do you really want a high-growth tire that's going to wear out quickly and is not as stable going down the track?
Super Stock tires are lightweight, low tread and high growth, designed for Super Stock racing, and work well in their arena. Many such tires are engineered for specific applications, but may not be the hot ticket for your combination. Be careful here. Also, unless you have a really low-horsepower car, round-track tires don't work well on straightline cars. We had a pair given to us, and they wouldn't hook up our thensecond Camaro for anything. Although the compound was not really hard (it sure wasn't as soft as a drag slick), the sidewalls are stiffened up for cornering, which hurts straightline performance.
Front tires are a bit easier to figure out. One can find "front runners" from as short as 23 inches up to 29 inches tall. One of the first questions to ask is, "Do they fit under the wheelwells, and can I turn them all the way from hard left to hard right without hitting components?"
Footbrake racers tend to go with the taller tires, which increase rollout-the distance traveled before exiting the staging beams-and slows down the car reaction time, which in some cases prevents red-lighting. They can also use different height front tires to help "tune" their car's reaction time. The basic rule is, a shorter tire equals quicker react, a taller tire equals slower react. Unfortunately, the only way to find out is to experiment.
Pro Tree racers prefer the shorter tires, which have less rollout and give quicker reaction times. Electronics-equipped cars racing off of a full Tree usually use the shorter tire, but with a delay box, front tire selection just isn't that critical. Lubbers noted that some Pro Stock racers are now going with a slightly taller tire, a incher. Although this does slow the reaction a little, it also decreases their elapsed time just a bit, which is worth a lot in that class.
Still, it is not easy to get exactly the right tire for your combination on the first try, but the reps we talked to say they can help get you into the ballpark. Also, all the manufacturers have knowledgeable people who can steer you in the right direction. If they sell you the right tire the first time, chances are you'll be back for more when it's replacement time.
But often it's up to you to determine exactly which tire is best. All said that you may have to experiment some to get the optimum tire for your combination. If you decide to call one of the tire manufacturers for help, make it easier for you and them by having your car information available. Knowing the car's weight, wheel sizes, current tire size, gear ratio, class you will be running in, and body style before you pick up the phone greatly increases your chances of getting a tire you will be happy with the first time around.
Other valuable sources of information are available on the Internet. Check out www.goodyear.com and look under "race tires" for information on their entire line of racing tires. Hoosier offers a similar deal at www.hwwe.com, under the tire specs button. BFGoodrich Drag Radial information can be found at www.eurotire.com/goodrich.
Even when you get the right tire for your combination, you still have to have a good chassis setup and follow proper burnout procedures, but that's another story.
Determining What's What
How can you determine your actual tire size and compound? For racing tire sizes, try this formula: nominal diameter times tread width times bead diameter. Example: A x x 15 is a inch tall, inch-wide slick that goes on a inch diameter wheel. Measurements are from an inflated tire under unloaded conditions.
DOT tires are similar, except sidewall-to-sidewall measurement is given instead of the tread width. Example: An inch tread width Mickey Thompson ET Street tire is designated as 26 x - Go figure. It has something to do with DOT regulations. Most resellers list the tread width right along with the tire size to avoid confusion.
Some fronts are listed just like the rears, like x - However, if you see a x 15, don't panic. It's just a inch-tall tire, a 29inch-tall tire is called x 15, and a inch tall tire is called x
So what do all those letters and numbers on slicks mean? For Mickeys, an "S" after the part number means it's a stiff sidewall. ST means stick shift compound. The Summit catalog notes the Hoosier stiff sidewall tire with an asterisk (*). In Goodyear's catalog or on their Web page, 1 means stiff sidewall, 2 means high growth, and 3 means Super Stock automatic. Firestone does not offer a stiff sidewall tire per se anymore, but they do have a special compound, F14, for stick shift cars in the Stock classes. Mike Crutchfield noted that where allowed, manual gearbox racers are building in slippage to the clutches, so that many combinations don't "know" whether they are being hit with a transbrake or a clutch.
A "W" after the size designation for Hoosier, Firestone, and Mickey Thompson means the tread is wider than the nominal number given in the tire size. In addition, the Summit catalog noted that an "A" after the part number indicates 2 inches added width.
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Weve all seen a videos of cars throwing the crank and rods on the ground at the starting line, numerous Honda videos that end in disaster. Recently, we found this little gem a Whipple-powered Chevrolet Joe Gibbs Edition Silverado attempting to make it down the track on a set of inch wheels wrapped in thinly stretched rubber bands.
Small Chevy trucks are becoming more and more present at local drag strips around the country. Its not uncommon to see a multitude of full-size trucks used as tow vehicles around the track, with some racers deciding to occasionally make a pass down the 1/4-mile stretch.
This Silverado is a prime example of how hairy a situation can get if youre rocking a set of wagon wheels at the track instead of thick side-walled drag radials or slicks. Theres a reason that race tires have some sidewall to them. Remember, spinning isnt winning.
After laying down a rubber patch that could compete with a Boeing during an airport landing, the truck gets sideways and targets the Corvette in the other lane. Crossing the centerline before the foot cone, and undoubtably making the Corvette owner rethink the decision to bring his car to the track, the driver is able to settle the truck down before this drag race gets out of hand.
After making a quick wheel and tire change to a more suitable set of drag racing tires, a second pass reviles the potential of this supercharged LS3. As the Christmas tree drops, the Silverado manages to get the jump, which provides an interesting outcome. Cracking out an impressive at 91 mph, it narrowly edges out the same red Corvette for the win. And in the process, it perfectly illustrates the differences, on back-to-back runs, of tires designed for
Drop some comments in the box below and give us your opinion on this supercharged, Silverado on 26s.
Slicks 26 inch drag
† High Growth Tire
ACCEPTABLE PRACTICE (EXCEPT ET STREET R, ET STREET R BIAS AND ET STREET S/S) FOR RIM WIDTH IS TREAD WIDTH PLUS OR MINUS ONE INCH.
WARNING: DO NOT USE ON DYNO.
IMPORTANT: ALL BIAS DRAG DRIVE TIRES MUST BE MATCHED TO BE WITHIN 1/2 INCH ROLL OUT.
NEVER USE RIM SCREWS ON RADIAL DRAG TIRES!
MICKEY THOMPSON COMPOUND SELECTION CHART
ST Suggested for manual transmissions (medium compound)
W Extra tread width (please note actual tread and section width on spec sheet)
S Stiff sidewall construction aids in quicker reaction time due to less tire distortion. Also good in high horsepower applications and for heavy cars (Over 3, lbs)
R Radial Construction
L2 For Jr. Dragsters
L6 Good for High Horsepower - Boosted Applications
L7 For Motorcycles
L8 Good Compound for General Use
M5 Good Compound for General Use
R1 Special Compound for ET Drag Radial
R2 Special Compound for ET Street S/S, ET Street R & ET Street Radial Pro
X5 Cooler running version of M5
X8 Cooler running version of L8
To identify the compound of your current M/T® ET Drag tires look at the serial number on the sidewall of the tire.
EXAMPLE: CY1J M5 FJ
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