Go small or go home. It sounds weird, but that’s the trend in the plethora of small-tire racing classes popping up all over the place. As horsepower levels continue to climb, sanctioning bodies are making things interesting by continuing to decrease tire size, whether the mandate is a 10.5-inch slick, a 275mm-wide drag radial, or an 8.5-inch slick. Incredibly, no one’s complaining about a lack of hook either, as drag racers are now running 6-second e.t.’s on 275mm radials. That’s in the quarter-mile, folks, not the eighth-mile! Leading the charge is Mickey Thompson Performance, one of the most legendary brands in all of motorsports. The company’s recently launched ET Street Radial Pro tires have decimated the performance barriers once associated with radials. Although blazingly fast radial cars are certainly making a lot of noise, Mickey Thompson’s vast array of bias-ply slicks are still getting the job done at dragstrips around the world. In order to catch up on the latest in tire technology, we had a long chat with Ken Warner of Mickey Thompson, covering topics ranging from air pressure to tire compounds, to burnout procedures, to tubes, to tire temperature, and everything in between.
Revolutionary RadialsMickey Thompson revolutionized drag radial technology over a decade ago with the introduction of its ET Street Radials, giving rise to a new wave of racing classes based on its popular 275mm-wide tire. The company recently improved upon the original to create the ET Street Radial Pro, and the results have been staggering. Many racers report that their cars run faster on the new 275mm ET Street Radial Pros than the older 315mm ET Street Radials. Likewise, racers are now ripping 6-second quarter-mile passes on these hot new radials. You read that right. Racers are now running 6s on radials, and making it look easy. So what improvements have been made that account for such a vast performance improvement “There are several factors at play, one being reduced void, which puts more rubber on the ground,” says Ken. “Most importantly, the construction of the tire has changed. Through extensive R&D and testing, we’ve been able to tune the carcass of the tire to absorb less power during the launch and throughout the run, this allows the tire to maintain its uniformity, stay planted, and roll with less resistance. If the tire absorbed more power it would distort and lose its uniformity.”
Radials or Slicks?With all the hype surrounding drag radials these days, casual enthusiasts might wonder why anyone would want to continue running bias-ply slicks. Even so, traditional bias-ply slicks are still the overwhelming drag tires of choice for the majority of racers for several reasons. “Bias-ply slicks and tires such as the ET Street definitely have a purpose. Cars utilizing manual-shift transmissions, in most cases, still use these types of tires due to their increased footprint and power absorbing carcass,” Ken explains. “Bias-ply tires are far more forgiving during launch, and thanks to their longer footprint, a clutch car can dump the clutch and have the tire spin in a more controlled manner. With a radial tire’s smaller footprint, there’s a greater chance of blowing off the tires. In many cases, bias-ply tires are the choice of many racers that have automatic and manual transmission race cars. They offer the benefit of consistency and reliability. Bias-ply tires can bridge the gap in cases where a race car doesn’t have the suspension to make consistent runs with radials or when simply index racing, where bias-ply tires are very consistent.”
Suspension TuningDrag radial racing classes are exploding in popularity, but since radials require different suspension tuning, many racers are in for a rude awakening when switching from slicks to radials. According to Ken, with radials the engine and suspension must be tuned in tandem to optimize traction. “The suspension must be set up in conjunction with the application of power. Unlike with slicks, you can’t just dump the clutch or leave the line at an enormous rpm,” says Ken. “Instead, the launch and how quickly the power is ramped in throughout the run have to be dialed in along with the suspension. Radials are far less forgiving, so you really have to plant the tire hard and keep it that way.”
Radial OptionsMickey Thompson has been in the drag radial game for so long that its catalog of radial offerings has grown to encompass several different types of usage. The original ET Street Radials are perfect for heads-up racing classes that require DOT-approved tires. As long as road conditions are dry, they can be driven on the street as well. Likewise, the ET Street Radial IIs have the same basic design, but are available in diameters up to 20 inches for late-model vehicles. In contrast, the ET Street Radial Pros are also DOT approved, but not intended for street use. Instead, they are tires purpose-built for 275mm radial classes and they feature a larger footprint and a revised carcass for enhanced grip. Last but not least, Mickey Thompson’s ET Drag Radials are a cross between a radial and a traditional slick, featuring radial construction with a grooveless tread surface. “The ET Drag Radials are outstanding performance tires. Their unique design makes them very popular in Competition Eliminator, Stock, and Super Stock classes,” says Ken.
“Designing tire compounds is tricky. Vehicle weight and transmission type play an important role in compounding, since they require different levels of controlled slip.” –Ken Warner
InspectionAlways looking to stretch a buck, racers sometimes buy used slicks. The caveat is that the condition of used slicks can vary wildly, but fortunately Ken has some helpful tips to assist with the assessment process. “New or used, there are a few things to always look for when inspecting race tires. Of course, rubber depth is a major factor since slicks have numerous 1/8-inch pin indicators instead the normal tread depth indicators found on street tires,” Ken explains. “These can be used to determine how much rubber is left on the carcass. Weather- and stress cracking is another major factor, since obviously you don’t want to use a set of tires that are aged or have so many runs that the carcass is worn to the point where the sidewalls are broken down. Moreover, if the tires have a blue tint to them, they have most likely been overheated. This is a result of too much abuse during a burnout. It’s also a good idea to measure the amount of run-out. An acceptable circumference variance is 1/4 to 1/2 inch. If the tires are used, they cannot be stretch-matched. Lastly, make sure to inspect the beads, especially with slicks that have been used with rim screws or bead locks. This needs to be looked at carefully, since some screws can go all the way through the bead. You won’t know if you have a problem until you mount the tires and air them up.”
TubesSome racers see tubes as an unnecessary accessory. Others swear by them, so where does Mickey Thompson stand on the matter? “The perception amongst most racers is that tubes add weight and expense. This is one of those ‘to each their own’ topics,” says Ken. “Many people use tubes for good reasons, as they add tire elongation or circumference during the run, and this in some cases serves as a much needed gear change to make it out the back of the track. Tubes also, stiffen the tire carcass, adding more sidewall strength and allowing the car to react quicker during launch. Finally, tubes don’t leak air like tubeless bias-ply drag tires do. Nothing is worse than getting to a race after a long haul only to find that the tires are flat.”
DeflationEveryone’s guilty of doing it at some point or another. That is, parking the race car in the garage only to realize that all the air has leaked out of the tires before you had a chance put them way for storage. This puts tremendous stress on the sidewalls, and should be avoided at all costs. “Generally, it’s not the performance of the tire that’s affected but rather the potential damage to the sidewall that’s the main issue. Those sidewalls are very thin, and having the sidewall folded up under a wheel can cut the sidewall and permanently ruin the tire,” says Ken. “To avoid this, put the car on jack stands to keep the tires off the floor to reduce flat-spotting. If the tires need to be stored while off of the car, keep them in a dry location away from hot or cold conditions.”
Managing WearSome racers can get a set of slicks to last an entire season in an 8-second car, while other racers go through multiple sets of tires per season in a 10-second car. According to Ken, this variation in tire wear is primarily attributable to the burnout procedure. “The burnout length has a significant effect on tire wear since most of the tire’s wear occurs in the burnout box,” Ken explains. “Additionally, if the tire is narrow it will generally wear quicker, and heavier cars will wear out tires more rapidly, as well. Some racers prefer to manage their tire life cycle by putting a maximum quantity of runs on them and then selling them in very good condition to other racers that are on tight budget.”
Tire TemperatureWear and tear aside, getting the burnout procedure just right is critical to maximizing hook. That said, how long of a burnout is long enough, and how should burnout length change throughout the day or evening? “This is a very difficult question to answer due to all the different variables that come into play. Basically, an overheated tire resulting from too much burnout is not good,” Ken quips. “The burnout brings heat, which brings out the sticky properties of the compound. However, if it gets too hot it will actually get too oily and slick, causing the unwanted blowing off of the tires. As track temperatures change through the day, the burnout procedure has to change with it. In the morning, when the track temperature is cool, you’ll have to put your foot into the burnout, and when the track temperature reaches the high point of the day, you’ll have to back off. Every car has its own traits, and the drivers have to experience how the car reacts in different conditions, log the info, and make changes as needed.”
RotatingTire rotating isn’t just for minivans and daily drivers. Rotating drag slicks from left to right is an excellent method for maximizing tire longevity. “Rotating the tires from side to side is a great technique for managing the tires. When the tires are run only in one direction, they tend to create a pattern or a feathered texture,” Ken explains. “The smoother the tires are, the better the adhesion to the track will be. Reversing the tire rotation is more predictable if they are done event-to-event rather than round to round. A car’s performance will be far more predictable if the tires are smooth. If they develop a great deal of texture or feathering then it might be a good decision to reverse the direction of rotation.”
Sidewall StiffnessIn addition to offering drag tires in over a dozen different compounds, Mickey Thompson builds tires with stiffer sidewalls as well. They generally work well in heavier vehicles and applications that require quicker reaction times. “By reducing sidewall contortion, stiff sidewall slicks improve reaction time because they wrap up less at launch,” says Ken. “They also provide a more stable run on the track and reduce rolling resistance. Honestly, they are not for everyone. Some cars need to hook the car harder with softer sidewall.”
Drag Tires and DynosMany hot rodders run their cars on chassis dynos with a set of slicks or drag radials bolted up, but according to Mickey Thompson this is a big no-no. “We greatly advise against using racing slicks or radials destined to see track duty on a dyno. Dyno runs generally last much longer than a dragstrip run,” says Ken. “Since a dyno pull involves accelerating the wheels for a sustained period of time, they produce a lot of heat in the tire’s compound. We suggest you use some street car tires or a backup set of take-off tires for dyno testing.”
PSIAlthough air pressure is an important factor in tire and suspension setup, it’s merely used as a way of gauging the total air volume inside a tire. Consequently, an air pressure level that works well in a large tire will be far too low in a smaller tire. “The ideal psi for a tire is going to be different for most applications due to variables such as tire size, car weight, and transmission type,” Ken explains. “Generally, the larger the tire diameter and section width, the lower the pressure will be due to the additional volume inside the tire cavity. We see tire pressure in slicks ranging from 5 psi all the way up to 22 psi. That’s a huge range.
SkinniesThe size of a slick is often determined by a rulebook or the size of the wheeltubs, but things aren’t as clear-cut with skinnies. The size of the front drag tires are often determined by the type of racing they will be used for. “For the most part, the primary factor in determining the size of the front tires is the target ride height, and the type of staging they will be performed,” says Ken. “Taller tires are preferable for a .500 Tree, since it allows for deeper staging and puts you closer to the finish line. Since a shorter tire moves more quickly through a .400 Tree, it nets a much quicker reaction time.”
Street TiresPeople naturally associate Mickey Thompson tires with drag racing, but the company also has a full line of high-performance street tires that stick like stink in the corners. “Mickey Thompson has been making high-performance specialty race tires since 1963. We like to race and we like to win,” says Ken. “It’s only natural for us to take all of that rich heritage and knowledge and take our products to the street. Our new line of Street Comp ultra-high-performance tires are awesome, and we’d put them up against any other tire out there. They are offered in a variety of sizes and can accommodate fitments for many applications, either staggered or the same size all around. They come in W and Y speed ratings, they feature an asymmetric tread design, and they handle excellent in both dry and wet conditions. We also offer our SC-5 wheels for late-model enthusiasts.”
“Extensive testing is required to formulate a tire compound. Different compounds offer different levels of hardness, softness, dryness, and adhesive qualities.” –Ken Warner