Mickey Thompson ET Street Radial Pro Tires - How It Works

Want to Hook Up Hard at the Track? Ken Warner of Mickey Thompson Tells How

Stephen Kim Aug 5, 2014 0 Comment(s)
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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.

Mickey Thompson E Street Radial Tires Wheelie 2/9

Revolutionary Radials

Mickey 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.”

Mickey Thompson E Street Radial Tires Pro Drag 3/9

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 Tuning

Drag 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 Options

Mickey 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.

Mickey Thompson Manual Compound Construction 4/9

“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

Inspection

Always 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.”

Mickey Thompson E Street Radial Tires 5/9

Tubes

Some 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.”

Deflation

Everyone’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.”

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