Drag Tire Tech Tips With Mickey Thompson
Other than the fun to be had, taking your hot street car to the dragstrip on its daily driver tires is nearly a useless exercise. Even high performance street tires must still be engineered to meet marketing parameters designed around long life, ride quality, noise, and fuel mileage. They are a total compromise between those factors and ultimate traction. Combine that compromise with a light car and a significant amount of power, and you’ll just be spinning the tires for at least the first 300 feet of the track, probably more, making a low e.t. impossible and testing data virtually useless.
Now, if you want to cut a decent 60-foot time on the dragstrip, you must have either dedicated slicks or, at the very minimum, a good set of drag radials. But just mounting a set of slicks to your car will not take you to the Incremental Timeslip Promised Land; there’s a lot to know about drag tires in order to get the optimum performance and life out of them. Where do you set the pressure? How do I know they’re still good? What are those screws doing in the fast guys’ wheels?
Talking with Carl Robinson on how to go fast on a drag tire
Mickey Thompson has been leading that tire category for longer than we can remember, especially when it comes to the street/strip or heads-up drag racing like you see in the NMCA, NMRA, PSCA, ADRL, and more, so we went to them (specifically, M/T’s Carl Robinson) to answer our Top Ten questions concerning drag slicks and radials. Here’s what they had to say.
There is really no break-in procedure. Using the tire in its intended application will “break” a tire in.
Carl Robinson: “There is really no break-in procedure. Using the tire in its intended application will “break” a tire in. Tire life can be negatively affected if you do an excessive burnout with the thought of “breaking the tire in,” though some professional classes pre-run the tires in order to shed weight and stabilize tire circumference.”
DZ: What is the best way to determine what pressure to run, or where does M/T feel the sweet spot is?
Robinson: “We like to refer to the pressure as an “operating range” versus a specific number. The way to determine the best operating range for your car is by testing at the track. There is typically a suggested range based on a couple of telltale parameters, such as weight and horsepower. Talk to others that have comparable set-ups. After establishing a base pressure you must start to document key parameters. Note what racetrack you’re at, the ambient temperature, relative cloud cover, and track temp. These key factors will establish the trends required to maximize your performance with tire pressure.”
DZ: Should I run tubes in my slicks, or not?
Robinson: “Over the last few years, racing tire tubes have taken on a new role. Originally developed before the integration of an inner liner to capture the compressed air within the tire, we now find significant benefits from installing tubes in tires ranging from 26.0/10-15 to the 33.0/10.5-16W tires used in the Pro Extreme series of the ADRL. The benefit comes from the support the tube provides. The tube keeps the tire round, and round is fast! However, there are always exceptions to the rule. Not all will see the same gains in performance. Cars running heads-up with high horsepower-to-weight ratio numbers benefit more than the dependable bracket-style race cars. Bracket cars can benefit from the consistency of the tubes’ air retention throughout a long day of racing. For some, the benefits outweigh the erosion of performance due to the additional weight of the tube.”
It was understood that more wheel screws equals less wrap-up in the tire and wheel package. This reduced wrap decreases 60-foot times and driver reaction times.
Robinson: “The wheel screws need to be understood as having a relationship to both safety and performance. Related to safety, if the choice is made to use tubes inside tires mounted on conventional wheels, you must use a minimum of 12 screws per side to secure the tire from rotating on the rim. This is required on all bias-ply racing tires to prevent immediate air release from tube failure. M/T does not recommend the use of wheel screws with radial tires.”
“Performance benefits have been discovered through the use of additional wheel screws. Take an opportunity to notice a small visual detail on your rear tire package. Many of us have looked over pictures of our car and critique the position and shape of the tire. Did you notice that the wrinkles in the sidewall line up with your wheel screws? So from this it was understood that more wheel screws equals less wrap-up in the tire and wheel package. This reduced wrap decreases 60-foot times and driver reaction times.”
DZ: And how about the same question regarding bead locks?
Robinson: “Bead lock wheels provide benefits in safety and performance. From a rules point of view, a standard of 200 mph speed (in the quarter mile) has been set as the guideline for bead lock use. The concern is that the tire, through centrifugal force, is trying to come off the bead seat. Wheels screws do not retain the tire on the bead seat—they stop rotation. The clamping system of the bead lock secures the tire and prevents rotation at the same time.
“Bead locks also have a direct effect on the way the tire is held, meaning it affects the tire much in the same way as wheel screws. Tire wrap-up is minimized. There is also a change in the potential growth-rate of the tire when clamped in a bead lock.”
DZ: Slicks don’t have wear indicators, so how do you know when they’re used up?
In many cases, tires will have surpassed their (high performance) service life well before the tread is worn down.
DZ: What is the recommended way to store tires, and how long of a shelf life do they have? In other words, if I have a set of slicks sitting in the garage for 4 years, un-mounted, are they still good?
Robinson: “Generally speaking, we prefer to store tires in a cool and dry environment mounted on wheels with 3 to 5 psi, off the ground and away from any UV A or B light. The reason we would want them mounted with air in them is to prevent the tire from shrinking in size. The physical parameters are avoided to prevent the deterioration of the designed properties of materials and chemicals in the tire. Four year old tires? Are they good? Well, if they were purchased with a specific goal in mind, like “we planned on running 10.5 inch tires,” then no. The tires are smaller now and you will not get them to grow back to the original size. Will they go down the track? Maybe…”
DZ: Tire growth at the top end obviously affects the overall gear ratio, and needs to be considered when setting the car up. But for reference, how much does a 28×10.5 ET Drag slick grow at 150 mph? 200 mph?
Robinson: “That’s a tough question, one that has as many variables as those that ask. The best way to determine the answer is to run the car and reverse-engineer the numbers. That compensates for the converter or clutch slip percentages and a bunch of other factors. One very sharp racer once told me if you put 30 psi in the tire, that will reflect your max tire growth. It worked for him!”
One very sharp racer once told me if you put 30 psi in the tire, that will reflect your max tire growth.
Robinson: “Despite all the rumors surrounding radial tire growth, we need to clear the facts on this. Radial tires do not grow. They may change shape due to centrifugal force but the components inside the carcass of a radial tire do not allow for any growth. They are circumferentially-wound steel plies. The plies or belts are not opposed at an angle as in a bias tire.”
DZ: What’s the highest mileage you’ve ever heard reported from a Drag Radial? Not fuel mileage, but actual number of miles driven on the tire?
Robinson: “We have heard from 3,000 to 5,000 miles driven as the high average in mileage. I like to reserve the question until the consumer has “used-up” a set or two due to his fascination with extraordinary traction!”