Mark Houlahan
Brand Manager, Mustang Monthly
June 24, 2011

Finally, Nitto Tires added that the sidewall and overall construction of the bias-ply slick is less rigid than a drag radial tire. Therefore, upon launch at a dragstrip, the footprint left by a bias-ply slick can be bigger than its drag radial equivalent. Also, the bias-ply slick being less rigid can be more "forgiving" if a driver spins the tires. However, if the track condition is optimal and well groomed, the rigidity of a drag radial can result in faster performance than the bias-ply slick.

A drag radial is a DOT-approved tire with actual tread that many outlaw street car racers use, while the radial slick looks just like a regular slick, the only difference is the internal construction

Drag Tires 101

We asked our tire manufacturers what they get the most questions about concerning drag tires and they were all fairly unanimous that it came down to tire pressure questions, type of tire for the car's horsepower or race class, and vehicle weight and its effects on tires. We also asked our tire companies if mixing construction types front-to-back is hazardous or not, as we've seen (and I'm sure you have too) Mustangs with bias-ply slicks on the back and their street radials up front.

Mickey Thompson's Kundrick agreed with our statement and told us that a trailered drag car is not a major issue because the car is only going straight down the dragstrip, but Mickey Thompson discourages the idea of mixing tire compounds for street use. "Yes, it is most definitely hazardous," Gullett from Coker added. Whether you choose to run bias-ply tires or radials, make sure the other end of the car has matching tires. The difference in construction makes the tires react differently, even when on the same car, so it can sometimes create a dangerous situation at speed.

Tire pressure questions are certainly at the top of the list, if not the number one question. As racers move forward and adapt to new technology, the radial-constructed drag tires take a different tire pressure than their old-school bias-ply tires they've used in the past.

Kundrick told us that in a racing scenario, when moving from a bias to a radial, the radial will almost always require more pressure to maximize its performance. "In general, when in discussion regarding tire pressure, we would ask two questions that we combine to yield a 'power-to-weight' ratio. Along that train of thought, the heavier the car, the higher the pressure. Also, when asked what air pressure is recommended, we would be likely to suggest an 'operating range' versus a specific number. The range being variable based on the ambient temperature, track conditions, and corrected altitude."

Gullett explains, "Tire pressure depends greatly on the weight of the vehicle. The heavier the vehicle, the more pressure it generally needs to perform at its potential. For vehicles over 3,200 pounds (most average street/strip cars), we suggest starting at 10 psi and adding pressure slowly until you reach the breaking point, in terms of traction. Running the most pressure possible reduces rolling resistance, thus making for quicker times. Radial slicks generally require 3-4 more psi than a bias-ply slick.

"For drag radial tires, such as our M&H Racemaster, you should never run below 24 psi on the street, and keep pressures above 15 psi at the track. The normal range of pressures, depending on the vehicle's weight and suspension setup is 15-20 psi." Weight is the biggest factor. Track conditions also affect how that car hooks, so consider that when you're tuning the air pressure or suspension. Horsepower, obviously, has an effect on overall traction, but the baseline tire pressures are geared mainly toward vehicle weight.

Nitto Tires stated that for on-road pressure, always refer to the factory recommended setting for the vehicle. This ensures a safe and reliable ride on the street. On the track, Nitto recommends starting at 20 psi and decrease/adjust from there. Monitor the tires and wheels to see if slippage occurs. If so, that means that the pressure can be too low. However, there are too many variables to consider having a standard one-size-fits all solution, Nitto tells us. Factors such as temperature, horsepower, weight, chassis, track condition, and more are all contributing factors to finding the optimal tire pressure settings.

"Bottom line is to consider that the tire has the potential of generating a certain level of 'spring rate.' The higher you can run the pressure, the faster the car will go. Go too high and the tire will slip; too low and the tire will change shape absorbing power and potentially deforming the contact patch creating more rolling resistance," Kundrick tells us.

Time For New Shoes

So, you're ready to hit the track with your classic Mustang or Ford and your baby needs a new set of track shoes. Don't worry, we've got you covered. Now that you've read all about bias and radial compounds and how they work, we had our tire companies show us what they offer in both bias and radial slicks, and DOT tires for your classic Ford. We know you want to hit the 'strip and see what your Mustang or Ford can do, and now you'll know what tire will work best for your ride and where to start with tire pressures to optimize your combination's traction. Lower e.t.'s here we come!

By design, the radial slicks are more stable, but you should never have any stability issues out of a bias-ply slick if the pressures are right and you have the appropriate suspension setup. The only reason people have issues with wobble or sway on the top end is related to tire pressure, or mixing bias-ply and radial tires on the same vehicle.

the footprint left by a bias-ply slick can be bigger than its drag radial equivalent

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