Rotate the Earth: Revisiting Drag Radial Tires Part 2

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In our last issue, we looked at the construction of drag radials (and in general, all radial tires). The layout is very different than that of a bias ply tire and it definitely has an effect upon performance. We pointed out that it gets dicey when a stick shift transmission enters the equation. Here, tuning with drag radials becomes more complicated. Of course, more complicated doesn’t really mean impossible. Some folks can make a drag radial work with a stick, but it does take some tuning dedication.

This time around, we’ll look at other factors that are inherent in drag radials. You might be surprised at what you see. Check the info with help from our friends at M&H Racemaster (PH: 800-299-8000; Website: https://mhracemaster.com):

Something you should consider is tire growth. Typically, a bias ply tire will grow (sometimes significantly) as the speed of the car increases. That means you have to pay attention to gearing (taking growth into account), tire pressure and, last but not least, clearance between the tire and adjacent sheet metal (usually the leading or trailing edges of a fender opening). In a tire such as the M&H Racemaster radial, growth is limited or almost non-existent. This is due to the construction of the tire: With the M&H tire, the tread consists of two plies of polyester, two plies of fiberglass and one ply of nylon. The sidewall is built with two plies of polyester. Here, the respective belts help to limit tire growth.

The last time around, we examined the burnout procedure. Little has changed, but it’s probably a good thing to repeat it. When it comes to their drag radial, M&H offers this advice: "A hard burnout is not necessary. For the first pass of the day, make a light to moderate burnout. After that, a light burnout should suffice. Continue the burnout until the engine starts to pull down. A dry hop after the burnout isn’t recommended. For a stick shift car, perform a light burnout, haze the tires and stage immediately. Generally speaking, drag radials work better with a light burnout rather than a hard burnout. Drag radials tires may require a fairly hard burnout on the first and second pass to break them in."

We also covered the range of drag radial tire pressures the last time around, but here’s a quick rule of thumb: On the track, for tires under 30 inches in diameter, start at 12 PSI (minimum) and work your way up. For tires over 30 inches in diameter, start at 11 PSI and work your way up. On the street, it’s a good idea to keep the tires above 25 PSI.

Also keep in mind that vehicle weight has a definite impact upon tire pressure. The heavier the car is, the more tire PSI you’ll need. Ambient temperature, track conditions and even altitude can have an effect upon tire PSI. And if you’ve noticed, drag radials typically prefer to operate at pressures a bit higher than their bias ply counterparts. Higher PSI tends to reduce rolling resistance (no secret, we’re sure) and in some cases, it can also improve ET. Go too high in pressure, though, and you know you will turn the tire. Run them too low and there’s a chance you can deform the contact patch, which will slow the car down.

Something else to ponder when talking drag radials is storage. Many of you know that bias ply tires don’t really like to sit inflated on the car over long periods of time - for example, over the racing off-season. The result is usually flat spots. Radials don’t have this issue, but there are a few things that will help when it comes to longevity. Where it’s best to air down a bias ply tire and take the load off (as with axle stands), you can leave a radial at operating pressure. Radials will last longer if they are aired down and the load is taken off. Keep the tires out of direct sunlight, protect them from fluorescent lights and isolate them from electric motors; for example, don’t store them near your big air compressor. The reason is that electric motors generate ozone. This, in turn, damages rubber. Don’t bother with tire dressings. Keep the sidewalls clean (soap and water is just fine) and don’t touch the tread surface.
All things considered, a drag radial-equipped car can theoretically run quicker than a bias-equipped counterpart. It offers a more stable platform than its bias-ply cousins. The car will tend to be easier to drive too, particularly on the big end of the track. Those are advantages we can all appreciate. For a closer look, check out the accompanying photos:

The M&H tire is built with a tread consisting of two plies of polyester, two plies of fiberglass and one ply of nylon. The sidewall is constructed with two plies of polyester. With this layout, tire growth is minimized.

Note the direction of rotation when mounting the tires. Like slicks, they’re directional.

When it comes to tire pressure on the street, it’s a good idea to keep the tires above 25 PSI. The track is a different matter: For tires under 30 inches in diameter, start at 12 PSI (minimum) and work up. For tires over 30 inches in diameter, start at 11 PSI and work up.

Radials don’t flat spot when stored, but there are a few things that will help when it comes to longevity. Where it’s best to air down a bias ply tire and take the load off (as with axle stands), you can leave radials at operating pressure. However, they will last longer if they are aired down and the load is taken off.

Keep the tires out of direct sunlight, protect them from fluorescent lights and isolate them from electric motors (e.g. right beside your big air compressor). The reason is, electric motors generate ozone and that damages rubber.