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It's All About Clamping the Tire
Story and photos by John DiBartolomeo , www.dragracingaction.com

Call it the effect of evolution, but drag racers always want to go faster. However, traveling the quarter-mile in a quicker amount of time than previously done sometimes falls into the scientific category of “cause and effect.” By accomplishing your goal, there are effects involved that can crop up with an ugly head. One of them has been in the tire department of today's NHRA/POWERade Pro Stock cars.

The bead lock wheel utilizes a ring that clamps the bead of the tire firmly in place. Its use came about from the circle track arena where high cornering speeds will force the tire off of the bead of the wheel.

Aficionados of our sport are quite familiar with the screws that are drilled through the edge of a slick's wheels to hold the tire in place. These were originally installed to combat the wheel from spinning inside the tire. When the tire becomes stuck to the pavement, the power of the engine wants to keep something spinning. When that happens, invariably the wheel will spin inside of the tire. When a tire tube is used, the tube's valve usually gets torn off. When a tube isn't used, the tire spins and thereby upsets the tire balance, causing a rather rough ride. The fix? Thread in a set of sheet metal screws through the bead area of the wheel, which allows the sharp end of the screw to protrude into the tire bead. This holds the tire in place. But alas, more power equals different problems.

As power levels go up, merely having several screws through the bead isn't enough. Case in point: Today's Top Fuel and Funny Cars have all been using bead-lock wheels for years. Originally designed for use in circle track configurations, these wheels utilize a ring that's bolted to the bead area of the wheel to clamp the tire firmly in place. As power and cornering speeds increased in that arena, the bead of the tire would have a tendency to fall right off the wheel. Obviously that's never a good thing, henceforth, bead-lock wheels.

This isn't just an add-on option to a wheel It requires a complete different design. The bead of the new wheel contains threaded inserts that the screws thread into.

Carl Robinson of Weld Wheels says, “There is a limit where the use of a bead-lock wheel is almost mandatory. We've surmised that whenever horsepower numbers approach the 1300-1400 range, the tires start to do funny things.”

Lester Garbicz of Mickey Thompson Tires said, “The first thing that happens is for the tire to try to dismount off the wheel. Using screws through the wheel to hold it just isn't enough. As speeds increase, the forces exerted on the tire also go up. We've found that speed seems to be the factor here; with somewhere around 200 miles per hour being the number we feel that a bead lock wheel is required.”

One of the first problems associated with horsepower, and eventually speeds, is the phenomenon known as tire shake. Here's where the tire distorts so much that it actually will go into a rattling effect, shaking everything connected to it from the wheel to the driver's butt. The next problem becomes the speed itself. As it increases, centrifugal force wants to throw the tire right off of the wheel. When this happens, that possible 32-inch tall tire grows in diameter considerably. In order for the tire to be able to do that, something has to give, and what does is the actual footprint of the tire. It becomes narrower, causing less of the tire to touch the ground. When this happens, a car that might need, let's say, a 14-inch wide tire, now only has 10-12-inches on the ground, which can cause handling problems. And along with this tread narrowing, comes sidewall, or bead narrowing.

In order for the tire to grow, the actual shape of it must change, and with that, the bead of the tire wants to be pulled inward, off of the bead of the wheel, as Garbicz alluded to. As can be easily understood, this is definitely not a good thing, and will usually result in an unwanted transformation of your vehicle into a pile of junk. The bead-lock wheel cures that ill. One needs only to view the steps Pro Stock racers have gone to in the past in an effort to utilize a standard wheel. As many as 48 screws were put through the side of the wheel to help stabilize it. And still it wasn't enough.



Proper mounting of a race tire onto a wheel requires much the same equipment it takes to perform the same job with a street tire. However, larger machines are necessary to mount the wider slicks. While this job can be done by hand, it requires quite a bit of effort to do it that way.

“The IHRA Pro Stock cars have been using the bead lock wheels for quite some time now,” Garbicz added. “They found that as they ran over that 200-mph number, they were having tire problems. Their bigger engines make quite a bit more power than the 500-cubic inch NHRA cars, so they noticed and cured the problem years earlier.”

IHRA has mandated the use of bead lock wheels on their Pro Stock cars for the 2004 season, but as Mike Baker of IHRA reports, “Our racers have been using the bead lock wheel for the last seven or so years all on their own. They've recognized the benefit of using them.”

For 2004, NHRA joined the fray with a ruling mandating the use of bead-lock wheels on their Pro Stock vehicles as well. With that, comes the use of a new size tire, necessitated because of the 16-inch bead-lock wheel, rather than the 15-inch wheel that has been used before.

Robinson said, “This wheel will hold the shape of the tire better, which will result in a better handling car, and it's exactly what the racers are now telling us.”

Because of the clamping action of the wheel, the tire sidewall actually will be stiffer. This has resulted in several of the tire companies re-designing their tires. Because of the way the tire bead is clamped, there is a natural tendency of it to stiffen the sidewall somewhat.

Bead lock wheels can very easily be mounted by hand; in fact that's the preferred method.

Garbicz says, “There are other wheel companies that have bead lock wheels that grab the bead of the tire in a different place. This changes how the sidewall of the tire reacts.”

Cause and effect will always rear its ugly head though. One such problem with the use of the new wheels is the extra weight involved. The ring and bolts associated with a bead lock wheel adds seven pounds to the wheel assembly. Robinson says, “We've now come out with a new Pro Stock version with titanium screws and only 18 bolts per side rather than 24. This has cut that weight down to 4-1/2 pounds.”

Because this weight is part of the rotating assembly of the wheel, it takes more power to turn it. In addition, the newer tire is slightly bigger in diameter and circumference, which causes changes in the overall gearing of the car. All of this has meant changes in several areas of the crew chief's tune-up. All the average spectator will probably notice is the larger outer wheel buckets necessary to cover these new tires. Some of the teams utilizing older cars have had to send them

Once the tire is in place on the wheel and the tire bead is in place on the lip of the wheel, the retaining ring is placed on the wheel and screwed tight. The dimension between the ring and the wheel is an exact distance that allows the tire to be clamped tight, yet not squished.

Robinson says, “What we've really done now is to just increase the margin of safety. With a wheel that'll hold the tire in shape better, most teams are reporting an increase in better handling. And to compensate for the weight problems, tire companies have designed a lighter tire, along with our lighter wheel.

“A Top Fuel or Funny Car needs the 24-bolts to adequately hold the tire, but the Pro Stock cars can get away with fewer bolts. These wheels can also now be used by Pro Mod teams that have always used the 24-bolt system.”

http://www.mickeythompsontires.com/Whether or not this new ruling change immediately shows up on the score boards, is a fact that remains to be seen. One thing is certain though. It will result in a better handling car for the drivers, which no doubt, will eventually lead to faster speeds and quicker elapsed times.

Mickey Thompson Tire Company

43455 Business Park

Temecula , CA 92590

(909) 587-0101 x151

www.mickeythompsontires.com

Weld Wheels

6600 Stadium Drive Dept DRA

Kansas City , MO 64129

816-922-6500

www.weldracing.com

 

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