The racing wheel is one of the most diverse components on a race car, varying greatly in appearance between each manufacturer. Each design may offer a unique presentation for the race car, but strength and durability need to outweigh the “looks” when it comes to the rolling stock on many of today’s fastest drag cars.
Classes ranging from NHRA Top Fuel to Top Sportsman require an SFI Foundation wheel certification. With the diverse population of drag classes out there, from nostalgia nitro to 10-inch tire outlaw classes, the requirements for certified wheels can fluctuate depending on your rulebook.
Like other various components ranging from seat belts to complete chassis, wheels built for the highest horsepower demands must pass a rigorous testing process to be certified. These tests are required for both front and rear wheels and have differing procedures for each.
“The SFI Foundation utilizes different outside laboratories that perform each testing procedure,” says Mike Hurst, SFI Foundation Technical Manager. “These wheel testing labs use the same machines used to test production wheels built for auto manufacturers. These labs are experts at the wheel testing process.”
I hate to say it, but pretty much every standard, certification, and testing criteria for use in motorsports safety program the SFI Foundation has developed were written with blood. – Mike Hurst, SFI Foundation
“These standards have been developed from experience,” Hurst continues. “We don’t just make up programs or specs on our own. It is the sanctioning bodies who come to us when they see a problem. It can be racing wheel failures, superchargers flying off of engines, or seat belts breaking. All of the certification processes we have developed quite simply help to separate the good from the bad for safety’s sake.”
The Certification Process
Wheel manufacturers submit wheels for testing that fall under what can be described as the most significant stress denominator. In other words, a specific wheel model is tested that has the smallest bolt pattern diameter, the largest width, and the greatest offset that will be offered for that part number. Beadlock wheel designs are not factored into the testing process. They do, however, have specific design requirements with the Top Fuel/Funny Car SFI 15.4 specifications.
A drag racing drive wheel is exposed to three different tests: dynamic cornering fatigue, dynamic radial fatigue, and a deflection test. The dynamic cornering fatigue test places the wheel in a test machine that clamps the wheel’s outer lip in a static position while an oscillating force is applied to the lug area. In the case of the SFI Foundation 15.1 wheel test, a load of 1,700 lb-ft is exercised for a total of 30,000 cycles.
The dynamic radial fatigue test subjects the test wheel to various forces that a wheel would experience with a test tire mounted. The testing machinery spins the tire and wheel against a rotating surface while loads are placed against the assembly. In the case of an SFI specified test, the wheel is subjected to a radial load of 2,000-pounds at 400,000 cycles.
The deflection test basically applies a bending force to the wheel between the plane of the bolt circle plate and the outer rim. In the case of 15.1 certifications, the force is gradually increased to a peak of 6,000 lb-ft. The amount of force and deflection derives an elastic limit for the wheel.
Two of the newest manufacturers to the game are RC Components and Race Star Industries. RC Components in recent seasons launched its RC Comp Series of drag race wheels, later adding a 16-inch version of its rear drive wheels for higher-horsepower applications. Race Star, likewise, stepped up to the big leagues a year ago with the unveiling of its forged Race Star Pro, the company’s first professional drag race wheel. Both manufacturers, thusly, have fresh knowledge of the SFI certification process.
“No wheel design is perfect right out of the box. That is why we believe in the physical testing process,” says L.B. Davis, owner of Race Star Industries. “We are in the process of testing right now on a new 16- x 18-inch wheel for Pro Modified applications. As an example, the wheel passes on a 5- on 5-inch and a 5- on 5-1/2-inch design, but you have to pass the SFI test with the worst-case scenario.”
The impact test shown here on an OEM-style wheel is similar to the SFI Foundation standards test applied to the SFI Spec 15.2 on drag race front wheels. Video courtesy Independent Test Services, Canton Michigan.
The same Pro Mod wheel design with a 5-on 4-3/4-inch bolt pattern has different static and strength properties combined with the same barrel configuration.
“The overall wheel design may require change when you simply tighten up that bolt pattern,” Davis continues. “The dynamic radial fatigue test is extremely effective when it comes to a big offset wheel.”
Following each of these individual tests, inspectors physically look for any fractures or metallurgic failures in the wheels or any loosening of the lug nuts. The testing process is repeated every 24-months to maintain certification.
“I think what is fantastic about the SFI certification process is that it gives every wheel manufacturer an even starting point to build its wheel designs,” comments Davis. “On Race Star rear wheels, by independently testing our spread wheel designs, we have a handle on what material and designs are required between, say, a 10- and 15-inch wide wheel, plus different offsets.”
Davis notes that the DOT testing option is a much more stringent testing procedure.
“We know that a race car doesn’t go down the track straight all the time,” he says. “But we want to know just what our wheels can take beyond the SFI pass or fail testing.”
The SFI parameters for drag racing front wheels include a different group of tests than the rears. SFI 15.2 certification requires an impact test along with the aforementioned dynamic radial fatigue test. With a test tire mounted on the wheel, the impact test consists of a “striker” machine with a Society of Automotive Engineering (SAE) specified striker that impacts the outer rim flange.
The mass of the striker is approximately 27kg. The only variable placed by the SFI foundation on the wheel test cites that the striker is to be dropped from 1.80-feet at ± .10-feet. Once the wheel takes that impact, it is inspected for specific damage, and is determined if the wheel/tire assembly will still hold air.
Overall, there are four different certification specs initiated for various racing applications. There are three drive wheel specs where different levels of testing parameters are required to match the level of horsepower/stress for different classes. The fourth is a front-wheel certification for various classes.
• Drag race drive wheels – SFI Spec 15.1
• Drag race front wheels – SFI Spec 15.2
• High horsepower drag race drive wheels – SFI Spec 15.3
• Top Fuel and Funny Car drag race drive beadlock wheels – SFI Spec 15.4
It is not straightforward to simply classify what SFI specification is applied to a current class. Those specifications are designated by the racing sanction and can vary. Racers need to research each organization they compete with to determine their specific rules.
Testing In Addition To The SFI Certification Process
“We use a wheel testing lab offering many forms of testing procedures for wheels. SFI certification is one of them,” explains Chris Cross, Vice President of Sales and Marketing at RC Components. “We also utilize an outside service that can digitally test our concept design before the wheel is actually made.”
Extracurricular strength testing can be performed on the computer as well as with test machinery.
“When we create a new design, it is then programmed as a three-dimensional (3D) computer model,” Cross says. “Once these 3D models are ready, they are sent for structural testing via computer software to see if they meet SFI standards. If the 3D drawing meets SFI standards, the design is then sent to be constructed into an actual wheel. The final step is to send the physical wheel to a testing lab for SFI validation testing.”
The SFI foundation gathers representatives from many factions of the overall drag racing community to develop and maintain the SFI specifications.
“Individuals from the drag racing sanctioning bodies, professionals from the manufacturers, race teams, and various safety experts are all pulled together,” Hurst says. “We meet and discuss problems, what kind of loads are we experiencing, and what kind of margin of safety do we want to incorporate into the testing requirements.”
Race Star credits a strong engineering effort led by Mike Kent, despite being a small company.
“The two of us go back and forth with the engineering strength and aesthetics,” Davis says. “When we finalize a new wheel design, it is the strength, or “bones” of the wheel, that means the most to us.”
The philosophy at Race Star is to go beyond passing the SFI validation tests.
“We do not just engineer to pass the SFI certification,” he says. “We believe in the testing process enough that we send some of our wheel lines, especially the front wheels, to the testing labs for a Department of Transportation (DOT) J2530 test. That test is fundamentally a cornering test. We feel pretty confident that our front wheels are going to take anything you throw at them.”
Certification of wheels is nothing new to the automotive industry in general. Aluminum and steel wheels that roll out on new cars have been put through rigorous testing for decades. The SFI foundation developed its test specifications for drag racing wheels based around the rigorous OEM testing.
Various wheel test facilities are located nationwide.
“Wheels are tested all the time for original equipment manufacturers,” Hurst says. “So, having them test drag race wheels to our load and duration parameters is nothing unusual for them.”
The machinery that tests OEM and racing wheels is as sophisticated as the race cars that use them. Several corporations have developed and offer wheel testing. Most of these overall tests for OEM applications fall under varied guidelines related to the SAE and DOT.
Chris Cross chimes in on the RC Components wheel design in relationship to strength.
“Our rear race wheels offer both rigidity and strength due to the interlocking lug design in our wheel centers,” he says. “The design attaches from the front side of the barrel and interlocks into lugs machined into both the barrel and center carrier. The radial load (torque) is absorbed by these interlocking lugs, taking the stress off the bolts attaching the center to the outer barrel.”
We addressed the 200-pound gorilla in the room with Hurst and the SFI Foundation. Racers often criticize the SFI and the racing sanction process concerning various racing hardware as a “money machine generating revenue for the SFI, racing sanctions, and manufacturers alike.” Hurst quickly refuted those claims.
“A current seat belt sticker costs 20-cents,” he says. “A wheel is approximately in the two-dollar range. Certainly, we’re a small, nonprofit company, and not a money generating thing.”
This eccentric mass machine demonstrates the dynamic cornering fatigue test required by The SFI Foundation. Video courtesy Independent Test Services, Canton Michigan.
He continues, “We realize that all the safety in the world doesn’t work if the racer can’t afford it. So, the actual conformance to the spec of a racing component is a fairly efficient program. One of the biggest expenses in the process is that the machine-testing can be expensive. But do we really want to skip that?”
Continuing Wheel Certification Criteria
Once a wheel design is approved and offered to the racing public, the process of ensuring those wheels continue to be safe is also addressed. On the side of newly manufactured wheels, checks and balances continue to monitor an approved wheel as to not vary from its approved material and dimensions.
The SFI Foundation literature describes the continued monitoring of wheels as a periodic revalidation. Manufacturers are required to resubmit each wheel model for testing once every 24 months following the date of the initial design.
On another level, the SFI Foundation retains the option to conduct random audit reviews. The foundation can purchase any given wheel though a commercial source and test for compliance with the specification. This stipulation can obviously take place if anyone questions a possible difference between wheels tested and wheels installed on race cars.
Compliance for certification to SFI specs has rules dictated by the sanctions, as well. In the continuing certification subject, those 15.4 certification level wheels used by Top Fuel and nitro Funny Car must be re-inspected every 24 months from the initial inspection.
Certification Track Record
Essentially, the SFI Foundation has zero input in the actual design or construction of a racing wheel. The SFI has established these series of initial tests and recertification programs to ensure a racer is going to use a wheel that has been tested to generally withstand the abuses the specific race car is going to dish out.
“Fundamentally, the companies design their own wheels,” Hurst says. “We don’t interfere with that. Wheels that have passed the series of tests required in the SFI Foundation specs have had a good track record. In my personal experience, and I’ve been here 7-1/2 years — wheels certified in the testing laboratory have a successful track record over time.”