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Home > LATEST STORIES > BEHIND BARS, Part II—The Development of the World’s Fastest Small-Tire Racecars, as Told by the People who Developed Them: The 275 and 315 Radial world’s never-ending quest for speed

BEHIND BARS, Part II—The Development of the World’s Fastest Small-Tire Racecars, as Told by the People who Developed Them: The 275 and 315 Radial world’s never-ending quest for speed

The small-tire game, which is mostly comprised of 275 and 315 radial tires these days, has its own set of challenges from a safety and performance standpoint. The quickest 315mm equipped rides go 3.70s on a good day, while the record for a 275-equipped ride is 3.97! Photo by Will McDougle @Krookid Photography

Written By John F. Katz

Photography Courtesy of the Manufacturers/Chassis Builders

As what launched as a truly outlaw, grudge-fueled, run-what-you-brung-to-the-unkempt-eighth-mile kind of racing has become increasingly sanctioned, standardized, professionalized—and costly—how has the 10-wide-tire classes retained their still gritty-seductive appeal?

Credit Mickey Thompson Tires for pushing tire technology in the radial ranks. The ET Street Pro tire debuted over six years ago and with it came a severe reduction in elapsed times.

“It’s the thrill of it,” replied Tim Lyons, owner of Lyons Custom Motorsports in Rossville, Georgia. “You’re on a 315mm radial (ed note—or 275) instead of a big-huge ol’ 34-1/2-inch slick, and you wonder, ‘How fast can I go on this small a tire?’ They don’t run wheelie bars. There are people arguing that they should, for safety, but most of the fans are watching them because they don’t have wheelie bars and they are doing 300-foot wheelies. And the fans can relate. When they see a new Mustang or C7 Corvette roll up, they say, ‘I have one of those in my driveway. I could do this, if I wanted to’. It also doesn’t hurt that the cars are still going faster. The fuel injection has come light-years,” Lyons continued. “Then there’s the converter technology, and the traction control. And track craft has come tremendously from where it used to be. We’re able to apply more power because the track is there for it.”

“Track prep is off the charts,” agreed Wade Hopkins, of Southern Speed Racing in Tupelo, Mississippi, “and 60-foots have really dropped for drag-radial cars. If you don’t have a double-frame-rail, rigid-built chassis, the car will flex and become inconsistent.”

And as a result, chassis have changed considerably in the past decade or even half decade—becoming stronger, safer, and more sophisticated in every way—as we’ll see in the lines that follow.

“Like Building A Ship In A Bottle”

“We now have small-tire cars producing the same 3,000 or 4,000 horsepower as a Pro Mod,” Lyons noted. “So basically what we’re doing now is building a Pro Mod inside a factory body. Ten years ago, or even five years ago, you’d never look inside a 275 car and see a double frame rail. Now pretty much all of these cars, at least all of the class leaders, are built with double frame rails. I heard one guy compare it to building a ship in a bottle, and it is a nightmare, a pain.”

All of the chassis builders we spoke with mentioned the increased number of bars to stiffen the chassis. The track preparation combined with horsepower and torque requires a stiff chassis to prevent twist.

Further complicating matters are the limitations of a stock wheelbase. “On a Mustang it’s 101 inches. So that’s all we’ve got, and we have to make 3,000 or 4,000 horsepower work within it.”

“We’re implementing Pro Stock and Pro Mod design into steel-body cars,” agreed Pat Fasnacht, co-owner of Racecraft in Madison Lake, Minnesota. “In the past, the chassis of, for example, a 275 car had a much more basic cage, with very little tubing added beyond what was required for certification. But with these cars moving from the 5s to the mid-to-low 4s, this could no longer be the norm. Our philosophy is that a chassis can never be too rigid. Rigidity enhances tuning predictability and consistency. All suspension pick-up points must be directly tied to the cage structure with tubing. You will see and feel larger results from smaller suspension adjustments in a well-designed car.”

“We don’t really look at the horsepower as a challenge,” commented David Zimmerman, owner of Team Z Motorsports in Taylor, Michigan. “It’s just a different type of engineering—a different type of thought—when building a car for small-tire racing with high horsepower.”

Southern Speed Racing rebuilt this iconic 1995 SVT Cobra a few times over the years. First, they crafted a radial-spec chassis for John Kolivas who used the car to win three NMRA championships. Then it underwent a double framerail conversion and Daniel Pharris used it to run in the 3s and chase the NMCA Radial Wars class. Currently, Dwanye Barbaree drives it for Russell Stone in VP Racing Fuels Street Outlaw.

“The biggest challenges are the weight of the steel body and the shortage of real estate,” said Fasnacht. “A stock body on a stock wheelbase, and especially the retention of a stock firewall location can make it difficult to obtain a desirable front-to-rear weight percentage. And depending on power-adder combinations and supporting components, weight can add up quickly”—even though, “in a correctly designed chassis, more than 75 pounds of structural sheet metal can be removed from most cars to offset the weight of the added tubing. So up-front planning is crucial, before the start of the build, and we regularly scale the car during the project.”

In contrast, a full-tube car “allows more room to add weight for a better weight distribution,” agreed Dennis McPherson, owner of DMC Racing in Halifax, Massachusetts, where “the stock-body cars are already difficult to get below minimum weight. So sometimes so you don’t always get the luxury of adding weight where you may need it.”

The structural changes have been incremental, said Lyons, as constructors pushed just past the rules, and sanctions adjusted to the reality on the race track.

One of the unique aspects of a racecar running drag radials is the extension in the rear upon launch. Several companies, like AFCO, Menscer Motorsports, Santhuff, and Strange Engineering, have designed rear shocks to complement the rear suspension setups by chassis builders and tuners to help the body separate and help drive the tire down into the surface. It is a radically different approach to setting up a slick-tire chassis combo.

“It used to be you couldn’t move the frame rail, you couldn’t notch the frame rail, you couldn’t do this, you couldn’t do that. Well now chassis builders have just done it, because the chassis needs it. We’re tying the chassis in so much better. If we’re putting this size motor in it to make this much horsepower, then we have to have that much more. And the rule makers have allowed it, because they want car counts. From their standpoint it is a safety feature, because as cars go faster, they need more cage for safety. And the chassis builders were going to do it anyway.”

Brent Hallmark, who heads Technical Sales at Southern Speed Racing, pointed in particular to two recent and terrifying crashes—Lyle Barnett hitting the wall while grappling with an engine fire in 2015, and Stevie “Fast” Jackson’s “flying car accident” (See lead photo) almost exactly one year later. Both drivers survived, but now “we see a lot more people with brand new fire suits—and a lot more people really paying attention to their roll cage, and how it ties into the chassis. The cars are getting so fast that you really have to pay attention to that.”

Cost-wise, added Lyons, “there is no difference” for construction or even maintenance between a steel-body Radial Wars car and a Pro Mod. In fact, “depending on which class you run in which sanction,” a steel-body car might cost you more.

When we talk about the body separating from the tire and having it drive the tire into the pavement, take a look at DeWayne Mills’ Camaro at rest on the starting line. Notice how the car sits low and level. Seconds later into the run, the chassis is leveraging the weight of the body to push the wheel and tire hard into the ground, as you can see from the down track shot where the top of the rear tire is now completely exposed.

The All-Tubing Alternative

And as McPherson pointed out, wherever outlaw events allow full-tube-chassis cars to compete in radial classes, the distinction between a 10-inch-wide car and a Pro Mod blurs considerably.

Racecraft showed off one of its rear-end housings that allow racers a significant amount of adjustments from varying lengths of shocks to suit the type of tire construction, as well as tire height to multiple mounting locations for the control arms or four-link. Also visible is the robust anti-roll bar, as everything is bigger and stronger to handle today’s insane horsepower output.

“At first glance you may not notice an difference at all,” Fasnacht added, “and we can’t say that any difference is 100-percent necessary’’—although “Pro Mods have wheelie bars, so their biggest chassis killer is tire shake. For our cars it’s wheel stands and blow-overs. So we like to build our chassis to survive bumper-dragging and hard landings.”

Even in an NMCA Radial Wars car, noted Hopkins, the only factory sheet metal is in the rear quarter panels. “Because of the mid plate and the double frame rails, we remove about 50 percent of the firewall. And we replace close to 100 percent of the floor pan. The new Camaros come from the factory with a plastic roof, and most Mustang drivers replace their outer roof skin with carbon fiber.” The class also allows “plus-or-minus three inches of wheelbase.”

Power, Planted

But whether built with tubing, sheet metal, or Federation-grade neutronium, the primary goal of a drag race chassis is to deliver power to the pavement. Zimmerman actually rates the legalization of full-tube chassis as the second most significant change in the past decade of small-tire racing. Number one was when the sanctions allowed four-link rear suspensions.

“The biggest changes have been in suspension setup,” agreed McPherson, “made available by multi-hole bracketry; and in shocks. All these cars require very large anti-roll bars and long shocks. Running these cars with no wheelie bars and putting down sub-one-second 60-foot times requires lots of testing and playing with shocks, chassis setup and weight placement.”

Some categories don’t allow wheelie bars, but they are available for use in the upper classes in NMCA and NMRA. Manny Buginga was one of the first to run a set in Street Outlaw, which is a rarity in the radial world. The car still exhibits a lot of extension in the back and the wheelie bars are used further down track rather than at the launch.

“We have to make that car hook at 60 feet, hard,” said Lyons. “But at the same time we don’t have wheelie bars and we have to keep the front end planted. So we’re doing all kinds of crazy stuff with the geometry to drive the front end down as it’s going down the track. And especially on a radial car, you want to keep the center of gravity low. There’s a point that’s too low that you don’t want to go past. But as a radial car leaves the starting line, both the front and the rear need to separate, and the rear shocks extend 3, 3-1/2, maybe 4 inches, to make the car work right. Instead of a slick car, where you’re squatting the chassis and the center of gravity tends to go lower, these cars actually go higher.”

“Cars in these classes cannot be as competitive at the stock ride height,” Fasnacht agreed, but require “a lower stance and the parts to support it. With g-meter readings now commonly in the mid-2s and above, a lower center of gravity becomes a big factor in performance. But equally important are extension or anti-squat capabilities. On a radial car, extension can range from 2-1/2 inches to 5 inches or more, as the car gains ground speed. This leverages the car’s weight as a multiplier to increase traction.”

Radial cars tend to drive into a wheelie rather than popping the front-end up at the launch like Stock or Super Stock style racecar. As the car moves out and the boost and ignition timing increase, the front-end begins to rise well past the 60-foot clocks.

McPherson cited today’s significantly better “understanding of how differently a drag radial works, as opposed to a slick. We set these cars up with huge amounts of separation in the rear suspension. Yet this needs to be controlled separation, which ties into the need for the latest in shock technology. Shocks play a huge part in making these small tire cars work.”

According to Hopkins, however, “There are different theories” regarding the ideal setup for radial tires. “We’ve worked with extension and compression. Typically, when you extend the rear shocks, you hit the tires real hard and apply a lot of traction for the first ten feet.” But somewhere between 100 and 200 feet, that traction begins to fade. “What we have found is that if we stay neutral or even compress just slightly off the starting line, we can apply more power further down the track. And with a lightweight car, we can still go sub-one-second on the 60-foot.”

The choice does depend greatly (but not entirely) on the weight of the car.  “If you look at a small-block turbo that can weigh 2,400-2,500 pounds, vs. a Hemi car that has to weigh 3,000 pounds, that’s a 500-600-pound difference on the same tire.”

More of everything—more bars, thicker and bigger anti-roll bars, double frame-rails, thick mid-plates built into the firewall, and the list goes on and on as chassis builders attempt to squeeze a Pro Modified-style chassis into a stock body with a factory length wheelbase.

In terms of specific hardware, a primary innovation has been a double row of holes on the rear-end mounting brackets. “A longer bracket with tighter adjustment holes allows a finer setting,” Fasnacht explained, “with a wider tuning window to accommodate various ride heights, tire sizes, and extension levels.”

And, of course, added Hopkins, “the shocks are now extremely high-tech. We use primarily multi-stage shocks from Santhuff, and we tune every car off the shocks sensors. We have a shock dyno in-house, but it’s just not enough. You have to look at so many other factors. We look at the air pressure in the tires. We look at what the sidewall is doing. A lot depends on the power level, what we are trying to do, and, honestly, what the customer can afford.”

The Radial vs. The Slick

“We have several customers who have swapped back and forth from the 315 radial to the 10.5 slick,” reported McPherson, requiring “different shocks, and a completely different chassis setup and weight placement.”

“The biggest changes are in set-up,” Fasnacht confirmed. “Depending on your class and your competitive anxiety, you might potentially change any of the following:

  1. Shocks and/or shock valving
  2. Springs (with the change in weight percentage)
  3. Gear ratios, transmission and rear end
  4. Converter and shift settings
  5. Power management or tune up
  6. Downforce by exhaust
  7. Instant center of the rear suspension
  8. Vertical and horizontal center of gravity
  9. Many other small settings and adjustments

“Our setups do accommodate variations in tire diameter, for example, running either a 275 or a 315 at the same ride height. We plan for sufficient room for the bigger tire, and our bracketry provides enough adjustability for the smaller.”

Trickle down techniques happen all the time in drag racing and Jeff Polivka’s 2013 Mustang Boss is a prime example. The car runs in the high 7s, but DMC Racing has prepared it like it would do to a Street Outlaw or Edelbrock Renegade racecar with Menscer shocks all around as well as an SFI 25.3 chassis spec and a lot of bars. It might not have a double frame-rail chassis, but Polivka’s S197 Mustang has way more bars than a 7-second car from ten years ago.

On the other hand, the differences in weight distribution and other factors are great enough that “if you’re trying to be a top-notch contender—king of your class—you kind of have to focus on one combo and stick with it,” said Lyons. “And understand that if you want to go over there and run another tire on your weekend off, well, it’s going to be a challenge.”

“You really want to specialize,” Hallmark agreed. “If you want to go with a radial, then focus in on that tire and make the best of it.”

That said, dual-purpose cars are becoming more “prevalent,” to use according to Zimmerman’s word. “If you’re spending 100K on a race car, you definitely do not want to pigeonhole yourself. Even in the grudge-racing world, there are more small-tire shootouts. When there’s 20 or 50K up for grabs, and tire size and wheelbase are the only rules, then everyone wants a chance.”

“It’s circling back around,” Lyons added. “Before the radials got real big, everything was on a slick. Then for a while everybody wanted a radial chassis. Now it’s evolving back. Most of our business is still based on radials, but we’re seeing more racers who are running both. They are running races in the summer when the track temperatures are 140 degrees, so it doesn’t matter what kind of prep they have, or what kind of tire you have on.  So they do want to have the ability to put on a slick, so we try to build chassis that are versatile, where we have enough suspension adjustment where we can put whatever tire on this car. And we can make it work.”

The FKR Mustang, owned and currently driven by Josh Klugger, is the first and only radial-equipped racecar to run in the 5s in the quarter-mile. The car is the handiwork of Racecraft and it features a “stock-style” rear suspension. It is capable of being run in a number of configurations with an assortment of tires, allowing the team to run anywhere on any weekend, regardless of rules.