You went to your first dragster race and noticed that the cars had enormously wide squishy rear tires. What exactly are wrinkle wall tires?
Thundering 1,000 feet of track at over 300 mph in a few seconds might seem like a simple Sunday cruise, but you know better. You are confident that these drivers are not putting their lives at risk without working out the science of every detail. (At least you hope they are). Since you don't want to appear stupid to your drag-racing buddies, you figure it's time to investigate some of the terminology and physics behind the sport. Then, you can hold your own in a conversation and show off to your friends the next time a funny car screeches down the strip.
Wrinkle wall tires are entirely smooth, wide tires used in drag racing. The sidewall wrinkles or shrinks because of the torque, allowing maximum surface contact. This effect makes for a stronger start with increased traction when maximum thrust is necessary for a compelling start.
It isn’t for the faint of heart if you know anything about drag-racing. Even more impressive is how people strap themselves in a car with an oversized engine and underinflated wide tires and streak down a straight road faster than greased lightning. These cars' excessive speeds are impressive, but watching the flames and feeling your nostrils sting with the scent of burnt rubber only fuels the questions in your brain. For example, what is the basic science behind a wrinkle wall tire? Why do drag racers constantly use them? What is their primary purpose?
So, let's analyze some of the physics principles that help these speed demons achieve such remarkable results. Maybe learning more about the science behind the sport can give you and your nerdy son something to talk about when you bring him to the strip.
What is the Science Behind a Wrinkle Wall Tire?
The top fuel dragster is the fastest legally sanctioned race car, with a 500 cubic inch engine that burns 15-20 gallons of nitromethane fuel. The typical dragster can produce over 11,000 horsepower, accelerating over 300 mph in under four seconds (they accelerate to 100 mph in 0.8 seconds). However, no top fuel dragster (or funny car) would make it down the track without specially designed tires, regardless of the size of their engine. Let’s examine some of the characteristics of this tire and figure out why they are so helpful in achieving such incredible results.
When the dragster approaches the start line, you might notice that the sidewalls of a dragster’s large rear tires seem to wrinkle or shrink. They might look like they are going flat, making you think they are unsafe to drive. Actually, the sidewalls have a flexible compound that allows the lower tire pressure and torque to twist up the rubber. The low pressure shrinks the tire's diameter, bunching more of the sidewall and forcing additional rubber to contact the road surface. The weight of the big engine and the stored up torque shifts the energy to the car's rear, so the car appears to squat. (The front end might even rise). The large rear tires, in this way, ensure that no part of the tire loses traction.
One of the other things you’ve seen is how the tires are also large, smooth and wide, which is another way of maximizing how much tire rubber meets the road. The bigger and broader the tire, the more rubber can wrinkle. The slick surface of the tire means a great deal of rubber is already making contact. Both the design and the composition of the tire help the car build up stored energy from the engine's output, enabling the dragster to channel the accelerating force in a straight line when it's time to race.
When the starting light turns green and the driver hits the gas, the stored up torque forces the tires to dig in and thrust the vehicle forward with maximum output. Since the squat has forced the rubber of the sidewalls to bunch just ahead of the contact point, the tires dig in harder on the pavement and provide more initial acceleration. This science is why the dragster lurches forward during the start.
As the dragster moves down the track, the wrinkled rubber smooths out (basically, the tire becomes taller so that the contact rubber becomes narrower and lengthens. The larger a tire is, the farther it travels in the same amount of time as a smaller one. The more distance the tire travels at high speeds, the more miles per hour, precisely what you want when racing a clock. (Since drag racing can come down to milliseconds, you can see why maximizing speed is essential). This growth allows the tire to deliver more speed, which means the engine's push is maximized, again translating into quicker race times.
At the end of the run, you probably notice the parachute that comes out of the tail of the top fuel dragster to aid in stopping the vehicle, but the engine and tires have roles to play. The engine shuts down so that the lack of compression helps reduce the speed, and the tires wrinkle or shrink again, increasing the contract surface, and improving resistance, slowing the car down. While the parachute does most of the work, the tires lend a hand, too.
What Modifications are Needed to Handle These Tires?
Often in drag racing, to accommodate the size of the tire, special modifications have to be made to the car (this is specifically true on closed wheel dragsters where the rear of the car is lifted). The suspension is rebuilt to handle the weight and size of the tire. (The average weight of a 36-inch tall, 17.5-inch wide slick is 48 pounds, nearly $1000 each).
The rim of each tire has a small bead lock ring that runs along the rim. The edge of the tire is between the rim and the rim lock and then locked into place with many heavy-duty bolts. Without the bead locks, the tire's rim would spin faster than the rubber of the tire could handle, and the stress would cause the tire to blow.
How Long do Wrinkle Wall Tires Last?
A dragster uses their slick tires for only a maximum of eight races, and after that, they have to be discarded and replaced. Sometimes they can be used as “slickers,” which help lay down rubber on the pavement, increasing the grip fresh wrinkle wall tires have.
How Long have Wrinkle Wall Tires Been Around?
Marvin & Henry (M & H Tires) made the first drag slick tire in 1957. The owner, Marvin Rifchin, was experimenting with a new rubber compound. The discovery produced a tire with more flexibility than standard highway tires. Rifchin received a call from an owner of a drag strip looking for a specially built tire that would provide better grip, having heard about the kind of compound Rifchin had been inventing. When Rifchin arrived at the strip, one of the racers had a blown tire, to which Rifchin offered a pair of “new” slicks he had brought with him. The driver was Serop “Setto” Postoian, an up and coming dragster. Setto drove a faster time than he ever had with a slick on the car.
During the height of drag racing, professional drivers like Big Daddy Garlits used slicks on their top fuel racers. M & H Tires continued to be the only manufacturer of racing slicks for many years until the company sold to Interco Tire Corporation in 2001. Rifchin was in his eighties when he retired and died in 2009 at 94 years old.
Why Does a Dragster Do a Burn-Out Before the Start Line?
Wrinkle wall tires are incredibly soft and very easy to puncture. A burnout helps heat the tire and ensures that no debris has gotten stuck to the tire's surface as it rolled from the pit to the starting line. The warmth of the tire means more contact with the road surface because the rubber compound has expanded, and the heat also helps more of the sidewall to shrivel forward.
Why is a Drag Strip only 1000 feet Long?
Due to safety concerns, the governing bodies of Top fuel drag racing have shortened the strip length to 1000 feet. Some drag strips are only 660 feet, which is a quarter of a mile long. The drag strip was shortened from 1320 feet to 1000 in 2008. (A horrific accident that year, where Scott Kalitta died, prompted the change. From that point forward, both the IHRA (International Hot Rod Association) and NHRA (National Hot Rod Association) implemented various safety protocols to protect drivers' lives.
Are Slicks Used in Other Motorsports?
Absolutely. Today, many other sports use tires with no tread, from motorcycle racing to formula one to even bicycles. Formula One racing did not allow slicks for several years because they were considered unsafe, particularly on wet pavement, where the tire loses traction and can easily hydroplane.
About THE AUTHOR
I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding