Drag Race 101: Suspension and Body

Body and Suspension Upgrades to Keep Your Strip Burner on the Track

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Sportsman Class competitors line up prior to their passes at the 2015 Summit Racing Equipment NHRA Southern Nationals May 16th, 2015. 

 

If you’ve been following drag racing for any length of time, you’ve seen a few really nasty wrecks. While it is true that many of these wrecks are due to engine malfunctions such as compressor failure due to over boost or too much nitromethane, quite a few are also due to loss of traction or contact with the track. No matter what the cause, they all happen too fast to do much to mitigate the results, it’s basically just hang on and pray and pop the chute. However, we can make suspension and body improvements and modifications to reduce the chances of crashing and burning. We’ll first take a look at what you can do with the suspension and then move to body mods and add-ons.

Get It on the Ground

The theories of aerodynamics state that air flowing under a car will have the tendency to try and lift that car off the ground. At lower speeds, the car isn’t forcing itself through the air fast enough to cause enough air pressure to cause lift, so we don’t worry about it that much. This is why that Camry you see sits about two to three inches higher off the ground than the Camaro. The closer your car’s underbelly is to the ground, the less lift and the more control and stability you have.

I’m not going to go into how to lower your car here, but if you’re interested, you can read about lowering your front end and then move to lowering the rear end. If you’ll be driving your strip burner on the streets, be sure to not slam it too far. In most states, you can’t slam it so much that the side skirts/fenders are closer to the ground than the lower bead of the wheels.

Get a Heavier Steering Wheel

Wait, what? A heavier steering wheel? Yep. A heavier steering wheel is normally going to be a bigger steering wheel, this means your steering inputs command smaller changes in the position and direction of the front wheels. When going as fast we are on the track, we have the natural inclination to over-correct when the car veers one way or another. Over-correcting causes instability which causes wrecks. We don’t want that.

The heavier steering wheel also absorbs fewer vibrations which can also affect our steering. Vibrations can also cause the wheel to slip in your hands, which would be really, really bad. Lastly, we have to put more effort into turning the wheel, which means we are less likely to accidentally turn the wheel.

Sit in the driver seat as you would during a pass. Place your hands on the wheel and turn it back and forth a bit, get the feel of it. Now, move your hands off the steering wheel by about an inch. Now make like you’re giving small steering inputs. If it feels comfortable, spread them a little more. When I’m building a race car, I mock up a frame of sorts so I can get the most accurate feel for a variety of wheel sizes to find the largest one that is still comfortable and doesn’t rub across my thighs as I’m driving. Mocking up a driver’s seat outside the car makes it a little easier since you can hold your hands still while someone else measures.

Something else that goes hand in hand with this is the depth of the “dish” in the steering wheel. Some steering wheels are almost flat, with the center portion of the wheel that mounts to the steering column being at or near the same level as the rim of the wheel, while others can have as much as four or five inches of dish. The amount of dish, along with seat placement, determines your hand placement and elbow angle. You want something that is comfortable and allows free movement. Some drivers like to have the wheel almost in their chest. I prefer a bit of extension to my arms with only a slight bend in my elbows.

Get Rid of the Worm Gear

 

Rack and pinion steering gives you much better control at high and low speeds.
Rack and pinion steering gives you much better control at high and low speeds.

 

If your strip burner is built around a newer car, go ahead and skip this section because the manufacturer beat me to it. If you’ve got an older car, please pay attention. The component that directly actuates the components that move the front wheels right and left is called a steering gear box. These are great if you’ve got a big truck, but not so much for our needs.

Attached to the end of the steering column inside the gear box is what’s known as a worm gear. As you turn the steering wheel, it meshes with another gear that causes the pitman arm to turn, causing the steering parallelogram to move left or right, directing your car left or right. This type of steering system works (obviously) but it is terribly inefficient and has too much “slop” or play. Sure, you can adjust it to remove some of the slop or play, but that causes the gears to grind, which causes them to fail earlier than they should.

Spring for a Pinto or Mustang II rack and pinion unit and yank the steering gear box. These are available from most aftermarket performance supply houses. They usually come as a complete kit. Complete disassembly of the old system and installation of the new rack and pinion is pretty straightforward and the kits all come with very detailed assembly and installation instructions.

Rack and pinion steering is more accurate for a couple reasons. A rack and pinion consists of a gear attached to the end of the steering column, a “regular” gear, not a worm gear. This is the pinion gear. The pinion gear rests and rides on the steering rack. The steering rack is basically a bar that runs from one of the rack tube to the other and has notches cut that the pinion gear meshes with to move the rack right and left. These gears mesh together much better than a worm gear and they don’t move against each other the way a worm gear does.

Drop the Belt!

Got power steering? You don’t want it in a car meant for drag racing. Why Mike? Why would you want a system designed to assist you in turning when all you’re doing is driving in a straight line? As you’re sitting in the staging lane before your pass, remove the power steering belt if your car has power steering. Better yet, if you’re converting to rack and pinion, just get a manual unit. Sure, you’ll have to expend a little effort getting back from the other end of the track after your pass, but you’ll have much more control while making the pass.

Wheelie Bars

Wheelie bars are designed to keep your car from flipping over backwards and to force the front wheels back to the ground after a wheelstand.
Wheelie bars are designed to keep your car from flipping over backwards and to force the front wheels back to the ground after a wheelstand.

 

Wheelie bars are those wheeled protrusions that extend from many dragsters. You can’t steer the car if the front wheels are off the ground. Sure, that wheelstand looks cool, but you have no control. If one drive wheel hooks up better than the other while your car is doing a wheelie, you’re done; you’re most likely going to meet the wall. Violently. I’ve also seen cars with gobs of torque roll straight over backwards.

Wheelie bars are designed to allow a bit of a wheelstand. Your front wheels will lift off the track a bit. Once the wheelstand hits its flex-limit, it will rebound, causing the front wheels to come back down, giving you back steering control. Wheelie bars typically attach to the rear end housing in some way. The exact method of attachment depends on the type you buy.

Traction Bars

 

Traction bars are designed to counteract axle housing twist to maintain traction in the rear wheels.
Traction bars are designed to counteract axle housing twist to maintain traction in the rear wheels.

 

Cars that generate lots of torque tend to develop wheel hop as the forward velocity of the vehicle catches up to the rotational velocity of the wheels. Here’s what happens: The Tree goes green and you hammer it, launching from the line. This immediate transfer or torque causes the differential housing to want to twist on the lift springs. This causes wheel hop and loss of drive force.

Traction bars are rigid pieces of steel, either boxed or tubular. They attach to the front mounting point of the leaf spring and to the bottom of the axle housing. When you launch, the differential begins to twist, but the traction bars resist this twist, keeping the wheels in contact with the road.

While not absolutely necessary, traction bars are also occasionally used with multi-link rear suspensions also. If you’ve built the rear suspension properly, you really shouldn’t need traction bars. If the springs you’ve installed are too soft, they can bend and twist vertically, causing the same wheel hop as with a leaf spring suspension.

Replace Worn Suspension Components with Quality Racing Parts

A rule of thumb I always follow when building a race car is to replace the bushings and steering components with high quality parts designed for the abuses of racing. This means tie rod ends, ball joints, control arm bushings, shock absorbers/MacPherson struts, and anything else I can think of, including the strut bar-the bar or rod extending from the lower control arm to the front bumper mounts. Don’t forget the rear suspension components either.

Ground Effects Kits

Admittedly this is more beneficial for those that will be road course and oval track racing. However, ever little bit helps. In aerodynamics parlance, ground effect is the turbulence caused by a mass in motion at high speed near the ground. In flight, it can be deadly and has been known to cause aircraft crashes. In auto racing it’s also been known to cause serious crashes. In auto racing, it can be used to help glue your car to the ground and provide stability and traction. For example, properly done and at the right speed, you can actually drive upside down and maintain control and stability. Yes, I said upside down.

Ground effects kits range from the really inexpensive to the ridiculously expensive. You don’t need to go wild; just enough to limit the air flowing under the vehicle chassis and properly channel it. Ground effects kits that we’d be using typically consist of front air dams, rear air dams, and side skirts. The front air dam and side skirts limit the air flowing under the car and channel it to where we can make use of it such as to cool the wheels and brakes or help enhance the “suction” holding us to the ground at speed. The rear air dam channels and accelerates the air running out from under our cars, again increasing our traction, car control, and safety.

Use the Wind to Push Down on the Rear

The wind can be both friend and foe to a drag racer. If you’ve done your homework and made the right modifications and improvements to your strip burner’s body, it can be your friend. Conversely, if you haven’t, it’ll be your enemy. You should make use of the wind as much as possible when racing.

At really high speeds, even if you’ve done everything listed above, the air flow around your car will still want to life the back end off the ground. That’s why the big boys like John Force sculpt the bodies of their cars to make the cars as aerodynamically efficient as possible and make maximum use of whole-car downforce.

One of the things we can do is to add some sort of an airfoil or spoiler at the rear of the vehicle. Since you and I probably won’t be going around 300MPH+ on our passes, we can squeak by with a nice rear spoiler or whale tail. Another reason we can get by with a spoiler is that the body of our car generates quite a bit of downforce at the front just by the air pushing down on it. The spoiler balances this front downforce which wants to lift the rear wheels with rear downforce by pushing the air rushing along the car’s body upward.

About Mike Aguilar 202 Articles
Mike's love of cars began in the early 1970's when his father started taking him to his Chevron service station. He's done pretty much everything in the automotive aftermarket from gas station island attendant, parts counter, mechanic, and new and used sales. Mike also has experience in the amateur ranks of many of racing's sanctioning bodies.
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