Down force is your friend. Just about all late models run on tracks that are under a mile in length. Corner speed is enhanced by applying every trick to create down force as drag is of little consequence for short tracks. Occasionally, race teams have asked me if they should lay the rear spoiler down on larger tracks to reduce drag. In general, you want the maximum spoiler angle allowed up to about 75 to 80 degrees on tracks 1 mile and under. More spoiler angle creates down force at the rear wheels helping to launch you off the corner. With the good initial run off the exit the engine horsepower gets your car off to a good start and the added drag on the straight is not worth considering. If more spoiler angle lets you get the throttle to the floor sooner then you will go faster and the effects of drag on the straight are not enough to take away the solid start off the corner.
Keeping your spoiler in the wind with plenty of spoiler supports will add consistent down-force at the rear wheels, helping to launch you off the corner.
Using your rear spoiler for down force is critical. You want to guide air off the roof and down the rear window with a smooth transition to the deck lid. Sometimes bodies have a sharp transition from the rear window to the deck lid area. If your rules allow you want to push up the deck lid to create a smooth transition to the rear window.
A smooth transition from the rear window to the deck lid area will reduce turbulence and allow the air to stick to the deck lid, flowing smoothly over the rear spoiler. Push the rear window up where it meets the deck lid as high as possible.
Fiberglass bodies allow for many options to create down force where you need it. You should consider your goals before mounting a new body. For example; if your car or track has a tendency to be tight (push) then you can help the problem by stacking the body to the front. Moving the body an inch forward is going to increase front down force significantly. If your car or track is consistently loose then setting the body back an inch is the way to go.
When mounting your body your goal is to have smooth and rounded transitions. If you can imagine airflow and think of air as wanting to stick to or follow your body lines. Sharp inside or outside body angles should be avoided at all costs as they create turbulence disrupting the air flow. Long rounded transitions allow the air to follow along the body and assists air in its natural tendency to follow surfaces.
During the next television Cup race pay attention to how the cars appear to track in comparison to the wall. You can visibly see how the bodies are mounted on an angle as compared to the centerline of the chassis. Engineers have discovered that they can pull the left front over and over hang the right rear quarter panel over the tire. Extending the RR out and keeping it in the wind creates down force on the RR which helps the car be more stable on corner entry. Skewing the RR quarter panel out keeps the spoiler in the wind on corner exit planting the RR for improved acceleration. Over hanging the body at the LF creates added down force on the tire that has the least load. With the front body panels offset to the left the car cuts better though out the turn. With a fiberglass body you can easily move your mounting points and mount your body on an angle for added speed.
Sealing the nose to the ground is paramount to making speed. Eliminating front lift and giving air the right start over the entire body equals more speed. This car has a "down force" body. If your rules allow, the wide panels and extra length are worth the investment.
The main reason a Big Bar Soft Set up works due to today’s bodies – they simply create way more down force than the vintage Camaro fiberglass bodies. If you go to a Sprint Car race on the dirt ask yourself which is faster; a winged Sprint car or a non winged Sprint car. On your late model your fiberglass body has significantly more surface area than a Sprint Car wing. Your assignment is to use the entire body to your advantage.. Sealing the nose piece to the track is the key to your Big Bar Soft Spring set up. Sealing the nose forces all of the air over the body. Any air that leaks under will cause lift and down force is lost. Making an adjustable valance will allow you to keep the nose down on the track with a combination of track conditions and car set ups.
An adjustable front valance will let you drop the nose right on the ground with a quick track adjustment. Getting the nose down for a perfect seal is a high-priority down-force item.
Your body should be a rigid structure at race speed. Any panels that are flapping are slowing you down. Flapping panels create unwanted turbulence and upset the airflow in an unpredictable fashion. If your front windshield and rear window deform in the wind you need to add supports until they are rock solid. Your rear spoiler needs to be solidly mounted and the use of several spoiler supports is a good idea. Fender supports should be used and attached at multiple points on the body to hold panels firmly in place.
If your hood deforms and flaps at speed not only are you losing down force but you are also diverting air away from the cowl intake potentially cutting critical air to the carburetor resulting in a loss of horsepower. Take the time to make sure your body panels are solid in the wind.
Using body braces to hold your body panels in place will give you a rigid foundation for maximum down force and air flow. This nose peice is clost to vertical at the sides. If you can, stretch the nose peice side panels out and let them angle back to the headlight which will make you more downforce. The nose piece is a critical element. If your rules allow then pull the nose piece out at the front of the tires as far as possible. If allowed stretch the bottom of the nose piece out along the bottom edge. The idea is to create a sleek angle verses having a bulldozer at the leading edge. An angle from the top of the hood to the track equals down force. Even the sides of the nose piece can be stretched out. If the sides are perfectly vertical then you are leaving a few extra pounds of down force on the table. If the nose piece angles out from the headlight down to the bottom edge you create surface area for air to push down on and more speed is found. If your rules enforcement is soft then add a splitter to the lower lip of the nose piece which will add front down force.
The fender wells are another area where attention to detail pays off. You can trim the fender wells at the right side of the car to fit closely to the wheels. On the left you can keep the front edge close to the tire but you must provide ample clearance from the top of the tire extending around the fender opening to the ground. It is critical to leave an escape route for air that gets trapped under the hood. If there is not enough escape area to relieve the air pressure from under your car will see lift and could be unstable at speed.
Exchanging down force for drag on a short track is nearly always a good idea. That said – be sure to avoid any parachutes. Make sure the front side of the wheel wells extends to the outside more than the opening on the backside of the wheel well. Be sure the windshield posts are slightly outside the window posts at the quarter window.
If your rules allow, you can use your body braces for a few extra pounds of down force. As the tires spin at speed they create wind. Placing panels or body braces to catch the wind from spinning tires equals more down force. While small improvements add up for added down force a major gain is found if your rules allow a “down force” body. The extra wide panels and longer length are the source of valuable surface area. More surface area equals more down force. If your competition has a down force body and you have a template body it is truly and unfair advantage.
Finding extra down force is like removing weight from your car – you discover improvements a few pounds at a time. After discovering the big gain areas you can tackle the small areas. A few pounds of down force here and a few there can really add up. Make sure the leading edges of everything on the underside of your car are rounded. Allowing air to move freely under the car adds to the down force numbers. If you can make sure the rear bumper cover is rounded at the bottom edge to allow air out from behind the car.
Go Forward – Move Ahead
Jeff Butcher
Courtesy of JOES Racing Products
5/31/09
http://www.joesracing.com/
