CROSS-BIND EXPLAINED, MEASURED, AND ADJUSTED
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WHAT IS CROSS BIND

Cross Bind is a term used in Soap Box Derby. It references an excessive downward force by two wheels that are diagonal from one another. Cross-Bind can only occur in a car that is running with the KING PINS torqued down very tight. This downward force is measured as Weight. In other words, you have Cross Bind when the left front and the right rear wheels are exerting more downward force then the right front and the left rear wheels. Of course you can also have Cross Bind if the right front and left rear wheels are exerting more downward force then the left front and the right rear wheels.

You can only have Cross-Bind if your front and rear axle king pins are torqued tight. One or both king pins loose can eliminate your Cross-Bind. However, it is desirable to run tight because you lose less energy with a tight set up. Not all tracks are best for running tight. Their starting ramp or track may have too much Cross-Bind to run tight. In that case you modify your torque to compensate.

CAN CROSS-BIND HURT YOU

When two diagonal wheels are exerting more force then the other two wheels you are at a disadvantage at the starting gate. This excess pressure makes it harder for them to start rolling. This translates into your car being slow off the starting ramp. The car that gets a good start is the one that wins. That is why we say, “You win at the top and you lose at the bottom.” Cross Bind also hurts you all the way down the track, but it is especially deadly off the starting ramp.

As we learn in SBD, when your car is going slow it is more susceptible to anything that might impede the starting or slow movement of your racer. Small imperfections in the track starting area can cause you to be slow at the start and cause you to lose the race. However this same small imperfection further down the track would not have the same affect on your car because of the Kinetic Energy you have with greater speed.

Cross Bind can occur in two ways. One way is when the surface the car is setting on is not flat and level. The second way is when the cars alignment and Cross-Bind are not properly adjusted (Axles are not parallel (level) with one another and the floorboard).

Proper alignment and cross-bind adjustment is when the front and rear axles are parallel (level) with one another and also parallel (level) with the floorboard of the car.

 

STARTING RAMP CROSS BIND

Every Soap Box Derby Local City Organization owes it to their race families to maintain their starting ramp so it is flat and level with no Cross Bind. If the starting ramp has Cross Bind it will cause your car to have Cross Bind when it is on the starting ramp. All race families should know how much cross-bind is in their starting ramps, if any.

If your track's starting ramp has Cross Bind, you will need to run your front axle king pin looser to eliminate the Cross Bind in your car on the starting ramp.

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Hillary Pierson 2004

HOW DO YOU GET RID OF CROSS BIND

Proper Cross Bind adjustment starts with your car's construction. During construction make sure your axles are installed as level as they can be to one another and to the floorboard. See more Cross-Bind construction tips in "Winning Ingredients for Kit Cars."

In this article we will continue with the Cross Bind final Adjustment. To perform the final adjustment the car must be completely assembled and your weight placed for racing. The forward and aft king pin bolts should be torqued to around 200 IN. LB.

The following Cross-Bind adjustment with Bed Rails is by Jerry Pierson. I use it with his permission. Jerry's Soap Box Derby accomplishments are legendary.

There are several methods to measure and adjust your Cross Bind; these are: Sighting across the axles from the front or the rear, Using a level positioned on the end of the axle and move it from axle to axle, Using 4 separate scales under each wheel, Using a flat concrete surface with your wheels on, or Building a parallel rail fixture.

In this article we will use a parallel fixture to check and adjust your car's Cross Bind. This method is a favorites of my friend Jerry Pearson. It is simple, fast, and accurate.

Use old bed frame rails to construct your Parallel Rail Fixture. The fixture side rails must be long enough to accommodate the wheelbase and the fixture must be wide enough to accept the max length of the axle square stock. The goal is to be able to set this parallelogram fixture up and lay a level across each end and make adjustments to each corner until the side rails are level, side to side, end to end and diagonally.

When your fixture is 100% level, sit your car on the fixture with the square stock of the axles sitting on the side rails at the same position on all four corners. Set the axle square stock ends on the rail, do not use the spindles. Now raise the front (or aft) end of the car just slightly off the rails and then back down until the axle makes contact with the rails. If both sides hit the rails at the same time, then you do not have cross bind. If one side hits the rail before the other, then you have cross bind. To remove this cross bind, loosen your front kingpin, (or your aft king pin) and put a . 004 feeler gage in between the two largest washers of your washer stack up against the side of the kingpin bolt. Now again torque your kingpin and recheck the car for cross bind. Continue this process with different thickness of feeler gages until both sides of your axle hit the side rails of your fixture at the same time.

Thanks Jerry Pierson for the above Cross Bind adjustment procedure with bed rails. Jerry's daughter Hillary won the 2004 Masters. See photo to the left.

A few things to consider when adjusting your Cross Bind are:

  • Car should be complete with weight placed for racing.
  • If using scales, make sure all wheels weight the same.
  • Make sure your two or four scales are calibrated the same.
  • Position the wheels all the way in using washers, or all positioned out, whichever you prefer.
  • Axles should be torqued to 175 to 200 IN-LBS. to measure your Cross Bind.
  • Place the shim between first and second washer above floorboard as shown in top left image.
  • Check your Cross-Bind often.

Because of the large area of the washers above and below the axles, 200 IN LBS torque might be too stiff for some tracks and starting ramps. Because of this, often people race with 100 IN-LBS. for the front axle to reduce cross-bind on the starting ramp and rough tracks. Only testing can give you the correct torque.

See "Winning Ingredients for Kit Cars" to find out what others are doing to adjust their Cross-Bind. There is also information for adjusting your Cross-Bind with scales, and information on which axle is best to shim.

WILL MY FRONT AXLE SHIM FALL OUT IF I'M RUNNING MY TORQUE LOOSE?

That's a good question. A friend of mine was concerned about the same thing.

If you loosen your axle king pin bolts you can eliminate all Cross-Bind. If you are loose enough to eliminate all Cross-Bind, you have no need for a shim! Take it out, or let it fall out, you do not need it!

REDUCING THE KING PIN TORQUE GETS RID OF CROSS-BIND, WHY DON'T WE JUST DO THAT?

Running your king pins tight gives you better continuity between the axle and the mounting hardware. This saves energy by not having loose parts Vibrating against each other wasting energy. So you start with your axle king pins tight and adjust to "0" Cross-Bind. If your starting ramp has no or little cross-bind, this is how you want to run. If the starting ramp has cross-bind, and or the track is rough, you adjust your forward king pin looser as needed.

By reducing the torque on your front, aft, or front and aft king pins you eliminate the Cross-Bind. How loose you run is dependent on the condition of the starting ramps and track.

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