Here we will be looking at the methods of correctly setting the center of the steering geometry, and why it is so important to the handling of your kart. There have been many ways demonstrated on how to do this, some more accurate than others. Because of the Ackerman effect and the way it contributes to changes in toe and weight jacking, it is perhaps one of the most overlooked and under valued settings to improve your kart’s handling.

The Ackerman geometry causes an increase in toe-out as the steering is turned. Extra toe-out also results in a change in the effective caster angle relative to the racing surface. When the steering center is not set correctly, this results in uneven weight jacking from left to right or vice versa. Ackerman also affects the rate at which each wheel turns (the reason Ackerman was invented in the first place) resulting in a different intended turn radius from one side to the other if set off center.

Essentially, the true steering center position is determined by the distance each stub axle turns each way (rate of turn) when you turn the steering wheel. When the rate of turn is equal in both the left and right directions, you have found the true steering center position. The good news is that if you already own a laser wheel alignment system, you can do this correctly without having to buy any other equipment.

A side effect of the Ackerman geometry is that when you turn the steering wheel approaching full lock, the stub axle actually will start to come back in the opposite direction at some point. We can make good use of this side effect to find the steering center. When the position that the stub axle changes direction is equal on both sides, you have an equal rate of turn on both stub axles. Under normal circumstances this position would be quite hard to measure, but by using your laser wheel alignment tool it becomes an easy exercise.

The first thing you will need is a piece of paper or plastic, or any other material that you can see the laser dot on the opposite side to where it is shining. This needs to be mounted in the middle of the kart so that when your wheel alignment system is mounted and switched on, you can see the dot move on the material at the point when it changes direction. It is important that you correctly set the piece of paper or plastic exactly in the middle of the kart. You can experiment by offsetting it from side to side to see the difference it makes in accuracy. On some karts the lasers will change direction just behind the steering column, on others it is just in front. On rare occasions the dots will actually hit the steering column. As the steering column is quite difficult to read off accurately, it is best not to use it as a reference. The way around this is to introduce enough toe with your tie rods to miss the column. You can adjust the toe back to normal when the center setting is complete.

When you have performed the above step, you can turn the steering wheel both ways and note the position where both dots change direction. We are really only interested in the position of the dots in the horizontal plane to set steering center, but as luck would have it, the difference in position of the dots in the vertical plane indicates a difference in caster from one side of the kart to the other. You can then adjust your tie rods to get both dots changing direction at the same point when you turn the steering wheel. Once this is done you have correctly found your true steering center position.

All that is left to do is center the steering wheel so that your laser wheel alignment tool is showing equal toe on each unit, and then adjust each tie rod an equal amount to set the desired amount of total toe. While you have your laser system mounted on the kart you might like to quickly confirm it’s correct calibration. Remember, this is easily done by swapping the units from one side to the other so they are mounted the opposite way to the manufacturer’s instructions, and confirming that they show the same amount of toe and camber. Again, the width of the laser dot (around 0.5mm according to the measuring scale on the unit) discrepancy in readings for this test would be an acceptable tolerance. Also note that the actual error is half this discrepancy because by swapping the units you are reading the total combined error of the system. Effectively this gives you an acceptable tolerance of plus or minus 0.25mm measurement error.
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