Caster controls how well the car turns. If you are looking at your car from the side, caster is the angle of an imaginary line between the upper and lower ball joints relative to vertical. If that line is angled so that the top leans toward the back of the car, that’s positive caster. If the top of the line leans toward the front of the car, that’s negative caster. Positive caster makes the car feel more stable and resists turning. If you are turning a car that has positive caster on both front wheels and you let go of the steering wheel, it will automatically straighten up. Negative caster does the opposite and usually makes the car feel darty. Racers rarely run negative caster.
Measuring caster is straightforward. Begin by locating the car on a flat, level surface. Make sure the wheels are pointed straight ahead. If you have toe-in set on the car, the toe needs to be returned to zero for now. It also helps to have turn plates underneath the front wheels to reduce turning resistance (easy to make turn plates….you will need 4- 12”x12” floor tiles(most home improvement centers sell left overs for .50 each) and a box of salt(free from the kitchen if you don’t get caught). Place 1 tile under each front tire, then sprinkle a liberal amount of salt and place the other tile on top. The salt acts a ball bearing and is easy to clean up.
Start by placing the stick against the wheel and extend stands. Place the gauge instead of sitting up, turned on its side. Zero the gauge. Remove the stick and gauge from wheel and turn the steering wheel (right or left) ¾ of a turn, (I use pin stripe to mark the steering wheel at 12 o’clock) hold gauge against the wheel and make note of the degree, example 12.4 V Now turn back to center and make the turn in the opposite direction ¾ of a turn and install gauge and you will have a reading example 14.3 V This indicates 2.1 degree of positive caster.
By turning the wheel a preset amount, you do not have to have turn plates or measure in degrees. I turn the wheel three quarters of a full turn since that is the most a racer will typically turn the steering wheel on the racetrack. If you are using turn plates, some gauge manufacturers recommend 20 degrees while other says 10-15 degrees. It really does not matter as long as you are consistent and turn the tires the same amount every time you check the caster. If you are using the tiles, you can use the corners as a reference for the bracket that extends out but you are relying on site only. Whether you turn the wheels to the right or left to begin the process also is not important as long as you are consistent.
I know this sounds confusing at first but once you have checked your caster once or twice it is really the easiest way we have found.
- Level the camber gauge. This is accomplished by placing the gauge in front of the tire and wheel you are checking. Turn the gauge on and the first reading you will see is the level of the surface you are working on. Example: If the reading on the gauge is 1.2 followed by the ^ arrow, this indicates the surface your working on is 1.2 degrees positive, the opposite would show on the gauge as 1.2 v or negative. Simply hit the zero button and the gauge will recalibrate and show on the screen as 0.00 and will hold this recalibrated number until the unit is turned off.
- Adjust for wheel height and size. The camber stick wheel contacts are adjustable for 15-16-17-18(or to your specs) inch wheels. The bottom contact is also adjustable for fine tuning to make sure you are working on a totally flat surface against the wheel. Adjust the arms on the stick to contact the surface you are working on, this eliminates having to hold the stick against the wheel and possibly getting inaccurate reading on the gauge. Use the arms as they are mounted or for hands free remove the arms and attach one to each side of the stick (extra bolt and washers supplied)
- Checking Camber. Place the gauge on the camber stick and record your camber. Example: 0.7 v indicates this wheel has less than 1 degree of negative camber. The only thing you really need to remember when using the gauge is ^ is positive, v is negative. In most cases you do not have to reset the gauge to level for each wheel but I would recommend until you have become totally familiar with the system to readjust for each wheel. As a side note, you can also place the gauge directly against the stick to check camber, the number that shows on the gauge will be plus or minus 90 degrees or vertical. If you use this method, taking our first example would be 89.3 v or 0.7 of negative camber.
- Adjust the height of each stick. Typically 6 inches is a great place to start your measurement. We made the cuts on the stands to measure 6” at a 45 degree angle. The extra bolts go on either side of the stands for stability.
- Place one stick on each side of you vehicle parallel with the tire. The stand should be to the outside of tire and wheel with the stick resting against the tire.
- Extend the tapes one in front of the tire and one behind the tire. Slide them under the vehicle until you each the opposite side. We have found working from right to left is easiest for us. Slide the clip of the tape measure into the slots of the left front and rear, return the right front and slide the extended tapes into the slots front and rear.
- Gently pull the tapes at the same time making sure the opposite side is seated against the tire.
- Read the tapes carefully. Typically you will have readings something like this:
Front measurement 75 ¼ – Rear measurement 75 1⁄8. This indicates that you have 1⁄8 of an inch of toe out. Easy way to remember this is if the front number is higher, you have toe out. If the rear number is higher then of course you have toe in.Remember, toe is actually measured from the center of the wheel, so double any number you have to get exact toe(example: 1⁄16 on the sticks equals 1⁄8 at the spindle. 1⁄32 of an inch can make a huge difference in the way your vehicle drives and responds so when you read the tapes, be as exact as possible. For the effects of toe in and toe out check the charts
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