In outdoor karts Eccentric Pills are used to adjust the caster and camber of go karts. Indoor karting will eventually lead you to driving and setting up your own outdoor kart. This article examines 16 point eccentrics. Similar rules should apply to 4, 8, 12 point eccentrics.
Eccentrics have an offset center point allowing you to offset the kingpin as you rotate the top and bottom pills. Not many people really understand them, and the information on the internet is scarce. I will try to fill in the blanks.
Typically these pills are considered to be Caster and Camber adjustments only, but they are actually much more than that as you will see, and they can seriously mess up a kart or bring it magically into alignment.
For this reason it is recommended that if you are fairly new, you should only touch your pills in the event that you have a serious problem and need to fix it, because as a new driver your biggest gains are going to come from mastering the line and refining your driver. Pill set adjustments only really start making a difference in lap times when the driver is consistently within .500 of the fast lap time.
So as a rule of thumb, get your driver right first, and worry about the kart second unless it is totally jacked up and you need to fix a bent and broken kart.
There are two ways to use them.
1. Zero pills where you have a center pill on the bottom, and then use only one on top (or bottom). This allows for an easier to conceptualize modification of your camber and caster.
2. Dual Eccentrics top and bottom. This is my preferred way of using eccentrics and the most confusing so we will discuss this method.
Throughout this guide I will use the following terminology to describe pill positions.
If you look at the picture above, I show a 16 point eccentric pill set. Note that the northmost position is labeled as #1 and the positions go clockwise to #16.
When making pill adjustments we will usually need to make changes to all 4 eccentrics on the LF and the RF top and bottom so I will refer to these as LF[1:1] and RF[1:1] for left front and right front.
Left Front represents the kart from the drivers perspective so it would be the front wheel closest to his left hand.
The first part of the number (seen as “[1:” in the [1:1] ) represents the top pill position and the second part of the number (seen as “:1]” in the [1:1]) represents the bottom pill position.
So if you see RF[2:16] This means to rotate the top pill counter clockwise from position #1 and to place the #2 hole in the place where the #1 hole used to be. So rotate 1 click CCW. Then rotate the bottom clockwise one click to move the #16 hole into the #1 position. LF[1:1]RF[1:1] would mean to set to North Neutral position where both top and bottom are set to position #1.
Note also that the #1 position is furthest from the center hole, and that the center hole is off center. This allows for a total displacement of each kingpin of 3 mm in the north/south axis and 3mm in the east/west axis. If applied equally to both wheels that means we have a total potential displacement of 6mm to the track width and relative length of the kart. This is enough of a range to create a serious displacement of the kart, so be careful.
Now if for example if we were to rotate through the 16 neutral positions from say [1:1] to [2:2] it would have the effect of moving the king pin forwards, upwards and outwards all at the same time.
Now you can’t move to [2:2] on both sides of the kart and remain balanced because you would be moving both sides in the same direction. Instead if you move the left front to [2:2] then you must move the right front to [16:16]. Now your track width has moved a total of 0.75mm and your kart wheel base has become 0.75mm shorter. Meanwhile your caster and camber has stayed the same, while your ride height raised just slightly.
For now that is inconsequential, but if you had to repair or adjust a kart that had lost it’s squareness, this is a great tool to have in the toolbox. You can adjust your squareness, without affecting your camber and caster and dial out tendencies to pull left and right, which can also remove drag from your straightline speed.
Dual Eccentrics allow for a total of 256 possible settings (16 top and 16 bottom). Of these 256 possible settings, 16 of them are actually neutral. Neutral means they do not try to change the caster or camber. They are the positions where the top and the bottom exactly line up.
This table shows the 16 neutral positions for the Right Front (RF) and how they affect ride height and track width in Millimeters. It also shows the corresponding LF setting for neutral and gives an estimate for the total width displacement of that position.
In this diagram red shows the bottom pill setting and black is the top. You can reverse this for the left and right, so on the left side the red would be on top and black on bottom.
From this you can see that you can make height, width and length adjustments just using the pills, which can be very handy for straightening out a bent kart.
Using Neutral Quadrants.
I find the easiest way to think of the neutral positions as starting points, and use the North, West, South, East most position as quadrant starting points depending on what you want to achieve.
North Quadrant – How to adjust Camber only….
Note in this picture, North Quadrant (Q1) starts at position[1:1] and we would place both sides of the kart into north Quadrant. This neutral position is great if you want to make camber adjustments. Because moving the top pill +/- 1 click will rock the king pin top left and right. Then you would make equal counter movements on the bottom to keep the king pin centered and to retain your caster. Note that the following settings all have the same caster. Note that if you number all your pills from 1 to 16, and then place them together on top and bottom, you can then make your camber adjustments by rotating both top and bottom the same amount. IE 1:1, 2:2, will actually move the top and bottom in opposite directions. Because of this the width adjustment top and bottom cancels each other out, and the kingpin rocks left and right on a center point.
If we continue instead of negative camber adjustments, we make positive camber adjustments.
As you can see, there are two settings that will rock the kingpin in or out, but one of them has a higher / lower ride height than the other and one can make the kart longer or shorter..
East Quadrant is achieved by going to [13:5]. This has the effect of moving the center axle holes into the left most position. Note if we were to use East Quadrant on one side, then we would have to use West Quadrant on the other side. But if we use North or South Quadrants then we use them equally on both sides.
Effect on width. Note also that if we use East Quadrant on the RF and West Quadrant on our LF then we just made our total kart length 1.5mm shorter than North Quadrant and also decreased our front track width by a total of 3mm. We have also raised our ride height by 1.5mm. In effect we have raised our center of gravity and should give the kart more bite and downforce. We have also reduced scrub radius so this should make the kart more eager to rotate.
East/West Quadrants – How to adjust Caster Only.
East/West Quadrants are where we would go to make micro caster changes. From this position we can rock the kingpins forward and backwards. Starting at RF[13:5] we get..
Checking and adjusting squareness using eccentrics.
If you only tweaked one side of the kart, then you would make one side longer than the other. You would also need a longer tie rod on one side of the kart and you would need to re-adjust all your steering alignment.
You could use the pills in this way to square up a kart that does not measure straight. Karts get bent all the time, typically a hit in the rear will bend the longitudinal struts that hold the rear bearing cassettes. These are made to be flexible like shock absorbers, but they also hold the bumper so if they get hit at an angle they are at risk of bending. When they do, your kart will show one side gets longer than the other, or one side is higher than the other, and it will start to pull left or right. Especially if you take your hands off the wheel. You can either get it on a rack or scales, and then bend it, or make emergency repairs using pill adjustment.
Sometimes even after getting the wheels evenly flat, you are still bent with one side longer than the other. You can then use the pills to dial it back in.
First to check straightness, you would take a magnet and place it on the front center of the rear axle, then get a metal tape measure and place it on the magnet to lock it to the front of the rear axle.
Next measure the distance from axle to kingpin top center on each wheel. Note that when you change your magnet to the other side of the axle that you want to make sure to be the exact same distance from your bearings to the magnet on each side.
To be square you want the distance to be identical.
Now check the distance to kingpin bottom, you also want these to be identical. You will find here if your steering yoke has been bent and tweaked.
If you are short on one side you can now use a neutral pill setting to make each side longer or shorter.
In the same way your steering tie rods should be the same length when at dead center. If they are not, you can use your neutral pill settings to lengthen one side of your kart. Even though this can have the effect of changing ride heights, width and length, I have found quite often that these adjustments actually bring all in line together as you would need. Something to do with the fact that the kart was probably in line at first, and after the bend, the height, length and width were all affected.
Which neutral to use?
Whether you start from North Quadrant, South Quadrant , East or West, doesn’t really matter in the scheme of things. And how you choose to go is up to you.
Some things to keep in mind though when dialing in the pills.
Lower ride height will lower your center of gravity and tend to give the kart more lateral force, less grip and make the front weight seem lighter under load. It can slow the weight transfer speed like taking a bar out might do. And it can help to reduce hop in a high grip situation. The lower ride height settings also lengthen the wheelbase, so they contribute to slower weight transitions and smoother slower rotations.
Higher ride height will raise your center of gravity and can help with an entry push giving you more bite on entry. It can help to fight a slide in the rear on exit, due to over steering. It can give you more grip in low grip situations or the wet. The higher ride height also makes your total length shorter, making your kart more darty and wanting to rotate faster. Which can make the rear more sensitive to slide. It will speed your weight transfer up.