Camber, caster, Ackerman

[r_chez_08]

Hi,
Ok, never really understood and looked into these when i made my kart, but I am going to give it a 'makeover' this summer and re do some bits.
As it has never really turned that well (compared to the ones at the track) i figured i would fix the angles.
Could someone please explain to me what camber, caster and ackerman is? And maybe show me some pics?(it has orobably already been done, sorry!)
Thanks!
Rob

[EastCoast]

Understanding Caster, Camber, Toe, and Ackerman

Caster Explained

To understand caster you need to picture an imaginary line that runs from through the upper ball joint and extends through the lower ball joint. From the side view the imaginary line will tilt forward or backward. The tilting of this imaginary line is defined as caster.

Caster is measured in degrees by using a caster camber gauge. If the imaginary line described above tilts towards the back of the car, at the top, then you will have positive caster. If the imaginary line tilts forward then you would have negative caster.

Positive caster provides the directional stability in your race car. Too much positive caster will make the steering effort difficult. Power steering will allow you to run more positive caster. Negative caster requires less steering effort but can cause the car to wander down the straightaway.

Camber Explained

Camber is the tilt of the tire as viewed from the front of the car. If the top of the tires lean toward the center of the car then you have negative camber. If the top of the tire tilts out away from the center of the car then you have positive camber.

Camber is measured with a caster camber gauge and is usually easily adjusted with shims or adjustable upper a -arms. Always check the toe when making camber or caster adjustments.

Toe - In Explained

Toe is the pointing in or pointing out of the front wheels as viewed from the top of the car. If the front wheels point in, toward the front of the car, at the front edge of the wheels then you have toe in. If the front wheels point out at the front edge then you have toe out.

In general, dune buggies and race cars are set with a small amount of toe out. The toe out provides directional stability. Toe out pulls on the tie rods taking out the tiny clearances that are built into the tie rod ends. Depending on the type of car typical toe readings are 1/16" to 1/4" out for tracks under 1/2 mile in length.

Toe can be set with a tape measure on the side walls of the tires. A tape is placed on the inside front of the tire as near the rim as possible or pick a good location on the tire tread if possible! (As close to center horizontal as possible) and then measured in the same location on the front edge of the other front tire. Remember to measure from the same locations each time you check the toe. Now check the rear side of the front tires as close to the center rear of the tires as possible. If this number is a smaller tape reading on the back edge this indicates toe out.

For a very precise reading you can scribe a line in each front tire. Use a tire scribe and spin each of the front tires to get your straight line. You can then measure between the two scribed lines with a tape measure or with a toe bar or with toe plates, a smaller measurement at the backside of the tire again, indicates toe out.

Ackerman Effect Explained

Ackerman is the difference in turn radius between the front tires. On oval track cars it can be desirable to create a situation where the left front tire turns faster than the right front tire. The Ackerman effect can help the car turn better through the center of the turn. You can measure the amount of Ackerman you currently have by using a set of turn plates. Typically, Ackerman is measured by turning the right front 10 degrees to the left. If you have Ackerman, the left front will travel further than the right front. A typical amount would be three degrees in 10 degrees of steering. To simplify, moving the right front from zero through 10 degrees of steering will cause the left front to move say 13 degrees in this scenario.

Ackerman is created by your front end geometry. Tie rods that angle forward from the inner pivot point out to the spindle will have more Ackerman.

[devino246]

You can read all that, or just look at this:

[gokart14]

check this out


http://www.bcot1.com/karting/

[toystory_4wd]

While Eastcoast provided some good info, and Devino too, I feel the Ackermann didn't get covered well enough for our purposes. In my own words-

As a four-wheeled vehicle travels through a curve, the tire on the inside of the curve follows a shorter path than the tire on the outside of the curve. This creates two needs-
1)the outside tire must turn faster than the inside tire. As our karts are typically rear wheel drive, let's suffice to say that since the front tires are freewheeling, this solves itself.

2)The inside tire must turn more (tighter, by a few degrees). If the tires always remain parallel to each other, this creates a scrubbing condition. Usually, the weight is thrown to the outside tire, so the inside tire actually scrubs sideways a bit thru the curve. This causes accelerated tire wear and poor handling. To correct this, we apply the Ackermann principle, so named after the fella that figured it out. Mr Ackermann determined that the tires must turn varying degrees as outlined above. Applying this principle as required for our purposes is quite easy.

Measure and mark dead centre on your rear axle, based on the contact patches of the rear tires. If your chassis is offset, or your wheels aren't at exactly the same spacing on both sides, don't use the frame for your measurement.

Now, move to the front of your kart, and locate your kingpins. These are the large bolts that your front spindles swivel on when you steer. Run a string from the kingpin centre to the rear axle centre. Repeat for the other side. Now- here's the trick- When you're setting up the steering arms (the tabs that your tie rods connect to on the spindles), all you have to do is make sure that when you drill the hole into the steering arm for the rod end, that hole MUST be centred somewhere along that string.

If you already have steering arms on your spindles and the rod end hole does not intersect with the string, simply cut the arm off and re-weld at the appropriate angle.

For karts that have forward-pointing arms, the same applies, only that you have to "extend" the string forward. When you're done, instead of the arms ending up slightly angled inward toward the framerails, they will be slightly angled out.

One last point- for the above geometry to hold true in practise, your tie rods should me more or less parallel with each other, and perpendicular (at right angles) to your framerails. Hope I've cleared this up for you.

[r_chez_08]

Thanks guys, and good diagrams devino, they helped the most.
Could someone give me suitable values for camber and caster?
Thanks
Rob

[EastCoast]

Originally Posted by toystory_4wd

While Eastcoast provided some good info.

LOL thanks I just used Google!

[toystory_4wd]

Doesn't matter where you got it- you provided it.

Caster can safely set around 10* up to about 15*. Camber can safely be set at 0*, as long as your KPI is decent. Now that I mention it...

KPI- or King Pin Inclination. Ideally, you shoul d be able to draw an imaginary line right thru the middle of your kingpin, and where that line hits the road should be the centre of your tire's contact patch. Setting up a kingpin angle generally involves welding your spindle brackets to your frame inclined at an appropriate angle (often, close to 10*). Then, your spindles get welded to the steering knuckles at the opposite angle. The result is this- With the wheels steered straight, the wheel is perpendicular to the road. As you steer, that KPI angle is altered by your caster angle, which helps you steer by loading up the inside front wheel while cornering.

[r_chez_08]

Ok, cool. When you say camber set at 0*, does it mean that the camber is approx 10* because of the kingpin angle being 10*, or does it mean that you need to weld the stub axle off 90* from the kingpin?
Wow there is alot more to steering geometry than i thought!
Rob

[redsox985]

I think camber's effects can be achieved through KPI which would require the reconfiguration of the spindles.

[r_chez_08]

Ok thanks. I will draw up some ideas for angles and what i am going to do and see what you guys think.
Rob

[toystory_4wd]

Redsox has my meaning. With the Kingpin angle at 10* inclined off the axle beam, and the spindle declined the same amount, actual static camber is 0*.

[r_chez_08]

Ok so is it like this picture

Or this one?

Im guessin the first, but surely that completely counteracts camber?
Sorry for the poor images, i am learning to use a drawing app on my ipod.
Rob

[gokart14]

are you sure you want to do that to your back axle. kinda confused when you say axle

[toystory_4wd]

First pic, Rchez. At rest there is Zero camber. The angles all combine to CREATE camber as the wheels are steered.

Gokart14- Back axle? You been reading this thread? Front axle! We're talking about steering geometry!

EDIT- Here's my crappy 5 minute Paint drawing of it...

[gokart14]

yes i have.... but dident think that go karts had a front axle. i understand what he is saying just dident understand what he ment by axle.

[r_chez_08]

Ok i get in now, thanks!
Gokart14- i meant stub axle, but did not have enough room to write it, because i had seen the spindle called stub axle before.
Rob

[toystory_4wd]

Not only is stub axle an appropriate term for spindle, but you can also use axle or axle beam to describe the frame's lateral structural member that spans between the spindle assemblies- which is no more or less of an axle than the rear "axle" on a 1wd kart, where the rear wheels ride on spindles and have a structural tube between them that we refer to as an axle.

[gokart14]

ya thats fine i was just a bit confused but that is what i was thinken

[r_chez_08]

ok one last question, if i have my steering arms what happens to the ackerman? do i just do the same angle on the other side of the kingpin?
Also, could I put a few strong springs eg. valvesprings on the kingpins for slight suspention?
Thanks
Rob