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Understanding Caster and Camber

Understanding Caster and Camber
Category: Comet Blog
Posted: 06-17-2014 09:33
Synopsis:

Multi-time WKA National Champion, All-Time Rock Island GP race winner and "Ace Chassis Tuner for Hire" Gary Lawson breaks down Caster and Camber in this article.


The topics of caster and camber are quite difficult to grasp for many in karting. Heck, it’s hard enough to just remember how to spell caster when referring to front-end geometry. Castor, on the other hand, is a lubricant commonly used in 2 cycle fuel mix.

Let’s first take a look at why caster is necessary and why it is so critical in karts. The solid rear axle design in karts makes it necessary for the inside tire to “unload,” or lift when cornering to enable the kart to turn. Caster is the main contributor to this process, although scrub radius, spindle kingpin inclination, and frame design also play an integral role.  Caster can be measured by the angle the kingpin bolt leans back toward the driver. This number can range anywhere from 8°  to over 20° . On the contrary, cars do not use nearly as much caster as karts (just a few degrees) because of the rear tires are independent and can turn at different rates

Now onto how it affects the handling of the kart… The first thing you will notice when a kart has a considerable amount of caster is the increased amount of strength it takes to turn the steering wheel.  Caster causes weight to move diagonally as you turn the wheel. As caster angle increases, you mechanically move more weight given the same degree of steering input.

Think of the kart as an “X.” The RF and LR are tied together, as are the LF and RR. The inside front wheel pushes into the track, while the outside front wheel travels in an upward arc away from the pavement. Again, this change in wheel height is to achieve wheel lift at the inside rear tire and allow the kart to turn without understeering (pushing).  Without caster the kart would constantly understeer, be inherently slow, and burn off the front tires in the process.

How much caster should you run and when should you adjust it? That is a key question when setting up a chassis. It is best to start at the factory recommended setting and adjust from there. If you deviate too far from this setting and are struggling, it is recommended that you start over at the factory settings. Many generalizations are made in karting. Unfortunately, there is rarely one concrete answer for any given situation.  That said, I will try to shed some light on situations that dictate varying degrees of caster.

It is generally accepted that:

Low HP classes - less caster (typically sportsman and 4cycle)
High HP classes- more caster (TAG, shifter, etc.)
Wet conditions- more caster or max caster
Tracks with tighter corners (ie. 180°  hairpins)- more caster
Tracks with wide sweeping corners- less caster

The most challenging decision is deciding whether increasing or decreasing caster will “free up” your kart. A “free” handling kart will release/accelerate out of the corner as quickly as possible. It will have as much forward grip as possible without binding the kart. To do this you must have some differential affect, and that is where caster again comes into play.

To assess which direction you need to go with caster (increase or decrease) requires a driver that has a good feel for the handling of their respective chassis.  Unfortunately, this is often not the case. As an example, the most overused and misleading term in karting is the word “tight.” I hear it almost constantly when a handling problem persists.  It is considered by many, mistakenly, as an all-encompassing term, which makes it extremely difficult to pinpoint the root of the problem. I’ve heard it used to describe many different handling issues including: understeer (pushing), hard to steer, hopping, and stuck to the track.

Although caster is not necessarily the best decision for each handling situation, here is a quick cheat sheet:

When to increase caster

Understeer (push)
Rear is stuck in the track (not lifting)
Kart is lying flat through the corner
Rain Conditions

When to decrease caster

Kart is physically hard to steer- decrease caster
Oversteer (loose)- decrease caster
Hopping-Decrease caster
Excessive wheel lift of the inside rear tire
Two-wheeling


Another important front end adjustment is Camber. Camber controls the contact patch of each front tire. A kart with negative camber will have the top of the tires leaning inward towards the driver, while the tire will lean outward away from the driver with positive camber. More positive camber will increase contact patch and induce sidewall flex, resulting in an increase in front grip. Negative camber will have the opposite effect.

Negative                 Positive                 Zero

    /   \                            \   /                        |  |

To measure camber you first need to choose a tool. Many in 2 cycle racing use the popular Sniper Laser System (measured in millimeters) that can be used on the kart stand.  Many 4 cycle racers use a camber tool that threads onto the front spindle made by Longacre, Intercomp, etc. (measured in degrees). These need to be used on a perfectly level surface (scale table) to provide an accurate readout.  You can also use alignment plates with a tape measure. Whatever method you choose it is important to always do it the same way so you have a controlled reference point.

Sometimes the most challenging decision on camber is simply where to start. The easy choice is to first consult the manufacturer. If you don’t have that option you need to take into account a few different things:

  1. Tire compound/design
  2. Class/speed
  3. Track temp/grip level

A slight negative setting is commonplace on most karts as a starting point. About 2mm or 1/2°   negative is acceptable.  

Cheat sheet for situations

Reasons to possibly increase negative camber:

-Track temp/grip level is increasing and kart is slow on corner exit
-Changing to a soft compound tire
-Too much overall front grip
-Sidewall rolling under
-Front end hopping
-Running a lower horsepower class
-Putting on new tires

Reasons to decrease negative camber or even run positive camber:

-High hp karts sometimes benefit from the increased grip of positive camber
-Understeer on corner entry
-Low grip track conditions
-Hard compound tires
-Tires are wearing down (the inside naturally wears more)

While your camber setting is important to be aware of, it should be considered a fine-tuning adjustment.  However, a quick camber check in between sessions can reveal a possible issue.  If you have a significant change in camber on one side it could indicate a bent kingpin, bent frame, or turned eccentric pill. All will have a drastic effect on performance.

Trial and error is a great way to learn in karting. Don’t be afraid to make a change and note the result on the stopwatch. Taking into account driver input is important, but many times it can be incorrect and lead to the wrong adjustment. Either way, don’t just hope your kart will get faster just by moving wheels in and out and adjusting air pressure. Don’t be afraid to get dirty and do some serious work! Lastly, don’t be afraid to ask for help. There are a lot of great people in karting that are willing to offer advice!

Gary Lawson
Prime Time Racing
Garylawson25@yahoo.com
440-567-9594  


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