Kart setup

As with any other sport, one needs to understand and abide by the rules and regulations that govern karting. Setting up a race kart chassis properly is 100% legal, providing one abides by the regulations, but requires an understanding of the basic technical principles that govern the handling, plus good feedback from the driver. The recommendations that follow have all been verified via numerous reliable sources, so should in theory work well.

Terminology

Bearing carrier or cassette: Usually two or three elements in which the rear axle bearings are mounted.

Caster: Rearward tilt angle (off vertical) of the kingpin on which the front wheel spindle pivots.

Camber: The tilting (off vertical) of the top of the front tyres toward each other is negative camber, and tilting out is positive camber. On a kart, usually expressed as millimetres.

Chassis lift: Raising of the inside rear wheel on corner entry. This lift or ‘jacking’ is caused by a combination of frame stiffness, axle stiffness, caster and other factors.

Chassis bind: A combination of elements including too much frame stiffness, overly stiff axle, etc. that cause the kart to have too much grip, thus restricting performance.

Chassis scaling: Weighing the kart and driver, preferably on digital scales, to determine weight distribution fore/aft and also side/side.

Darting: An unstable condition where the kart is overly responsive to steering input.

Grip: The level of adhesion between the kart tyres and the track.

Hopping: Bouncing of the kart as the throttle is applied near the apex of the turn.

Jacking effect: Raising of the inside rear wheel on corner entry caused by a combination of frame stiffness, axle stiffness, caster and other factors.

Kingpin: The pin or bolt on which an individual front wheel spindle pivots.

Live axle: A one-piece rear axle without a differential. A differential allows the outside wheel to rotate independently of the inside wheel when the vehicle is cornering. A one-piece axle forces both rear tyres to try and rotate at the same speed, and since they are following different radius curves around the corner, one tyre loses the fight.

Oversteer: A tendency for the rear of the kart to slide outward at corner entry or mid-corner. This tendency must be occurring as the kart enters the corner, and not on the corner exit when the application of power can cause a ‘power induced oversteer’.

Power induced oversteer: A tendency for the rear of the kart to slide outward at corner exit under hard power application. Steady state throttle should not upset the chassis balance.

Push/kick: Occurs near the apex of the turn as the kart transitions from braking to the application of the throttle. The kart rear end kicks out suddenly at the apex.

Ride height: The distance of the kart chassis, either front or rear, from the track surface.

Seat strut: A brace mounted between the seat back and the bearing carrier to add stiffness to the rear of the kart chassis.

Side bite: Lateral adhesion between the kart tyres and the track surface.

Spindle bolt: The bolt or pin (a.k.a. kingpin) on which the individual front wheel spindle pivots.

Torsion bar: A bar that is used to alter stiffness by adding reinforcement to the kart frame.

Toe in: The condition of front-end alignment when the front edges of the tyres are closer to each other than the rear edges.

Toe out: The condition of front-end alignment when the rear edges of the tyres are closer to each other than the front edges.

Track: The overall measured width of the front or rear, taken from the outside edges of the tyres.

Understeer: A condition when the kart will not turn into the corner due to a lack of front end grip and is also known as ‘push’.

Weight distribution: The percentage of total weight on each tyre, alternatively the front half of the kart compared to rear half (front/rear weight distribution).

Wet tyres: Soft compound tyres with full tread used under wet track or rain conditions.

Wheel spacer: A metal ring that slides over the front axle to change the front width (i.e. track) of the kart.

Basic chassis theory

A kart is a unit made up of tubes that flex fairly easily, and powered through a live axle (one without a differential). The chassis is thus designed in a manner to allow it to turn the only way it can without having a rear differential i.e. with the inside rear tyre lifting off the track on corner entry. The outer rear tyre then drives the kart around the corner because the opposite rear tyre is off the track surface. If the inner tyre does not lift, then no matter how much you turn the steering wheel, the front of the chassis will want to keep going straight thus creating an understeer or ‘push’ condition. The kart and the driver should do most of the work of changing direction early in the corner, so they can drive smoothly off the corner and not bog the kart down. NB - before completely changing the kart’s set up, be sure the problem isn’t due to the nut sitting behind the steering wheel.

When a chassis lifts up the rear wheel properly, then the chassis can pivot and turn. Therefore, the kart must be set up with sufficient side grip to enable the inner-rear tyre to lift upon entry as it is faster to drive the kart through the corner than to try and slide through. In general, when the chassis elements (axles, torsion bars, etc.) are on soft settings, the kart has less grip. The more rigid these become via altering of settings the more grip the kart will have, and eventually, the chassis will get too firm to perform properly.

It is best to work on the end of the kart that is not handling well. If, for example, the problem is understeer, then try to solve the problem by first adding more front grip. If that doesn’t solve the problem, then try taking grip away from the rear to balance the chassis. When correctly set up, the steering effort will be reduced and the kart will become more driveable as everything will be in balance, with neither end too tight or too loose.

If you turn the steering wheel and the motor load increases, the chassis is ‘bound’ and wasting power, so free up the chassis and gain power. If a kart has too much side bite it will feel great in the corners but loses speed because it is ‘bound’. Because the engine can’t gain power to overcome any excess resistance the kart simply goes slower, and if this is due to bad alignment, the kart will probably also handle poorly. Engine power is wasted in several ways, including –

Brake pad drag
Friction in the wheel bearings
Incorrect wheel alignment
Misaligned engine & rear sprockets.

Ballast weights can be moved around to fine tune the handling characteristics of the chassis. Moving weight to the front of the kart will provide more front end grip. Be careful to not add too much front end weight, as it can make the kart prone to larger understeer and oversteer swings when at the traction limit. If weight is moved to the rear of the kart, the effect will be more rear end grip. Weight can also be moved vertically up or down, and moving the ballast weights (or the driver) upwards via a seat adjustment will provide more grip as it achieves more weight transfer to the wheels.

A correctly set up chassis tells the driver if the kart is sliding with too little grip or hopping with too much grip. When the kart is set up correctly, it will provide maximum grip through all corners, and this is where the greatest saving in lap times can be made.

Initial chassis setup

Normal track conditions

The settings below are recommended as a good starting point for a dry track with normal levels of grip (not slippery, or with high amounts of rubber that provide a lot of grip). The front settings on the kart should be adjusted using a Sniper laser or similar.

Weight distribution should be ~43% front, ~57% rear and 50/50% side to side.
Front ride height should be on the lowest setting.
Rear ride height should be higher than the front.
Tyre pressures should be set around 1,0 bar (refer chapter entitled ‘Tyre setup’).
Front toe out should be set between 0mm and 3mm (smaller motors tend towards zero).
Camber should be set between 0mm and 2mm negative per side (always use same conditions when checking).
Caster adjusters should be set at the central points on top and bottom (to be adjusted later after feedback received from the driver).
Side pod bars need to be loose, but with bolts tightened.
Seat should be fitted using the standard mounting points.
Seat struts (if allowed in your class) should be in place.

Low grip track

Alter the ‘normal track’ settings in line with the recommendations below as a starting point for a dry track with little grip. These types of tracks are often referred to as ‘green’, given the inherent lack of grip in them.

Front ride height should be raised as more front grip is needed.
Rear ride height should be as high as possible to increase grip.
Axle should be medium to stiff.
There should be at least two seat struts on each side of the seat.
Rear torsion bar should be in, and positioned in the flat setting as a starting point.
Caster should be increased.

High grip track

Alter the ‘normal track’ settings in line with the recommendations below as a starting point for a dry track with a high amount of grip, or perhaps one with a lot of rubber laid down. The objective here is to remove grip from the kart.

Rear ride height should be as low as possible (axle in highest position).
Axle should be soft.
Loosen or remove the seat struts.
Rear torsion bar should be removed.
Increase negative camber.
Decrease caster - try less caster as grip comes up, and more as tyres wear.

Front end adjustments

Front end adjustments include track width, toe setting, Ackermann, camber, caster, and ride height. Changes to these settings are usually made when handling problems occur at the entry to the corner.

Front width

Refer Figure 1 below. The most common adjustment made to change the handling of a kart is by working with its front track, or front end width. Widening the front track will create more of a jacking effect when the wheels are turned. This will result in more front end grip and quicker turn in. Narrowing the front track will have the opposite effect, and this will result in slower turn in and less front end bite. Also, the lack of jacking effect will not raise the inside rear tyre (as much) on corner entry, preventing the kart from rotating into the corner (as much) and increasing a ‘push’ condition due to the excess traction provided by both rear wheels remaining on the track.

If the kart pushes or understeers entering a corner, widen the front track (the spacers provided are usually 5mm or 10mm wide). If the front track is at maximum width and the kart still pushes, move the front wheels back to your starting position and increase the caster. In this scenario, you might also re-examine the seat position. If the kart is overly grippy or ‘binds’ on the front when the wheels are turned, reverse the procedure. A very general rule of thumb is - the less available grip, the more scrub radius (increase in front width), caster and starting tyre pressure should be used.

Toe in/out

Refer Figure 2. Front end bite and steering response can be corrected by simple adjustments, and the toe setting is a good place to start. Remember to set the steering
dead ahead during front wheel alignment.

Toe settings will affect weight transfer, top speed and cornering response. The more toe in or toe out, the slower top speed becomes due to excessive drag by the tyres. Despite this negative effect, increasing the toe out will increase initial cornering response, thus giving the driver a better turn into the corner and reducing understeer. However, if the kart is overly sensitive to steering wheel movement at the point of turn in and begins to oversteer, the toe out settings may be too high. With toe out, the inside front wheel moves down in relation to the chassis slightly more than it will with zero toe or toe in. On a dry surface, a toe setting of zero to 3mm out (closer to zero for lower powered karts) is recommended. For a very high speed track, setting close to zero toe also may help top speed. Toe in is not normally used on a kart.

Remember that the kart chassis will deflect under the driver’s weight and this deflection can affect toe, caster and camber settings in particular. Generally, the goal is to have zero toe when the chassis is loaded with the weight of the driver and fuel sitting on the track, and thus a heavier driver will need slightly more unloaded toe out than a lighter driver.

On high speed tracks in particular (as opposed to the tighter sprint tracks), most karts will probably handle and accelerate better with the toe set to absolute zero when the kart is fully loaded on the ground. However, on sprint tracks, slight toe out will help turn-in to corners, but rarely more than 2mm (on each side), except in wet conditions, when larger toe out setting can be helpful.

When setting the amount of toe, make sure that the toe is equal on each side. If you change caster and/or camber settings or front ride height, you will have to recheck toe as well.

Ackermann

Refer Figure 3. Ackermann steering makes the front tyres turn at a different rate. For example, the front inside tyre will turn more than the outside tyre when turning into a corner. This creates a faster steering response, thus causing flex through the chassis when turning.

Adding Ackermann makes the kart steer more positively and lifts the inside rear tyre at an increasing rate as steering is added. At the same time, the driver will notice a decreased amount of steering input needed to turn the kart (because the inside rear wheel is being ‘jacked’ more). As a result, the kart becomes more sensitive to the driver’s input. In contrast, decreasing Ackermann makes the kart steer more slowly and more steering input is needed to corner.

As shown in Figure 3, the spindles will usually have 2 or 3 tie rod hole locations – using the inside hole increases Ackermann, while the outside hole decreases Ackermann. The tie rods can be lengthened or shortened to fit any hole. Make sure you have sufficient threads on the rod ends when using the outer holes, and if not, fit longer tie rods.

Caster/camber adjusters

Generally, karts are quite sensitive to caster adjustments and are not as sensitive to camber changes. Caster has the greatest effect at corner entry and during the first third of the corner. Camber has the greatest effect in the middle third of the corner. The final third of the corner is controlled largely by rear axle setup. If changes in these areas don’t produce any real change on the track, it’s probable that the seat position is incorrect and you are out of the tuning ‘window’. When caster and camber are both set correctly, there will be even wear across the tyre face.

Caster

Refer Figure 4. Caster affects the grip of both the front and rear of a kart. It does this by transferring weight to the opposite rear wheel during cornering. Although it may seem complicated, there are a few simple rules to follow when adjusting caster.

Generally, more caster equals more front bite and less caster equals less front bite. If the caster is decreased (less kingpin angle to the vertical), the kart will be easier to steer. It may be advisable to decrease the caster setting if the track conditions are providing too much grip and the kart will free up and be more drivable if the caster is removed in this scenario.

The driver may want to add caster if the conditions are cold. This will offer more front grip, less rear grip and help eliminate understeer. It is particularly useful in wet weather conditions. Caster also causes a change of camber when the steering is turned, resulting in more negative camber on the outside front wheel and more positive camber on the inside front wheel.

Importantly, increased caster also increases the jacking effect on the front wheels which helps unload the rear axle (inside wheel) more on corner entry. If a soft rear axle is being used, it is possible that increasing caster will alleviate an understeering condition by unloading the rear axle more and help balance the chassis. Since the rear tyre is lifting sooner in the corner, there is effectively less rear grip at that point in time. Generally, karts are fairly sensitive to caster changes and therefore it is quite effective as a primary tuning tool.

Camber

Refer Figure 5. Camber is usually adjusted when the track surface is wet. In these conditions, the driver can negatively adjust the camber to find more grip. Camber is the setting mostly responsible for maintaining the maximum outside front tyre rubber on the road in the corners, particularly at mid-corner. Setting camber to zero will nearly always be the best starting point and can be fine-tuned using tyre wear or tyre temperatures across the tread as a guide.

Front ride height

Refer Figure 6. Raising the kart’s front ride height raises the karts CG as well as moving it further back i.e. there is more weight transfer on cornering (lowering the ride height provides the opposite result). The increased weight transfer translates directly to increased grip and is thus useful for removing an understeer condition. Another effect of having moved the CG rearwards is that it creates more rear end grip throughout the entire corner as well as making the rear of the kart sit flatter. Taken to the extreme, and the kart will sit too flat through the corner i.e. the inside rear wheel cannot lift off the track - the engine then bogs down because it is trying to drive both rear tires through different arcs via a fixed back axle.

Rear end adjustments

The rear end adjustments include, track width, rear ride height, axle stiffness, bearing locations and seat struts. Changes to these settings are usually made when handling problems occur on the exit of the corner.

Rear track

Refer Figure 7. The general rule is to run the rear of the kart as wide as feasible (but within specifications), assuming the chassis is performing well. Also, a wider rear track will provide a smoother ride. A smaller track width will provide more grip, but at the expense of stability. If necessary, change the rear track in 3mm to 5mm increments, as most chassis are very responsive to minor changes if the seat is in the correct position. In summary,

Narrower track: more grip, but less stable.
Wider track: more stable, but less grip.

Axle stiffness

The axle has a very strong influence on rear grip characteristics and in almost all cases, you should use a mid-range axle. The hard or stiff axle doesn’t flex like a soft one and forces energy into the tyres, thus making them work harder and provide more grip. It is used when the weather is cold, or in slippery track conditions. The softer axle is used if conditions are extremely grippy or where excess rubber has built up on the track.

In general, high power karts need stiffer axles for more traction. Lower power karts have a greater need to ‘free up’ the chassis and will run softer axles. The rear axle acts like a spring and the softer the spring, the more/longer the inside rear wheel will stay up. Tall drivers generally will need softer axles to help reduce grip.

Rear ride height

Refer Figure 8. Most chassis have two or three settings for the rear ride height. Ride height is literally how high the kart is above the track, so raising the ride height of the rear of the kart will require placing the bearing carrier bolts in the lower bolt holes.

The chassis should be run with a higher ride height for better grip. The higher ride height creates more leverage, which gives more weight transfer to the outside tyres and the result of this is increased grip. Lowering the ride height will have the opposite effect and cause the kart to have less rear grip and possibly oversteer. Only in cases where there are very grippy track conditions should the ride height be decreased.

Seat struts

Seat struts should run from the very top of the seat to the two outer bearing cassettes. On the motor side, it may only be possible to use one strut. The seat struts allow the high leverage point of the driver to transfer load to the rear tyres which essentially creates more rear end bite. When seat struts are removed, the driver’s high leverage point is not taken advantage of and minimal load is transferred to the rear tyres. Usually, one would want to remove or loosen seat struts if trying to reduce rear grip. Tall drivers, for example, will have less need for seat struts.

Bumpers

The front bumper bolts (to the chassis points) should remain tight at all times. There is a school of thought that loosening the rear bumper will provide less grip at that end of the kart and in theory this is correct.

Side pod bars

In almost all circumstances, leave the side pod bars loose. Tightening the side pod bars will give the kart more side bite and generally tighten the chassis. Let the bars fit loosely in the chassis, but be sure the bolts themselves are tight (also use nyloc nuts).

Tyre pressures

For most applications, you should stay between 0,8bar and 1,5bar. In general, the higher the tyre pressure, the faster the tyres will come up to temperature and the more grip they will have. However, if too much air pressure is used, the contact patch with the track surface will be reduced, the usable section of the tyre may overheat, pressures could climb even higher, and as a result adhesion and tyre life will be reduced.

Bearing carriers

The axle bearing carriers can have an influence on the axle stiffness since the portion of the axle between the bearing and the hub is the part that flexes. If you widen the rear track, you are losing a bit of traction because the distance from the bearing carrier to the hub is greater. The normal installation is with the long bearing race (carrier) pointed inward.

To effectively soften the rear axle a bit, the third bearing (if fitted to your class of kart) can be set loose in the frame housing. The normal bolts are replaced by bolts of a smaller cross-section and the bearing is not secured with locking screws to the axle.

Turning the long race of the axle bearings outward will stiffen the axle ends and gain grip. Bolting the third bearing securely in place and tightening the set screws to the axle will also stiffen the axle and increase grip.

Remember, the bearings all function like fulcrums with the axle working like a lever, so the flexing on both sides of the bearings affect the overall stiffness of the rear assembly. If the centre bearing is not moving smoothly in its hanger, it can absorb and release energy in an uncontrolled manner which can cause hopping in the corners.

Rear axle assembly run-out

The wheels, axle, hubs and tyres will all inevitably have a certain amount of run-out or deviation from being perfectly round. Sometimes these small individual irregularities can add to each other to form a significant out of round condition. This will, in effect, often feel like an out of balance tyre and will tend to upset the kart at the middle and exit of the turn when dynamic loading is greatest.

The kart may feel loose and hopping, but the effect can be subtle to the driver. The tuner may keep trying to tighten the kart to the point of binding, but the problem could be run-out. Careful assembly of components will help minimize run-out by using the irregularities of each individual element to balance each other and not provide a cumulative problem.

Brakes

Refer Figures 9 & 10. The brake pedal pressure can be adjusted if it doesn’t suit your driving style. The higher the actuating rod on the pedal, the more pedal pressure is required whilst a lower setting will make the brake more sensitive and require less pedal pressure. On the master cylinder end, there are two positions available. The higher setting will produce a more sensitive brake requiring less pedal pressure. Pedal pressure should never be spongy, and if so, the system must be bled. Brakes can also tend to ‘drag’, and when this happens it usually manifests itself as the engine having no top end speed, so check them on a regular basis.

**Figure 9 - Brake pressure adjustment (brake pedal end)**

**Figure 10 - Brake pressure adjustment (master cylinder end)**

Torsion bars

Refer Figure 11. There are essentially two types of torsion bars available. The first is a tubular unit with differing wall thicknesses available, so the thicker the wall the stiffer it becomes. The second type is a tubular unit that has a flattened portion in the centre of its length. When the flat portion is ‘horizontal’ it is fairly flexible, whilst if it is turned to ‘vertical’ it becomes a lot stiffer. In general, having a more rigid frame produces more tyre grip. Having more frame flex, reduces tyre grip. Torsion bars are available for the front (and also rear for some makes of chassis) of the kart, and can be left out when you want to reduce grip either at the front (or the rear or both ends). A stiffer frame configuration is used in low grips situations, such as a damp or wet track that doesn't provide a lot of tyre traction. In a low grip situation the installation of the torsion bar will not increase the rear end grip by much due to the fact that it will not allow the chassis to transfer weight and lift up the inside wheel as much (or as long).

Tyres

Temperatures will vary somewhat from one tyre to another. Try for equal temperatures across the tyre face. The following are some basic troubleshooting guidelines.

Too much heat in the centre of the tread usually indicates too much pressure in that tyre.
A cooler centre usually indicates too little pressure in that tyre.
Hottest on both interior edges at the front end usually indicates too much negative camber.
Hottest on both interior edges combined with turn-in oversteer usually indicates too much caster.
Too cool on the interior edges at the front end usually indicates more negative camber is required.

A properly inflated tyre on a properly aligned chassis will have a slightly grained surface (not unlike sandpaper). A tyre that is running too cool is not being used aggressively enough to build up heat, and it will be smooth with no graining. If there is smooth graining, but the interior edge of the tyre is showing small strips of rubber or much more aggressive rubber deposits that look like the rubber is being overheated, then the kart is probably running too much caster, camber, or there is another condition that is overheating that edge. That edge will look different to the rest of the tyre because it is running hotter.

Hopping of kart

Hopping on a kart is one of the most annoying things and can take a lot of work to cure because it can be the result of two sets of circumstances, each requiring a different fix. Tall drivers, because of their height, tend to apply a rapid weight transfer to the outside rear wheel when cornering which effectively tries to flip the kart. This pulls the inside rear wheel off the track much more rapidly than one would expect and the chassis effectively becomes a loaded spring wanting to force the wheel back onto the track as fast as possible - which of course it does, and continues to do so while the driver is fighting the throttle and getting his ribs bruised in the process. The fix is to get the centre of gravity as low as possible by moving ballast weights, altering the seat height, moving the seat backwards, lowering rear ride height, or softening the rear of the kart.

If the kart is not lifting the inside rear wheel particularly high and dropping it violently back onto the track, then the hop being experienced is usually due to the tyre ‘letting go’. Lateral forces build up in the tyre and the shape of the contact patch with the track alters as the tyre deflects. When they reach a certain limit and deflection becomes extreme, everything releases and the tyre rebounds to its normal shape and starts the whole process again. It usually feels more like a ‘chatter’ than multiple hops sideways and often occurs on green tracks. The fix is to run higher tyre pressures and also to increase the rear grip.

Gear ratios

Too large a sprocket on the back of the kart and you will probably be fast through the tighter parts of the track and in the slower corners, but once you hit the long straights you are going to be a sitting duck (it’s like driving in 4th gear when everyone else is in 6th). On the other hand if you have too small a rear sprocket you might be like a rocket at the end of the straight, but you’ll lose too much on the tighter corners and slower parts of the track to really benefit from the increased maximum speed.

If, for example, the gear ratio for a given track is always an 11-81 for the fast drivers, then put on an 11-81 and run that ratio until you are competitive. Adding a couple teeth because the driver isn’t getting through the corners very well or because the kart isn’t cornering as well as it should isn’t really a very good fix. You need to fix the real cause of those problems before you mess with gear ratios.

Going larger at the rear in wet conditions can help a lot. If you switch to rain tyres then adding 3 or more teeth would not be unreasonable. This is because the engine revs are not so high and adding teeth provides more pull out of the corner. As the track dries and the corner speeds increase, then running less teeth becomes more and more important. What ratio you run in the rain is always an educated guess, but the wetter the track the more teeth you add, and the drier the track the less teeth you add.

Wet weather conditions

Obviously the first change is fitting of rain tyres. Beyond that, racing in the wet is extremely challenging, even more so if you’re stuck with a dry set up. The changes below will serve to improve adhesion in the wet.

First, a word or two about driving in the wet. Get some RainX for the outside of your visor, a good anti-fog agent for the inside of your visor, and a plastic rain suit to wear over your driving suit. The typical racing line contains oil, water and rubber - this is not a good combination in the wet. You want to spend as little time on the normal racing line as possible. In the wet, the proper driving line is to ‘square’ the corners and cross-over the normal racing line, instead of following it. A good portion of body English (leaning the driver’s body to the outside of the corner) is also useful in an effort to properly load the outside front tyre when turning into a corner.

Move the front wheels out as far as possible. Some manufacturers have extensions that attach to the spindle, making it possible for the front track to increase even more.
Rear track should be moved in as far as possible.
Set front ride height as high as possible.
Set front end for maximum caster and increase camber if possible.
Increase tyre pressures as this will make the tyres heat up faster. Low tyre temperatures can be a significant problem in the wet.
If you have time, run a medium stiffness axle.
Remove torsion bars.
Move the rear of the seat up around 25mm above normal settings. If time will not allow such a change, place a thick folded towel or padding in the seat to raise the driver.
Rear ride height should be as high as possible.
Shield water from splashing on the brake rotor (fixing a number panel in front of the brake caliper should accomplish this).
Tape each side pod closed if it has holes.
Spray ignition with a water repellent such as WD-40.
Drill two holes in the seat bottom for drainage.
Cut a plastic container and tape it to the air box in such a way that if serves to block water from directly entering the air inlets. A word of warning however, as this might not be allowed for your class.

Air density and jetting

Any engine produces its maximum power when it is running the correct air/fuel mixture for the atmospheric conditions prevailing at that time. On a kart, this is controlled largely via the main jet and to a much lesser extent via the fuel or air screw on the carburettor. Relying on gut feel, that it’s warmer/colder, or that it feels more/less humid, etc. to make jetting changes is a real hit and miss approach.

Air density is the mass of air in a given volume and it is dependent on temperature, pressure and humidity, so the lower the density, the less oxygen is available (thus less fuel required as well) for combustion and vice versa. Contrary to popular belief, humid air is less dense than drier air as it contains water vapour which is lighter than both nitrogen and oxygen. Relative Air Density (RAD) is the ratio of the calculated air density to the air density at sea level using standard reference conditions. By using a RAD meter combined with some track testing, one can establish a baseline i.e. which jet is working best on the kart and what the RAD is at that time. When conditions change, the RAD will also, and knowing the percentage change, one can then make far more informed decisions on what needs to be done with the jetting or the fuel screw.

Types of camber/caster adjusters

Essentially there are two types of adjusters that are fitted to the front end yokes of a kart viz. an older type that has an offset ‘pill’ with either 4, 8 or 20 adjustment holes, or a later version Sniper type adjuster. Figure 12 illustrates both types.

The Sniper type of adjuster allows one to adjust the camber and caster totally independently of each other. On the other hand, with a pill adjuster, the kingpin bolt is fitted through an offset hole in the pill. The underside of the pill has a raised circular flange that fits into a machined hole at the top of each yoke. Therefore, when the pill is rotated in the yoke, the kingpin bolt has no option but to move either inwards/outwards as well as fore/aft at the same time i.e. it is nigh on impossible to make a camber adjustment without affecting the caster and vice-versa.

Troubleshooting handling

A word of warning - Never change more than one item at a time or you won’t know what is helping or hurting your setup!

Front end of kart is not gripping in corners (understeering)

Move front hubs out one wheel spacer on both spindles.
If front of kart becomes too wide, move wheels back to original spacing and increase caster (be sure to re-check toe & camber settings).
Raise rear tyre pressures by 0,1bar.
Raise the front ride height.
Add more toe out.
Increase caster.
Add weight to the front of the kart.

Rear end is sliding (loose) at entrance of the corner, or there is too much front bite

Move front hubs in one wheel spacer on both spindles.
Lower rear tyre pressures by 0,1bar.
Move weight away from the front of the kart.
Lower the front ride height (be sure to re-check toe, caster and camber settings).
Remove caster (be sure to re-check toe & camber settings).
Reduce the Ackermann setting.
Decrease rear track.
Raise rear ride height.
If a third bearing carrier is fitted, loosen bolts completely.
Fit a stiffer axle.

Kart is hopping in the corners

Establish type of hop (violent or tyre chatter) and act accordingly.

If tall driver and violent hopping, lower any ballast to a lower vertical position (especially in the rear of the kart), move the seat backwards, angle the rear of the seat down, lower the rear ride height, change to a softer axle, remove additional seat struts if fitted.
If tyre chatter is present, increase rear tyre pressures by 0,1bar, decrease rear track, fit stiffer axle.

Kart is sliding on all four wheels too much, or there is not enough side bite

Tighten up (stiffen) the torsion bars.
Lower the hot tyre pressures by 0,1bar.

Kart is not drifting enough on all four wheels, or there is too much side bite

Loosen up (or remove) the torsion bars.
Raise the tyre pressures by 0,1bar.

Kart is tight at the exit of the corner, or the front end is understeering at the exit of the corner

Reduce the rear track.
Raise the air pressure in the rear tyres by 0,1bar.
Change to a softer axle.
Lower any ballast at the rear of the kart to a lower vertical position.
Remove one set of seat struts (leaving 1 on each side).
Lower the rear ride height.

Kart understeers or oversteers, but only in one direction

Check that kart corner weights are equal.
Check for a twisted or bent chassis.
Check that settings are equal on both sides of the kart.
Check equal side to side tyre pressures.

Kart is darty on the straights and dives rapidly into the corners

Check the toe settings as there may be too much toe out.
Move front hubs out at least one spacer on both spindles.

Kart suffers from push/kick

Move the seat forward.
Decrease the rear track width.
Increase the front track width.
Increase the rear tyre pressures.

Emile McGregor - MSA Technical Consultant