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- - The Kart - - Setup Info - - Starting Karting - - Race Reports - -

SETUP:

Handling – The basics.

The most important thing to remember when setting up a kart (or any other vehicle for that matter!) is to only make one change at a time so that the driver can feel the difference that one change made to the way the vehicle drives. This rule should only be broken when there are obvious major problems with the handling and a solution is already known. This is important because unless a large amount of testing has been completed and well documented it may be a waste of time changing a few things at a time since the driver cannot tell which settings make a difference. At worst the changes could cancel each other out to some extent!

As mentioned throughout this website, in a competitive environment the most important thing to do is to set the vehicle up to achieve the quickest lap times, which may not be the most comfortable setup for the driver. However, by no means ignore the thoughts of the driver on ease of control etc. of the vehicle, as consistency is almost as important as outright speed!! Its no good having a vehicle that can produce very fast times but is difficult to control, as this will fatigue the driver and ultimately result in only a handful of fast times throughout a race with the rest being slower due to mistakes.

 

Some of the terms explained

Any vehicle will handle in one of three different ways round a specific corner, that is it will understeer (or ‘push’ in the US), be neutral, or oversteer (‘loose’ in the US). These are reasonably self explanatory but are explained as so:

Understeer is when the driver turns the wheel and the vehicle tends to slide straight on rather than follow the line of the corner. This is when the balance of grip is towards the rear of the vehicle.

Oversteer is when the opposite happens; the front follows the desired line around the corner but the rear tends to drift wide, and in extreme cases this can cause a spin. This is caused by the balance of grip being on the front of the vehicle.

Neutral is when the vehicle neither understeers nor oversteers, and put simply, the front and rear wheels both follow the desired line around the corner.

It is important to remember that some drivers may prefer the vehicle to be set up in different ways depending on their driving style. It is also worthwhile to point out that on a given track it is not unusual for the kart to understeer round some corners and oversteer round others. This can be down to a number of factors including setup, track surface, road camber, or the drivers inputs.

In karting there are also two other phenomenon which are more specific to karting than in cars, not to say that it does not occur when car racing! That is sliding and hopping. Both are experienced when the kart ultimately loses grip, however the mechanics of the two effects are very different. Sliding occurs when the tyres lose grip, causing the kart to slide rather than to follow the desired line around the corner. Hopping is caused by the outside tyres refusing to slide, and instead ‘hop’ across the surface of the track. These two effects can be seen at any meet and are obvious to spectators.

Jonathan MacGregor in his 125cc Rotax Max kart entering the bottom hairpin in the June round of the SYKC championship

 

Changes

In order to adjust the way the kart handles, there are many things on the kart that can be changed to essentially add/remove grip. These include:

- Tyre pressures
- Changing the track (width of the wheels front or back or both)
- Changes in steering geometry (toe, camber and castor where available on some chassis)
- Changing the stiffness of the chassis (addition of torsion bars, seat stays, bearing mounts etc)
- Weight distribution (addition of ballast, seat position) and ride height

 

Tyre Pressures

Tyre pressures can be altered easily and are one of the most important things to get right to achieve fast lap times. Not only can they be changed all at once, it is also sometimes preferable to run different pressures at the front than the back in order to achieve the correct handling balance. In order to fully appreciate how and why the tyres behave the way they do, it is neceesary to have a good understanding of tyre dynamics. A comprehensive explanation of tyre dynamics can be found here.

In general, increasing the tyre pressures increases both final operating temperature and the speed at which the tyres get up to temperature. Clearly reducing the pressure will have the opposite effect; on hot days or for longer races it is normal to reduce the tyre pressures to gain the best performance.

It is difficult to judge what the ideal operating temperature should be for the tyres, however a good guide is looking at the tyres after the race. A tyre running at the correct temperature will look slightly grained and have an appearance like orange peel. Running the tyres at too high a temperature for any sustained period of time can permanently damage the chemical makeup of the tyre and it will never regain its top performance qualities.

Increasing tyre pressure (significantly) also reduces the footprint of the tyre, which is the area of contact that the tyre makes with the road. This is important to remember, and can be especially useful in wet racing. If there is a lot of standing water and the driver is experience aquaplaning, the team have found that it is sometimes advantageous to increase tyre pressure to reduce the tyres footprint, therefore increasing pressure on the road and helping to cut through the water more effectively. This does, however, tend to lead to increased wear in the centre of the tyre. In general for wet conditions, the drier the track, the lower the pressures. Exact values can only be assessed by the driver.

 

Changing The Track

Adjustment of the track of the kart is one of the other major settings that most teams use to fine tune the handling of the kart. Adjustment can be made at both the front and rear of the kart.

Increasing rear track loses grip from the rear. Conversely increasing front track increasing the directness of the steering, increasing the grip on turn in (desirable in wet conditions).

It is also worth considering that increasing front track also has an affect on overall steering geometry and the amount of jacking that will occur. Jacking is the term used to describe the effect when the karts inside rear wheel lifts round a corner. This can be desirable since the back axle is solid, and since the inside rear wheel travels a shorter distance than the outside, extra drag occurs if both wheels are in contact with the floor, thus slowing the kart down. Increased front track can help induce rear wheel jacking, particularly in slower corners. It is evident when watching most kart races, but the rear wheel only has to be fractions of a millimetre off the floor for this to have an effect.

Jonathan MacGregor in his 125cc Rotax Max kart exiting the bottom hairpin in the June round of the SYKC championship

Steering Geometry

Most kart classes in the UK allow steering geometry changes to be made to fine tune the handling of the chassis. These changes generally only have a very subtle effect.

Changes can be made to the toe, the Ackerman (a complex subject!) and caster and or camber (depending on chassis).

Changing the toe in/out adds an amount of scrub to the tyres which can change the characteristics of the steering geometry and also helps improve straight line stability, however extra drag can result. (Toe in refers to when the wheels point towards the front of the kart when viewed from above, and toe out is when the wheels point towards the rear). It is usual to run the front wheels with a small amount of toe out (2mm or so) when the kart is on its trolley being setup, since when the driver is in the kart the chassis flex pulls the wheels into the neutral position, resulting in zero toe. This is done to minimise drag. In wet conditions a driver may feel it necessary to alter the toe settings to achieve the desired steering characteristics.

Ackerman is essentially the differential between the angle of turn between the outside and inside front wheels when the steering wheel is turned. This is done to allow for the fact that the inside wheel has a shorter distance to travel round the corner since it is on a smaller radius, However Ackerman can be changed to alter the ratios of the amount of turn in between inside and outside wheels in order to change the handling characteristics of the kart at different points in the corner. Decreasing the Ackerman angle will give a less direct turn into the corner but may help to scrub off less speed on exit. More complex information on Ackerman and its effects can be found here.

Camber is the 'tilt' of the wheel when viewed from the front of the kart. Positive camber is when the wheels point outwards at the top and negative camber is when the wheels point inwards at the top. Negative camber increases the amount of cornering force available (and so ultimate grip), however increased levels can lead to reduced straight line performance due to extra drag being induced. A low camber angle will reduce the amount of rear wheel jacking as described earlier. Castor has a similar effect on a kart, and is defined as the angle that the stub axle pivot line (the kingpin) makes with the vertical when viewed from the side. Increased castor will also increase straight line stability and make the steering feel stiffer. These effects are complex (especially when coupled with suspension effects as on cars) and are explained more thoroughly here.

 

Stiffness

Increasing the stiffness of the chassis at the rear increases the amount of grip on the rear of the kart on smooth and high grip tracks in dry conditions. On bumpy tracks it may occasionally be advantageous to not run such a stiff setup in order to maximise contact with the road, however this is rare. Stiffening the chassis can be done in many different ways. Tightening bumpers and side pod brackets, the addition of torsion bars and seat stays, changing the type of back axle for a stiffer or solid one (and adding in another rear axle bearing where possible) as well as having a different stiffness' seat and seat mounting can all increase the stiffness of the chassis. In wet conditions it is common for teams to reduce the stiffness of the chassis in order to maximise chassis flex and grip levels. However this is only effective with certain driving styles so its up to the individual driver to test out various setups and determine what is quickest for them.

 

Weight Distribution and Ride Height

Weight distribution and ride height are strongly associated. It is important when a team first gets a chassis to firstly fit the seat in such a manner that the weight distribution is (as a minimum) roughly equal left to right, and ideally that the front to rear distribution is also correct. It is also important that the seat is comfortable for the driver, however if some comfort has to be sacrificed in order to get a good weight distribution then this may be worthwhile. However, remember, an uncomfortable driver is not a fast driver! Distractions such as driver comfort can easily lead to a performance loss. Weight distribution or rough seat positioning data should be available from the kart manufacturer. This changes slightly from class to class. Essentially increased weight over one end/side will increase grip on that end or side. Likewise ride height is a subtle way of altering the handling balance; the closer the chassis is to the floor at one end, the more grip that end will have in relation to the other. Teams sometimes alter front ride height settings in the wet in order to aid turn in.

 

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