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Kart Tech Tips

Documentation

CRG Kart Tuning Manual   (pdf format)

Rotax Parts Manual   (pdf format)

CRG Parts Manual   (pdf format)

Maxter Parts Manual   (pdf format)

Rotax 125 MAX DD2 Manual  (pdf format)

CHASIS SET UP — A COMPLETE BREAKDOWN

Adjustment Specifics & Handling Effect

Front Track Width

Wide

A wide front track will add grip to the front end. It will also help the kart rotate in the corner due to the "jacking effect" which occurs when the wheels are turned into a corner. This concept can be seen easily when the kart is on the stand. By turning the steering wheel, you can watch as the inside tire goes down and the outside goes up. The "weight jacking" allows the inside rear wheel to lift up more, allowing the kart to rotate as it is powered by the outside rear tire. The wider the front track, the more pronounced (the "jacking effect").

Narrow

A narrow front track width will result in less scrub, providing better turning up front. A loss of the "jacking effect" is the trade-off. While the front will track around the corner better by getting more grip, without the lifting of the inside rear wheel, the kart will not rotate in the corner.

Front Ride Height

High Frame

To raise the chassis, lower the spindle in its carrier by moving the washers from the bottom to the top. By raising the front ride height, you effectively raise the center of gravity in the kart and will be increasing the side bite on the tire, making it grip harder. If you go too high however, the raised CG will make the kart "bicycle" or pick up its inside wheels.

Low Frame

To lower the chassis, raise the spindle in its carrier by moving the washers from the top to the bottom. By lowering the front ride height, you will take side bite away from the tires and allow them to slide instead of grip. This will decrease the grip in the front-end.

Front End Alignment

Toe-Out

Toe-out is recommended for sprint track applications. It helps the kart on turn-in although it will make the kart wander slightly on high-speed straight-aways.

Zero

Zero toe can be used on road race tracks in an effort to gain top end speed.

Tire Pressure

Higher

Increasing tire pressure will help the tire build heat quicker, providing increased grip in fewer laps. Too much pressure will heat the tire too quickly and result in excessive tire wear in a short number of laps. Finding the middle ground between heat/grip and tire wear is the key. Try to get the pressures so that they will increase no more than 2-3 lb. during a session.

Lower

Lower tire pressure will not allow the tire to come up to temperature as quickly and will likely result in a loose condition until the tires heat up and begin to grip.

Caster

Positive

Caster is normally adjusted using an offset adjustment pill at the top of the spindle carrier. The spindle can be tipped forward or back simply by turning the adjustment pill. To add or to put caster into the chassis, turn the pill so that the offset hole is towards the back of the kart, leaning the spindle back. This will give you more front grip.

Negative

Taking caster out of the chassis is accomplished by turning the adjustment pill so that the offset hole is pointing forward. This will stand the spindle up and will take grip out of the front end. Many teams take caster out of the chassis during qualifying, when the kart has fresh tires and does not need to fight for front grip.

Torsion Bars

Assorted

Torsion bars are essentially removable frame rails that are clamped to the chassis to control the amount of flex that a chassis has. By removing these bars, you can make the chassis stiffer or softer depending on the conditions.

Seat Struts

Assorted

Seat struts are bars mounted from the sides of the seat to the bearing hangers. They take advantage of the largest mass in the kart — the driver — utilizing this weight, transferring it straight to the rear tire, planting it hard. This will give you more grip.

Axle

Soft

A soft axle will flex more under load, absorbing the energy transferred during cornering, taking away from the tires. This absorption will not make the tires grip as hard and will therefore take grip out of the rear.

Hard

A hard axle will not flex like the soft axle, forcing the energy to the tires, which will make them work harder and provide more grip in the rear of the kart.

Hubs

Long

Different lengths of hubs affect chassis handling in a similar fashion to the different flex rates of an axle. The assorted lengths of hubs will control the flex of the axle. Therefore, long hubs will make the axle stiffer on the segment of the axle outside of the bearing hangers. This will make the tire bite and will result in increased rear grip, similar to a stiff axle.

Medium/Sort

Medium and short hubs will work conversely to the long hubs. The shorter the hubs the more the axle will flex. Increased axle flex means increased energy absorption that will allow the tires to slide. By going to small hubs you will decrease the amount of rear grip.

Rear Track Width

Wide

When discussing grip in relation to track width, there are boundaries when going too far that can cause the kart to become loose. Within limits, a wider rear track will be more stable and will provide more grip.

Narrow

A narrow rear track will be less stable at speed and will give the chassis less rear grip.

Troubleshooting

Entry Push, Kart goes straight when wheel is turned

  • Too much rear bite
    • Softer rear axle
    • Shorter rear hubs
    • Lower rear ride-height
  • Not enough front end bite
    • Widen front end.
    • Add caster.
    • Raise front ride-height.
    • Move seat forward.

Exit push, The kart will not turn on exiting

  • Kart not rotating
    • Soften rear axle.
    • Sorter rear hubs.
    • Lower rear ride-height
  • No jacking effect.
    • Widen front end.
    • Add caster.

Loose on entry, Rear slides out on entry of a turn

  • Too much front end bite
    • Lower front ride-height
    • Narrow front end.
    • Take out caster.
    • Move seat back.
  • Not enough rear bite
    • Stiffer rear axle.
    • Longer rear hubs.
    • Increase rear ride height.
    • Add seat struts.
  • Brake bias problem
    • Dial in more rear brake (if not locking rear brakes)
    • Dial in more front brake (in not locking up rear on entry)

Not enough rear bite

  • Widen rear track width.
  • Stiffer rear axle.
  • Longer rear hubs.
  • Add seat struts.

We invite you to e-mail your questions or requests so that we may assist in ensuring the your kart-related question is answered by the professionals at CRG-America.

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