Scaling the kart is perhaps the most important thing a driver or team can do to ensure proper handling of their machine. When the kart is scaled properly, the ideal weight distribution is achieved. As a result, the kart will have the potential to perform at its optimum level. If the kart is not scaled properly, the opposite will be true. The machine will never perform at its optimum level, nor will it respond positively to chassis adjustments. Some common problems of an improperly scaled kart include under-steer, excessive or insufficient load on any one tire, chassis binding, and lack of side bite in cornering among many other problems. An improper weight distribution can also lead to incorrect diagnosis of handling problems at the track. For most karts, the following weight distribution is recommended:
- 43% Front Weight
- 57% Rear Weight
- 50% / 50% Left / Right Weight
These are just recommended starting points. Weight can be moved around at the track to fine tune the handling characteristics of the chassis. Moving weight to the front of the kart will provide more front-end grip. 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. Moving the weight upwards will provide more grip wherever the weight is located. For example, if weight is placed high on the seat, we could expect more grip in the rear of the kart. If weight is placed lower on the seat, we would expect the kart to lose rear-end grip.
The seat placement is the single most important weight adjustment on the kart and is done before the scaling process. Proper seat placement may result in almost perfect weight distribution before the weight is added to the kart. Each manufacturer has different instructions for doing this, and it is wise to follow those instructions as carefully as possible. If you have bought a used kart and do not have instructions, call your local dealer and they should be cooperative.
Scaling the Kart
The following steps are very important to the scaling accuracy of your kart.
- Ensure that the floor is level. To compensate for a floor that is not level, place shims under the appropriate corner scales.
- Set castor and camber that is consistent on both sides of the kart.
- Set spindle heights consistently on both sides of the kart.
- Set toe (always remember to set toe after setting caster and camber) and center the steering wheel. If the wheels are not centered during weighing, the geometry of the kart will cause each corner to be loaded incorrectly. As a result, the readings on your scales will be false.
- Check the tyres to make sure they are at a race setting.
- Add weight in the appropriate place to approximate a typical race fuel load. Remember that fuel weights are dynamic. They will change during the race.
- Have the driver sit in his/her normal driving position before the scale reading is taken. Try to avoid unnecessary movements of the head or arms, as these actions will result in a false reading. As well, the driver should wear full race gear during weighing to have the highest level of accuracy possible.
- Zero all scales and take the reading.
Adjusting Kart Weight
If the weight distribution is off after the scaling process is complete, adding weight can aid in perfecting the distribution. As is the case with many drivers, weight usually has to be added anyway. Many manufacturers give detailed instructions where to place weight in order to improve the distribution. However, a good rule is to center the weight somewhere on the seat, given that the mass of the kart needs to be centered as best as possible. Adding weight to the seat aids in this. While adding weight to the seat is the best method, filling the frame with lead shot is not. The lead will shift during cornering, cause handling problems, and will deaden the chassis responsiveness.
If the driver does not need to add weight, they are probably at the weight limit of their class. Drivers in this case are always reluctant to add weight just to improve the weight distribution. However, there is evidence that adding the weight to perfect the weight distribution is more beneficial than leaving the ten pounds off. It is ultimately up to the driver to test both methods, then choose the quickest alternative.
After the correct distribution is achieved, the driver should make one more observation. The front wheels should weigh within five pounds of each other. The same situation applies to the rear wheels too. If this is not the case, re-check the factors effecting weight distribution given above and re-scale the kart. If the problem still exists, you may have to readjust the seat again and start the process all over again. Only then will the proper distribution be achieved.