Tyre Setting

Adjusting the tyre to chassis and driving conditions

Racing kart tyre size is given by numbers such as 11 x 6.00-5, which is a different system than that used for ordinary tyres. In this example, 11 indicates tyre diameter, 6.00 shows the tyre width and the 5 indicates rim diameter. Measurements are in inches but the figures are rough estimate. For more precise dimensions, refer to the tire dimension chart below.

The first thing that must be determined for a kart tyre proper inflation pressure if you want to get the best performance from any individual kart tyre. That is easily said, but the real problem is the word "proper" because it meaning varies delicately with condition?s such as driver, frame, course layout, road surface, weather and temperature, to name but a few. The manufacturer?s approved pressure is from 11 to 23 psi and the proper inflation pressure should be selected from that range to match individual conditions. Lowing inflation pressure improves grip because the effective contact area is increased and there is a better tyre cushioning effect. If pressure is lowered too far, however, contact becomes uneven and driving is more difficult.

 Air pressure setting

contact shape
contact pressure
contact area
Tyre stiffens (Suspension effect)

The best way is for each individual to determine the regular inflation pressure for himself or herself . 16 psi can be considered a good starting point for both front and rear tyres. Drive for a while with the tyre inflated to this pressure and then change inflation pressure from 1-3 psi until you find the inflation pressure you think is best.

 Lets now take a look at some examples of settings to meet changing conditions.

• Change in atmospheric temperature: The general rule is to raise inflation pressure slightly as the temperature falls and lower it as the temperature rises. If there is a distinct difference between morning and afternoon temperatures, raise the inflation pressure a little in the morning for a better grip by increasing the load to generate heat. Lower it in the afternoon to reduce generation of heat by the tire. This rule applies for summer and winter also.
• Understeering / Oversteering: Raise rear tire pressure about 3 psi to correct understeering and lower inflation pressure in the rear tires by the same amount to counteract oversteering. The opposite is also true for front tire inflation pressure. This should not be changed, however, because tire stiffness caused by the proper inflation pressure is needed on the front wheels.
• Compounds: Tire pressure can be raised when using the hard compound SL tires. With the high grip compound, it can be lowered.
• Variations in road surface: Lots of rubber residue on the road surface causes greater resistance and on such a surface it is good to lower air pressure to reduce heat generation by the tire. This holds especially true in summer.  
• Wet tire: Use the same inflation pressure as for dry conditions or raise the pressure 1-6 psi. When the track dries out, however, a heavy load is imposed on the pattern blocks on the corners and the tires are subject to coarse abrasion. The best remedy is to change to the slicks as soon as possible but it?s also possible to use wet tires, with reduced inflation pressure, for driving with a good grip. Coarse abrasion also affects slick tires if m of the road surface is very high, when drifting or putting a heavy load on the tires. Use the same remedies to this as explained above for wet tires.

Setting is also easier is the rim width is changed. Overall stiffness is changed uniformly as inflation pressure is varied but by changing the rim width, lateral and vertical stiffness, especially lateral stiffness, can be greatly varied. Furthermore, since the contact area does not change appreciably as it does with a alteration in inflation pressure, grip remains the same but fine changes can be made in manoeuverability (steering response, smooth slides, true following of the rear tires). For example, if the rear slide is not smooth, a wider rim than standard is called for. However, the range in which rim width can be varied is within ± 0.5 inches (approx. 13mm).

Manoeuverability can also be changed by varying tire size (tread width). On racing circuits with many braking points or on karts with powerful engines, larger rear tires will improve braking and traction force. On circuits and frames that cause understeering, large front tires can be used or smaller rim size. Oversteering is corrected by doing the opposite. For drifting, a smaller size with less grip is indicated but when more grip is needed a larger size is called for.

The external diameter (circumference length) of a tire varies in response to different conditions. This must be taken into consideration also when selecting the gear ratios. It is generally accepted that the gear number must be changed for each 12-15mm change in the length of the circumference. This amount of change in diameter occurs quite easily with a variation in inflation pressure and other conditions.

Change in diameter