Adjusting the tire to machine and driving conditions
Racing kart tire size is given by numbers such as 11 x 6.00-5, which is a different system than that used for ordinary tires. In this example, 11 indicates tire diameter, 6.00 shows the tire 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 tire proper inflation pressure if you want to get the best performance from any individual kart tire. That is easily said, but the real problem is the word "proper" because it meaning varies delicately with conditions such as driver, frame, course layout, road surface, weather and temperature, to name but a few. The manufacturers 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 tire cushioning effect. If pressure is lowered too far, however, contact becomes uneven and driving is more difficult.
Air pressure setting
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 tires. Drive for a while with the tire 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.
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 maneuverability (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).
Maneuverability 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
|High air pressure||Dia. increases|
|Low air pressure||Dia. decreases|
|Immediately after mounting new tire on rim||Dia. small|
|Some time after mounting new tire
(stabilizes after about 6 hours)
|Tire temperature rises (after running)||Dia. increases|
|Worn tire||Dia. decreases|
|High speed running||Dia. increases|
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