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Reset: Go Kart calibration manual – US / OS

For karting, the phenomenon of substeer / oversteer is very extreme. When you don’t hit the direction enough, US will happen, and if you hit the direction a little more, OS will happen. This problem is mainly caused by the weak grip of the front wheels.
This situation will also lead to excessive wear of the front wheels.
For a professional driver, the wear degree of the four wheels should be the same. Novices generally wear the front tires obviously.
The operation mode of the go kart is to slam the steering wheel to just enough to enter the bend, and then continuously make millimeter level adjustments in the bend. The higher the level, the less corrections will be made, and the wear degree of the front tire will be alleviated.
After your technology reaches a certain level, you must solve this problem before you want to improve it. Not only do you need to make your handling more and more accurate, but also the handling feeling of the car should be more in line with your habits, which can not only improve your lap speed, but also solve the problem of inconsistent wear of the front and rear wheels.
Let’s start with the more basic camber and caster:
Caster: refers to the angle of caster axis perpendicular to the ground. The change of operation feeling by adjusting caster is the largest in karting, which directly affects the weight of the steering wheel; It also has a significant impact on the car’s grip performance.
There is a simple formula:
Smaller caster = lighter steering wheel = easier steering + more flexible body
Larger caster = heavier steering wheel = more stable at high speeds
When you use a larger caster, you will get more feedback from the steering wheel in corners (greater righting force) and the car’s grip performance will be better. For example, the car in high-speed corners will be more stable and the car is less likely to lose control when braking hard. The smaller caster is the opposite.
When the grip provided by the track is insufficient, the car can be more stable by raising the caster. When the track has provided a lot of grip, it can make the car easier to turn by lowering the caster. In low-speed tracks with many corners, we can consider reducing caster to improve our performance in corners.
When using new tires, the grip performance will be exceptionally good when the tires are just opened. Therefore, for drivers who are not used to using new tires, it can be considered to reduce caster appropriately to alleviate this situation in the case of new tires, so as to ensure that drivers are more confident in qualifying.
It is difficult to say that the OS / US trend can be directly changed after adjustment, but the weight of the steering wheel will indeed change. So another aspect of adjusting caster is to cater to the driver’s driving habits. The steering wheel is hard, which is more suitable for smaller casters, and vice versa.
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Camper: camber angle. The purpose of adjustment is to make the car’s tires contact the ground as much as possible when turning, so as to improve the cornering grip and reduce the resistance when driving in a straight line. It has less impact on the handling of the car than caster, but it has a more obvious impact on the wear of one side of the tire.
⬇ Plan view (view from the front of the vehicle) this is a negative camber angle. Valgus is a positive camber.
For karting, the rear wheel is connected by one shaft, so only the camber of the front wheel can be adjusted. We try our best to control the tire wear at an appropriate level, and we can also ensure that the front wheels can have sufficient stability in corners. (need to cooperate with toe in / out) this requires us to carefully feel the actual situation of the car in the curve.
Do not use too large negative camber angle, because it may lead to excessive wear on the inner side of the front wheel, resulting in worse and worse grip in the later part of the race. Especially in the game, we should make a good choice. When it can be solved through caster, try not to use the inclination angle.
Basically, there is no need to consider the impact on braking. Because karting relies entirely on rear wheel braking.
The use of positive camber is rare.
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Toe in / out — literal translation: inner eight characters / outer eight characters. ⬇ Top view
This is generally the part that needs to be adjusted after camber changes. When you adjust the camber angle of the front wheel, because it will slightly affect the rolling direction of the front wheel at the same time (you can throw a coin to observe, figuratively speaking, when the motorcycle bends), you may need to adjust the rolling direction of the front wheel to offset the impact, so as to reduce the wear on one side of the tire. For example, when using a negative camber angle, you may need to use toe out to offset the tendency of the tire to roll to the side of the car, and also reduce the burden on the inside of the tire.
Theoretically, toe out is the OS trend and toe in is the US trend.
Similar to camber, toe in is generally not used.
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Rear wheel grip:
The grip performance of the rear wheel mainly depends on the stiffness of the rear. We can adjust the track width of the two wheels, replace the rear axle with different soft and hard, replace the hub seat with different length, and adjust the tightness of the buckle of the rear axle.
Longer rear wheel track + softer rear axle + shorter hub seat + loosen buckle = lower grip = OS trend
Closer rear wheel track + harder rear axle + longer hub seat + tightening buckle = higher grip = US trend
However, when you narrow the track, you do get more rear wheel grip, but your cornering limit does decrease. When you relax the track width, although the rear wheels do lose grip, the limit becomes higher in corners (especially in high-speed corners).
In rainy days, change the hard axle and narrow the rear wheel track. In short, the higher the rigidity of the rear of the frame, the better. Make sure you can enter the corner more aggressively and the car can really accelerate when you exit the corner. Otherwise, if the rear wheel skids after accelerating out of the corner, you will hardly accelerate in the process of recovery. (especially hard to save)
Front wheel track:
It’s basically the opposite of the rear wheel. When you widen the track width of the front wheel, it is the understeer trend, and when you narrow it, it is the oversteer trend. In general, it will not receive the narrowest, except that it may be used when the curve is particularly compact.
In rainy days, the front wheel track should be widened to improve the stability in bending. Incidentally, the auxiliary effect of braking before rainy days is very significant. At present, the domestic CKC rules in 2016 have not been issued, and it is uncertain whether the front brake system is allowed to be used.
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Summary: caster can bring significant changes in grip and driving experience. First find your general adjustment direction through caster’s adjustment, and then adjust camber, toe in / out, etc. to make further improvement, which must be done every time you arrive at a new track.
Calibration purpose:
① Cater to drivers’ driving habits
② The trend of car traction most suitable for a certain track and weather conditions (biased to us / OS / neutral)
③ Control tire wear

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