![]() It acts as a self-centering mechanism that uses the weight of the car to bring the wheel back to the central point. What matters is what we do with it and how we can use it to our advantage.Īs mentioned earlier, KPI is mostly a consequence of not being able to fit all the unsprung components in a structurally limited space. It’s going to be there, whether we like it or not. It all depends on the width of the tire, stiffness of the tire, all the other suspension angles working together create the final handling characteristics of the vehicle. There are no universal rules around what KPI is supposed to do. At high speeds, the self-centering effect is more caster-dominant. This lifting force has a self-centering effect on the steering wheel at slow speeds which adds to straight-line stability. So when the wheels turn, they dig into the ground and actually lift the car up slightly. The reason why KPI produces a lifting force is that this angle makes the wheel axle trajectory travel in an upside-down arc, as opposed to traveling in a perfectly horizontal plane. Producing a lifting force that has a self centering effect on the steering wheel just like the caster angle does.Since we cannot do this, we have to rely on an inclined steering axis.īesides that, KPI fulfills other important purposes such as:.Hypothetically if we were able to do that, we could achieve a perfectly vertical steering axis and zero scrub radius at the same time. Due to a structural limitation, there’s no way to cram your control arms, steering knuckle, and brakes into your wheel, there’s just not enough space.Why King Pin Inclination ExistsĪt first glance, KPI seems rather redundant, but it exists for a reason: In other words, king pin inclination refers to how diagonal the steering axis is in comparison to the vertical axis. See the angle between line A and line B? That’s the steering axis inclination or suspension king pin inclination. Line A passes through the upper and lower ball joint on your control arm. Visualize your car from either the front or rear view. King Pin Inclination Explainedīefore we get into what king pin inclination is, you need to know what the vertical axis is - it is an imaginary line that passes through the center of the tire vertically. This means that the steering axis inevitably has to be inclined. ![]() It is virtually impossible to have a king pin that can allow for a perfectly vertical steering axis. Why do they do that? Because modern cars are required to pack a lot more unsprung components around the inner-wheel area. Modern-day suspension systems have done away with real king pins and use dual ball joints instead. To visualize this, picture a line that passes through the two ball joints where your wheel mounts to your steering knuckle.įun fact: The term “king pin axis” gets its name from older cars that used to have an actual vertical physical pin about which the entire wheel would turn. The steering axis and king pin angle axis are exactly the same - it is an imaginary line about which your entire wheel pivots as it turns. ![]() The core principles remain the same when these concepts are applied to other suspension types like the McPherson strut. Suspension concepts are easier to explain in the context of double-wishbone suspensions. Steering Axis ExplainedĪ quick note before we start we’ve used double wishbone or double A-arm suspension type as the main example throughout this guide. Why then do cars do this? And does it have any detrimental effects? Read on as we explain king pin inclination - what it is, what it does, and why you should know about it. We’ve explained this in our positive and negative wheel camber article.
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