-aids directional control, No grip! time for me to take a break...you guys got any questions? Interesting to read, though. tire loading...note the change in Roll Center location..camber changes. You have to control Sprung Weight and its effect on weight transfer, i.e. Scrub radius is the distance from the steer axis to the centre of the tyre contact patch at ground level and wheel centre offset is the distance from the kingpin axis to the wheel centre. Mike.............very interesting reading. S -aids self centring of the steering, Positive caster improves straight line tracking because the caster line (the line drawn through the steering pivot when viewed from the side) intersects the ground ahead of the contact patch of the tire. The inclination of the steering axis is measured as the angle between the steering axis and the centerline of the wheel. Lets look at the true suspension mounting points on a Formula Car. A positive kingpin inclination occurs when the steering axis points outward. The Ackerman effect can help the car turn better through the center of the turn since it builds TOE OUT dynamically, thus eliminating the requirement of running a lot of static TOE OUT That twill make excessive drag. Designing suspension mounting points- ifin you do not have access to the software I mentioned and you do not yet have the car built, you can pick up the old Number 2 pencil and start drawing. Blackboots and Wheels in Motion offer new tyre fitting, bespoke wheel alignment and geometry services at our state of the art workshop facility in Chesham Buckinghamshire. The most critical element is to have the best balance between Mass placement and RC location so that the car turns in the middle of the corners. BUMP STEER-As a front wheel moves up and down through its suspension travel, unless the steering is directly connected to the A frame, the wheel will tend to turn either left or right when the steering wheel is held firmly in the same position. We can see the effect of wheel rate regarding spring placement. The included angle is an angle measured in degrees, and is generated as a result of adding the sum of the camber angle, when positive, to the sum of the kingpin inclination, and subtracting the sum of the camber angle when negative, from the sum of the kingpin inclination. As these forces are equal both sides of the vehicle should not deviate from straight ahead, if for instance one wheel hits a bump then the two forces would not be equal, this would cause the driver to correct this force by turning the steering wheel, The wheel that hits the bump will have a greater turning action around the upper and lower swivel joints, so to control the directional stability of the vehicle, the inclination of the upper and lower swivel joints must have an equal addition and subtraction to their inclination, in addition, the wheels camber angle on compression will equal the loss of the inclination, so guaranteeing a couple between the inclined and declined kpi. On a MacPherson strut, the top pivot point is the strut bearing, and the bottom point is the lower ball joint. The distance between these points is known as the scrub radius. B.J.I - ball joint inclination. (2) If the scrub radius is positive the wheel tends to toe-out. Kingpin inclination is the angle between true vertical and a line drawn through the upper and lower Ball Joints (BJ). Kingpin Inclination. produce vertical displacement of the vehicle in during steering in an upward direction. Castor angle, ϕ, is defined as the angle measured in the side elevation between the steering (kingpin) axis and the vertical. I wish I was at the point in my automotive tinkering to design a suspension. The greater the steering axis angle the greater the weight loading caused by positive caster. Conventional coil over shock A-arm layout and the Formula Car inboard suspension which has a lot less unsprung weight. Vertical laoding creates downfroce on the outside tire so the more vertical loading there is the better the outside tire sticks during cornering. you asked about loads on each wheel..well here is an example of our old door slammer running on a medium banked asphalt track. It can be said that the included angle is used as a form of diagnostics, to determine if there is damage to the frame supporting the directional wheels geometry, and if the included angle is adding or subtracting, a value to the scrub radius, concluding whether this weight of the vehicle is distributed evenly across the tyre, or is adding weight to the inner, or outer edges, causing, adverse or uneven wear. With positive kingpin inclination (most passenger cars) this line would reach the ground at a point outboard of the centre point of the tyre’s contact patch. The kingpin inclination is positive (normal situation) if the steering axis centre line is set inwards towards the top of the vertical line. You can measure the amount of Ackerman you currently have by using a set of turn plates. Note that once you measure the FC, it is pretty easy to determine the Camber change regarding Bump and Droop. A typical amount would be three degrees in 10 degrees of steering. King-pin/ball joints (along with caster) provide directional stability in vehicles. Steering Axis Inclination (SAI) is also known as King Pin Inclination (KPI). Positive scrub. (1) If the scrub radius is negative the wheel tends to toe-in. This is what permits a bicycle rider to take his hand s of the handle bars and the front wheel still goes straight. independent suspension, the upper pivot point (ball joint) is set to the rear of the lower pivot point. When a wheel is steered it will lean out at the top, towards positive camber if the kingpin inclination angle is positive. The ‘Steering Axis’ is the axis around which the wheel assembly swivels as it turns to the right or left. When a car has positive caster and turns left, the left front corner will rise and the right front corner will dip. Unfortunately I'm at the will of aftermarket parts manufacturers until then! Castor angle is measured in degrees and taken as positive if the top of the steering axis leans towards the rear as shown in Figure 4.28. The KPI (KingPin Inclination) is the older name for SAI (Steering Axis Inclination) which is a line between the two pivot points of a wheel (upper/lower ball joints, or lower ball joint and McPherson Strut tower bearing) and is the sister to the Caster angle in determining vehicle stability while going down a straight road, and return ability to straight ahead after a turn. The amount of this is small but not to neglect if the track includes tight turns. the lower front roll center will create more vertical loading on the outside tire contact patch. As a biological metaphor Reasons for having low Roll Centers ( RC) - I can not say this too often...Racing is about Tires, Tires , Tires. Remember..its all about tire contact patch. The kingpin inclination also contributes to the scrub radius of the steered wheel, the distance between the centre of the tyre contact patch and where the kingpin axis intersects the ground. KPI Kingpin angle is measured in Degrees and is positive when the top of the steering axis points towards the centre of the car. Kingpin inclination affects the Steer camber. This downward loading is why the tire traction increases as the track banking angle increases. The kingpin inclination (KPI) is the angle between vertical axis of the upright and the vertical axis through the center line of the wheel. as am old racer once told me... too much positive caster builds the drives arms..if you ever drove a car with too much caster, your arms would ache after a few laps. The included angle is an angle measured in degrees, and is generated as a result of adding the sum of the camber angle, when positive, to the sum of the kingpin inclination, and subtracting the sum of the camber angle when negative, from the sum of the kingpin inclination, The kpi is the angle formed between the true vertical, and the centre line through the ball joints or struts, the term kpi is no longer relevant since it is reliant on older forms of construction, in fact, as far back as the horse and cart, the evolution of new technology forming the cars geometry, commanded new terminology such as S.A.I and B.J.I, my preference is K.P.I as this term is recognized globally. An understeered car feels more stable as it has a tendency to correct itself. Now that the lines have been drawn form the IC on each side to the upper and lower BJ centers, these lines which converge to the IC will dictate the planes on which the inner pivot points must be located for the upper and lower control arms on each side. For a better experience, please enable JavaScript in your browser before proceeding. You have to use the proper springs and Anti Roll Bar ( sway bar in Kentucky) to counter the Roll. Let us also assume we can not manipulate Mass placement in the race car ( can not offset the engine, and rules dictate minimum engine height, percent left side weight, percent front to rear weight. Good stuff so far, spring selection and wheel rates next please. Compare our prices to the fast fit operators and then come and experience the Blackboots and Wheels in Motion difference. Positive camber is defined as the tops of the wheels tipping away from the vehicle. Conductive nature in crystal structures revealed at magnification of 10 million times, Six-wavelength spectroscopy can offer new details of surface of Venus, Examination of Theia 456 finds its nearly 500 stars were born at same time, Books for Race Car Design and Construction, Rotation angle measurement of pedal with ball and socket joint, Calculating the coldest outside temperature my campervan can be in and still be warm inside, Calculating Hydraulic Press Pressure on a Skateboard :), Finding Force and Energy from an indentation into a volume. Roll center height determines what percentage of the overturning moment 9 inside to outside weight transfer) will be distributed onto the tire contact patch a downforce, and wha tpercentage isrecieved as lateral loading against the tires tread face. Caster is a directional control angle, but not a tire wearing angle. If you have Ackerman, the left front will travel further than the right front. Effect on vehicle behavior Camber plays an … Just like a shopping cart caster, the wheel is forced behind the pivot allowing the vehicle to track in a straight line. Positive caster is when the top of the spindle steering axis is tilted to the rear of the car. The main effect of this is to introduce a turning moment. before we get int oin board suspension lay out and formula car wheel rate calculations..i need to dig out my notes on "how to calculate the proper springs for a given race car" both ..front and rear...because if you do not know where to start as a base line it will take days at the track to trial and error the set up until it gets close.. Ok, here is how we determine the proper springs for each corner of the race car. However, steering axis inclination is the line passing thru' the center of the king-pin/ball joints that tilts inwards (towards the center of the vehicle). 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