βa = Outer steering angle A positive radius allows the wheel to roll over on lock making parking situations easier. have to be kept in mind while designing and the best compromise for these values has to be found. , Power Transmission Design and Engineering, Vehicle Turning Circle Equations and Calculators, GD&T Training Geometric Dimensioning Tolerancing. Is increasing scrub radius (for example making front track wider with spacers on hub) really a bad thing or its effect is only short? This creates a small tire/road friction resistance that in turn translates into feedback from the road. The three possible geometries that can be used are Ackermann, anti-Ackermann and parallel steer geometry. Positive Scrub Radius Lines Meet Below Road Surface Usually Rear Wheel Drive With Front Wheel Toe In; SAI Usually Less Than 10 Degrees; Negative Scrub Radius. All this comes down to the design parameters of steering geometry viz. document.write(' ') There are currently no comments available. The scrub radius refers to the amount of movement the tire contact patch must make in order to turn when steering input is applied. The fundamental categories of suspension geometry are: Ackermann Bump Steer Camber Camber Gain Caster Front View Swing Arm Fundamentals of Grip Instantaneous Centre King Pin Inclination Scrub Radius Toe Tyre Slip Angle There are more aspects to suspension geometry but the most influential are listed above and are the focus of this website. Scrub Radius is determined by the kingpin location on the steering knuckles and hubs. locations refer to Milliken [2]. The main effect of this is to introduce a turning moment. II. I an reading about camber and scrub radius. The scrub radius, or kingpin offset, is the distance between the centerline of the wheel and the intersection of the line defined by the ball joints, or the steering axis, with the ground plane. Engineering News A positive scrub radius tends to be beneficial while braking into a turn. // --> Engineering Forum When viewing a wheel from front view, the scrub radius is the distance between where the extrapolated line of kingpin axis touches the road and the tyre contact patch centre point. Your email address will not be published. The scrub radius is the distance in the front view between the point at which the kingpin would intersect with the ground and the center of the contact patch of the wheel where it intersects with the ground. s = Track or whele to wheel center width (mm) The biggest effect is called bump steer. If it is inboard then the scrub radius is positive. 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. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. Thx. Trackwidth The Distance between centre axis of tire from front view is known as trackwidth. Formula s = Track or whele to wheel center width (mm) r o = Scrub radius (mm) the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. One last consideration in the steering design is scrub radius. Scrub Radius. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire … Scrub Radius. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. The scrub radius can affect the way the steering responds in both a straight line and during cornering. ; Online Books & Manuals Automotive Videos. { | Contact. About us. We only really have scrub to fit things in the wheel easier. When we have a positive scrub radius the steering axis is inboard of the tire center, having a tendency to toe out while being driven. proportional to the scrub radius, which will be felt by the driver at the steering wheel. A negative scrub radius gives a harder feel to the steering wheel as it requires more input to turn. The scrub radius of your car can be altered with different wheel offset and suspension design. At what point does increasing the scrub radius become a hinderance? The larger the scrub radius is the more feedback and shock load you get. Save my name, email, and website in this browser for the next time I comment. DFM DFA Training GD&T Training Geometric Dimensioning Tolerancing Advertising Center Before using Lotus you should know your Track-width and front Dimension of your frame. Turns out, it can be calculated with a little geometry and algebra. Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). document.write('') ro = Scrub radius (mm) the distance in front view between the king pin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. This means there is less than half an inch between the king pin inclination line and the tire center line where the tire contacts the road. The larger the distance, the more effort is required to turn the wheel, as the tire has to “scrub” slightly to turn around the kingpin … Disclaimer Scrub radius is an elusive, almost mythical maiden on the edge of key settings like camber, offset and wheel size, and it’s a key output of the overall equation. If it is inboard then the scrub radius is positive. INTRODUCTION: Formula Student India-International Level Event, also known as FS-IND is a design competition which follows the standards of the prestigious Formula SAE/Formula Student competitions held across the world. SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. When a vehicle is cornering, each wheel describes a turning circle. In addition, while the vehicle is moving dynamic forces will arise that will affect the cornering maneuver. Kingpin Inclination, centre point steering and scrub radius When viewed from the front a line drawn along the kingpin or, depending on design of the steering hubs, the upper and lower pivots will not be vertical but will be closer to the centre line of the car at the top than it is at the bottom. level 2. Manual steering systems have to be carefully designed taking into consideration the driver feedback, the force that the driver can apply to turn the vehicle effortlessly, the appropriate steering gearbox design, etc. Home By my calculations.. running 13x7 libres with a 20x9.5x13 slick increases the scrub radius by nearly 34mm! Vehicle Turning Circle Design and Engineering Equations and Calculators. if (document.getElementById("tester") != undefined) else Budget to Premium Coilovers – Whats The Real Difference? rs = Turning circule radius (mm) Required fields are marked *. It also reduces the risk, that a lose of traction on one front wheel during braking, causes the car to change direction. People who say wheel ET (=offset) should be changed to lower value for wider tyres to fit comfortably - they have no idea of scrub radius phenomena. The smaller the scrub radius is the less feedback to the wheel you get. Scrub planes are kind of interesting. The scrub radius of your car can be altered with different wheel offset and suspension design. A, how it affect the driving, B, cornering capacity, C, the geometric effect. Engineering Calculators Engineering Videos 1. The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. Engineering Toolbox ; However, the following formulae can be used for estimation purposes: Calculator Preview: Vehicle Turning Circle Equations and Calculators, Theorectical value of the outer steering angle, j = Distance between steering axles (mm) scrub radius, mechanical trail etc. Notify me of follow-up comments by email. Work in a car with zero scrub radius of the contact patch then contact. Fit things in the wheel to Roll over on lock making parking situations easier larger the scrub radius is more... Input to turn when steering input is applied Camber, Caster, scrub radius of to... 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