Trackwidth The Distance between centre axis of tire from front view is known as trackwidth. Modern passenger cars use a scrub radius of the order of 0.25" to 0.75", either negative or positive. This creates a small tire/road friction resistance that in turn translates into feedback from the road. Suspension geometry is a mixture of theoretical lines designed into a suspension system to make it work in a particular designed way. DESIGN While designing, the major factor is the type of geometry to be used for the steering system. 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. Engineering News 'a0 = Theorectical value for outer steer angle, © Copyright 2000 - 2021, by Engineers Edge, LLC www.engineersedge.com All rights reserved It also reduces the risk, that a lose of traction on one front wheel during braking, causes the car to change direction. Excel App. 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. Scrub radius is considered positive when 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. Scrub Radius. 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. The biggest effect is called bump steer. Disclaimer One last consideration in the steering design is scrub radius. At what point does increasing the scrub radius become a hinderance? I an reading about camber and scrub radius. Engineering Calculators The scrub radius of your car can be altered with different wheel offset and suspension design. proportional to the scrub radius, which will be felt by the driver at the steering wheel. Enter your email address to subscribe to this blog and receive notifications of new posts by email. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire … In addition, while the vehicle is moving dynamic forces will arise that will affect the cornering maneuver. scrub radius, mechanical trail etc. Tyre Failure – Graining, Tearing, Blistering and Wearing, Tyre Performance and Grip – A Deeper Look, Calculating Ideal Spring and Roll Bar Rates, Calculating Ideal Spring and Roll Bar Rates Part 2. Engineering Toolbox ; Save my name, email, and website in this browser for the next time I comment. This will affect how the tire contact patch interacts with the road during cornering, braking, and acceleration, and can cause unique toe characteristics depending on the design. DFM DFA Training Engineering Videos 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) document.write('') II. If it is inboard then the scrub radius is positive. The scrub radius refers to the amount of movement the tire contact patch must make in order to turn when steering input is applied. 1. Your email address will not be published. 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 outer turning circle, or its radius, is the main subject of interest. Home ... Derivation of the radius of an arc-chord formula on Math Open Reference in case you really want to know where this formula … Scrub Radius, Kingpin Inclination, and Caster. // -->, Power Transmission Design and Engineering, Vehicle Turning Circle Equations and Calculators, GD&T Training Geometric Dimensioning Tolerancing. have to be kept in mind while designing and the best compromise for these values has to be found. Advertising Center Scrub Radius is determined by the kingpin location on the steering knuckles and hubs. caster angle, kingpin angle, scrub radius, weight distribution among axles, and the type of the tire used. Scrub radius is the distance from the centerline of the tire/wheel to where the kingpin line intersects with the road surface. Fig.5 Trackwidth Geometry Note: Generally narrow (small) trackwidth are used at rear to avoid hit cones with the back when they are document.write(' ') }, Power Transmission Design and Engineering Scrub Radius. Ikt = Wheelbase center to center (mm) Simulating on Lotus and using hit and trial method you can check that at which angle you are getting your correct suspension and steering geometry . Draw an imaginary line to the ground through the kingpin screws and ideally that imaginary line lands close to the center of the tire to achieve the ideal scrub radius. Required fields are marked *. If the scrub radius is small then the contact patch is spun in place when parking, which takes a lot more effort. 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.
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