scrub radius formula

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 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. β i = Inner steering angle β a = Outer steering angle { Automotive Videos. Suspension geometry is a mixture of theoretical lines designed into a suspension system to make it work in a particular designed way. locations refer to Milliken [2]. { else In addition, while the vehicle is moving dynamic forces will arise that will affect the cornering maneuver. A positive scrub radius tends to be beneficial while braking into a turn. I have reached out recently to "Ford Performance", as well as Dean Martin of KOHR Racing on the exact scrub radius numbers. have to be kept in mind while designing and the best compromise for these values has to be found. SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. Wheel-Size.com is a Wheel Guide and catalogue. This creates a small tire/road friction resistance that in turn translates into feedback from the road. scrub radius, mechanical trail etc. DFM DFA Training Before using Lotus you should know your Track-width and front Dimension of your frame. 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 (document.getElementById("tester") != undefined) Engineering Calculators // --> All three are shown in the figure below. By my calculations.. running 13x7 libres with a 20x9.5x13 slick increases the scrub radius by nearly 34mm! Formula SAE and Formula Student are collegiate engineering competitions with over 500 participating schools that challenge teams of students to design and build a formula style car. 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. 4 How does it influence resistance during longitudinal accelerations and at costant speed? If it is inboard then the scrub radius is positive. We only really have scrub to fit things in the wheel easier. 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 . As you could deduce, when you turn the front wheels they do not turn right on the patch but on the axis of suspension, so the tire scrub the road, thus the name "scrub radius". Notify me of follow-up comments by email. Engineering Videos Thx. 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. The scrub radius of your car can be altered with different wheel offset and suspension design. Ikt = Wheelbase center to center (mm) 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. The scrub radius is shown at the bottom at .427”. Scrub Radius. Engineering News When a vehicle is cornering, each wheel describes a turning circle. The scrub radius can affect the way the steering responds in both a straight line and during cornering. ; 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. Required fields are marked *. βa = Outer steering angle 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) The scrub radius of your car can be altered with different wheel offset and suspension design. 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. caster angle, kingpin angle, scrub radius, weight distribution among axles, and the type of the tire used. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. | Contact. Trackwidth The Distance between centre axis of tire from front view is known as trackwidth. Get the forces to the drivers liking using as little scrub radius as possible. By playing with wheel offset and size it appears you can curve the increase scrub radius back … Downloads 'a0 = Theorectical value for outer steer angle, © Copyright 2000 - 2021, by Engineers Edge, LLC www.engineersedge.com All rights reserved The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. Older cars used a scrub radius of up to 4 inches, positive. Engineering and Design Applications. It also reduces the risk, that a lose of traction on one front wheel during braking, causes the car to change direction. | Feedback | Advertising Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window). 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. // -->, Power Transmission Design and Engineering, Vehicle Turning Circle Equations and Calculators, GD&T Training Geometric Dimensioning Tolerancing. A, how it affect the driving, B, cornering capacity, C, the geometric effect. Scrub radius helps this feel by providing feedback from the contact patch. 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 … Advertising Center 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. A negative scrub radius gives a harder feel to the steering wheel as it requires more input to turn. Training Online Engineering 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. Home II. The larger the scrub radius is the more feedback and shock load you get. Having a small scrub radius is beneficial as it allows the wheel to react less to braking inputs due to the smaller moment arm and increases steering stability under braking conditions. GD&T Training Geometric Dimensioning Tolerancing Turns out, it can be calculated with a little geometry and algebra. Your email address will not be published. Keywords: KPI, Camber, Caster, Scrub Radius, Roll Centre, Instantaneous Centre. A positive radius allows the wheel to roll over on lock making parking situations easier. There are currently no comments available. level 2. Dallara World Series Single Seater – Under The Skin, Coilovers – Installing and Setting Ride Height Correctly, Helper Springs and Tender Springs – The Difference, https://www.youtube.com/watch?v=_Ksbfn40adA. rs = Turning circule radius (mm) The scrub radius of your car can be altered with different wheel offset and suspension design. About us. 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. Scrub Radius is determined by the kingpin location on the steering knuckles and hubs. I an reading about camber and scrub radius. The biggest effect is called bump steer. The smaller the scrub radius is the less feedback to the wheel you get. The three possible geometries that can be used are Ackermann, anti-Ackermann and parallel steer geometry. 1. 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. document.write(''); Enter your email address to subscribe to this blog and receive notifications of new posts by email. Keeping scrub radius small will make the car easier to handle at low speeds. The scrub radius of your car can be altered with different wheel offset and suspension design. Save my name, email, and website in this browser for the next time I comment. Scrub Radius. With a small amount of scrub radius, the tire is turned about the kingpin axis, slightly offset from the tire’s centerline. Scrub radius is considered positive when Engineering Book Store I need a map of how big to make the radius of the blade. 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. 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. Scrub Radius and Wheel-Offset Positive Scrub Radius. If it is inboard then the scrub radius is positive. The main effect of this is to introduce a turning moment. A positive scrub radius tends to be beneficial while braking into a turn. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. Scrub planes are kind of interesting. In a car with zero scrub radius the tire pivots around a central axis without dragging the tire forward or rearward.