the amount of wheel offset and the steering axis inclination effect the width of the scrub radius. The other side of this is I am not sure how much going from 0 scrub radius to +3” of positive scrub radius really affects things. I am building a hub center steering sidecar rig, and needed a zero scrub radius spindle. The caster is a side-view issue. The scrub radius would only go down by 1 mm. Tire height is reduced below the axle by deformation. Hello friend and welcome to racingaspirations.com - the home of some of the best visual motorsport calculators I believe you will find on the internet and all available to try for as long as you like free of charge. The location of the steering gear linkage or rack can have a … It has the biggest influence on the steering's self centering feel. SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. I've done my own calculations as far as putting really wide wheels on my car and found the offsets should be a lot higher for "proper" fitment. My question is, what effect (if any) will a positive or a negative scrub radius have on the centralising of the steering, whilst moving in a forward direction? Scrub Radius- this is the tires turning radius about the steering axis. Enter as much or as little information as you like and the calculator will validate the data then apply it … If the scrub radius is zero, then the tire has to be twisted on the ground, and the steering effort is highest. save. If it is inboard then the scrub radius is positive. Β F. Where: j = Distance between steering axles (mm) I kt = Wheelbase center to center (mm) 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. To calculate, it uses trig and the spindle angle of the strut and the change in tire height to calculate the change in scrub radius from this. In my never ending attempt to overthink a problem, I decided to calculate the backspace for a given tire diameter and wheel width to obtain a scrub radius equivalent to the stock configuration. On a RWD car, even if the tyre loads are equal, tyre drag will tend to load the wheels toward toe-out with a positive scrub radius (usual) or toe-in with a negative scrub radius. However, too large of a scrub radius makes the steering very sensitive to … Before using Lotus you should know your Track-width and front Dimension of your frame. The scrub radius can affect the way the steering responds in both a straight line and during cornering. To calculate the radius of a circle by using the circumference, take the circumference of the circle and divide it by 2 times π. The distance between the centerline of the tire and where this line meets the ground is your scrub radius. We only really have scrub to fit things in the wheel easier. 3 comments. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire … On a MacPherson strut, the top pivot point is the strut bearing, and the bottom point is the lower ball joint. 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 biggest effect is called bump steer. Here is the 'mathy' part. The scrub radius is the distance between the two, where both touch the road. report. Former oldies. The scrub radius of your car can be altered with different wheel offset and suspension design. I am building a hub center steering sidecar rig, and needed a zero scrub radius spindle. A positive scrub radius tends to be beneficial while braking into a turn. The larger the scrub radius is the more feedback and shock load you get. With a small amount of scrub radius, the tire is turned about the kingpin axis, slightly offset from the tire’s centerline. The distance from the kingpin axis to the wheel centre plane measured horizontally at axle height is called Spindle length. Learning how to build Lotus Seven replicas...together! Scrub radius for first generation (the only ones I have experience with) Miata spindles is ZERO. ... Any idea on how to calculate it using the forces and moments that are given as output? Joined: Mar 6, 2010 Likes Received: 2 Location: On the limits of adhesion. Steering axis inclination; Effects of SAI; Scrub radius 88 Audi Quatro, 91 Honda Accord, 94 Nissan Sentra, 98 VW Jetta, 02 VW Jetta, 08 Mazda 6, ( not listed , Bikes , Trucks or Vans ) Yes it is. Former oldies. The smaller the scrub radius is the less feedback to the wheel you get. That is with the stock 14" rim and stock size tire. 3. If these two lines intersect at ground level, then you are said to have zero scrub. share. 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 . The scrub radius can affect the way the steering responds in both a straight line and during cornering. It is only referred to as positive or negative. hide. ... Any idea on how to calculate it using the forces and moments that are given as output? Wheel-Size.com is a Wheel Guide and catalogue. I just added in the correct Miata knuckle measurements (from an NA Miata, I believe that's what you're using?). This is a … NOTE: Scrub Radius is defined as the point of intersection of the king pin angle (a line drawn through the upper and lower ball joints and the mid line plane (steering plane) of the wheel (tire). The scrub radius is the distance on the ground between the centerline of the tire contact patch and the point at which the SAI intersects the ground. level 2. https://autosystempro.com/scrub-radius-suspension-design-explained Get the forces to the drivers liking using as little scrub radius as possible. It is much easier to measure from a picture. The scrub radius is a front-view issue. The steering gear and linkage or the rack and pinion connects the tie rods to … strimmer Forum Member. If the scrub radius is small then the contact patch is spun in place when parking, which takes a lot more effort. Reporting Open the Macpherson Geometry Calculator or the Suspension Geometry Calculator Click so it becomes if it isn't already. 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. The main advantage is improved feedback and road feel. Thanks scrub radius calculator from tiresize! The scrub radius is the distance on the ground between the centerline of the tire contact patch and the point at which the SAI intersects the ground. This is an exmaple of a suspension geometry with positive scrub radius. … The distance between where the SLA and the centerline to the wheel intersect the ground is called the scrub radius. I now get a scrub radius of .65 inches. Se ha producido un error en el navegador. Wheel-Size.com is a Wheel Guide and catalogue. STRIMMER. 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. That should be an imperceptible change. Discussion in 'Chassis' started by strimmer, Sep 8, 2010. I am currently running zero 'Scrub Radius'on the front wheels of my Cobra. Scrub radius, to my knowledge, cannot be calculated to an exact number. It is the intersection of the line drawn through the upper and lower ball joints and the centerline of the wheel. I've never found an equation - its always been a ruler or a drawing. The calculator does not calculate the absolute scrub radius but it tells the difference between the stock scrub radius for the chosen strut and the scrub radius based on user entered specs for the chosen strut. The Miata was the only one I … Sketched up the wheel/upright on a piece of poster board and ended up with a scrub radius of 5/8", so that's good... Next up is making a 1/2 scale string computer out of some thin wood, then playing around with roll centers and pick up points... Yep, I was mistaken. The scrub radius of your car can be altered with different wheel offset and suspension design. From a front view of the car, draw a line between the ball joints and make it intersect the ground. Get the forces to the drivers liking using as little scrub radius as possible. Copy of Scrub Radius Prompt 5,20,8.5,60 Inner,Outer,total Inner Rim Diameter (inches),Rim Width (inches),Offset (mm),Tire Width (mm),Sidewall,Spacer (mm),Select Strut,Rim Backspace (mm),Hub to Rim Edge(mm),Effective Offset (mm),Tire Height (mm),Tire Height (inch),Scrub radius … The scrub radius can affect the way the steering responds in both a straight line and during cornering. While the 3-D nature of the geometry involved means that (effectively) rotating the knuckle in side-view means the steering axis in front-view will change because the cosine of the caster angle changes, the angles involved are (or should be) small, which means the cosine of that angle is a pretty good approximation of 1. To find my actual scrub radius, I need to combine that triangle with another triangle. To visualize scrub radius, stand in front of your car. It has the biggest influence on the steering's self centering feel. It could be positive, negative or zero. If you make the scrub radius large enough you induce large moments (torque) while braking that (maybe) could cause fatigue in the suspension elements but I've never heard of a suspension breaking because of it. Recently I realized that changing the wheel offsets (or using spacers) to adjust the track width affects the scrub radius (a.k.a. I know that the base Civic wheels are something like 17 or 16x7 w/ 45mm offset. What Is Scrub Radius? 3. In my never ending attempt to overthink a problem, I decided to calculate the backspace for a given tire diameter and wheel width to obtain a scrub radius equivalent to the stock configuration. Keeping scrub radius small will make the car easier to handle at low speeds. Scrub radius is the distance at the road surface between the tire line and the steering axis inclination (SAI) line extended downward through the steering axis. 3 comments. Before using Lotus you should know your Track-width and front Dimension of your frame. 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