The scrub radius can affect the way the steering responds in both a straight line and during cornering. 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. Recently I realized that changing the wheel offsets (or using spacers) to adjust the track width affects the scrub radius (a.k.a. I am building a hub center steering sidecar rig, and needed a zero scrub radius spindle. The thing is, I know this will alter the scrub radius (beside other things like bearing load, etc) and after reading something about this I didn't came to a certain conclusion regarding how this will affect the handling of a clio (182 cup suspension with 16" … Scrub radius, to my knowledge, cannot be calculated to an exact number. Thanks scrub radius calculator from tiresize! The scrub radius would only go down by 1 mm. level 2. Yes it is. The caster is a side-view issue. Wheel-Size.com is a Wheel Guide and catalogue. Scrub radius. STRIMMER. The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. The scrub radius is the distance in front view between the kingpin axis and the center of the contact patch of the wheel, where both would theoretically touch the road. The main advantage is improved feedback and road feel. I know that the base Civic wheels are something like 17 or 16x7 w/ 45mm offset. I used the tire-calculator at Wheel-Size.com to compare the oem set up, (which assumed the oem set up had a zero scrub radius) to the new rims and tires and it calculated the new scrub radius to be positive 21/32″ scrub radius which is approximately 5/8″ or 16.67mm. 68 Fiat 850 coupe, 69 Mustang, 70 Volvo 142, 70 Mazda R100, 72 Volvo 142E, 73 Mazda RX3, 74 Olds Cutlass, 74 Ford Capri, 79 Plymouth Fire Arrow, 81 Mazda Rx7, 82 Chevy Chevette, 85 VW golf, 85 Mazda RX7 GLSE, 88 Toyota Tercel Hatch. If they meet at the ground surface the scrub radius is Zero. Las cotizaciones no provienen de todos los mercados y pueden tardar hasta 20 minutos en aparecer. widen the track, and b.) 2"| Page" Figure"2:Less caster,lesscaster"lead " " Figure2b:Greatercaster,greatercasterlead % When%cornering,% Z Á ] P Z v } v ] v P P [ } u ] v } Z } v ] v P ( } X d Z } v ] v P If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. Last year I bought a new 2016 Jeep Wrangler Unlimited Sahara. That is with the stock 14" rim and stock size 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. If these two lines intersect at ground level, then you are said to have zero scrub. About us. Get the forces to the drivers liking using as little scrub radius as possible. Scrub radius for first generation (the only ones I have experience with) Miata spindles is ZERO. print to the axle centre is called Scrub or Scrub radius. While scrub radius plays a part in handling, it's not much. 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. Steering axis inclination; Effects of SAI; Scrub radius 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. 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 … The kingpin axis is the line between the upper and lower ball joints of the hub. On a MacPherson strut, the top pivot point is the strut bearing, and the bottom point is the lower ball joint. save. Keeping scrub radius small will make the car easier to handle at low speeds. The larger the scrub radius is the more feedback and shock load you get. My guess after running the numbers and reading some information about front end geometry and steering stability that +3” is a whole crap load and it’s going to create a much more exciting ride but in a bad way. 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. That is with the stock 14" rim and stock size tire. Discussion in 'Chassis' started by strimmer, Sep 8, 2010. The scrub radius is 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 steering gear and linkage or the rack and pinion connects the tie rods to the steering knuckles. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire … A positive scrub radius tends to be beneficial while braking into a turn. The thing is, I know this will alter the scrub radius (beside other things like bearing load, etc) and after reading something about this I didn't came to a certain conclusion regarding how this will affect the handling of a clio (182 cup suspension with 16" ET 37 wheels I … Enter as much or as little information as you like and the calculator will validate the data then apply it … level 2. The distance between where the SLA and the centerline to the wheel intersect the ground is called the scrub radius. The OP, by his post, does understand the effect of the gross change to the scrub and probably any detrimental effect of steering all for looks. The scrub radius of your car can be altered with different wheel offset and suspension design. 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. 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 … If it is inboard then the scrub radius is positive. I am currently running zero 'Scrub Radius'on the front wheels of my Cobra. 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. 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. I did mis-read the OP. The scrub radius is 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. report. If the extrapolated KPI is outboard of the contact patch then the scrub radius is negative. If these two lines intersect at ground level, then you are said to have zero scrub. 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. Torque due to … 4% : Implementation of all the corrective actions, not only improved steering returnability by 40% but also helped in reducing the cycle time in design … Running Gear - Suspension, Brakes, Steering, wheels and tires, http://www.pbase.com/ninerjoe/lotus_19_build, It is currently January 17, 2021, 9:22 am. I use these calculators to develop my own car and you can follow my progress as well as the practical application of the calculators within my blog. Torque steer sets in and a considerable amount of kickback is felt. It has the biggest influence on the steering's self centering feel. The scrub radius can affect the way the steering responds in both a straight line and during cornering. Tu navegador no tiene JavaScript activado, por lo cual no se puede abrir este archivo. share. 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. Basically, the scrub radius is the Edge A of the small triangle left over, under the ground. 3 comments. … To visualize scrub radius, stand in front of your car. La información se proporciona "tal cual", y solamente con un propósito informativo, no con objetivos comerciales ni de asesoramiento. Before using Lotus you should know your Track-width and front Dimension of your frame. bias the lateral weight distribution. However, too large of a scrub radius makes the steering very sensitive to … It is only referred to as positive or negative. Scrub Radius- this is the tires turning radius about the steering axis. Scroll down and select " Scrub Radius Left ", " Scrub Radius Right ", " Tire Contact Patch Width Left " and/or " Tire... Click Apply For a circle with a circumference of 15, you would divide 15 by 2 times 3.14 and round the decimal point to your answer of … With a small amount of scrub radius, the tire is turned about the kingpin axis, slightly offset from the tire’s centerline. The location of the steering gear linkage or rack can have a … I now get a scrub radius of .65 inches. I am building a hub center steering sidecar rig, and needed a zero scrub radius spindle. https://autosystempro.com/scrub-radius-suspension-design-explained Contents. hide. strimmer Forum Member. Positive Scrub Radius: Steering effort increases because the wheel has to scrub around a larger contact patch. Seems very close to what you're getting. If it is inboard then the scrub radius is positive. From a front view of the car, draw a line between the ball joints and make it intersect the ground. To find my actual scrub radius, I need to combine that triangle with another triangle. The distance between the centerline of the tire and where this line meets the ground is your scrub radius. The distance from the kingpin axis to the wheel centre plane measured horizontally at axle height is called Spindle length. Negative Scrub Radius: Most front wheel drive cars use negative scrub radius. The scrub radius is a front-view issue. Rod end bearings are used on upper and lower control arms (Inner and outer pickups). Former oldies. Actívalo y vuelve a cargarlo. Tire height is reduced below the axle by deformation. This creates a small tire/road friction resistance that in turn translates into feedback from the road. This is an exmaple of a suspension geometry with positive scrub radius. Braking in turn Directional stability Scrub radius : 2% . Hence a small scrub radius will make the car less sensitive to changes in steering when braking. Ive been experimenting with wheel offsets to a.) 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. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire data that you need for … report. 3. That should be an imperceptible change. 3 comments. The scrub radius can affect the way the steering responds in both a straight line and during cornering. Former oldies. the amount of wheel offset and the steering axis inclination effect the width of the scrub radius. Learning how to build Lotus Seven replicas...together! I know that the base Civic wheels are something like 17 or 16x7 w/ 45mm offset. I've never found an equation - its always been a ruler or a drawing. 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. Picture two imaginary lines, one represents the steering axis, and the other represents your wheel’s centerline. ... Any idea on how to calculate it using the forces and moments that are given as output? To calculate the radius of a circle by using the circumference, take the circumference of the circle and divide it by 2 times π. We only really have scrub to fit things in the wheel easier. Se ha producido un error en el navegador. The smaller the scrub radius is the less feedback to the wheel you get. Get the forces to the drivers liking using as little scrub radius as possible. 88 Audi Quatro, 91 Honda Accord, 94 Nissan Sentra, 98 VW Jetta, 02 VW Jetta, 08 Mazda 6, ( not listed , Bikes , Trucks or Vans ) (Shorter tires than stock increase the scrub radius [ceteris paribus]) This is added to the change in "effective" offset; "effective" because spacers change the perceived offset of the wheel. 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. While scrub radius plays a part in handling, it's not much. Fig.4 Kingpin Inclination Front and Side View Note: … This assumes that the stock wheel is roughly a 28.9x9.3r15, with a stock wheel that has a … Here is the 'mathy' part. It could be positive, negative or zero. I've searched high and low, but can't seem to find out how everyone is calculating their scrub radius. Figure shows the kingpin geometry. Braking in turn Steering effort : Scrub radius . The caster is a side-view issue. From a front view of the car, draw a line between the ball joints and make it intersect the ground. The distance between the centerline of the tire and where this line meets the ground is your scrub radius. A week after purchase, and before I'd really had a chance to drive it stock, I ran out and changed to larger tires and aftermarket wheels at 4 wheel parts in Sherman Oaks. 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. Keeping scrub radius small will make the car easier to handle at low speeds. The steering gear and linkage or the rack and pinion connects the tie rods to … Algunas características de Excel no se pueden mostrar en Hojas de cálculo de Google, por lo que se perderán si haces cambios. If the scrub radius is small then the contact patch is spun in place when parking, which takes a lot more effort. We only really have scrub to fit things in the wheel easier. About us. The distance between where the SLA and the centerline to the wheel intersect the ground is called the scrub radius. In real life, since the tire is compressed at the bottom due to weight, this will increase the scrub radius a bit. Advertisement. This assumes that the stock wheel is roughly a 28.9x9.3r15, with a stock wheel that has a … 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. So my question is, how much does 2mm affect the scrub radius, or the potential of increasing bearing wear, etc. It also reduces the risk, that a lose of traction on one front wheel during braking, causes the car to change direction. In brief - to maintain oem scrub radius, keep to original ET value, but feel free to bolt on a wider wheel if such is felt to be a necessity. It is much easier to measure from a picture. It could be calculated but the missing dimension in your list is the distance between where the KPI crosses the wheel mounting surface relative to the to the stub axle center. The scrub radius is shown at the bottom at.427”. Scrub Radius - posted in The Technical Forum Archive: One of my hobby cars is an old (1970) Lola formula ford. hide. 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 Miata was the only one I … The steering gear and linkage or the rack and pinion connects the tie rods to … More back spacing ( wheel offset) and larger steering angle narrows the scrub radius. View unanswered posts | View active topics, Board index » The North American Locost Forums » Running Gear - Suspension, Brakes, Steering, wheels and tires, Users browsing this forum: Majestic-12 [Bot] and 12 guests. 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. It has the biggest influence on the steering's self centering feel. This is a … 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? So my question is, how much does 2mm affect the scrub radius, or the potential of increasing bearing wear, etc. 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. save. 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. Usually when talking about scrub radius the topic is handling on the track. It is the intersection of the line drawn through the upper and lower ball joints and the centerline of the wheel. The scrub radius is a front-view issue. A large scrub radius gives lighter steering because the tires can roll in an arc as the steering wheel is turned. I just added in the correct Miata knuckle measurements (from an NA Miata, I believe that's what you're using?). The Miata was the only one I found, although I believe there are others. If they meet at the ground surface the scrub radius is Zero. 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). If the scrub radius is small then the contact patch is spun in place when parking, which takes a lot more effort. 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. 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. How much depends on the tire pressure and corner weight. 3. 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. 88 Audi Quatro, 91 Honda Accord, 94 Nissan Sentra, 98 VW Jetta, 02 VW Jetta, 08 Mazda 6, ( not listed , Bikes , Trucks or Vans ) Hence a small scrub radius will make the car less sensitive to changes in steering when braking. 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). Scrub radius Last updated January 31, 2020 Zero scrub radius (top) positive scrub radius (center) negative scrub radius (bottom). 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. 2"| Page" Figure"2:Less caster,lesscaster"lead " " Figure2b:Greatercaster,greatercasterlead % When%cornering,% Z Á ] P Z v } v ] v P P [ } u ] v } Z } v ] v P ( } X d Z } v ] v P What Is Scrub Radius? Wheel-Size.com is a Wheel Guide and catalogue. Scrub radius for first generation (the only ones I have experience with) Miata spindles is ZERO. Scrub radius : 10% . ... Any idea on how to calculate it using the forces and moments that are given as output? The biggest effect is called bump steer. share. 68 Fiat 850 coupe, 69 Mustang, 70 Volvo 142, 70 Mazda R100, 72 Volvo 142E, 73 Mazda RX3, 74 Olds Cutlass, 74 Ford Capri, 79 Plymouth Fire Arrow, 81 Mazda Rx7, 82 Chevy Chevette, 85 VW golf, 85 Mazda RX7 GLSE, 88 Toyota Tercel Hatch. 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. Reporting Open the Macpherson Geometry Calculator or the Suspension Geometry Calculator Click so it becomes if it isn't already. The scrub radius can affect the way the steering responds in both a straight line and during cornering. Before using Lotus you should know your Track-width and front Dimension of your frame. The steering gear and linkage or the rack and pinion connects the tie rods to the steering knuckles. The scrub radius is the distance between the two, where both touch the road. Joined: Mar 6, 2010 Likes Received: 2 Location: On the limits of adhesion. SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. My actual upper kingpin is at 17-5/8" above ground (measured 14-3/8" to axle centerline plus 3-1/8" for half knuckle height) 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. If the scrub radius is zero, then the tire has to be twisted on the ground, and the steering effort is highest. Scrub radius helps this feel by providing feedback from the contact patch. 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 of your car can be altered with different wheel offset and suspension design. This wheel is about three pounds lighter than the 20-inch wheel, so … It also reduces the risk, that a lose of traction on one front wheel during braking, causes the car to change direction. Positive scrub is generally preferred in racing.