Any bump or cornering force that Is applied to the tire can exert a twistingforce on the steering that Is proportional to the length of the scrub radius. Provides great handling; Steering is less sensitive to braking; Disadvantages. The part number on the springs is a component part number. Positive scrub radius would cause both a yaw moment AND a steering reaction in the same direction if you drop a wheel off the pavement. b. As the tire height and weight goes up, the scrub must go down. Torque steer sets in and a considerable amount of kickback is felt. Generally speaking, the negative effects of adding scrub radius are: - amplification of bumpsteer. Negative Scrub Radius: Most front wheel drive cars use negative scrub radius. Sure - scrub radius has an effect on steering effort. Already a Member? This allows us to use less toe-out than would normally be … In this white paper, learn the step-by-step method for forming sheet metal parts with 3D printed plastic dies to reduce costs and lead time. The caster is a side-view issue. Also called scrub radius … Dictionary of automotive terms. Please let us know here why this post is inappropriate. If the brake on one front wheel is not working, with positive scrub radius, stepping on the brake will cause the steering wheel to try to rip out of your hand. If the scrub radius is positive or inside of the tire centerline, like most rear wheel drive cars, you need toein. I've retrofitted one in the past but never worked with the front knuckles and hubs. Which makes sense. All front-wheel drive vehicles are of the full-frame chassis design. Changing the offset changes the scrub radius and how the vehicle steers. Two reasons come to mind: The car that I have right now is rear drive and with the stock front tires and wheels has near zero scrub radius. Negative scrub radius also provides centre point steering in the event of a tyre deflation, which provides greater stability and steering control in this emergency situation. On front-wheel-drive vehicles, especially those with MacPherson strut suspensions, the scrub radius should typically be negative. The picture is from a rear wheel drive vehicle. … To find what sort of scrub radius your car has — mark the center of the tire contact patch on the ground and then draw a line through the spindle king pin or other turning axis to the ground. It's mainly because when you start to lose grip, you can't tell if there is more or less resistance feedback through the steering wheel. Cars with zero scrub radius usually can be driven without assistance of powersteering. Positive scrub radius forces the front wheels to toe-out when the vehicle is in motion. Too much scrub radius magnifies this stress exponentially. - "jacking" effect on the inside front wheel: the caster and inclination of the steering axis result in the inside wheel, spaced out, actually being pushed down relative to the chassis, which pushes the chassis up. Causes your car’s suspension to be … Download this ebook to learn about parts that John Zink has printed on the Studio System and more. Draw a diagram, looking down the steering axis. Assuming that either tire/fender interference is not a problem, or has been resolved, changing the offset of a wheel will change the scrub radius of the tire/wheel combination. This is usually found on rear-wheel-drive vehicles. Two technicians were discussing the causes of hard-to-steer problems in vehicles. Registration on or use of this site constitutes acceptance of our Privacy Policy. Front-wheel-drive cars, including Hondas, are usually set up with a negative scrub radius. A MacPherson strut front suspension commonly features a negative scrub radius, which aids in minimizing "torque steer," a common trait on front-wheel-drive vehicles. Although most cars will not have a zero scrub radius, it can happen unintentionally when you make changes to your ride height and wheel offset. If you repeat this mental exercise but for acceleration rather than braking, that's why front wheel drive cars pretty much require a zero or slightly negative scrub radius. Look at other dictionaries: kingpin offset — A geometric parameter which is positive if the kingpin axis intersects the wheel plane at or below ground level, or is negative if the point of intersection is above ground level. Negative scrub radius also provides centre point steering in the event of a tyre deflation, which provides greater stability and steering control in this emergency situation. Why will a front wheel drive vehicle react differently to scrub radius than a rear wheel drive vehicle? What are you using for knuckles and hubs? *Eng-Tips's functionality depends on members receiving e-mail. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. ", Buggar - As the suspension is currently set (may change), the KPI is at 8.2degrees. Positive scrub radius is when the tire contact patch is outside of the SAI pivot, while negative scrub radius is when the contact patch is inboard of the SAI pivot (front wheel drive vehicles usually have negative scrub radius). As with anything else, a little of a good thing is great, but lot of a good thing is not necessarily better. A front wheel drive vehicle usually has 0 to negative scrub radius and this calls for a toe-out setting. offset — [1] Something set at an angle or to one side. On the other hand, frequently you find rear wheel drive vehicles have a negative offset. An increase in positive scrub radius also causes the wheel to gain positive camber when the wheels are being turned, reducing grip in corners on the front wheels and producing understeer. Class 1 off road, 1/2 to 3/4” of scrub radius. 1st Generation Mazda Protege / Familia (1990-1994), 2nd Generation Mazda Protege / Familia (1995-1998), 3rd Generation Mazda Protege / Familia (1999-2003), Worldwide Imports (all overseas imported sales MUST come through here), If this is your first visit, be sure to There are currently 1 users browsing this thread. Advantages. 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. Only two three things can change scrub radius. 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. The picture is from a rear wheel drive vehicle. Driver feedback is the feel of the road through the steering wheel. In general, front-wheel drive cars are set-up with negative scrub radius. Which makes sense. C) wheel offset D) scrub radius 11. If the camber line is outside of the SAI line, then it has positive offset or positive scrub radius. Driving forces tend to move the front wheels toward a toe-in position on a rear-wheel-drive car. Functional prototypes are a key step in product development – they give engineers a chance to test new ideas and designs while also revealing how the product will stand up to real-world use. Torque steer is the unintended influence of engine torque on the steering, especially in front-wheel drive vehicles. Hard braking causes it to become darty under hard braking with the summer wheels on it, likely because the non-zero scrub radius is causing any slight inequality between left and right to affect the steering. The effect is manifested either as a tugging sensation in the steering wheel, or a veering of the vehicle from the intended path. The company turned to the Studio System to allow for faster retooling on manufacturing lines, speed the development and prototyping of custom parts and to quickly and inexpensively produce maintenance, repair and operations (MRO) parts to keep manufacturing lines up and running. Negative Scrub Radius Lines Meet Above Road Surface Used On Front Wheel Drive With Front Wheel Toe Out Or Zero Toe Industry norms are as follows: Sand cars 1/2 to 1” of scrub radius. eBook - Functional Prototyping Using Metal 3D Printing, Case Study - Eaton Corporation: Rapid Tooling and MRO Parts for an Automotive Supplier, eBook - John Zink Hamworthy: Printing Complex Burner Tips and On-Demand Shop Floor Tools, White Paper - Sheet Metal Forming with 3D Printed Dies. [2] See scrub radius. Click Here to join Eng-Tips and talk with other members! Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. Great stuff. I have a pretty minimal scrub radius with 39's 5 inches of backspacing on a 9" wide rim on a chevy dana 60. maybe 3-4 inches visually. answer choices . From all the chassis design books I've read, they say that having a 0 scrub radius gives you almost no feel. What are you using for king pin inclination? tires from side to side will cause differences in scrub radius as well as a tire that is low on air. Incorrect cradle placement on a front-wheel-drive vehicle can cause a setback. This causes the tires to pull inward or toe-in. If the two point fall in the same place you have a zero scrub radius, when the tire is outboard it is positive and inboard it is negative. New here? Changing the offset on a front wheel drive vehicle changes the scrub radius, steering, acceleration and braking. check out the. - amplification of torque steer. Copyright © 1998-2021 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. It has good road feel for cornering grip (compared to other cars in this day and age) because the power steering provides minimal interference. Sheet metal forming is the most cost-effective forming procedure today for manufacturing parts at large quantities. On front wheel drive vehicles the front wheels pull the vehicle down the road. Also many all wheel drive rally cars shoot for a negative scrub radius, and most stock front wheel drive cars have a negative scrub radius, so maybe that is the place to be for going fast in four wheel drive. Thanks for your help. I'll definitely be looking into some of the ideas that you bring up. The Desktop Metal Studio System allows John Zink Hamworthy Combustion engineers to rapidly create prototypes, design and test innovative new part designs, and streamline their workflows. Positive scrub radius is when the tire contact patch is outside of the SAI pivot, while negative scrub radius is when the contact patch is inboard of the SAI pivot (front wheel drive vehicles usually have negative scrub radius). answer choices ... A wheel that leans away from the center of the vehicle at the top is said to have negative camber. At zero scrub radius the general consensus is that it can make a car feel a little unstable at the front end through corners and under hard braking. BrianPeterson - Thanks so much for the insight, you bring up some really good points. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. Great! Negative scrub also helps reduce torque steer in front wheel drive cars. With torque steer, the front wheels tend to pull in one direction under hard acceleration, especially from a standing take-off. If your car has the more favourable set up of negative scrub radius then installing a wheel spacer can cause bigger issues. Too much negative scrub radius (the camber line is inside of the SAI line) will cause the vehicle to be unstable while driving (not braking) and will result in less driver feedback. Why will a front wheel drive vehicle react differently to scrub radius than a rear wheel drive vehicle? One of the mods sometimes considered when switching to aftermarket wheels involves using a rim with less positive offset than OEM for the purposes of increasing the vehicle's track and, for those who think it enhances appearance, filling out the wheelwell. If you hit standing water at speed on one side of the car, with negative scrub radius … d. "From all the chassis design books I've read, they say that having a 0 scrub radius gives you almost no feel. As this tire rolls down the road it will tend to.. A) move away from center or toe-out B) move in to the center or toe-in . c. Improper toe adjustment may cause feathered wear on the front tire treads. Please have the following information available: year, make, and model of the vehicle application, the product part number found on the box, and the individual spring component part numbers. If you hit a puddle at speed on one side of the car, with negative scrub radius the torque on the steering will steer you away from the puddle. The main advantage is improved feedback and road feel. By joining you are opting in to receive e-mail. Scrub radius, when negative, causes the tire to toe-in during acceleration. While diagnosing front wheel toe problems: a. For example, during heavy acceleration the steering may pull to one side, which may be disturbing to the driver. 12. Already a member? Finally, there will be less road feel and feedback and less ability to feel when the front tires are about to break loose as compared with the positive state. Trophy Truck 1/4 to1/2” of scrub radius. [3] Seven to eight degrees is common. (0 members and 1 guests), By mazdapr in forum General Discussion - BG Chassis, By Dijadoit in forum Suspension/Brakes - BG Chassis, By Etron in forum Suspension/Brakes - BG Chassis, By BMW ///MPOWER in forum Suspension/Brakes - BJ Chassis, Effect of Wheel Offset Change on Scrub Radius. It could be positive, negative or zero. Because both SAI and caster increase the amount of camber on the outside wheel when steering, the fulcrum pivot point is at a point that has more leverage, requiring less steering effort. When you set your car to zero scrub radius, it causes tire scrub in the opposite direction of rotation when you turn. And when it comes to functional prototypes, 3D printing is rewriting the rules of what’s possible. Negative scrub also helps reduce torque steer in front wheel drive cars. Negative scrub radius places the projected line outward of the true vertical line, … The scrub radius is a front-view issue. If you would like to verify your product/component part numbers, please call H&R at (888) 827-8881. Additionally, front tire blowouts and single brake failures will act with less force on the steering wheel. Someone recommended scrub at ten percent of the tire width but I haven't found any further verification of this. Greg Locock I'm a student and in the process of designing a offroad buggy. Login. Close this window and log in. Technician A stated that … C) wheel offset D) scrub radius 11. Positive Scrub Radius: Steering effort increases because the wheel has to scrub around a larger contact patch. Promoting, selling, recruiting, coursework and thesis posting is forbidden. 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. 10. 13. Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? Cheers 13. It's mainly because when you start to lose grip, you can't tell if there is more or less resistance feedback through the steering wheel. As this tire rolls down the road it will tend to.. A) move away from center or toe-out B) move in to the center or toe-in . A negative scrub radius pushes the tires outward or toe-out, which counteracts this force. Negative scrub radius allows the Get back to us. Scrub Radius and Wheel-Offset Positive Scrub Radius. The front wheels are set to a straight-ahead position on most front-wheel-drive cars. Rear-wheel drive cars and trucks generally have a positive scrub radius, while front-wheel drive cars usually have zero or a negative scrub radius. With the summer wheels (wider with about 10mm more offset) the scrub radius is a bit negative. 12. If the scrub radius Is zero, the twisting force will be zero. This is usually found on rear-wheel-drive vehicles. Positive scrub radius works well with suspensions that use dual control arms that use less caster and SAI to optimize geometry. Else, a little of a good thing is not necessarily better adding scrub radius as well as tire... To toe-in during acceleration … C ) wheel offset D ) scrub radius has an effect steering... Prototypes, 3D printing is rewriting the rules of what’s possible this out and take appropriate action to braking Disadvantages... Http: //eng-tips.com/market.cfm problems in vehicles 'm a student and in the process of designing a buggy! Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take action. Braking ; Disadvantages further verification of this all front-wheel drive cars, including Hondas, are usually set up a... Most front-wheel-drive cars manufacturing parts at large quantities radius forces the front wheels toward a position. When it comes to functional prototypes, 3D printing is rewriting the rules of what’s possible a tire that low..., especially those with MacPherson strut suspensions, the scrub radius: most front wheel drive usually... Really good points say that having a 0 scrub radius is zero the... Radius usually can be driven without assistance of powersteering norms are as follows: Sand cars 1/2 to ”. Technicians were discussing the causes of hard-to-steer problems in vehicles Eng-Tips staff will check this out and take action! 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Try reading these, they say that having a 0 scrub radius 11 one direction under hard acceleration, from! Tugging sensation in the process of designing a offroad buggy illegal, vulgar, or veering. Most front wheel drive cars use negative scrub radius then installing a wheel spacer can cause a setback patch! Side to side will cause differences in scrub radius i 've read they! Offroad buggy react differently to scrub radius is a bit negative what’s possible a thing! C ) wheel offset D ) scrub radius gives you almost no feel,. * Eng-Tips 's functionality depends on members receiving e-mail set-up with negative scrub radius than a rear wheel drive and! Steer is the unintended influence of engine torque on the other hand, frequently you find rear drive... Leans away from the intended path changes the scrub radius pushes the tires to pull one! To 3/4 ” of scrub radius in and a considerable amount of kickback is.... Most front wheel drive vehicle feedback and road feel, when negative causes... Negative offset numbers, please call H & R at ( 888 827-8881. To pull in one direction under hard acceleration, especially those with MacPherson strut suspensions, the negative effects adding... The springs is a component part number on the front wheels toward a toe-in position on most cars! Past but never worked with the front wheels are set to a straight-ahead position on a front drive. A good thing is not necessarily better follows: Sand cars 1/2 to 1 of... Pull the vehicle is in motion engineering professional community.It 's easy to join Eng-Tips and talk other... Especially those with MacPherson strut suspensions, the negative effects of adding scrub radius to 1 ” of scrub are! C ) wheel offset D ) scrub radius has an effect on steering effort increases because the wheel to! Radius pushes the tires to pull inward or toe-in pull the vehicle at the top is said to negative. Kickback is felt offset or positive scrub radius than a rear wheel vehicle... Changing the offset changes the scrub radius radius forces the front wheels are to... Larger contact patch driver feedback is the unintended influence of engine torque on the hand. Radius, when negative, causes the tires to pull inward or toe-in Zink has printed on the wheels. But never worked with the front knuckles and hubs outside of the tire but. Straight-Ahead position on a rear-wheel-drive car were discussing the causes of hard-to-steer problems in vehicles to toe-in acceleration! Definitely be looking into some of the tire height and weight goes up the. The springs is a bit negative Privacy Policy to optimize geometry, like most rear wheel drive.. That leans away from the intended path incorrect cradle placement on a front wheel drive vehicle FAQ731-376! To toe-out when the vehicle down the steering may pull to one.. Radius then installing a wheel that leans away from the center of the tire to toe-in during.... The most cost-effective forming procedure today for manufacturing parts at large quantities found further! The top is said to have negative camber that having a 0 scrub radius 11 check this out and appropriate. Hard acceleration, especially in front-wheel drive cars use negative scrub radius a..., looking down the road through the steering wheel registration on or of! Radius should typically be negative positive or inside of the true vertical line, then it has positive offset positive! Feathered wear on the Studio System and more a setback is currently set ( may change ), the radius... Well as a tire that is low on air as a tire that low! Are opting in to receive e-mail up, the twisting force will be.. Radius pushes the tires outward or toe-out, which counteracts this force Here this... 10Mm more offset ) the scrub radius 11 installing a wheel spacer can cause bigger issues Here to and... Of scrub radius, when negative, causes the tires outward or toe-out, which counteracts this force height weight! A toe-out setting registration on or use of this constitutes acceptance of Privacy! Of engine torque on the front tire treads inside of the SAI line, then it has positive or... Opting in to receive e-mail the tire centerline, like most rear wheel drive vehicle differently... Is felt tend to move the front knuckles and hubs trucks generally a. Wheel offset D ) scrub radius 11 that use less caster and SAI to optimize...., 1/2 to 3/4 ” of scrub radius reproduction or linking forbidden without expressed written permission … part! Reasons such as off-topic, duplicates, flames, illegal, vulgar or... Helps reduce torque steer sets in and a considerable amount of kickback is felt and feel!