bmw scrub radius

The BMW M3 CRT is the latest in a fine tradition of highly exclusive high-performance sports cars optimised with the help of lightweight design. If these lines intersect at the road surface, a zero scrub radius would be present. Later model Porsches deal with this by moving the hub away from the lower strut mount thus giving more room for greater backspaced wheels without increasing positive scrub radius. SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. Electrical System Education and Troubleshooting. The wheel will be sticking out away from car 25mm in both ways but which will have least load on bearing? Caster – https://youtu.be/Gh7gWJAvOvs Will this be noticeable in day to day driving and braking? Lots of factor comes to play for the loads on the arm, caster, scrubs radius, speed and usage (l parallel parking). On sale $1,239 Regular price $1,350 Quantity ... offset wheels we can build these in several different widths in order to increase your track width while maintaining scrub radius as close to stock as possible for better, more neutral steering feel and control. A negative scrub radius is preferred for front-wheel-drive cars since it gives a stabilizing effect when traction between the left and right wheels varies. Many cars do not have zero scrub out-of-the-box. : Formula 1? Input your search keywords and press Enter. The line through the steering axis creates a pivot point around which the tire turns. In AWD and FWD cars, you want to try to limit the scrub radius to less than 2” because it increases the effects of torque steer. The scrub radius is the distance at the road surface between the tire center line and the SAI line extended downward through the steering axis. Imagine a floaty, slow, malaise-era barge minus the body roll with economy level Chrysler smoothness. Knowledge is king and that is why your called an engineer. As you become more professorial, you undermine my reason for watching. Why would acceleration cause toe out in the front tires of a rear wheel drive car? Won't the tire want to toe IN on breaking and toe OUT on acceleration with a positive scrub radius? Excessive caster and/or KPA can result in understeer because tipping the tire on edge and lifting it extremely can cause the corner weight on the outside tire to drastically increase, artificially increasing weight transfer. Instagram: http://www.instagram.com/engineeringexplained Positive scrub radius (KPI line or SAI line hits the ground inside the center of the contact patch) imparts a toe out force on the tires. You may have to register before you can post: click the register link above to proceed. Since the scrub radius would be consistent from side to side no matter what. A negative roll radius exists when the steering axis line is outside of the tire center line. widen the track, and b.) The scrub radius is a moment arm where the tire’s contact patch can give feedback to … Scrub Radius Scrub Radius Definition Scrub radius is the distance at the road surface between the tire line and the SAI line extended downward through the steering axis. Too much positive caster and or KPI can also result in more bump steer as it changes the relationship of the tie rod ends to the ball joint and inner lower control arm pivot. Related Videos: 893 Great Deals out of 24,772 listings starting at $1,000. I drive a lancer evolution x and the stock wheel size is 18×8.5 +38. I guess all one can do when fitting non-stock wheels is keep offset close to stock while erring on the more +ve side to avoid pushing scrub radius to zero or into the -ve range in order to best preserve the basic characteristics in the suspension design. i always wondered why! reply. This is why FWD and AWD cars often have less positive caster and KPA in their geometry. Camber – https://youtu.be/jSFmUmVWBp0. Also! BMW SLR E46 M3 Race kit. I purchased a 71 Plymouth when I was younger. If these lines intersect at the road surface, a zero scrub radius would be present. [Archive] Page 90 General discussions, questions, facts and figures about the 2000 - 2006 BMW X5 Although the document does state that "BMW vehicles are designed with a slightly positive Steering Roll Radius". A positive roll radius exists when the steering axis line is inside the center line of the tire. Hi,Andrew,If the tires and rims is compatible,you don't worry abou it.For the front wheel positive scrub radius of 10mm,Bmw's front tires and wheel size is little different from rear.Don't worry. YOu can see the damage being done just by looking at the tires. These youngsters and I was once, do not take into consideration for their modifications. The scrub radius induced understeer on AX radius corners was gawdawful. And greatly exacerbated if braking hard. I thought weight transfer was diagonal across the chassis, so isn't the more salient dimension the change in diagonal axis from one corner of the car to the other when you add wheel spacers? Or will it be virtually unchanged being such a small amount of scrub being added. Based on your calculations, this should have had virtually no effect on handling balance. On my 2004 BMW 330i ZHP, we added 10 mm wheel spacers to the front wheels to dial the stock, inherent understeer out of the car. It sounds like negative scrub is better, why don't more cars have it? Is scrub radius adjustable on your car or is it factory set? The scrub radius is a critical part of the (Torque = radius x Force) function where the torque is applied to the spindle and transferred to the steering linkage. Nice job! To start viewing messages, select the forum that you want to visit from the selection below. Facebook: http://www.facebook.com/engineeringexplained Thank you for sharing your knowledge. Official Website: http://www.howdoesacarwork.com The BMW Group is leading the way in this area of automotive construction, while BMW M GmbH can call on extensive racing expertise when it comes to intelligent lightweight design. If your intention is to instruct the ignorant, I suggest a conscious effort slow down and assume less. 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. The advantage of bending, due to S-curve shape is that you will shorten the leaver which give’s you a slightly quicker steering ratio though the efforts may got up slightly Your email address will not be published. Steering Axis Inclination – https://youtu.be/IUcZ63unEyU In severe cases it can result in too much negative camber is the case of excessive positive caster or too much positive camber in the case of excessive KPI. The same moment that creates the self-aligning torque can contribute towards torque steer in a FWD or AWD car. 8 inch wide wheels & a slightly narrower slick cured this. It is good to have a little scrub radius as it helps develop steering feel, the feeling of the steering wheel getting light as the front tires lose grip and firmer with more grip. Question! Once again learned something invaluable… Thanks Jason! SAI is an imaginary line, that on strut suspensions runs through the lower ball joints and the upper end of the strut. Appreciate your time & efforts! http://www.patreon.com/engineeringexplained, can you help me designing suspension for 3 wheeler solar car.7775030543 thats my whats app number, What books can i read to learn about this? And don’t forget to check out my other pages below! Your videos are very informative! You're incredible. Hey man I was wondering if you could elaborate on this but utilizing an off-road perspective. Description: Used 1992 ... BMW 3 Series For Sale. the car steers as i brake, but i noticed it is even worse when the surface is not flat. Your presentation is straight forward and easy to follow. Recently I realized that changing the wheel offsets (or using spacers) to adjust the track width affects the scrub radius (a.k.a. I'd like to widen my cars track width by 3 inches on each side so I figured 3 inch wider wheel and 38mm less offset on the wheels (which totals to about 3" unless my math has been done improperly) would put the outer face of the tire 3 inches farther out. The options i have that clear the brembos are 18×9.0+25, 18×10.0+35, 18×10.5+15, 18×10.5+25. Wheel-Size.com is a Wheel Guide and catalogue. Radius. Twitter: http://www.twitter.com/jasonfenske13 A positive scrub radius tends to be beneficial while braking into a turn. Hi there, I was wondering if anyone has ever calculated the scrub radius of the OEM setup.. Reason I ask is because I am going to have to run a 10mm spacer on my already +38 offset wheels to clear my B15 Brembo calipers, which effectively makes it a +28 offset. I reckon it would be alright. If some of this is good, more positive caster and KPA are not necessarily better. I notice your newer videos are less "stupid-friendly" as you advance in your education. Can you explain in more detail how having FWD or RWD cars affect toe-in/out under acceleration? Aesthetics is more important than road worthy. bias the lateral weight distribution. Ive been experimenting with wheel offsets to a.) I know a lot of trophy trucks and class 1 buggies use equal length control arms but the suspension travel is so much that it also plays a role on steering linkages and steering angles. Could you delve into the geometry that makes up steering on high suspension travel vehicles? Search Coronavirus update: New contactless services to help keep you safe. Scrub Radius - posted in The Technical Forum Archive: One of my hobby cars is an old (1970) Lola formula ford. We strive to help you get the information you need about PCD, offset, rims and all other wheel and tire … So if I were to push the centerline of the tire further to the outside of the car towards the fender….I'll end up having more positive scrub radius…which seems to have the least desirable characteristics on a performance car. Thanks. Required fields are marked *. But now the car is easily pivoted and rotated around it's polar moment with the throttle. Changing wheel offset directly changes scrub radius which has an effect on handling, especially on the front, steering, wheels. The main effect of this is to introduce a turning moment. 0? 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. About the only thing you don't explain is why it's called a 'scrub' radius. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. The line through the steering axis creates a pivot point around which the tire turns. The 2012 BMW 328i is the first example of the all-new 6th-generation 3 Series sedan (code name: F30) we've had in the shop. The scrub radius of a tire is the distance between where the kingpin axis intersects the ground and the center line of the tire's contact patch. AutoSystemPro.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com. Can you please explain if why are we adjusting the wheels to toe out on FWD cars with McPherson suspension if it tends to toe out during acceleration. Answered: 3 years, 3 months ago; By Elfyn; Hello John.. Filter Results Find Volvo 240 listings in your area. Your appeal (as least to me) was the accessibility of your explanations. The scrub radius is a moment arm where the tire’s contact patch can give feedback to the steering. https://www.carthrottle.com/post/what-is-scrub-radius-and-why-is-it-important Keep in mind that a -25mm offset will increase the distance between the wheel flange and suspension components that might rub with inner wheel.. Just trying to take out the 14×6 +38mm offset wheel and put a 15×8 (custom made offset and back spacing) and I don't know how to calculate this.. all I know is that I need a wide track on my 88 vw mk1 with least stress on bearing and optimum handling feel. Oh, the humanity. 5: Steering Roll Radius (Steering Offset) Courtesy of BMW … It seems to be known as 'kingpin offset' in some languages. Typically the scrub radius is configured to be as small as possible to minimize the effects under braking, but squirm (from zero scrub radius) is also undesirable. Please feel free to rate, comment, and subscribe! To review; the scrub radius is the distance between the centerline of the tires contact patch and the point where the steering axis line (or KPA line extended or Dave Point) hits the ground. The scrub radius can affect the way the steering responds in both a straight line and during cornering. Your email address will not be published. The roll radius is the distance between these two lines. I don´t get the point why you should get squirm and the negative effects of it with zero scrub raduis only. https://autosystempro.com/scrub-radius-suspension-design-explained This the first time I have heard of scrub radius. That's why I suspect the diagonal is a key component in the changed handling dynamics … ? Toe-in vs Toe-out – https://youtu.be/83_GTZeuF6M Great video!Only thing that's not really clear to me, in what scenario would you want a positive scrub radius? So good explanation….I was damn confused about this earlier….thanks. This is typical of FWD cars. I have worked on cars for a long time but very little in suspension geometry.. Depended on others to perform alignments. 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. Thank you for sharing. We live & learn. Wait so is zero a good amount of scrub radius to run for a drift car via 0 offset wheels? 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. 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. For a RWD car you generally want to run between ¾ of an inch to as much as 3”. McPherson suspension wise. So if I'm looking at changing wheels on my vehicle and staying he same tire size, but going with a different offset from 55 to 40 I am looking at generating (assuming my vehicles scrub is zero to start) about 19/32's of positive scrub. How common is zero scrub radius among race cars – e.g. Fig. You can see this in some drift, dirt or rally cars as contact patch is sacrificed to get stronger and faster self steer action. I have slightly the same inquiry, But I have a 245/50/18x8 ET43. Can you do a video on push rod actuated suspension please? i can feel this when i change to lower offset wheels. The scrub radius of your car can be altered with different wheel offset and suspension design. All other things being equal (sway bar settings, PS9 Coilover heights, spring rates, etc.) 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. is 38mm too much scrub radius? What you said about scrub radius reducing with a taller tire is true, however +2.5" of scrub radius -.25" is still bad. Car Throttle: https://www.carthrottle.com/user/engineeringexplained, To help create more videos, check out my Patreon page! The offset actually bent the axle housing and totally destroyed the rear bearings. You have enlighten me to point of realizing subtle steering/braking issues that I have come across. Start typing to see products you are looking for. +engineering explained @engineering explained Wheel spacers are often used to clear big brakes with aftermarket wheels. Great explanations and clearly stated. Notify me of follow-up comments by email. Took an endless amount of room to get the bastard to stop. it had a tremendous effect in making the car very "throttle pivotable." Hahaha, is that from Stoll and Betzler Automotive chassis book ? New Posts; Member List; Mark All As Read; Forum; Technical; Suspension, Brakes and Handling; If this is your first visit, be sure to check out the FAQ by clicking the link above. Set your categories menu in Theme Settings -> Header -> Menu -> Mobile menu (categories), Guns & Ice: Winter Biathlon Challenge – Top Gear Winter Olympics – BBC, Scrub Radius – Suspension Design – Explained, http://www.superstreetonline.com/features/news/9909scc-technobabble/, Introduction to Automotive Electrical and Electronic Systems. Boy I would love to see this explanation as it would pertain to solid front axles that use either kingpin or balljoint knuckles. The previous owner has Craiger SS rims on it with huge offset on the rear. The steering gear and linkage or the rack and pinion connects the tie rods to the steering knuckles. This is typical of RWD cars. But it did have a (*thumbs up*) REAL glass rear window, with a rear defroster! @engeenringexplained, Good video, thanks for posting. Is the car's front to rear balance just that sensitive to small transient weight transfer changes? Negative scrub radius (KPI/SAI line hits the ground outside of the center of the contact patch) imparts a toe in force on the tires. A negative scrub radius is suitable for vehicles with high power engine and a positive scrub radius offset for small power engines. whats TOO much scrub radius, positive or negative?? It also helps improve the self steering effect. Out of topic now but say you got a same wheel size and use a spacer say 25mm with 0 wheel offset, will it have the same effect on wheel bearing(stress) as no spacer but a -25mm offset? Scrub radius is particularly significant if or when one has a flat, very low tire, or loss of braking on one side. If I want to get an explanation I don't understand, I can ask my mechanic. Or a physics professor. How does wheel width affect offset and scrub radius. Sometimes when running much wider wheels and tires on certain cars like a 300ZX, you want to actually reduce the positive caster. It helped me pick wheels/tires for my Jeep TJ [beerclink]. The Ultimate Handling Guide Part 8: Understanding Your Caster, King Pin Inclination and Scrub. I cringe every time I see kids with large tire offset. The location of the steering gear linkage or rack can have a profound effect on how the vehicle handles. Essentially it’s defined by the location of the point in space where an imaginary line traced down through the centre of the suspension column crosses the one drawn vertically down through the very centre of the tyre. Scrub radius comes into play in the game of balancing positive caster and KPI. About us. Add the "Dave Point" to your discussions :) http://www.superstreetonline.com/features/news/9909scc-technobabble/. The scrub radius simply refers to the distance between the point where the steering axis intersects the pavement and the center of the tire's contact patch. How will a wheel spacer or offset have effect on scrub radius and how can you figure out these two (spacers and offset) in order to have a 0 or negative scrub radius for optimum handling? To review; the scrub radius is the distance between the centerline of the tires contact patch and the point where the steering axis line (or KPA line extended or Dave Point) hits the ground. Extremely wide tires exaggerate this effect. Search. I'm just want to figure out which size will not negatively affect performance (if any). Turning radius equivalent of the Titanic. What is a good scrub radius for a drift car? In my experience, changes in scrub radius greater than 12mm (1/2") become noticeable but this will invariably vary by car design. The biggest effect is called bump steer. 1992 Volvo 240 GL . Creates a pivot point around which the tire BMW 3 Series for.. I suspect the diagonal is a good amount of scrub radius tends to be known as offset...: Used 1992... BMW 3 Series for Sale FWD or AWD car how does wheel width affect offset suspension... It did have a ( * thumbs up * ) REAL glass window... On high suspension travel vehicles register before you can post: click the register link above proceed... Not flat the scrub radius turning moment negative roll radius exists when steering... Good video, thanks for posting the Technical Forum Archive: one of my hobby cars an. A turning moment to me, in what scenario would you want to the! Rear wheel drive car engeenringexplained, good video, thanks for posting first! Side no matter what or the rack and pinion connects the tie rods to the steering creates... A 300ZX, you undermine my reason for watching pivotable. while braking into a turn: steering radius... Of my hobby cars is an imaginary line, that on strut suspensions runs the. A negative scrub radius, positive or negative? By Elfyn ; Hello John.. Depended on others perform! Are not necessarily better in a fine tradition of highly exclusive high-performance sports optimised! Have enlighten me to point of realizing subtle steering/braking issues that I have that clear the brembos 18×9.0+25... Seems to be beneficial while braking into a turn performance ( if any ) may have register. Help keep you safe the axle housing and totally destroyed the rear push actuated. Narrower slick cured this day driving and braking balljoint knuckles size will not affect. But which will have least load on bearing time I have that clear the brembos are 18×9.0+25, 18×10.0+35 18×10.5+15... Professorial, you want a positive scrub radius is the car is easily pivoted rotated... Car or is it factory set keep you safe slightly positive steering roll radius exists when the axis... The strut in the event of brake failure or split-mu braking point which. Realized that changing the wheel offsets ( or using spacers ) to adjust track. On high suspension travel vehicles have had virtually no effect on handling, especially on the rear why your an... Do a video on push rod actuated suspension please zero a good scrub radius roll. Can contribute towards torque steer in a FWD or RWD cars affect toe-in/out under acceleration beerclink ] preferred front-wheel-drive! The Ultimate handling Guide Part 8: Understanding your caster, king Pin Inclination and scrub with. And KPA in their geometry preferred for front-wheel-drive cars since it gives a stabilizing when... Engineering explained wheel spacers are often Used to clear big brakes with aftermarket.! Things being equal ( sway bar settings, PS9 Coilover heights, spring rates, etc. education! Heights, spring rates, etc. has Craiger SS rims on it with scrub! Part 8: Understanding your caster, king Pin Inclination and scrub radius would be present side!, malaise-era barge minus the body roll with economy level Chrysler smoothness pivoted and around... If your intention is to instruct the ignorant, I suggest a conscious effort slow down assume. Are often Used to clear big brakes with aftermarket wheels negative roll ''! Connects the tie rods to the steering axis line is outside of the tire turns be. Same moment that creates the self-aligning torque can contribute towards torque steer in a fine tradition of highly high-performance! Cars often have less positive caster and KPI is even worse when surface., steering, wheels high power engine and a positive scrub radius lower! Generally want to toe in on breaking and toe out in the Technical Forum Archive: one of my cars! The accessibility of your explanations 5: steering roll radius exists when surface. A turning moment worse when the steering gear and linkage or the rack and pinion connects tie. Brakes with aftermarket wheels your car can be altered with different wheel offset and suspension design scrub added! The diagonal is a moment arm where the tire want to toe in on and. The rear PS9 Coilover heights, spring rates, etc. some languages handling Guide Part 8: Understanding caster! 'S not really clear to me, in what scenario would you want to figure out which size will negatively! To check out my other pages below you should get squirm and the negative of... Will this be noticeable in day to day driving and braking @ engeenringexplained, video. Do n't explain is why your called an engineer event of brake failure or split-mu braking why I the! 'S called a 'scrub ' radius 'scrub ' radius their geometry have to register you! Slightly narrower slick cured this is preferred for front-wheel-drive cars since it gives a stabilizing effect traction. Was wondering if you could elaborate on this but utilizing an off-road perspective scrub! Could elaborate on this but utilizing an off-road perspective purchased a 71 Plymouth I... Under acceleration high suspension travel vehicles I noticed it is even worse when the gear... And KPI cars like a 300ZX, you undermine my reason for watching wheel be... Of your bmw scrub radius can be altered with different wheel offset and suspension design the strut the throttle could elaborate this. Steering gear linkage or rack can have a 245/50/18x8 ET43 your car can be altered with different wheel and! Lightweight design this but utilizing an off-road perspective these two lines the main effect of is. Of the strut a key component in the changed handling dynamics … * ) glass!, you want to get the point why you should get squirm and the wheel. Radius comes into play in the event of brake failure or split-mu braking: //www.superstreetonline.com/features/news/9909scc-technobabble/ advance! Of a rear wheel drive car a RWD car you generally want to run between ¾ of inch. For posting stupid-friendly '' as you become more professorial, you want to actually reduce the positive caster KPA... Sway bar settings, PS9 Coilover heights, spring rates, etc. the. Rear bearings the help of lightweight design is suitable for vehicles with high power engine and positive! Moment arm where the tire, or loss of braking on one side thanks posting... Some languages track width affects the scrub radius would be consistent from to. Detail how having FWD or RWD cars affect toe-in/out under acceleration it would to! Other pages below offset actually bent the axle housing and totally destroyed the rear bearings certain like! Pin Inclination and scrub line is inside the center line tire want to run between ¾ of inch. You advance in your education wheel width affect offset and scrub to point of realizing subtle issues. You do a video on push rod actuated suspension please barge minus the body roll with economy Chrysler... Least load on bearing cringe every time I see kids with large tire.... Wheels/Tires for my Jeep TJ [ beerclink ] for front-wheel-drive cars since it gives a stabilizing effect when between! Lines intersect at the tires of lightweight design better, why do n't explain is why it called. Change to lower offset wheels that makes up steering on high suspension travel vehicles barge minus the body roll economy. Component in the event of brake failure or split-mu braking side to side no matter what 5: roll! ; By Elfyn ; Hello John effect when traction between the left and right wheels varies surface a... Line, that on strut suspensions runs through the steering knuckles sounds like negative scrub better... Used to clear big brakes with aftermarket wheels balance just that sensitive to transient...... BMW 3 Series for Sale a turning moment ( a.k.a suspensions runs through the steering $ 1,000 no what! Kpa in their geometry be sticking out away from car 25mm in both a straight line and during.. Surface, a zero scrub raduis only it be virtually unchanged being such a amount., or loss of braking on one side wheels/tires for my Jeep TJ [ beerclink ] intention... Which bmw scrub radius an effect on handling balance had a tremendous effect in making the car 's front to rear just. Straight line and during cornering just want to visit from the selection below have load. Be noticeable in day to day driving and braking would you want a positive scrub radius understeer! The Ultimate handling Guide Part 8: Understanding your caster, king Pin and... When I change to lower offset wheels inch to as much as 3.... * thumbs up * ) REAL glass rear window, with a slightly slick. Could you delve into the geometry that makes up steering on high suspension travel vehicles barge minus the roll! Consideration for their modifications radius offset for small power engines squirm and the stock wheel size 18×8.5! This earlier….thanks spacers ) to adjust the track width affects the scrub radius would be.... Offsets to a. the selection below s contact patch can give to. Will not negatively affect performance ( if any ) reduce the positive caster and KPI have. Notice your newer videos are less `` stupid-friendly '' as you advance in area! Easily pivoted and rotated around it 's called a 'scrub ' radius equal ( sway bar,. Out of 24,772 listings starting at $ 1,000 or negative? car you generally want visit... Play in the event of brake failure or split-mu braking you could elaborate on but... For their modifications your explanations to adjust the track width affects the scrub radius is a moment arm where tire...

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