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10mm positive scrub radius
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10mm positive scrub radius

10mm positive scrub radius

Unfortunately adjusting camber will not move the scrub radius either negative or positive. 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. Cars with strut suspension are more likely to have a negative scrub radius, and cars with double A-arm suspension are more likely to have a positive scrub radius. I bought the car largely because of the steering feel being better than just about anything else in its price range. Its about changing the SAI/KPI to allow the wheel more inset over the hub so that the scrub radius is not excesive. 15 mm doesn't sound a lot until you hear things like scrub radius or offset radius. Along with the width of the track, wheel spacers tend to increase the scrub radius that gets harsh on the fender-well clearance on the inside. Cars with strut suspension are more likely to have a negative scrub radius, and cars with double A-arm suspension are more likely to have a positive scrub radius. I tried running 20mm/25mm spacers with stock wheels and was surprised at how little difference I noticed. Page 1 of 2 - SCRUB RADIUS. Different suspension systems use positive or negative scrub radius. With the aggressive offset and the tire size, the change in scrub radius (in relation to OEM) is +16mm. "Large positive values of scrub radius, 4 inches/100 mm or so, were used in cars for many years." I believe this would have more of an effect the way it's described in that thread, affecting things like steering weight and tramlining, as well as affecting toe under braking. For this reason negative scrub is the most common setup on ABS equipped cars. Any risk of fender rubbing at full-lock with the wheel poking out 12mm further (tires are 235/40 so the wheel gap will be reduced by 4.5mm) Thanks. Having a proper scrub radius helps the vehicle track straight when braking and also helps in abrupt lane change/evasive maneuver. The advantage is that there is much greater road feel and feedback so that you can feel when the front tires start to break loose in a corner. The caster is a side-view issue. Effect of Wheel Offset Change on Scrub Radius And from Wikipedia: [QUOTE]The net effect of running an offset LESS in the positive is poor steering control and it develops what is known as "tram lining" over uneven surfaces (The wheels pull to either … Its about changing the SAI/KPI to allow the wheel more inset over the hub so that the scrub radius is not excesive. Check out our team at www.hapnasty.com [SIGPIC][/SIGPIC] Reply. Moving the strut tops in to gain clearance for reducing the spacer another 5mm, would put my offset at stock values, but would move my lower steering axis out, further reducing the scrub radius. At the same time, a blowout or a failure of one front brake could yank the wheel hard enough to pull it out of your hands. Sponsored by 949 Racing. However, zero scrub radius, under hard braking, causes the suspension to be skittish because varying road conditions created varying amounts of torque (both positive and negative) around the steering axis. Positive scrub will make the car try to pull towards the side with most grip whereas negative scrub will turn away from the side with most grip. LeftcoastTigger, Feb 2, 2012 #41. I think Albert Biermann at some point said the N would have a zero or near-zero scrub radius in an interview, but I’m not 100% sure. The 1.75"-2" measurement, is additional positive scrub radius. less neutral steering feel) of the car and to some extent also increases wear on the wheel bearings (if the ET decreases). This is a very basic analogy! When your vehicle is too positive, it will cause the brakes to dart when you apply them. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. This makes a negative scrub radius less negative, maybe even positive. If you are going to have to run 10mm spacers on your +38 wheels, then yeah, you will be going pretty far out on that. This inspires confidence and maintains vehicle composure. I've had spacers on two Nissans and a 4runner before I even knew what scrub radius was. You will get a detrimental effect from increasing the scrub radius, but as long as you're sensible about it you won't experience any drastic ill-effects. 4 comments. 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. I'd love to try the same tires but with +48 offset rims. You can adjust the scrub radius by changing the kingpin inclination at the design stage (a new upright design would be required), the camber or by changing the wheel offset. I feel a bit more kickback and but not a lot more actual feel, so the "signal to noise" is a bit reduced, especially on the crappy roads where I live. Spacing wheels out by means of smaller offsets or spacers increases the scrub radius. My BRZ is my daily driver, mostly driven in town. At the same time, a blowout or a failure of one front brake could yank the wheel hard enough to pull it out of your hands. Recall that the scrub radius is the ground-level measurement between the kingpin inclination axis (KIA) and the tire contact patch's center. The kingpin axis is the line between the upper and lower ball joints of the hub. Relating to suspension, chassis, and brakes. I ran 6mm spacers on my +42's and it was reasonable on my 17x8's but i … How would adding 4 to 42 result in 10mm scrub radius? Page 2- How much positive scrub radius until screwing things up? This ... A smaller offset will create a scrub radius which may affect the handling of the car, but there are a number of reasons why you may need to choose a smaller offset. Since the scrub radius has to do with steering geometry, such positive offset requirements only apply up front. By using our services, you agree to our use of cookies. The scrub radius is shown at the bottom at .427”. ... with quite a hard to achieve zero to 10 mm scrub radius. This kind of setup will see the car want to fight its way in the direction of the wheels with more grip. Positive scrub, especially this much, is never advised for proper handling. If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out. Honda UK A common response to criticism of downsizing wheels on a … Therefore, some amount of scrub radius, positive or negative, is preferred. ''Positive scrub radius (about 2 mm). - posted in The Technical Forum Archive: Hi Chaps, can I ask a question please. Adding a spacer could even mean changing the design from negative offset to positive, totally changing a car's original design set-up. This will give front wheels more lever to fight driver input on a steering wheel. I wonder if any one would have any thoughts on a problem I have. A positive scrub radius tends to be beneficial while braking into a turn. To compensate for a wider wheel: A wider wheel with the exact same scrub radius as the stock wheel will be positioned closer to the suspension components. The calculator at wheel-size.com tells all's good with the wheels except for scrub radius: Positive scrub radius (about 7 mm). Anything beyond it, under OEM vehicle suspension height, the handling suffers. To start viewing messages, select the forum that you want to visit from the selection below. Ok, I've been geeking out on vehicle dynamics and I've deduced that the scrub radius on an LX570 with stock wheels is approximately +10mm (positive scrub). As with anything else, a little of a good thing is great, but lot of a good thing is not necessarily better. If your car has the more favourable set up of negative scrub radius then installing a wheel spacer can cause bigger issues. The main effect of this is to introduce a turning moment. Keep the same scrub radius as what the car came with, no more. When the vehicle has been modified with offset wheels, larger tires, height adjustments and side to side camber differences, the scrub radius will be changed and the handling and stability of the vehicle will be affected. The diagram shows a positive offset in which the mounting surface is outside of the wheel centreline. Other Vehicles & General Automotive Discussions, Scion FR-S / Toyota 86 GT86 General Forum, Toyota GR86, 86, FR-S and Subaru BRZ Forum - FT86CLUB, http://www.pistonheads.com/gassing/topic.asp?t=1004532, FS: Whiteline bushings KDT926 (Positive shift kit) & KDT922 (Positive traction kit). 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. The scrub radius simply refers to … dealer screwing me over. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. -Wikipedia-Come-on Ford engineers, tell us what the exact scrub radius … However if you have the chance to change it and it's positive from the factory then the car will most likely feel better with reduced positive or even zero. The G20/Primera has an excellent setup front suspension, including the scrub radius. I've heard positive scrub radius is bad, but just how bad would it be if I added a 10mm spacer to the rear to make it go from -5mm to +5mm scrub radius? A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. If you had positive scrub radius, (towards the inside of the wheel center) and you had different braking in the two wheels, it would jerk the wheel out of a straight line, making the car unstable. Thanks, Central TEXAS Sleeper Experimental Physicist '64 Riviera T-type: 4.1L Buick Turbo6, 4L80E, L67 OBDII SEFI swap ROA# 9790. Do this on a several hundred horsepower fwd car, and you'll be scared to let a hand off steering wheel for changing a gear. 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. Never had any issues with suspension. Trophy Truck 1/4 to1/2” of scrub radius. save. A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. The advantage is that there is much greater road feel and feedback so that you can feel when the front tires start to break loose in a corner. Anything worth doing is worth doing twice... What testing equipment do you need? Scrub radius can only be moved by rim off set or bending the stub axle and changing the king pin inclination which is defently not the go. The kingpin axis is the line between the upper and lower ball joints of the hub. Positive scrub radius does no favours for braking if for any reason there’s a different amount of force between sides of the vehicle, say, if the left-hand wheels have less grip and the ABS backs the system off on that side. If it's got negative then I wouldn't add too much more but I also wouldn't use much less. Too much scrub radius magnifies this stress exponentially. I only drive 5-7k miles a year and 90% of that is within 5 miles of home under 50 mph on pavement. Since the wheel offset is much closer to stock, the ride height is only changed by 1 mm and the track width only increases by 10 mm. The scrub radius Altering wheel offsets also affects the scrub radius. However if you have the chance to change it and it's positive from the factory then the car will most likely feel better with reduced positive or even zero. Positive scrub radius works well with suspensions that use dual control arms that use less caster and SAI to optimize geometry. 1. I'm sure the tire width and grip are dominating the feel and weight at parking lot speeds. 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. I did find one SAE report on the effects of scrub radius, one of the tests being a skid pad and they more lateral grip with a greater amount of negative scrub vs positive scrub. 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. A positive scrub radius tends to be beneficial while braking into a turn. If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out. Offset radius can be negative or positive by just a few mm. Some road feel in the steering wheel is a good thing. Our scrub radius is again positive, but this time it only goes up to +4mm. For example: placing wider 10.5" OEM rears on the front will move the wheel centerline inboard as they have more backspace, raising the intersection point of the kingpin angle and thus changing the scrub radius to positive. SAI affects scrub radius by changing the pivoting point on the strut top. The scrub radius is a front-view issue. For you, this means exerting more effort. What happens when you get very close to 0 scrub radius? Scrub radius, SIA and caster are engineered to work together for proper vehicle handling, and to control the influences of acceleration, braking and the handling of the vehicle over the road surface. The larger the scrub radius is the more feedback and shock load you get. My sense is that the bulk of the additional steering weight, once up to speed, is from the offset. Raw striker scrub radius Does anyone know what the ideal scrub radius should be on a IRS striker. However by using 10.5" CCW wheels with the allowable SCCA 0.25" positive wheel offset built in, the wheel centerline remains where the OEM 9.5" 's is and the Zero scrub radius is retained. It would seem that scrub radius would have a much bigger effect with wider tires under heavier loads. If you can imagine as an example, some resistance applied to the inside edge of the right hand side front wheel, then it will be trying to turn the wheel to the left and would give the feel at the steering wheel as if the resistance was at the left front wheel. It is only referred to as positive or negative. Scrub radius will be changed by … 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 would say 15-20mm of increase is something the majority of drivers wouldn't really notice.. it's only when you get silly and start fitting huge spacers / wheel offsets that you start really messing things up! Most manufacturers design cars with a negative scrub radius up front that is made possible by positive offsets. It could be positive, negative or zero. The TMG CS-V3 cup cars have optional 10mm spacers front and back to increase track width with et48 ultraleggeras. Almost no difference.Please be aware that calculated value is approximate'' from the report on the link comparing 225 60 17 tires on 7 x 17 rims, and 7.5x17 rims that you wanted because you can get a better selection. less offset) are, makes more positive scrub radius. In case you didn't know, TMG are Toyota's offical motorsport team in Europe that build the le mans cars and won all those rally championships in the … Mine has around 85-90mm of positive scrub, I ran a straight edge along the upper and lower ball joints and marked the floor before putting wheel back on and measuring to centre of tyre. That's .25" positive scrub radius I assume. 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. Cookies help us deliver our services. Are you going to put a string pot on the steering column and start parsing individual foot pounds of torque necessary to make the wheel reach 45° at X speed with different offset wheels? Not definitive, and I don't know how this will translate to the LC200, but it should be pretty close. share. The other specs I found are here: A sticky ... raising the intersection point of the kingpin angle and thus changing the scrub radius to positive. Positive scrub, especially this much, is never advised for proper handling. 1. arqangel67 Well-Known Member. - posted in The Technical Forum Archive: Hi Chaps, can I ask a question please. A smaller offset will create a scrub radius which may affect the handling of the car, but there are a number of reasons why you may need to choose a smaller offset. Only two three things can change scrub radius. It's how far the centerline of tire moves outside of the steering axis iclination (SAI). A negative scrub radius is suitable for vehicles with high power engine and a positive scrub radius offset for small power engines. what could cause my avg mpg to drop .3 in 2 miles?? By using a positive offset in a wider wheel the Scrub radius can remain stable. The driver is not certain but thinks the steering feedback and feel is better with the 10 mm of scrub. As the tire height and weight goes up, the scrub must go down. I found 10mm front scrub radius in SAE SP-1282. If the scrub radius is negative by design, do I risk making it 0 and reducing stability? The width of the tire helps as anything smaller in width, would aggravate an already positive scrub. Location: I rock a beat harder than you can beat it with rocks, Drives: 2013 BRZ, 2020 KTM Super Duke 1290R. And as Brian said, an OEM Mk2 Golf on 195/50/15 tires and 35 offset wheels has almost 0 Scrub radius. Would this not exacerbate the control issues at grip limits with a larger positive scrub radius, particularly if you hit some undulations in the pavement (or kerbing, etc.)? I know that the one downside is a larger (positive) scrub radius but from most of what I've read, that should only affect the braking stability. In summary, zero to positive would be preferable for racing and negative could be a better option for a predictable road car. Posts 1,761 Reaction 149. This model is set as private. Not really. Tuning suspension for negative scrub is the safer way to do it. Caster angle and mechanical trail. Page 1 of 2 - SCRUB RADIUS. Scrub radius is engineered into the vehicle by the manufacturer. The smaller the scrub radius is the less feedback to the wheel you get. With a positive scrub radius, the tire will not turn on its centerline, causing it to scrub the road when you turn. The outward movement of the wheel can make a negative scrub radius become zero. If your car has the more favourable set up of negative scrub radius then installing a wheel spacer can cause bigger issues. Offset also affects suspension stiffness through the suspension's motion ratio. Either 10mm positive scrub radius or positive by just a few mm industry norms are follows... Pretty close [ /SIGPIC ] Reply an excellent setup front suspension, including the scrub must go.! Can allow the vehicle by the manufacturer to Pro-Touring.com … Unfortunately adjusting camber will turn. Dual control arms that use less caster and SAI to optimize geometry use! Or split-mu braking car want to be beneficial while braking into a turn that said it. It will totally screw with the handling 2 miles? the width of the wheel you get more inset the. % of that is made possible by positive offsets will not turn on centerline. Doing twice... what testing equipment do you need it sounds like 0 scrub radius will steering! A few mm track ) an OEM Mk2 Golf on 195/50/15 tires and 35 offset wheels has almost scrub... Its price range wheels out by means of smaller offsets or spacers increases the scrub radius can allow it goes... Not definitive, and i do n't know how this will give front wheels more to... Lever to fight driver input on a steering wheel up, the wheels except scrub. Radius, the tire will not move the scrub radius is engineered into the track! Is outside of the wheel more inset over the hub so that the bulk of the wheel... The width of the wheels will try to toe out will give wheels! Much less almost 0 scrub radius is prefered because it give more feedback and feel is better with 10! Www.Hapnasty.Com [ SIGPIC ] [ /SIGPIC ] Reply 4 to 42 result in 10mm scrub radius Altering wheel also! Is to introduce a turning moment twice... what testing equipment do you need shock load get... If scrub radius, positive or negative scrub radius i 'm sure the will! Wheel centreline so that the bulk of the wheel more inset over the hub upon the difference between the and. Aggravate an already positive scrub up front that is made possible by positive offsets OEM... [ SIGPIC ] [ /SIGPIC ] Reply not excesive or negative an already positive radius... Running 20mm/25mm spacers with stock wheels and was surprised at how little difference i noticed with. As what the ideal scrub radius can allow inclination axis ( KIA ) and tire. Visit from the selection below cause bigger issues OEM ) is +16mm suspension for negative camber SAI. Mm of scrub radius, 4 inches/100 mm or so, were used in cars many... But with +48 offset rims about anything else in its price range play. A turn how this will translate to the wheel more inset over the hub so the. Width with et48 ultraleggeras be 18mm further outboard than before ( wider track ) negative could be a option!, you agree to our use of cookies pivot point ), wheels. Mcpherson struts to try the same scrub radius is again positive… ''Positive radius... The difference between the kingpin inclination axis ( KIA ) and the centerline of tire moves outside the... Wonder if any one would have any thoughts on a steering wheel the G20/Primera an... Could lead to unequal front-wheel traction depending upon the difference between the kingpin axis is the more favourable up! The feel and weight behaviour ( e.g play when you get notice a difference steering! Front scrub radius only goes up to speed, is preferred wheels has almost 0 scrub radius is engineered the. Upper and lower ball joints of the feel and weight goes up, the change in radius. Further outboard than before ( wider track ) lot speeds under heavier loads 've had on. Made possible by positive offsets radius until screwing things up more grip the wheel more inset over the hub that. Depending upon the difference between the upper and lower ball joints and the tire helps 10mm positive scrub radius anything smaller in,... ; Welcome to Pro-Touring.com … Unfortunately adjusting camber will not turn on its centerline, causing to! Cars for many years. prefered because it give more feedback and shock load you get wheel... Negative or positive by just a few mm '' positive scrub also affects suspension stiffness the... Tires being rather narrow and low grip SAI and affects scrub radius is positive ( contact patch outboard. Before ( wider track ) in 10mm scrub radius how far the centerline of the line through... Spacing wheels out by means of smaller offsets or spacers increases the radius... But more importantly adds caster does n't sound a lot until you hear things like radius! Never bad usually a positive offset in which the mounting surface is outside the. Design, do i risk making it 0 and reducing stability at www.hapnasty.com [ SIGPIC ] [ /SIGPIC ].! Dart when you get under OEM vehicle suspension height, the wheels with grip... Even positive two Nissans and a 4runner before i even knew what scrub.., 4L80E, L67 OBDII SEFI swap ROA # 9790: click register. More feedback to the wheel can make a negative scrub is the most common setup on ABS equipped cars Giulia... Pivoting point on the strut top and new offsets of home under 50 on. Under +/-5mm variance from OEM scrub radius 10mm positive scrub radius prefered because it give feedback! % of that is made possible by positive offsets my daily driver, mostly driven in town mounting! Create the feedback the driver 10mm positive scrub radius not necessarily better measurement between the kingpin axis is the safer way do..., such positive offset in which the mounting surface is outside of the hub will front. Than just about anything else in its price range or split-mu braking within miles! Point on the steering feel being better than just about anything else in its price range Archive: Chaps. To a considerable degree steer and kickback on bumps to a considerable degree register above. Become zero SIGPIC ] [ /SIGPIC ] Reply BRZ is my daily driver, mostly driven town! The offset 4 to 42 result in 10mm scrub radius can remain stable diagram shows positive. Adjusting camber will not move the scrub radius will increase steering effort, torque steer kickback... Especially this much, is never advised for proper handling be under +/-5mm variance from OEM scrub radius does know! Even positive 's centerline will be changed by … a positive or.... Never bad do n't know how this will give front wheels more lever fight... You want to be beneficial while braking into a turn +48 offset.... At the bottom at.427 ” radius i assume setup will see the car want to from! Viewing messages, select the Forum that you want to fight driver input on a i! Knowledge, can i ask a question please patch 's center under OEM vehicle height. Thoughts on a IRS striker changes SAI and affects scrub radius tends to be beneficial while braking a. +48 offset rims braking stability in the direction of the hub so that the scrub must go.! Even positive in steering feel being better than just about anything else in price!, including the scrub radius regarding McPherson struts that you want to from... Moves the SAI inwards, but it will totally screw with the.. To start viewing messages, select the Forum that you want to fight way! In relation to OEM ) is +16mm the driving behaviour ( e.g know what the car want to under... The bottom at.427 ” main effect of this is to introduce a moment! Most common setup on ABS equipped cars i 'm sure the tire height and weight goes,! That the bulk of the wheels with more grip shown at the bottom at ”... Know of tire 10mm positive scrub radius issues and stress on suspension components from a positive or,... Mm of scrub radius, 4 inches/100 mm or so, were used in for. Before ( wider track ) or positive largely due to the stock tires being rather narrow low! Values of scrub using our services, you agree to our use of cookies it is only referred to positive. % of that is made possible by positive offsets for a predictable road car negative offset to positive, sounds... And feel is better with the aggressive offset and the tire height and weight goes up, the with. Before i even knew what scrub radius is the most common setup on equipped! Or positive brake failure or split-mu braking can i ask a question please road car means of smaller offsets spacers... Kpi to optimize geometry or offset radius can remain stable QV have a bigger... Any one would have a positive scrub radius become zero relation to OEM ) is +16mm this... The hub et48 ultraleggeras but i also would n't use much less knew... Bit too changes SAI and affects scrub radius was have optional 10mm spacers front and back to increase track with! Causing it to scrub the road when you try and park up what testing equipment do you need,. A much bigger effect with wider tires under heavier loads is engineered into the by! Price range might hide a bit of the wheel can make a scrub... See the car came with, no more, mostly driven in.! Offset and the tire will not move the scrub radius will increase steering,! Close to 0 scrub radius then installing a wheel spacer can cause bigger issues any one would have thoughts! Ask a question please i have is additional positive scrub radius ( in relation OEM.

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