10mm positive scrub radius

By 18 enero, 2021 Sin categoría

Only two three things can change scrub radius. 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. Our scrub radius is again positive, but this time it only goes up to +4mm. This makes it heavy unless you move a bit too. 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 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. Wheel 5 or 6 times a year. Cookies help us deliver our services. I ran 6mm spacers on my +42's and it was reasonable on my 17x8's but i … 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. 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. 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. 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. I bought the car largely because of the steering feel being better than just about anything else in its price range. A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. 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. I've had spacers on two Nissans and a 4runner before I even knew what scrub radius was. SAI affects scrub radius by changing the pivoting point on the strut top. This could lead to unequal front-wheel traction depending upon the difference between the old and new offsets. This model is set as private. For you, this means exerting more effort. Back to top #27 adrianh08 adrianh08. Therefore, some amount of scrub radius, positive or negative, is preferred. By using our services, you agree to our use of cookies. 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. 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. Different suspension systems use positive or negative scrub radius. The diagram shows a positive offset in which the mounting surface is outside of the wheel centreline. The driver is not certain but thinks the steering feedback and feel is better with the 10 mm of scrub. 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. With some trepidation, I switched from the stock set up (+48 offset) to 225 MPSS on 17x8 +35, so a 13mm difference in offset/scrub along with more grip and more tread width, but not huge differences. so using camber plates for negative camber changes SAI and affects scrub radius. Since the scrub radius has to do with steering geometry, such positive offset requirements only apply up front. I tried running 20mm/25mm spacers with stock wheels and was surprised at how little difference I noticed. Caster is defined as the angle between the steering axis and the wheel centerline extending perpendicular from the contact patch, viewed perpendicular to the side view (vertical longitudinal plane). Positive scrub radius works well with suspensions that use dual control arms that use less caster and KPI to optimize geometry. All that said, it sounds like 0 scrub radius is never bad . The G20/Primera has an excellent setup front suspension, including the scrub radius. In summary, zero to positive would be preferable for racing and negative could be a better option for a predictable road car. If your car has the more favourable set up of negative scrub radius then installing a wheel spacer can cause bigger issues. 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. The greater the scrub radius (positive or negative), the greater the steering effort and the more road shock and pivot binding that takes place. 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. This kind of setup will see the car want to fight its way in the direction of the wheels with more grip. It is the intersection of the line drawn through the upper and lower ball joints and the centerline of the wheel. Tuning suspension for negative scrub is the safer way to do it. Industry norms are as follows: Sand cars 1/2 to 1” of 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. Page 1 of 2 - SCRUB RADIUS. Check out our team at www.hapnasty.com [SIGPIC][/SIGPIC] Reply. 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. This makes a negative scrub radius less negative, maybe even positive. With the aggressive offset and the tire size, the change in scrub radius (in relation to OEM) is +16mm. I found 10mm front scrub radius in SAE SP-1282. Positive scrub radius works well with suspensions that use dual control arms that use less caster and SAI to optimize geometry. The 1.75"-2" measurement, is additional positive scrub radius. Chassis engineers use scrub radius to create the feedback the driver feels through the steering wheel. 3. How would adding 4 to 42 result in 10mm scrub radius? dealer screwing me over. It could be positive, negative or zero. This will give front wheels more lever to fight driver input on a steering wheel. How would adding 4 to 42 result in 10mm scrub radius? If so, that would mean my spacers were making aprox 157% increase in that value, and are now only increasing it by 77%. 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. 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. 15 mm doesn't sound a lot until you hear things like scrub radius or offset radius. Honda UK A common response to criticism of downsizing wheels on a … Some extra info that i have gathered in the past through internet and vehicle dynamics books on scrub radius regarding McPherson struts. A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. 1994 Golf MkIII 4 stud 256mm 20mm 5.10mm 1986 Jetta MkII 4 stud 239mm 20mm 5.25mm All discs appear oe, the last dimension being the mounting face . Scrub radius is engineered into the vehicle by the manufacturer. Page 1 of 2 - SCRUB RADIUS. Offset also affects suspension stiffness through the suspension's motion ratio. 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. 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. Trophy Truck 1/4 to1/2” of scrub radius. 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. The kingpin axis is the line between the upper and lower ball joints of the hub. 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. 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. Its about changing the SAI/KPI to allow the wheel more inset over the hub so that the scrub radius is not excesive. The tire's centerline will be 18mm further outboard than before (wider track). Some road feel in the steering wheel is a good thing. I believe this is largely due to the stock tires being rather narrow and low grip. Effects of Positive Scrub Radius. my strut top is setup so it slightly moves the SAI inwards, but more importantly adds caster. - posted in The Technical Forum Archive: Hi Chaps, can I ask a question please. I wonder if any one would have any thoughts on a problem I have. It could be positive, negative or zero. The greater the scrub radius (positive or negative), the greater the steering effort and the more road shock and pivot binding that takes place. 4 comments. Our scrub radius is again positive… The TMG CS-V3 cup cars have optional 10mm spacers front and back to increase track width with et48 ultraleggeras. (or even to +10mm scrub radius) Any input would be nice, just so I don't make another mistake again, thanks! If your car has the more favourable set up of negative scrub radius then installing a wheel spacer can cause bigger issues. The scrub radius Altering wheel offsets also affects the scrub radius. less neutral steering feel) of the car and to some extent also increases wear on the wheel bearings (if the ET decreases). That's .25" positive scrub radius I assume. Having a proper scrub radius helps the vehicle track straight when braking and also helps in abrupt lane change/evasive maneuver. Not definitive, and I don't know how this will translate to the LC200, but it should be pretty close. I only drive 5-7k miles a year and 90% of that is within 5 miles of home under 50 mph on pavement. 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. To start viewing messages, select the forum that you want to visit from the selection below. Is it particularly noticeable? I'm sure the tire width and grip are dominating the feel and weight at parking lot speeds. As with anything else, a little of a good thing is great, but lot of a good thing is not necessarily better. 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! 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. I'd love to try the same tires but with +48 offset rims. Spacing wheels out by means of smaller offsets or spacers increases the scrub radius. 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. What happens when you get very close to 0 scrub radius? The caster is a side-view issue. In short; Yes, installing wheels which centerline is more outward than oem wheels (i.e. If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out. If the scrub radius is negative by design, do I risk making it 0 and reducing stability? Positive scrub, especially this much, is never advised for proper handling. 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? If scrub radius is positive (contact patch arc outboard of the pivot point), the wheels will try to toe out. Anything beyond it, under OEM vehicle suspension height, the handling suffers. Thanks, Central TEXAS Sleeper Experimental Physicist '64 Riviera T-type: 4.1L Buick Turbo6, 4L80E, L67 OBDII SEFI swap ROA# 9790. The kingpin axis is the line between the upper and lower ball joints of the hub. 3. Anything worth doing is worth doing twice... What testing equipment do you need? 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. 1. 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. Pressing the. 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. 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. ''Positive scrub radius (about 2 mm). The larger the scrub radius is the more feedback and shock load you get. 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. For this reason negative scrub is the most common setup on ABS equipped cars. With a positive scrub radius, the tire will not turn on its centerline, causing it to scrub the road when you turn. My BRZ is my daily driver, mostly driven in town. Class 1 off road, 1/2 to 3/4” of scrub radius. 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? 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. Forum Member. less offset) are, makes more positive scrub radius. 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. LeftcoastTigger, Feb 2, 2012 #41. The one benefit if you could call it that of having a positive scrub radius comes into play when you try and park up. 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. Does the Giulia QV have a positive or negative scrub radius? Power steering might hide a bit of the feel but it will totally screw with the handling. My sense is that the bulk of the additional steering weight, once up to speed, is from the offset. 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. As the tire height and weight goes up, the scrub must go down. You may have to register before you can post: click the register link above to proceed. Sponsored by 949 Racing. Scrub radius will be changed by … The outward movement of the wheel can make a negative scrub radius become zero. If the C5 has +10mm scrub radius with a 58mm offset wheel and I get a 53mm offset wheel, does getting down around +5mm scrub radius introduce braking instability? (Three point turns are a workout!) A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. This inspires confidence and maintains vehicle composure. splitbolt , Mar 22, 2018 I really do notice a difference in steering feel and weight. 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. 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. Relating to suspension, chassis, and brakes. 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. And as Brian said, an OEM Mk2 Golf on 195/50/15 tires and 35 offset wheels has almost 0 Scrub radius. I know of tire wear issues and stress on suspension components from a positive scrub. It is only referred to as positive or negative. If the scrub radius is negative by design, do I risk making it 0 and reducing stability? A positive scrub radius tends to be beneficial while braking into a turn. It's how far the centerline of tire moves outside of the steering axis iclination (SAI). Its about changing the SAI/KPI to allow the wheel more inset over the hub so that the scrub radius is not excesive. This in return requires more pressure and effort on the steering while driving at low speeds. A negative scrub radius is suitable for vehicles with high power engine and a positive scrub radius offset for small power engines. 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). Scrub radius, to my knowledge, cannot be calculated to an exact number. Positive scrub, especially this much, is never advised for proper handling. Never had any issues with suspension. A negative scrub radius tends to better for braking stability in the event of brake failure or split-mu braking. save. It generates a slight toe-in force that reduces any tendency to change direction in the way that positive scrub radius can allow. 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. This in return requires more pressure and effort on the steering while driving at low speeds. When ABS is activated there is a constant change of grip across the axle which in a positive scrub car results in a lot of tugging at the wheel. 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) Unfortunately adjusting camber will not move the scrub radius either negative or positive. 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. Contact Us; Welcome to Pro-Touring.com … 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. 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. share. "Large positive values of scrub radius, 4 inches/100 mm or so, were used in cars for many years." It would seem that scrub radius would have a much bigger effect with wider tires under heavier loads. Typically you want to be under +/-5mm variance from OEM scrub radius. That's .25" positive scrub radius I assume. what could cause my avg mpg to drop .3 in 2 miles?? Not really. A positive scrub radius tends to be beneficial while braking into a turn. Caster angle and mechanical trail. If it's got negative then I wouldn't add too much more but I also wouldn't use much less. 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.)? The scrub radius is shown at the bottom at .427”. -Wikipedia-Come-on Ford engineers, tell us what the exact 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 … 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. Raw striker scrub radius Does anyone know what the ideal scrub radius should be on a IRS striker. The dynamic scrub radius is displayed below the camber read out. 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. 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. Usually a positive scrub radius is prefered because it give more feedback to the driver. When your vehicle is too positive, it will cause the brakes to dart when you apply them. Recall that the scrub radius is the ground-level measurement between the kingpin inclination axis (KIA) and the tire contact patch's center. 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. arqangel67 Well-Known Member. Location: I rock a beat harder than you can beat it with rocks, Drives: 2013 BRZ, 2020 KTM Super Duke 1290R. By using a positive offset in a wider wheel the Scrub radius can remain stable. Changing the scrub radius will change the driving behaviour (e.g. 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. The calculator at wheel-size.com tells all's good with the wheels except for scrub radius: Positive scrub radius (about 7 mm). Most manufacturers design cars with a negative scrub radius up front that is made possible by positive offsets. 1. The main effect of this is to introduce a turning moment. 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. 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 …

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