cot δ o = (t/2 + e) / y. and cot θ = (t/2 - e) / y . Braking in turn Steering effort : Scrub radius . From experience, unless you are going ridiculous offsets (ie "deep dish" wheels), effect on scrub radius doesn't change enough to affect handling, etc. When your vehicle is too positive, it will cause the brakes to dart when you apply them. However, according to the tire sizing calculator at https://www.wheel-size.com this setup will increase the scrub radius by 1 7/32" and "may affect your the car's handling." Howdy, Since I have the pleasure of redesigning my front suspension on my '64 Riviera, I can design for whatever offset wheel I want. Effects of Positive Scrub Radius A positive scrub radius tends to be beneficial while braking into a turn. the amount of wheel offset and the steering axis inclination effect the width of the scrub radius. I'm basing most of the design off of the C5/6 Corvette and using the same upright. Both can create dramatically different handling characteristics at the limit, and for the street especially, all of those are highly undesirable. Also with caster, if the angle is neg the weight of the car is before the steering so you get a car that is easier to steer. Positive or negative scrub radius is relative to this point. I Know that it has to do with the relation between the pivot point of the steering tire and the centerline of the contact patch, but I do now know how it is affected by changing the offset with wider aftermarket tires. The thing is, I know this will alter the scrub radius (beside other things like bearing load, etc) and after reading something about this I didn't came to a certain conclusion regarding how this will affect the handling of a clio (182 cup suspension with 16" ET 37 … A positive scrub radius tends to be beneficial while braking into a turn. As the tire height and weight goes up, the scrub must go down. When the engineers are designing a suspension system for a vehicle they need to take into consideration how the suspension impacts the handling characteristics of the vehicle not only when the vehicle is traveling down the road, but when braking, torque steer, and when a tire becomes flat. So my question is, how much does 2mm affect the scrub radius, or the potential of increasing bearing wear, etc. Drop a wheel off and the vehicle takes off into the ditch. 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. Does anyone here have an idea of how to explain scrub radius? Disclaimer: I know that the base Civic wheels are something like 17 or 16x7 w/ 45mm offset. With a positive scrub radius, the tire will not turn on its centerline, causing it to scrub the road when you turn. If so, what is the affect either way? The more I read, the more variables there are and the more they affect each other. Positive Scrub Radius. Only two three things can change scrub radius. Industry norms are as follows: Sand cars 1/2 to 1” of scrub radius. then cot δ o - cot θ = 2 e / y. since triangle D MAQ is similar to triangle D MCF e / y = (t / 2) / b. then . Positive Scrub Radius. A negative scrub radius gives a harder feel to the steering wheel as it requires more input to turn. The balance between positive caster, KPI and scrub radius is particularly critical in high powered FWD and AWD cars as all of these factors can really affect torque steer. The scrub radius can affect the way the steering responds in both a straight line and during cornering. If the two lines cross exactly at the tyre’s contact patch with the road, there’s no scrub radius, which I think is what TLC were singing about in their 1999 hit single No Scrubs. Does it matter if your scrub radius is positive or negative? _____ 1994 LSi, Laguna Blue SVX Appeal 1992 LS-L, Ebony Pearl SVX -Rated ... Also, the wider your wheels and tires are, the more your scrub offset will affect the vehicle's handling. It is positive when the angle is inclined inward toward the center of the vehicle and negative when the angle is inclined outward. if a car has no scrub radius the car will act darty and will react too quickly to change. cot δ o - cot θ = 2 e / y. cot δ o - cot θ = t / b. then form equation (*) and the above equation we can conclude (θ = δ i). Positive scrub radius works well with suspensions that use dual control arms that use less caster and SAI to optimize geometry. Different wheels or tires from side to side will cause differences in scrub radius as well as a tire that is low on air. Hi, i had stock 205/65r16 with 6jj 50offset alloys & tires, Now i have uograded to 215/65r16 with 6.5j 40offset alloy & tyres, the scrub radius of positive 8mm has increased, its a rear wheel driven toyota body on frame MUV will it affect the handling & what about suspension life, is it going to take a toil. A lot of people that choose a much lower offset end up modifying other components on their cars to compensate for fitment (i.e., rolling fenders, adjusting camber). However since I do want to make an effort to maximize the handling and comfort of the suspension, how important is scrub radius? Scrub radius : 2% . 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. 3,539 posts. wish I knew how to extrapolate data and compare the scrub radius of a wider wheel with a higher offset vs thinner wheels with smaller offset.Would the scrub radius between those actually be the same? Modern ABS-equipped cars have much smaller scrub radius, actually. Having a small scrub radius is beneficial as it allows the wheel to react less to braking inputs due to the smaller moment arm and increases steering stability under braking conditions. The distance between where the SLA and the centerline to the wheel intersect the ground is called the scrub radius. While included angle problems will affect the scrub radius, it is not the only thing that will affect it. Scrub Radius- this is the tires turning radius about the steering axis. That said, you're never going to feel it on the street and would probably have a hard time feeling on the track. If you increase width by 25mm, then your offset will need to change by 12.5mm to keep the same theoretical scrub radius - but changing caster and camber will also affect the steering weight too. Automotive Videos. Scrub radius can be changed accidentally a number of ways. An excessively negative scrub radius will require greater steering effort, while excessive positive scrub radius (where the tread center essentially moves further outboard) can not only affect handling and ease of steering, but also over-stress wheel bearings. If the lines cross below the contact patch, theoretically underground, then it’s positive scrub radius. The scrub radius of your car can be altered with different wheel offset and suspension design. The Ultimate Handling Guide Part VIII: Understanding Your Caster, King Pin Inclination and Scrub By Mike Kojima Understanding what caster does and how to use it is a powerful tool in the box of a suspension tuner. As with anything else, a little of a good thing is great, but lot of a good thing is not necessarily better. RichardD. I've never understood why it took until the 1970s to figure this out and I still don't understand why vehicles are built with a significant positive scrub radius today. 206 months Negative scrub also helps reduce torque steer in front wheel drive cars. Class 1 off road, 1/2 to 3/4” of scrub radius. Trophy Truck 1/4 to1/2” of scrub radius. 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. A lower positive wheel offset will typically result in the wheels being more flush to the fender, giving the vehicle a more aggressive look. Too much scrub radius magnifies this stress exponentially. If some of this is good, more positive caster and KPA are not necessarily better. 4% : Implementation of all the corrective actions, not only improved steering returnability by 40% but also helped in reducing the cycle time in design and validation by 80%. For you, this means exerting more effort. All of the various rubber bushings and stock performance parts, designed with comfort for the typical driver in mind, are going to be the limiting factors that impact handling way before offset does. C5, for example, has +0.275" up front. Changing the diameter of wheels and tires affects scrub radius, as does the distance that the center of the wheel and tire sits relative to the vehicle body, which is called wheel offset. Symptoms of modified scrub radius include the tendency for the steering wheel to 'rip' out of the … It would have been nice to include those info, but I guess that would be somewhat beyond the scope of the article. My guess, the RS is slightly positive since it's more of a performance car. Tramlining is very different to handling 'on rails'. It either becomes smaller or larger. 1) It increases the front scrub radius, which can increase the steering effort and affect the feel and kickback. The best you can do is measure it yourself to see how changing wheel offsets will affect it. 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. Positive Scrub Radius Lines Meet Below Road Surface [/B] Having ventured into the 2.5-2.75 positive scrub radius … Offset does affect handling. What if you had a vertical line as caster like a forklift does, how do you think the handling … A positive radius allows the wheel to roll over on lock making parking situations easier. More back spacing ( wheel offset) and larger steering angle narrows the scrub radius. FWD and AWD cars, as well as IRS-equipped RWD cars, have small amount negative scrub radius for similar but different reasons. Scrub radius is one of those angles that are built into the vehicle and is non-adjustable. SAI and camber also affect scrub radius since we are changing the angles that determine scrub radius. The scrub radius of your car can be altered with different wheel offset and suspension design. For those who are into this sort of thing, I found a helpful explanation of how changes in scrub radius impact handling posted by someone going by the username "goldstar" on what appears to be a Mazda Protege forum. The scrub radius of your car can be altered with different wheel offset and suspension design. The effect on handling would be what ? 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. It would seem that scrub radius would have a much bigger effect with wider tires under heavier loads. Does anyone know what the factory scrub radius is on the SVX ... fender flexing needs to be done to get into positive scrub territory.

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