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. Handling EFFECT OF WHEEL GEOMETRY PARAMETERS ON VEHICLE … Too much scrub radius causes all of the problems I listed in the beginning. Rear wheel drive sports cars can come with positive scrub radius for razor sharp handling. Sep 8, 2012. Wheel Fitment - Scrub Radius The scrub radius can affect the way the steering responds in both a straight line and during cornering. Answer: It's the distance (Along the rotating axis) between the face at the centre of the wheel that bolts to the hub and the centre line of the tyre contact patch (the centre of the tread all around the tyre). 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. Thanks for all the help as I’m totally new to the car scene but learning a lot! When a vehicle has been changed into lower height tires and wheels with increased positive offset, it causes a big increase in scrub radius. An excessively negative scrub radius tends to increase steering effort, while excessive positive scrub radius (where the load of the tread is moved moves further outboard) can not only affect handling and ease of steering, but can overstress wheel bearings as well. 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. Should I be limiting myself to wheels with an offset within a few mm of the stock 48mm? Out, Effect on Handling/Steering Feel With a smooth surface or uniform left & right bumps, this is not noticed as the forces would cancel each other out. On a rear-wheel-drive vehicle with positive scrub radius, the vehicle’s forward motion and the friction between the tyre and the road causes a force which tends to move the front wheels back (toe-out), keeping the vehicle heading straight ahead. Anyone with practical experience with putting front spacers or decreased offset wheels and the qualitative, if any, effect on handling? Scrub radius is often forgotten but is no less important than any of the other aspects. Pros: The car feels much more stable at all speeds, but especially at high speed cornering. The distance between where the SLA and the centerline to the wheel intersect the ground is called the scrub radius. I have been unable to find the spec for scrub radius from the factory, so my plan is to take my Jeep into work an put it on the rack and measure it next week. Fig 5 - scrub radius . Recently I realized that changing the wheel offsets (or using spacers) to adjust the track width affects the scrub radius (a.k.a. References In all RWD situations it should be varying amounts of toe in to counteract the spreading effect of the forward thrust of the vehicle and the contact patch/scrub radius/caster/etc. Scrub radius will be changed by 13 mm, this may affect the car's handling. A negative scrub radius is suitable for vehicles with high power engine and a positive scrub radius offset for small power engines. 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). Squirm Squirm occurs when the scrub radius is at zero. Negative scrub also helps reduce torque steer in front wheel drive cars. My question is: How come so many people are running the 35mm offset when the positive scrub radius will cause more wear? The relation of toe to scrub radius. The link is setup with this in it. On most cars, changing offset by just 5 mm is enough to notice a change in the car’s handling because it changes scrub radius by the same amount, and that might already be only a few millimeters. On most OEM wheels, offset is positive (contact patch slightly inboard), and it can have a major effect on steering feel and stability during acceleration and braking. A positive scrub radius will increase steering effort, torque steer and kickback on bumps to a considerable degree. Vehicle designers take into account the suspension geometry, spindle height and wheel/tire width to come up with an appropriate value for the scrub radius to ensure the car handles well and drives properly (safely). Scrub radius is a function of SAI, or steering axis inclination. The improved handling that wheel spacers grant comes with a downside: increased steering effort. Because then the wheel spacer will cause it to increase. A front wheel drive vehicle usually has 0 to negative scrub radius and this calls for a toe-out setting. In the case of a negative scrub radius, problem becomes even more serious. Changing the scrub radius will change the driving behaviour (e.g. Some road feel in the steering wheel is a good thing. CRX2EVO. New Derry, PA Posts 1,265 There's a LOT to that simple question. When the Scrub Radius is towards the inside of the tyre tread then the vehicle has Positive Scrub Radius and vice versa. Many of us didn’t realise what had hit us when we scrambled to adjust to the sudden upheaval of the workplace, switching to remote work with little or no preparation, or deemed an essential worker and asked to continue business-as-usual in highly unusual … 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. The smaller the scrub radius the less feedback to the wheel you get. On most cars, changing offset by just 5 mm is enough to notice a change in the car’s handling because it changes scrub radius by the same amount, and that might already be only a few millimeters. The problem with the Turbo's is their positive srcrub-radius. The purpose of toe angle is to compensate for tolerances in steering linkage and the effect of positive/negative scrub radius when the vehicle travels down the road. The positive scrub radius has had some benefits and drawbacks to my driving experience. Ive been experimenting with wheel offsets to a.) 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