If the line touches the road outboard of the contact patch, scrub radius is negative (see Figure 2). If the line touches the road inboard of the contact patch, scrub radius is positive.
#BEST OFFSET DRIVER 2019 PATCH#
The distance between the center of the tire’s contact patch and the point where that line touches the road is the scrub radius. Looking at the car head-on, imagine a line drawn from the upper strut mount or upper ball joint and down through the lower ball joint, and then on down to the road. The radius of that arc is the distance between the pivot point that you are holding and the tip that moves through the arc.Now make another drawing to put that arc on the car. As you swing the other end left and right, the tip doesn’t move in a straight line, it moves through an arc. To visualize this, lay a pen on the table and hold the top end still. When the front wheels are steered left or right, the center of the contact patch doesn’t just pivot around a single point it swings through a slight arc. That’s because on the front suspension, wheel offset determines “scrub radius.” We can describe that by looking at how the contact patch moves in a turn.
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. If the flange is outside the center of the contact patch (closer to the curb), offset is positive (see Figure 1). If the flange is inside the center of the contact patch (closer to the center of the car), offset is negative. However, offset might be easier to visualize with a few simple drawings that focus on the tire contact patch.When the surface of the mounting flange is exactly aligned with the center of the tire contact patch, offset is zero.
You’ve probably read about “wheel offset,” typically described as the distance between the centerline of the wheel and the face of the wheel’s mounting flange where it touches the hub. Offset, scrub radius and contact patch are the only three technical terms we need to understand. This article is about the basics of understanding and measuring wheel offset. However, it is important to get it right, because getting the offset wrong risks badly damaging the replacement wheels and tires as well as suspension components, and can put the driver at serious risk of a blowout. It’s a concept that is often very difficult for customers to understand, and can be an enormously difficult concept for service professionals to explain. Offset also can be one of the most difficult factors to get right when replacing wheels. Perhaps the most important factor in choosing and installing new wheels is the proper handling of wheel offset.
#BEST OFFSET DRIVER 2019 PLUS#
A chart of approved wheel widths for tire sizes is available in the Ultimate Wheel & Tire Plus Sizing Guide (and the Tire Guide ().ģ. The wheel must be the correct and approved width for the size of tire that it will carry. The same theory applies to mounting wheels one-inch less than the originals in that case, the process would be called Minus-One sizing.Ģ. In this example, the process is called Plus-One sizing. For example, when you mount and balance wheels that are an inch larger than the originals, the profile of the new tires must be an inch smaller in order to keep the same overall tire/wheel diameter. When you are changing the size of the wheels, the overall diameter of the tire and wheel assembly must remain the same to keep the proper speedometer and odometer settings. With this in mind, there are three factors that consumers and service professionals must take into account when choosing and installing a different size of wheel.ġ. Everything from the shock absorber’s top bushing right down to the tire contact patch is designed to work together as one complete system.Ĭhanging the design or material or just the adjustment of any one part can have an impact on the car’s handling and braking, not to mention the way the car feels as it rolls down the road. Bob UlrichĪ car’s chassis is more than the sum of its parts. It never hurts to be more informed about a topic so important to the handling and safety of a vehicle.
#BEST OFFSET DRIVER 2019 DOWNLOAD#
Just follow these three simple steps: 1) Go to 2) Click on our White Paper channel and 3) download “ Helping your customer understand why wheel offset matters” by Jacques Gordon. If it leaves you wanting more, we can accommodate you. So as part of the 100th anniversary of Modern Tire Dealer, we collected our wheel offset stories from 2013-2017 and combined them into a shortened primer for measuring wheel offset. Surprisingly it isn’t.īased on our feedback, when we write about wheel offset, it is a social media sensation for us! And despite the exclamation point, that statement is not hyperbole. After so many years of publishing our Performance Handbook - 26 years and counting! - you might think it would be hard to pick our most popular stories.
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