Top Reason Why Car Wheels Are Getting Flatter These Days

Car Wheels
Car Wheels

Years ago, cars came standard with tyres that had a deep dish design.   Deep dish wheels has become shallower over time as technology advanced, until they were basically flat on the outside around 20 years ago. What caused this to occur? In a nutshell, what happened was “steering.” The transition from deep dish to flat wheels can be attributed to advancements in the steering system, specifically the popularity and benefits of pinion and rack steering Tyres Peacehaven Car Wheels

Why Is It Necessary To Reduce The ‘scrub Radius’ In Rack And Pinion Steering? As Well As Why Flat Wheels Are Beneficial

A kingpin axis, also known as a steering axis, is found in all front suspensions. It is the axis around which your front wheels spin when you steer the car. It describes one of the suspension’s key characteristics: the caster angle, which we won’t go into here. For the time being, just know that the location of this line, which reflects your steering axis, comparative to the tyre contact area and the middle of the wheel is essential for comprehending why the appearance of wheels has changed so dramatically over the years wheel balancing Peacehaven.

We can measure the “scrub radius” by extending the kingpin axis with an imaginary line that follows it until it overlaps the ground. This is the distance between the point where the kingpin axis collides the ground and the middle of the tyre contact patch.

A large scrub radius transmits a significant amount of torque through the steering wheel. This is not acceptable Car Wheels.

When you press the brakes in a car, the reaction force, combined with the scrub radius, generates a force around the kingpin axis, attempting to steer the suspension. The steering system and the driver’s hands on the wheel are what prevent the suspension from steering.

We can calculate the distance between the kingpin axis and the middle of the wheel. This is known as the “kingpin offset.” When you drive over a bump or through a hole in the road, the force is acting on the suspension at the center of the wheel, and this force, combined with the kingpin offset, tries to guide the suspension.

Again, the only thing preventing the suspension from steering is the steering system and the driver’s hands on the wheel. The feeling is like that of  a kick-back to the driver and, if severe enough, can rip the steering wheel from your hands. A few of you may have had this experience before.

How Reduced Scrub Radius Causes Flat Tires

Now a suspension engineer cannot prevent individuals from traveling through potholes and over hiccups along the way, so the only thing the technician can do to minimize kick-back is to create the kingpin offset and scrub radius as tiny as possible in order to reduce overall force around the kingpin axis.

However, like almost everything else, other situations get in the way. The brakes, in particular, cause problems. The brakes must also fit within the wheel, limiting how much farther outboard we can place the lower ball joint.

 If we wanted to move the kingpin axis further outboard to get a relatively small scrub radius or kingpin offset, we’d have to move the lower ball joint outboard, which would also move the brake rotor outboard. But take a look at the caliper. It’s right behind the wheel’s spokes. Relocating the caliper outboard would imply pushing the wheel spokes outboard.

Why Old-School Steering Systems Desire ‘Scrub Radius.’ And How Deep-Dish Wheels Can Assist

Before rack and pinion steering became prevalent in Car Wheels, cars were using a steering system called ball/nut, also known as a steering box. This system used a worm gear to turn a sector shaft, which was linked to a pitman arm.

Sadly, while worm gears are very efficient at torque multiplication, they do not enjoy being back-driven, so turning a worm gear type steering box by attempting to push on the pitman arm is extremely difficult (the output shaft). This is due to the same concept that provides torque multiplication when having to turn the input shaft (this, along with large-radius steering wheels, is why older cars could do without power steering) also provides torque reduction when trying to push on the pitman arm. In other sentences, while turning the input shaft requires very little force to spin a worm gear, turning the output shaft necessitates an enormous amount of torque.

Cadillac introduced the recirculating ball in 1940, which was a key change of the worm gear steering system. The worm gear was replaced by a series of balls moving in a track that formed the teeth of the gears in this design.

Everyone was content with the worm gear type steering box for a while until someone made the decision to devise the rack and pinion steering gear. 

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