A car’s suspension geometry plays one of the most significant roles in how the car handles and how comfortable it is. Among the things included in suspension geometry is the caster angle. When looking at your car from the side, the caster angle is the slope created by an imaginary line going from the upper to the lower ball joint.
The caster angle is expressed in degrees, and it can be either positive or negative. A positive caster angle occurs when the upper pivot point is tucked further toward the driver, while a negative caster angle occurs when the lower pivot point is closer to the driver. Both positive and negative caster angles have an effect on handling, each in its own way.
In this article, we’ll cover important aspects of caster angle, what are its effects, and types, and why it’s important for performance and racing cars.
Camber and Caster Angle Are Not The Same
If you want to know your car’s suspension geometry, you should know that camber and caster angles are not the same thing. We’ve already covered what caster angle is, and even though they have similar names, they’re completely different angles that don’t have anything to do with one another.
A camber angle measures how tilted the wheels are when you’re looking at the car from the front or back. Increasing the camber angle is a popular modification because it provides an aggressive stance, and it also increases the car’s handling capabilities.
How Is Caster Angle Adjusted?
When it comes to caster angle, most people will say that adjusting is impossible. In cases where the suspension components are stock, this statement is true unless you have special caster alignment tools, which is highly unlikely. This is why the only way to adjust the caster angle is to take your car to a professional suspension alignment shop.
To be able to adjust the caster angle on your car by yourself, you’ll need a number of aftermarket suspension parts specifically made so caster angle adjustment would be possible. The options include adjustable arms, offset bushes, offset top mounts, and adjustable hubs.
The most common way of adjusting the caster angle includes using offset caster bushes. These bushes are installed to the lower wishbone, and once installed, they can’t be adjusted anymore. Replacing your stock bushes with offset caster bushes requires precision, so if you’re not experienced in this type of work, it’s better to leave it to a professional.
Adjustable arms are aftermarket components that are the simplest to adjust. Unlike factory arms, adjustable arms have an adjustable tension rod that allows simple caster adjustment. The great thing about these aftermarket arms is that you can adjust them repeatedly until you find the right caster adjustment that works best for you. It will take some time, but given that other adjustable components are either more complicated or unadjustable after installation, it’s no wonder why adjustable arms are amongst the most popular modifications.
Lastly, the offset top mounts are a great addition to any car that requires both caster and camber adjustment frequently. They’re mounted on top of coilovers, but make sure to get a pair that allows caster adjustment, because not all models offer this feature.
Types of Caster Angle
There are three types of caster angles. Positive, neutral, and negative. Each has its advantages and disadvantages.
We’ve already explained what each type of caster angle looks like from a technical side. If you imagine a chopper, this is what a positive caster looks like. Negative, on the other hand, looks like a wheel on a trolley. Just imagining this tells you a lot about the stability each option offers. Positive caster is found in the vast majority of cars today because it offers high-speed stability and it has a self-aligning torque that allows a smoother corner exit. This is important for both driving in a straight line, but also in cornering.
Although it doesn’t seem like a positive caster angle has any shortcomings, it does require additional steering effort. In modern cars, this isn’t such an issue given the fact that power steering is featured by default in most cars. It does matter in older cars without power steering, and in racing vehicles where the power steering is removed for weight-saving purposes.
A negative caster angle has only one notable benefit which is extremely easy steering with or without power steering. Disadvantages, however, make this option a very unpopular one. The disadvantages include little to no feedback on the wheel position, unstable steering, and unpredictable handling.
What Does Caster Angle Affect?
Out of all the suspension geometry adjustment options, the caster angle is the least known, but it’s as important as any other adjustment. The caster angle affects the car’s high-speed stability, front-end cornering effectiveness, and steering effort.
In the previous section, we’ve covered how each type of caster angle affects each of these features. The reason why the vast majority of cars have a positive caster angle is that it’s the only one that offers safe driving characteristics.
Why is Caster Angle Important For Performance Cars?
The caster angle is just one of many adjustments that improve the car’s handling. Thinking it can make a big difference alone is a common misconception, but in combination with aftermarket parts and specific adjustments, it’s something no serious driver should ignore.
When it comes to racing cars, every improvement helps, no matter how big or small. The caster angle, combined with other suspension geometry adjustments, improves overall handling, and exit speeds after turns. This alone can reduce lap times significantly, regardless of the fact that the driver will experience increased steering effort. An increased caster angle also increases the car’s stability in high-speed straights, which is essentially everything you need to go through the track as fast as possible.
The effect of adjusted caster angle isn’t felt as much on regular daily driven cars, but when you start modifying your car and altering the suspension geometry and power, the caster angle will become more important.