Relaxation length: What is it & what affects It?

As you continue to learn more about tires, there are certain tire dynamics or physical forces that you may find hard to understand. These dynamics explain why your tires behave the way they do while you drive.

SimpleTire.com can help you easily understand these aspects of tire dynamics and physical science.

Beyond giving you a better understanding of tires and how they play into the grand scheme of a vehicle's design, knowing these dynamics can make you a safer driver. Relaxation length is one of the easier tire dynamics to understand.

What Is Relaxation Length?

Relaxation length is directly related to the other tire dynamics that occur when you turn your vehicle. Relaxation length is the distance a tire travels after you turn your steering wheel but before the tire is actually able to grip the road and turn the vehicle.

The relaxation length is calculated once the tire's force builds up to 63% of what's needed to turn the vehicle. It is an important factor in responsive handling. Relaxation length varies from tire to tire and is affected by a number of issues.

If you drive a sports car, you may be concerned with the relaxation length's effect on wheel wobble. Also called speed wobble, this is the shimmy effect that tires and wheels can experience during maneuvering or at higher speeds.

What Affects Relaxation Length?

The shorter the relaxation length, the better handling the tire will offer. That sounds simple enough. However, a tire's relaxation length is not always the same. Relaxation length depends on the force a tire creates. The tire's force changes with how fast it's traveling, how much weight it's loaded with, and what kind of road it's on.

Tire and vehicle engineers measure relaxation length with different variables along these lines. If you drive on a tire within the limits that vehicle manufacturers set for it, you should get good results.

However, tires are often put through a different set of tests by vehicle owners.

Speed

Driving in excess of the speed limit is one variable that greatly affects the measure of relaxation length. Your tires will not hold up to cornering maneuvers if you drive above the speed they're rated for. If you drive too fast, your tires may fail you when you attempt to corner.

Load

Putting more weight on your vehicle than is deemed appropriate by the tire and vehicle's manufacturers may cause additional deformation and result in an increased relaxation length. Due to the relation of relaxation length to speed wobble, driving vehicles that are loaded too heavily can be particularly dangerous, especially when traveling at highway speeds. In short, you may lose control of your vehicle while turning if you weigh it down too much.

Weather

Wet road surfaces also create variances in relaxation length. Cornering force relies on friction in order for the tire to keep its traction around a turn. On slippery road surfaces created by rain, ice, or snow, tires may struggle to grip the road during a turn.

Most often, this under-steering phenomenon is referred to as drifting. Oversteer will result in a vehicle spinning completely around. While controlled drifts are one aspect of a racing driver's repertoire, it's not something you want to experience while you drive down the road each day.