High-Speed Uniformity Testing
Our tire testing experts can provide state-of-the-art high-speed uniformity and cleat testing to measure and evaluate your tire performance as it relates to noise, vibration, and harshness (NVH).
The Effects of Flat Spotting on Tire Technology Performance - with Cliff Hodges
As vehicle and tire technologies continue to evolve, Smithers is keen to investigate how flat spotting may influence the entire industry. We spoke to Cliff Hodges, Technical Director of the Smithers Tire & Wheel Test Laboratory to gain more insight on this issue. In our discussion, we explored the implications of flat spotting on future tire development and performance standards.
Let’s start with the basics on what flat spotting is and common causes for this occurrence in tires?
Flat spotting occurs when a load is placed on a stationary tire for an extended period, resulting in a temporary deformation of the tire tread. This deformation creates "flat spots," which can lead to noticeable variations in ride comfort once the vehicle resumes driving. Rubber compounds are the most dominant factor in creating flat spotting. All tires are going to deform, it’s a matter of how fast the rubber will return to its designed state. Vehicle placard pressure may serve as a contributing factor. If a vehicle has a lower pressure than others, it can increase the tire footprint, and the flat spot is created. This should also be considered by OEMs.Can you explain the specific challenges that flat spotting presents in high-speed applications?
Typically, the high-speed ride and comfort are most affected by flat spotting. What’s more - significant deformation can lead to long-term damage to suspension components, especially if the variation becomes permanent.How does high-speed uniformity testing assess the occurrence of flat spotting in tires? What measures are taken during this process?
Each OEM has their own specification and protocol, but each begins with a pre-flat spotting test. These uniformity measurements are typically run at one speed, load, and pressure combination for a period – each specification varies. After completion, flat spotting is applied using a rig designed to replicate the load or displacement conditions observed during the uniformity test. After the flat-spotting term, the tire is reinstalled on the high-speed uniformity (HSU) rig to repeat the pre-test protocol. The HSU rig can measure a significant number of harmonics and is sensitive enough to pick up slight differences in variation. To vehicle OEMs, the most important measurement is the 1st or 2nd radial harmonic, since these harmonics match the frequency of tire rotation and are the most dominant in ride comfort. The variation deltas between the pre- and post-test measurements are used to identify the decay curve over a period of kilometers, which signifies how long it will take for the deformation to return to a more normal state.Given this, what corrective actions can be implemented once flat spotting issues are identified during high-speed uniformity evaluations?
There is typically a control tire used with each flat spot evaluation, where the control is a proven OE tire from another vehicle platform or the same but previous year. Metrics of the target tire are compared to the control and understanding of the control tire components can aid in highlighting areas to improve the target tire. This could involve reevaluating compounds or reinforcement materials or structure. It just depends on each individual scenario.How important is it to incorporate flat spotting considerations during the tire development process, especially for new EVs entering the market?
It is all about trade-offs. Looking at a performance spider graph, when one area of performance is improved, another may worsen. Certain vehicle programs may value tire wear over handling performance – or the handling may only go down a minimal percentage and could be acceptable in either case.Tire and vehicle manufacturers frequently collaborate on submissions. Normal development cycles go through a variety of different design departments, such as ride and handling, NVH, tread design, construction design, etc. This collaboration would involve several departments working together.
Given the increase in EV sales, what future trends or technology are tire companies and vehicle OEMs utilizing in relation to flat spotting?
This is a function of the vehicle weight and distribution. Inherently, tires are going to experience more static load than current ICE vehicles of the same model. As a result, some companies have created structure components to counteract the deformation of the rubber. Others have reduced the amount of rubber on the tread carcass, which can reduce the rubber’s displacement under load. Some have created gel-like inserts in the tire meant to support the tire and reduce the amount of time needed for a tire to re-conform.Tire manufacturers have combatted vehicle weight by reinforcing the construction, but rubber compounds must be considered in light of these new vehicles. However as battery technology improves, vehicles become lighter. When vehicles become lighter, other factors like range and tire tread wear will improve. But an improvement made now will only help in those situations.
To learn more about flat spotting or to discuss a testing project, contact Cliff Hodges, Technical Director, Tire and Wheel Testing at chodges@smithers.com.