[CapriRacer]

From Tire Business May 8, 2023

How does temperature affect rolling resistance?

By Erin Pustay Beaven

GREENVILLE, S.C.

Range can be a very tricky thing. Electric vehicle range is, simply, inconsistent.

It changes over time, across driving conditions and with temperature fluctuations. And while there are a number of factors contributing to the fluctuation in range, it’s understood tires play a role. Especially when it comes to colder temperatures.

And that leaves a lot of questions to be answered. Questions such as: Exactly how much of an EV’s drop in range can be attributed to the tires? And how does temperature fluctuation impact rolling resistance?

That’s exactly what Smithers is working to solve, according to Matt Kent, technical director of the Smithers Tire & Wheel Center in Ravenna, Ohio. Because answering those questions — among others — gives the industry the leverage it needs to design tires better targeted for new mobility.

“Electric vehicles show a significant decrease in range in cold temperatures,” Kent said during his presentation at the recent Clemson University Global Tire Industry Conference in Greenville. “But current test standards only evaluate rolling resistance at room temperature — it’s actually 24 degrees C. And understanding rolling resistance performance at cold temperatures could provide an opportunity for tire design improvements to support an increase in range.”

When it comes to testing and ultimately understanding the ways in which cold temperatures impact rolling resistance, Smithers is turning to its Suzhou, China, facility, which houses a cold chamber rolling resistance machine.

This machine, Kent said, is capable of testing tires at temperatures ranging from 40 degrees C to -40 degrees C.

“It has been really interesting seeing the data and seeing them bring this thing online,” Kent said.

Using a torque method for the study, Smithers tested four different tire brands, each of them at four temperatures—35, 25, -10 and -20 degrees C.

What the team found, Kent said, was “the trends were all the same. But the big difference was they all performed very differently down here at the lower temperature.”

Each of the tires showed significant increases in rolling resistance as the ambient temperatures dropped. With each drop in temperature, the rolling resistance increased.

Tire rolling resistance performance is strongly influenced by temperature,” Kent said. “RRC increased as temperature decreased and is more sensitive at low temperatures as opposed to high temperatures. So clearly, we have a lot of data at 24 degrees C, and around that range there’s some difference, but they are not hugely substantial.”

In the Smithers study, the best performing tire showed a 56% increase in rolling resistance between the highest and lowest temperatures, while the worst performing tire, Kent said, saw rolling resistance increase by 116% between the highest and lowest temperatures.

And this, of course, is just the start. Smithers plans to take its testing further and expects to have further data compiled by the summer of 2023. Additional tests, Kent said, include examination of EV-specific tires that are a mixture of original equipment and replacement tire fitments.