High-Speed Rolling Resistance Above Standard SAE Speeds

Every tire loses energy as it rolls. That's rolling resistance (RR): a small amount of drag created as the tire flexes and recovers with each rotation – also known as hysteretic response. Much like highway driven vehicles, whether ICE or electric, rolling resistance plays a critical role in fuel efficiency and battery range. Current RR standards deal primarily with highway/city speeds, while neglecting high speed conditions in data regression. Now that motorsports have integrated hybrid and full electric power units, those highways RR standards provide little to no suitable conditions for prediction range. It is becoming increasingly more important for motorsports engineers to predict range throughout the race.

Smithers Tire and Wheel Test Lab recently completed rolling resistance testing up to 190 mph, the first time this type of test has been run at that speed for this application. Smithers Technical Director Cliff Hodges explains why standard test methods fall short of typical race speeds, what it took to extend testing that far, and why the results matter for racing teams and tire manufacturers moving to hybrid and electric power units.

How is rolling resistance typically measured?

The most common way to measure rolling resistance is the coast-down method, defined in SAE J2452. The tire is spun up to speed, then allowed to coast down while sensors measure how much force it takes to slow it. Running this at a few different speeds, loads, and tire pressures produces a formula that predicts rolling resistance across a range of conditions.

As written, SAE J2452 covers speeds between about 9 and 71 mph. That's the range most passenger and light truck tires operate in, so it's a reasonable window for everyday vehicle development. However, it's nowhere near a racing tire's operating range.

Why doesn't the standard test cover higher speeds?

Because it was never built to handle higher speeds. The formula in SAE J2452 is proven to be accurate within the 9-71 mph range. Stretching that same formula out to 190 mph would mean assuming a race tire behaves the same way a passenger tire does at nearly three times the speed it was designed to handle. At higher speeds, a tire heats up differently, its contact with the road changes, and the way it flexes shifts. A formula that doesn't account for those changes will give you a number, just not necessarily an accurate one.

This gap matters most for racing teams running hybrid or full electric power units, where rolling resistance feeds directly into how much energy the  system has to work with over a race. This can be critical for power regenerative settings and overtaking systems.

How did Smithers extend the test to 190 MPH?

Rather than stretch the existing formula, Smithers ran the test directly at 190 mph. A few things had to change to make that possible:

• A machine rated for the speed

  Testing ran on equipment capable of up to 235 mph, leaving margin above the 190-mile-per-hour target rather than running at the platform's limit.

• More sensitive instruments

  At extreme speeds, forces like air resistance are large compared to the rolling resistance signal itself. Precise load and torque sensors that are installed at the spindle and in line with the flywheel, are needed to isolate that signal accurately.

• Validating the method

  Rather than borrow confidence from the original standard, the team verified that results were repeatable and consistent at the extended speed range before relying on them.

• Realistic load and pressure conditions

  Testing used load and pressure combinations that reflect actual racing use, not the settings defined for everyday passenger tires – even thought some of the same differences between the conditions were left the same.

Who is this most relevant to?

This test was developed for motorsport: racing series and tire manufacturers working with hybrid and electric power units, where accurate rolling resistance data at true operating speed feeds directly into energy management and race strategy. However, the same approach extends to high-performance passenger and commercial EVs that spend sustained time at highway or track speeds, though motorsport is where the need is most immediate.

Why does this matter for racing teams and tire manufacturers?

Energy management is now a race strategy problem, not just tire durability. As racing series bring hybrid power units on board, every watt lost to rolling resistance is a watt the hybrid system can't deploy elsewhere in the lap.

Testing directly at 190 mph also creates a new kind of development insight for tire manufacturers: instead of one data point at a single speed, engineers can now see how rolling resistance trends change across a race tire's full operating range. That helps inform tire construction and compound decisions early, before a design ever reaches on-track validation – balancing the age-old decision between grip and rolling resistance.

How can Smithers support high-speed rolling resistance testing?

Smithers operates high-speed uniformity testing equipment capable of speeds up to 235 mph, instrumented with high-resolution spindle load cells and precision torque measurement. For racing teams and tire manufacturers that need rolling resistance data beyond standard test speeds, reach out to Cliff Hodges or learn more about our complete tire testing capabilities.