How Different Wheels Changed Our Toyota Prius Prime's Fuel Economy

• The 2024 Toyota Prius Prime SE and 2023 Prius Prime XSE returned notably different results in the Car and Driver 75-mph highway fuel-economy test.

• Equipped with 17-inch wheels, the SE returned 49 mpg, while the XSE with its larger 19-inch wheels achieved 46 mpg on the same test.

• Along with the smaller wheels and tires, the SE has a slightly more slippery drag coefficient and tips the scales at 55 pounds lighter than the XSE.

Welcome to Car and Driver's Testing Hub, where we zoom in on the test numbers. We've been pushing vehicles to their limits since 1956 to provide objective data to bolster our subjective impressions (you can see how we test here).

The Toyota Prius Hybrid has long been hailed as a master of the fuel-economy game, and the plug-in-hybrid Prius Prime only adds to its success. That isn't to say that all Prius Primes are built the same. The 2024 Prius Prime SE and 2023 Prius Prime XSE returned notably different results in our 75-mph highway fuel-economy test.

Despite the disparity, both cars achieved better results than most other internal-combustion cars can achieve. The XSE we tested was equipped with 19-inch wheels wrapped in 195/50 Michelin Primary A/S tires and returned 46 mpg. Not bad at all. The SE we tested was equipped with a set of 17-inch wheels, wore 195/60 Toyo Extensa A/S tires, and bettered the XSE with a result of 49 mpg.

There are several factors at play here, starting with each model's drag. According to Toyota, the SE's coefficient of drag measures 0.27, while the XSE's measures a less slippery 0.29. With virtually the same front end, the differences likely come down to the wheels and tires.

The main culprit behind the XSE's worse result is the larger 19-inch wheels. The larger rollers result in 0.4 inch more ride height and add to the rotating mass. The wheel design also plays a large part, with the SE wheels using large covers that help with aerodynamics.

Thanks to punching a larger hole through the air, the wider the tires are, the less efficient they become. Since these tires were the same width, they likely didn't affect the results. However, we should note that different tire models produce slightly different aerodynamics and have different rolling resistances that could impact the results.

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