# Are Perseverance's wheels really this big?

Business Insider's What is it like to drive the Perseverance rover remotely? A NASA engineer explains the challenges of piloting the vehicle's journey across Mars. includes the following:

(Heather Justice, a NASA engineer from the Perseverance rover team) said: "An example of that would be the autonomous navigation where we've done a lot of improvements on the software so that the rover can drive further on its own. Hopefully in the long term that will make it easier for us to get longer drives in which will let us get to the places that science really wants us to go to."

"There have also been hardware improvements, where the wheels are different from Curiosity so that they are more robust to drive over sharp rocks," she added.

The quote is accompanied by the image and caption below.

Question: The wheel looks a lot bigger than I'd thought it was. Could this possibly have been a 2x model? How large are these wheels exactly?

Adam Steltzner, Perseverance chief engineer, shows a rover wheel during a NASA Perseverance rover mission engineering and technology overview.

• Sure, it's real size, and the person next to it is a Lego minifigure. Mar 29 at 1:08
• The median distance between a male human's waistline and a male human's eye-level is 57.6 cm. The bottom of the wheel is a good 10 cm above the man's waistline, and the top is a perhaps 5 cm above eye-level. Those guesstimates make that 57.6 cm figure entirely consistent with the quoted 52.5 cm diameter. Mar 29 at 5:31
• If I had to drive a car on Mars, I would opt for 31-35" tyres. At least, that's what I do for Mars-like terrains and Preserverance-sized vehicles down here. Mar 29 at 9:31
• How big did you think Perseverance itself was? It's car-sized, so car-sized wheels make sense (and car wheel are big when you put them next to you). But I also keep forgetting that Perseverance and Curiosity are this big. In my mind they are still cute Sojourner-like brave little explorers. Mar 29 at 9:55
• @JanFabry for some reason I really thought that the wheels were about 20 cm. Ya I guess I must have taken wheels from previous generations. Wow, this thing must be pretty tall, maybe 3 meters? Geez what a monster!
– uhoh
Mar 29 at 10:07

The wheels are

52.5 centimeters (20.7-inches) in diameter

Source Mars Rover Wheels

The wheel pictured, if real, must be closer to the camera than the head and torso of the individual pictured.

• I see, so it's probably a combination of them being $\sqrt{2}$ larger than I thought and $\sqrt{2}$ larger again in the photo because due to perspective.
– uhoh
Mar 29 at 1:44
• I've seen one in-person. It was definitely larger than I thought. I'd say that image only makes it one $\sqrt{2}$ larger than in reality. Mar 29 at 5:54
• There is very little if any foreshortening in the image, @uhoh. Mar 29 at 5:55
• @DavidHammen If the photo didn't have such a shallow depth of focus I'd take the Fourier transform of the fabric grid of the left and right sleeve to get a ratio of the distances for some estimate, but then realized the tread period on the front and back are both visible. I eyeball only about a 6% difference from front to back pixel-wise, so once again you're right! ;-)
– uhoh
Mar 29 at 9:46

While @OrganicMarble's answer confirms the size numerically, I've just run across If Necessary, Mars Rover Curiosity Could Rip Its Own Wheels Off to Stay Mobile; Curiosity's wheel wear shouldn't be a problem for years, but if things get bad, JPL has a plan to minimize risk with a "wheel shedding" maneuver which includes a photo of a JPL engineer holding an extensively tested and worn specimine of a Curiosity wheel, and it's indeed huge!

Left: a “critically damaged” MSL flight wheel used for testing with 19 broken grousers. Right: JPL engineer Amanda Steffy holds a wheel that was tested to failure on the Scarecrow rover in the JPL Mars Yard.