Photo: Korea Institute of Machinery and Materials (KIMM)
God and my readers know how much I miss spare tires. I firmly believe that battery electric vehicles (BEVs) have no excuse not to bring them back, and that the only viable option, short of spare tires, would be if someone could sell airless tires that performed as well as regular tires and were just as affordable. A team of scientists from the Korea Institute of Machinery and Materials (KIMM) may have found the solution to this goal, inspired by water droplets. Their discovery is as elegant as it is promising, as the video embedded in this article clearly shows.
When you think of airless tires, you probably only wonder how good they will be on the road. However, ask anyone who is into off-roading and their concerns will be very different. These guys often lower the tire pressure on their vehicles so that they have more traction on some rough terrain. Airless tires will always perform like properly calibrated regular tires. Going off-road would require changing airless tires depending on the terrain. If KIMM's invention ever made it to production lines, this would not be necessary.
Water droplets, or any droplets, have a surface tension that helps them maintain a round shape. Scientists at KIMM explored this concept with a wheel made of a smart chain that works like a tread. Each link (or block, as scientists call them) has a design that allows them to have varying distances from each other. When they’re aligned to form a circle, the eccentric pivot housing will allow them to be farther apart than when they’re at angles pointing toward the hub. That’s what happens when this “tread” is allowed to bend inward whenever it encounters obstacles on the ground.
Photo: Korea Institute of Machinery and Materials (KIMM)
This chain is connected to the wheel hub by several metal spokes. Instead of sensors and multiple actuators, the only moving parts on this wheel are two rings around the hub axle. When the wheel needs to have what scientists call a “high modulus state,” these rings are spaced as far apart as possible. This makes the metal spokes tighter, moves the blocks further apart, and causes the wheel to behave like a regular tire with proper pressure for road use and high speeds.
If the hub rings are pushed closer together, the “low-modulus state” creates low surface tension, leaving the wire spokes looser and pushing the chain links closer together. In that situation, the chain will be flexible enough to allow the wheel to climb obstacles with a radius of up to 1.3 times that. That means it could even climb stairs that meet this condition, something a car wouldn’t do under normal conditions. While off-road enthusiasts might just smile at the promise this ability holds, it’s not designed to make them happy. The KIMM scientists actually had robots in mind when they conceived this. Instead of having legs or tracks, robots could use this deformable wheel to move more efficiently.
While it is possible to use these wheels in cars, there are several questions that need to be answered before that happens. How many miles would such a wheel last before the “smart chain” would need to be replaced, if that’s possible? Would this wheel have a cover to prevent dirt, sand, and other elements from damaging its metal spokes and even the hub rings? In the video below, one of the scientists controls the deformable wheels with a remote control, but how would it work in a car? Would a computer take care of everything? Would the driver have the ability to manually set the wheel’s behavior? What would happen if the hub rings stopped working for any reason? Are these wheels repairable or simply replaceable? Most importantly, how much would they cost?
Photo: Korea Institute of Machinery and Materials (KIMM)
This may seem trivial, but it has important safety implications, which anyone willing to sell such wheels will have to answer for before the authorities allow them to be used on public roads.
For now, let’s just acknowledge that this is a very interesting concept. If it ever makes it to production lines, it might initially only be suitable for robots or more expensive equipment, which was its primary goal, as the scientists themselves mention in their study. This should be a major step until the technology is mature enough for mass-produced vehicles. Off-road machines will have to stick with regular tires that can be inflated with air at the whim of their drivers for quite some time. Those who don’t plan on leaving the road can get the airless tires that the big brands are currently developing. They’ll do just fine, though they’re not meant to climb stairs. For all of us who want spare tires to make a comeback, it looks like we’ll have to wait for a new technology to replace them. There’s no sign of any automaker considering this option. While they do add mass and make cars more expensive to build, spare tires offer peace of mind to customers, especially those who take regular road trips. Unfortunately, you’ll have to rely on tow trucks instead.
