Tubeless tire: The interesting physics behind it

Suppose you and your friends are going somewhere for a ride. One car has a tubed tire while another has a tubeless tire. What happens if both cars get punctured at the same moment? Which car can handle a situation better? If your answer is the car with tubeless tires, then you are absolutely right! The tubeless tire doesn’t flattens and vice-versa for the tubed.
You can observe in the fig 1 to understand how an accident happens when a tire flattens. As the tubed tire flattens suddenly, its radius is reduced and the car suddenly takes a turn. As the driver attempts to control the car, the car becomes uncontrollable, resulting in a devastating accident.

Tubeless tires are self-explanatory so it will take time for releasing air from the tire. Let's understand the details of tubed tire and tubeless tire.

Fig 1 : Tubed tire flattens

If you know the basics of previously popular tubed tires. So first we will discuss about tires and why the tubeless tire concept came out.

How do tubed tires work?

The tubed tire consists of an inflatable tube that holds the air in the tire(refer fig 2). Valve attached with the tube is an inlet to fill the air. The tube is located between the rim and tire. There is a hole in the rim that allows the tube valve to fit in.

Fig 2 : Tubed tire

Here is the scenario of the tube tire puncture, when the nail pierces the tube, air will suddenly leak out of it. So I will explain this with two designs. I can either leave the tube’s valve not attached to the rim, or secondly I can fix the valve with the rim as shown in fig 3. Majority of the air particles will leak out from the tube and get trapped between the tube and tire.

Fig 3 : Valve free to move vs valve fixed with rim

So, do you think the fixed valve design is a good one? Because it flattens slowly. If you think so, this will lead to a catastrophe. The issue is that if the high-pressure air cannot escape from the tire, then the tire will go for a blast(refer fig 4).

Fig 4 : Tubed tire blast

In the tubed tire case, we must allow the sudden escape of air to save the tire. Due to this the valve is not fitted to the rim in the tubed tire design. Which is also the reason why the tire flattens out suddenly during a puncture. Another important aspect of the tire is to ensure that the tire always remains inside the rim, even when the vehicle takes sharp turns. Here a pair of metallic beads is inserted inside the tire as I have shown in fig 5. Please remember this design aspect for later explanation.

Fig 5 : Tire inside the rim

Sticky tape balloon experiment

I did an easy experiment with two air balloons, you can try it out too. One balloon is covered by sticky tape and the other is just a normal balloon. When I prick the balloons with a needle the normal balloon suddenly explodes and the sticky tape balloon leaks very slowly. Can you guess why it happens? This is the technique which is used in tubeless tires. Let me connect the analogy for you.

Let’s take the tubed tire’s inflated tube. It is impermeable. In tubed tires, during puncture the tube loses air and contracts suddenly as shown in fig 6.

Fig 6 : Tube flat inside tire

Now, let's see how we can avoid sudden flats in tubeless tires during puncture. During puncture the tube hole expands and allows air to escape as shown in the fig 7a. The tube needs good structural support to prevent the expanding hole. We can achieve this by glueing it to the tire’s inner walls. The tire is strong enough to hold the tube together. Thus the puncture hole on the tube will not expand as shown in the figure 7b. The tire is rigid enough to keep the hole small for slow leakage of air. Pressurised air escapes through it slowly and steadily. We have now achieved a safer tire, so no sudden tire flats!

Fig 7a : Hole expansion of tubed tire
Fig 7b : Prevention of hole expansion tubeless tire

To make this design more practical, the tube material stuck to the tire arrangement is fitted with a rim. This rim has a hole to fit the valve. The valve is inserted from the inside portion of the rim and it is so made that when pulled out it locks properly. Finally you have tubeless tires (refer fig 7c).

Fig 7c : Tubeless tire

Rim design of tubeless tyres

The new tubeless tire design will only be leak proof with some specially designed rims. First, see what happens when you try the old rim. Here, the pressurised air can easily escape as shown in fig 8.

Fig 8 : Air leak using this rim design

To make the tire air proof, the tubeless tire edges need a good locking mechanism with the rim. This is why engineers added an additional protrusion called a ‘hump’ on the rim(refer fig 9). This perfectly locks the tire onto the rim so that the air doesn’t escape at all.

Fig 9 : New rim design with hump

How are tires fitted?

However, this hump presents a new challenge with the tire bead. The tire has less flexibility. How can I get it to fit on the rim? Engineers have come up with a clever solution for this problem. They made the rim well asymmetrical in shape(refer fig 10).

Fig 10 : Tire fitting

For this rim design, fitting the tire is easily possible by applying force in a particular way as I have shown in fig 11. The bead is just slightly allowed to stretch.

Fig 11 : Applying force for fitting tire inside rim

The tire fits perfectly. Only the upper right side bead will face some difficulty in fitting. This region also can be fitted when I fill the tire with the compressed air as shown in the fig 12.

Fig 12 : Air compressed in the tire

Did you know that tubeless tires have a self-repairing mechanism? It is a latex-based sealant method. liquid self-repairs the hole. To ensure that the latex sealant performs as intended, you will have to refill it with a new one every 3-4 months. You can convert a tubed tire to a tubeless tire. The only condition here is that your rim must have the hump to provide airtight locking.

That's it for today! I hope you understand and enjoy this explanation of tubeless tire.

Thanks for reading!


Yogeshwari S Gaddam

Yogeshwari S Gaddam, B.E in electrical engineering, currently she is working at Lesics Engineers Pvt. Ltd. as a manager. Each day she encounters new challenges and loves the complexity that each project requires. Yogeshwari has done projects such as Tesla model-3's motor(IPM-SynRM), RMF, SynRM motors, Etc. To know more about the author check this link.