Unexpected tyre trouble: How a missing valve cap led to a roadside mystery
While driving, the steering wheel jerked, and I heard knocking sounds from underneath the car. I knew something was wrong with the wheel, but nothing seemed to have broken off. Could it have come loose? The real cause turned out to be simple yet surprising.
The air from the tyre can deflate in two ways: through a hole in the tyre or a damaged valve. In an off-road vehicle, there's another way—between the tyre and the rim when driving with low pressure. In this case, something unexpected happened, which seemed very obvious once I understood the cause.
Indeed, in the Toyota Hilux test, I was driving at low pressure because I was navigating problematic sandy terrain. The pressure was about 1.5 bar (22 psi). After leaving the terrain, I went about 60 kilometres (37 miles) on asphalt roads, and nothing happened. There was no time to inflate the tyre, so I did it only after arriving at my destination and handling my errands.
Upon arriving at my destination and parking the car for over an hour, the pressure was still 1.5 bar (22 psi). I drove to a petrol station to adjust it to the recommended 2.3 bar (33 psi) and continued driving. After a few minutes, the air suddenly deflated from the tyre.
Looking for the root cause
After changing the wheel and getting home, I decided to find the cause myself. I inflated the tyre and started looking for a hole. This seemed the only likely scenario. Unfortunately, I found nothing. Air also wasn’t escaping through the valve. Interestingly, after a day, the pressure remained the same.
I had no idea what could be causing it. I showed a photo of the wheel to someone more experienced in off-roading than me. He immediately pointed out one detail and surprised me by asking, "Were you driving on sand?" I confirmed although I added that the air deflated much later after inflating the tyre. For him, it was already clear.
He pointed to one detail and wrote: "You don't have a valve cap, so you had sand in the valve. When you inflated the tyre, the sand got pushed into the valve, blocking it momentarily, so the air suddenly deflated. When the air escaped, it pushed out some of the sand. The rest was probably removed when you inflated the tyre again."
In summary, you learn something new daily, and such apparent things sometimes don't even come to mind. The experienced off-roader said you always need a valve cap because even mud can cause damage. And if you don’t have one, it’s worth letting out a bit of air before inflating the tyre to blow out the dirt from the valve.
