How bad is driving on a flat tire for 40 km?

Question

Yesterday I noticed that it took a considerable larger amount of force to turn the steering wheel. It was stiff at low speed (compared to the usual feeling), turning onto streets and parking was not easy but manageable. I did not know what the problem was, so I was just thinking of getting my car checked the next day.

Then I washed my car and noticed that one of the front tires was completely (EDIT: very, I've never seen it that flat but I don't know if that's "completely") flat. I am pretty sure the tire looked ok when I left my car 12 hours ago, so I figure it must have gotten flat in the past 12 hours, and probably contributed to the stiff steering wheel. I drove to a repair shop, where they said I probably hit a nail or something. They removed the tire, patched it somehow (I saw the technician removed something with a metal tool then applied some kind of glue, but I did not have a clear view to see exactly what he did), pumped it and put it back. The steering feels alright afterwards. They charged me for around USD 10 equivalent (I am not in the US).

My question is, how bad is the damage to the tire? Maximum speed was 120 km/h, and I drove around 40~45 km before I got it fixed. Should I expect a significantly shorter tire lifespan? Should I replace all tires at the next service interval?

Are there any other maintenance steps I should take after this simple fix? E.g. should I go to a shop and ask for the tire balance be checked?

Answer 1

If the tyre was really low or literally flat, driving for 40km with it at higher speeds will probably have made it disintegrate on the inside. I had someone come in the workshop a few days ago with a similar situation. We dismounted the tyre, and saw it filled with rubberpowder that had come loose from the tyre wall inside. Not just a bit, but hands full.

A tyre wall is not nearly as thick as it's thread, and so weakening the wall really weakens the whole tyre. It can easily make for a blowout. I can assure you that you really don't want that at higher speeds, while braking, or at all actually. It's very dangerous as it can completely make you lose the control of your car. I'd have the tyre dismounted, and inspected for damage. If any is visible, replace it, and preferably also the tyre on the opposite side of the axle. Invisible damage may also been dealed, so if you want to play it safe, replace to be sure.

While you're at it, inspect the surface on the rim where it contacts with the tyre. If the rim has made contact with the road, it may have got some spiky barbs on it, and they can do damage to the tyre.

Answer 2

If a tire is very low you can still drive and not damage the tire unless you hit any bumps. The issue is that even the smallest bump can cause the rim to hit the ground and pinch the tire which can over-stress the rubber.

Long term, the flex of the sidewall on a very low tire will damage the rubber because it's bending and flexing more than it should and generating heat the whole time. Your 40km is probably getting close to this "long term" scenario, but it really depends on what shape the tires were in to begin with. In either case, the amount of possible damage is proportional to the pressure of the tire, and you don't really know how much of those 40km the tire was dangerously low.

So, it's very likely that the tire sidewall was over-stressed and could pull apart some time in the future. The guys that fixed the flat could have inspected the tire inside and out and gave a more informed opinion than I can, but they may have just plugged the hole and not given it a second look. You may want to take it to a shop that deals primarily with tires and get an expert opinion. A blow out is not what you want to deal with.

Now, if the tire is completely flat and the rim is pinching the tire, even driving a block can damage a tire beyond repair. Even if the tire is not visibly torn, the bead and sidewall are taking some serious stress when all the car's weight is on the rim.