I recently had one of my car tires punctured by a screw. It lost pressure only very slowly, it probably took a couple of days before I noticed the tire was below pressure. The guys from the tire company removed the screw, and then somehow "fixed" the tire. They claim it is as good and reliable as a new tire. I don't know on what that claim is based. My question is: is this indeed true?
The tire was actually very new, I bought it just 2 weeks ago. It's s Continental Premium Contact 2 if that would matter...
I refuse to save money on tires because I believe they play a crucial role in road safety. I am now a bit worried that this fixed tire can cause a blowout more easily.
I am looking for something a little more substantial than your own experience or just "common knowledge". Have any tests or scientific studies been done about this subject?
In the UK (for example), tyre repairs must, by law, conform to British Standard BSAU159f:1990. It is likely that equivalent standards exist in your locale.
Provided that the repair is made to the standard, the tyre will be safe to use.
I imagine the standards apply to normal road use, not when the vehicle is to be used for motorsport or under extreme conditions.
With a bit of searching you can find the results of testing by standards bodies of commercial repair products. For example one tested for 70 minutes at up to 320 KPH (200 MPH) by TUV at the manufacturer's request.
are, supposing the fix has been done properly, repaired tires in general as good as new ones. If the answer is no, then I know for sure that my specific tire at least has a chance of being unsafe, and I can have it replaced by a new one.
You are asking three different things, and I think that is the cause of the confusion here.
"As good as new" is something quite different from "safe", and still different from whether replacing the tire it is a good idea.
A repaired tire is usually not as good as a new one. If only for the fact that is has already been a used one before the repair was done. Here's one property that severely suffers by the fact that there has been a damage (although repaired): the price you can get when trying to sell it. Unfortunately, I don't have literature substantiate this claim, but here's an experiment you can conduct:
Buy new tires, and sell them (providing the original bill) in order to determine the market value.
Buy new tires. Drive them for a while. Sell (providing the original bill) to determine the market value.
Buy new tires. Drive them for the same while. Take them off, puncture them with a small hole in the repairable area and have the puncture repaired. This way, the repair does not interfere with safety, and no other damage can have happened. Sell (providing the original bill and the repair bill) to determine the market value.
Surrogate experiment: call a few tire companies and ask them about the price for these 3 categories. Ask also for rationales of how they arrive at their price.
Do not forget to tell us the outcome of your experiment.
However, all this doesn't necessarily have anything to do with the actual safety of the tire. It is like asking wheter a rather new car is as good as a new one after it had an accident and the damage was properly repaired.
Personally, while I have been buying and driving used tires, I wouldn't buy repaired car/truck tires: In order to be OK with a repaired tire,
I'd insist on personally inspecting the inside of the tire.
I'd insist on know the history of the damage and repair
A tire that slowly goes flat is no option.
Points 2 and 3 I cannot possibly check when buying a tire.
As for the safety, let me add to @RedGrittyBrick's excellent answer some further points about tire repair in Germany (which I consider equivalent to the linked UK rules).
First, the repair instructions (the UK ones linked by @RedGrittyBrick, do, too!) include that the person doing the repair has to check the interior of the tire for signs of other damage (as e.g. due to low pressure driving).
For the tire workshop, selling a new tire probably means more profit earned in less time. Together with the liability question this is a strong incentive to accept the repair order only if they are absolutely certain that the repair is safe.
So, it is possible to repair cretain tire damages safely. @RedGrittyBrick showed that before already. IMHO you cannot possibly get any further answer to the safety question.
It is easy to find evidence about the danger of improper tire repair, like this. However, I did not find any statistics on the reliability of properly done repair.
To add 3 more data points to the discussion: I've personally been driving 3 tires (light truck 2.8 t, vmax 110 km/h) that had been punctured (by something leaving < 1mm hole) on a parking and have been repaired. I never drove them at too low pressure. I've been driving then something between 25000 and 50000 km thereafter. I have to double-check but I think one of them is still "in service". The others meanwhile were replaced, but their "end" had nothing to do with that puncture or repair.
That is 0 repair-related failures out of 3 cases, which translates to a 95% confidence interval for the true probability of a failure after properly done repair between 0 and 70%. This illustrates that 3 data points do not allow much conclusions. But they are a starting point for collecting more evidence.
Last, but not least, for the third question you ask "Should I buy a new tire?", I recommend quickly calculating how much a new tire costs, and balance that againt the hours you're still going to spend on worrying about the repaired tire. Could it be that the hourly wage for your worries is very low? In that case, you may want decide to buy a new tire regardless of the technical condition of the repaired tire.